Robert G Baker, Ph.D.

Vocalization frequency and duration are coded in separate hindbrain nuclei
Chagnaud, Boris P; Baker, Robert; Bass, Andrew H
2011 ;2:346-346, Nature communications
Temporal patterning is an essential feature of neural networks producing precisely timed behaviours such as vocalizations that are widely used in vertebrate social communication. Here we show that intrinsic and network properties of separate hindbrain neuronal populations encode the natural call attributes of frequency and duration in vocal fish. Intracellular structure/function analyses indicate that call duration is encoded by a sustained membrane depolarization in vocal prepacemaker neurons that innervate downstream pacemaker neurons. Pacemaker neurons, in turn, encode call frequency by rhythmic, ultrafast oscillations in their membrane potential. Pharmacological manipulations show prepacemaker activity to be independent of pacemaker function, thus accounting for natural variation in duration which is the predominant feature distinguishing call types. Prepacemaker neurons also innervate key hindbrain auditory nuclei thereby effectively serving as a call-duration corollary discharge. We propose that premotor compartmentalization of neurons coding distinct acoustic attributes is a fundamental trait of hindbrain vocal pattern generators among vertebrates
— id: 136618, year: 2011, vol: 2, page: 346, stat: Journal Article,

Encoding of eye position in the goldfish horizontal oculomotor neural integrator
Debowy, Owen; Baker, Robert
2011 Feb;105(2):896-909, Journal of neurophysiology
Monocular organization of the goldfish horizontal neural integrator was studied during spontaneous scanning saccadic and fixation behaviors. Analysis of neuronal firing rates revealed a population of ipsilateral (37%), conjugate (59%), and contralateral (4%) eye position neurons. When monocular optokinetic stimuli were employed to maximize disjunctive horizontal eye movements, the sampled population changed to 57, 39, and 4%. Monocular eye tracking could be elicited at different gain and phase with the integrator time constant independently modified for each eye by either centripetal (leak) or centrifugal (instability) drifting visual stimuli. Acute midline separation between the hindbrain oculomotor integrators did not affect either monocularity or time constant tuning, corroborating that left and right eye positions are independently encoded within each integrator. Together these findings suggest that the 'ipsilateral' and 'conjugate/contralateral' integrator neurons primarily target abducens motoneurons and internuclear neurons, respectively. The commissural pathway is proposed to select the conjugate/contralateral eye position neurons and act as a feedfoward inhibition affecting null eye position, oculomotor range, and saccade pattern
— id: 122690, year: 2011, vol: 105, page: 896, stat: Journal Article,

Monocular eye position specificity in the oculomotor neural integrator
Okamura N.; Baker R.; Hirata Y.
2011 ;12:?-?, BMC Neuroscience
Background: The oculomotor neural integrator (NI) is a conceptual neuronal mechanism that maintains eye position after each scanning saccade without visual feedback in the dark. Saccades are triggered by an impulse-like activity of brain stem burst neurons that, similar to a mathematical function, must be integrated to produce a step-like motor command. The impulse- and step-like signals are combined in motor neurons to produce a rapid saccadic eye movement followed by a stable eye position. In the Laplace domain, a perfect integrator is described as 1/s and an imperfect one as 1/(s+a) with a positive a being 'leaky' and a negative a, 'unstable'. Experimentally, the NI was found to be modifiable by using visual feedback paradigms to imitate either 'leaky' or 'unstable' behaviors [1]. In goldfish, neurons exhibiting a highly correlated NI activity have been found in the hindbrain Area I [1]. A recent study demonstrated 3 types of neurons in Area I: ipsilateral (37%), conjugate (59%), and contralateral (4%) [2]. The ipsi- and contralateral neurons increased their firing rate when the ipsi- and contralateral eye positions changed in the temporal and nasal direction, respectively. By contrast, the conjugate neurons did not distinguish between the eyes and fired in both cases. This finding predicts that if the visual feedback paradigm would be applied exclusively to either a nasal or temporal hemi-field of one eye, the effect of training would not be confined to the trained hemi-field. Methods: To test this prediction, we conducted visual feedback NI training in goldfish. The fish were gently restrained at the center of a cylindrical water tank with a planetarium projecting random dots on a white wall. Eye position was monitored by the search coil technique while spontaneous scanning saccades occurred in both directions about a central neutral position. For monocular visual-feedback NI training, the L eye was occluded and the planetarium rotated by a servomotor at a speed proportional to R eye position. When planetarium motion was either centrifugal or centripetal to the selected neutral position, the NI could be trained to be either leaky or unstable, respectively. In the current study we employed R eye unstable only training of both hemi-fields or only one hemi-field (nasal or temporal) by turning off the planetarium when eye position was in the other hemi-field. Results: Nasal only unstable training (n=8) made the NI significantly unstable in the trained R eye hemi-field, but leaky in the untrained R eye hemi-field. The training also affected the NI for the untrained L eye such that it was leaky in the nasal and unstable in the temporal hemi-field. Combined nasal and temporal unstable training (n=9) resulted in a significantly unstable NI for the trained nasal hemi-field, but almost no change in the trained temporal hemi-field. In the untrained L eye, the NI was significantly unstable in the temporal hemi-field but almost no change in the nasal hemi-field. In contrast, temporal only unstable training (n=9) produced just a small change in the NI for that hemi-field and an even smaller leak in the untrained nasal hemi-field. In the L eye there was a small change towards unstable in the nasal hemi-field with hardly any difference in the temporal hemi-field. Conclusions: The present results demonstrate that unstable training of a single hemi-field makes the NI leaky for the opposite hemi-field of the same eye as well as 'unstable and leaky' for hemi-fields in the untrained eye. This experimental finding was predictable from ipsilateral and conjugate Area I neuronal activity [2]. However, the small amount of learning after temporal only and even less after both temporal and nasal unstable training was not foreseen. These results are being further evaluated directly by recording from Area I neurons throughout training and memory
— id: 146282, year: 2011, vol: 12, page: ?, stat: Journal Article,

Neurovascular development in the embryonic zebrafish hindbrain
Ulrich, Florian; Ma, Leung-Hang; Baker, Robert G; Torres-Vazquez, Jesus
2011 Sep 1;357(1):134-151, Developmental biology (Orlando)
The brain is made of billions of highly metabolically active neurons whose activities provide the seat for cognitive, affective, sensory and motor functions. The cerebral vasculature meets the brain's unusually high demand for oxygen and glucose by providing it with the largest blood supply of any organ. Accordingly, disorders of the cerebral vasculature, such as congenital vascular malformations, stroke and tumors, compromise neuronal function and survival and often have crippling or fatal consequences. Yet, the assembly of the cerebral vasculature is a process that remains poorly understood. Here we exploit the physical and optical accessibility of the zebrafish embryo to characterize cerebral vascular development within the embryonic hindbrain. We find that this process is primarily driven by endothelial cell migration and follows a two-step sequence. First, perineural vessels with stereotypical anatomies are formed along the ventro-lateral surface of the neuroectoderm. Second, angiogenic sprouts derived from a subset of perineural vessels migrate into the hindbrain to form the intraneural vasculature. We find that these angiogenic sprouts reproducibly penetrate into the hindbrain via the rhombomere centers, where differentiated neurons reside, and that specific rhombomeres are invariably vascularized first. While the anatomy of intraneural vessels is variable from animal to animal, some aspects of the connectivity of perineural and intraneural vessels occur reproducibly within particular hindbrain locales. Using a chemical inhibitor of VEGF signaling we determine stage-specific requirements for this pathway in the formation of the hindbrain vasculature. Finally, we show that a subset of hindbrain vessels is aligned and/or in very close proximity to stereotypical neuron clusters and axon tracts. Using endothelium-deficient cloche mutants we show that the endothelium is dispensable for the organization and maintenance of these stereotypical neuron clusters and axon tracts in the early hindbrain. However, the cerebellum's upper rhombic lip and the optic tectum are abnormal in clo. Overall, this study provides a detailed, multi-stage characterization of early zebrafish hindbrain neurovascular development with cellular resolution up to the third day of age. This work thus serves as a useful reference for the neurovascular characterization of mutants, morphants and drug-treated embryos
— id: 137873, year: 2011, vol: 357, page: 134, stat: Journal Article,

Carboxypeptidase A6 in zebrafish development and implications for VIth cranial nerve pathfinding
Lyons, Peter J; Ma, Leung-hang; Baker, Robert; Fricker, Lloyd D
2010 ;5(9):e12967-e12967, PLoS ONE
Carboxypeptidase A6 (CPA6) is an extracellular protease that cleaves carboxy-terminal hydrophobic amino acids and has been implicated in the defective innervation of the lateral rectus muscle by the VIth cranial nerve in Duane syndrome. In order to investigate the role of CPA6 in development, in particular its potential role in axon guidance, the zebrafish ortholog was identified and cloned. Zebrafish CPA6 was secreted and interacted with the extracellular matrix where it had a neutral pH optimum and specificity for C-terminal hydrophobic amino acids. Transient mRNA expression was found in newly formed somites, pectoral fin buds, the stomodeum and a conspicuous condensation posterior to the eye. Markers showed this tissue was not myogenic in nature. Rather, the CPA6 localization overlapped with a chondrogenic site which subsequently forms the walls of a myodome surrounding the lateral rectus muscle. No other zebrafish CPA gene exhibited a similar expression profile. Morpholino-mediated knockdown of CPA6 combined with retrograde labeling and horizontal eye movement analyses demonstrated that deficiency of CPA6 alone did not affect either VIth nerve development or function in the zebrafish. We suggest that mutations in other genes and/or enhancer elements, together with defective CPA6 expression, may be required for altered VIth nerve pathfinding. If mutations in CPA6 contribute to Duane syndrome, our results also suggest that Duane syndrome can be a chondrogenic rather than a myogenic or neurogenic developmental disorder
— id: 139622, year: 2010, vol: 5, page: e12967, stat: Journal Article,

Ancestry of motor innervation to pectoral fin and forelimb
Ma, Leung-Hang; Gilland, Edwin; Bass, Andrew H; Baker, Robert
2010 Jul 27;1(4):1-8, Nature communications
Motor innervation to the tetrapod forelimb and fish pectoral fin is assumed to share a conserved spinal cord origin, despite major structural and functional innovations of the appendage during the vertebrate water-to-land transition. In this paper, we present anatomical and embryological evidence showing that pectoral motoneurons also originate in the hindbrain among ray-finned fish. New and previous data for lobe-finned fish, a group that includes tetrapods, and more basal cartilaginous fish showed pectoral innervation that was consistent with a hindbrain-spinal origin of motoneurons. Together, these findings support a hindbrain-spinal phenotype as the ancestral vertebrate condition that originated as a postural adaptation for pectoral control of head orientation. A phylogenetic analysis indicated that Hox gene modules were shared in fish and tetrapod pectoral systems. We propose that evolutionary shifts in Hox gene expression along the body axis provided a transcriptional mechanism allowing eventual decoupling of pectoral motoneurons from the hindbrain much like their target appendage gained independence from the head
— id: 114059, year: 2010, vol: 1, page: 1, stat: Journal Article,

Mosaic hoxb4a neuronal pleiotropism in zebrafish caudal hindbrain
Ma, Leung-Hang; Punnamoottil, Beena; Rinkwitz, Silke; Baker, Robert
2009 ;4(6):e5944-e5944, PLoS ONE
To better understand how individual genes and experience influence behavior, the role of a single homeotic unit, hoxb4a, was comprehensively analyzed in vivo by clonal and retrograde fluorescent labeling of caudal hindbrain neurons in a zebrafish enhancer-trap YFP line. A quantitative spatiotemporal neuronal atlas showed hoxb4a activity to be highly variable and mosaic in rhombomere 7-8 reticular, motoneuronal and precerebellar nuclei with expression decreasing differentially in all subgroups through juvenile stages. The extensive Hox mosaicism and widespread pleiotropism demonstrate that the same transcriptional protein plays a role in the development of circuits that drive behaviors from autonomic through motor function including cerebellar regulation. We propose that the continuous presence of hoxb4a positive neurons may provide a developmental plasticity for behavior-specific circuits to accommodate experience- and growth-related changes. Hence, the ubiquitous hoxb4a pleitropism and modularity likely offer an adaptable transcriptional element for circuit modification during both growth and evolution
— id: 100205, year: 2009, vol: 4, page: e5944, stat: Journal Article,

Evolutionary origins for social vocalization in a vertebrate hindbrain-spinal compartment
Bass, AH; Gilland, EH; Baker, R
2008 JUL 18 ;321(5887):417-421, Science
The macroevolutionary events leading to neural innovations for social communication, such as vocalization, are essentially unexplored. Many fish vocalize during female courtship and territorial defense, as do amphibians, birds, and mammals. Here, we map the neural circuitry for vocalization in larval fish and show that the vocal network develops in a segment-like region across the most caudal hindbrain and rostral spinal cord. Taxonomic analysis demonstrates a highly conserved pattern between fish and all major lineages of vocal tetrapods. We propose that the vocal basis for acoustic communication among vertebrates evolved from an ancestrally shared developmental compartment already present in the early fishes
— id: 86854, year: 2008, vol: 321, page: 417, stat: Journal Article,

Semicircular canal size determines the developmental onset of angular vestibuloocular reflexes in larval Xenopus
Lambert, Francois M; Beck, James C; Baker, Robert; Straka, Hans
2008 Aug 6;28(32):8086-8095, Journal of neuroscience
Semicircular canals have been sensors of angular acceleration for 450 million years. This vertebrate adaptation enhances survival by implementing postural and visual stabilization during motion in a three-dimensional environment. We used an integrated neuroethological approach in larval Xenopus to demonstrate that semicircular canal dimensions, and not the function of other elements, determines the onset of angular acceleration detection. Before angular vestibuloocular function in either the vertical or horizontal planes, at stages 47 and 48, respectively, each individual component of the vestibuloocular system was shown to be operational: extraocular muscles could be activated, central neural pathways were complete, and canal hair cells were capable of evoking graded responses. For Xenopus, a minimum semicircular canal lumen radius of 60 microm was necessary to permit endolymph displacement sufficient for sensor function at peak accelerations of 400 degrees /s(2). An intra-animal comparison demonstrated that this size is reached in the vertical canals earlier in development than in the horizontal canals, corresponding to the earlier onset of vertical canal-activated ocular motor behavior. Because size constitutes a biophysical threshold for canal-evoked behavior in other vertebrates, such as zebrafish, we suggest that the semicircular canal lumen and canal circuit radius are limiting the onset of vestibular function in all small vertebrates. Given that the onset of gravitoinertial acceleration detection precedes angular acceleration detection by up to 10 d in Xenopus, these results question how the known precise spatial patterning of utricular and canal afferents in adults is achieved during development
— id: 140345, year: 2008, vol: 28, page: 8086, stat: Journal Article,

Erratum: Channel, neuronal and clinical function in sodium channelopathies: From genotype to phenotype
Aksay, Emre; Olasagasti, Itsaso; Mensh, Brett D; Baker, Robert; Goldman, Mark S; Tank, David W
2007 ;10(4):798-798 Apr, Nature neuroscience
Reports an error in 'Channel, neuronal and clinical function in sodium channelopathies: From genotype to phenotype' by Stephen G. Waxman (Nature Neuroscience, 2007[Apr], Vol 10[4], 405-409). In the version of this article initially published, the online publication date was incorrectly given as 25 February 2007. The correct date is 27 March 2007. This error has been corrected in the PDF version of the article. (The following abstract of the original article appeared in record 2008-04974-022). In neural integrators, transient inputs are accumulated into persistent firing rates that are a neural correlate of short-term memory. Integrators often contain two opposing cell populations that increase and decrease sustained firing as a stored parameter value rises. A leading hypothesis for the mechanism of persistence is positive feedback through mutual inhibition between these opposing populations. We tested predictions of this hypothesis in the goldfish oculomotor velocity-to-position integrator by measuring the eye position and firing rates of one population, while pharmacologically silencing the opposing one. In complementary experiments, we measured responses in a partially silenced single population. Contrary to predictions, induced drifts in neural firing were limited to half of the oculomotor range. We built network models with synaptic-input thresholds to demonstrate a new hypothesis suggested by these data: mutual inhibition between the populations does not provide positive feedback in support of integration, but rather coordinates persistent activity intrinsic to each population. (PsycINFO Database Record (c) 2008 APA, all rights reserved)
— id: 82817, year: 2007, vol: 10, page: 798, stat: Journal Article,

Functional dissection of circuitry in a neural integrator
Aksay, Emre; Olasagasti, Itsaso; Mensh, Brett D; Baker, Robert; Goldman, Mark S; Tank, David W
2007 Apr;10(4):494-504, Nature neuroscience
In neural integrators, transient inputs are accumulated into persistent firing rates that are a neural correlate of short-term memory. Integrators often contain two opposing cell populations that increase and decrease sustained firing as a stored parameter value rises. A leading hypothesis for the mechanism of persistence is positive feedback through mutual inhibition between these opposing populations. We tested predictions of this hypothesis in the goldfish oculomotor velocity-to-position integrator by measuring the eye position and firing rates of one population, while pharmacologically silencing the opposing one. In complementary experiments, we measured responses in a partially silenced single population. Contrary to predictions, induced drifts in neural firing were limited to half of the oculomotor range. We built network models with synaptic-input thresholds to demonstrate a new hypothesis suggested by these data: mutual inhibition between the populations does not provide positive feedback in support of integration, but rather coordinates persistent activity intrinsic to each population
— id: 138037, year: 2007, vol: 10, page: 494, stat: Journal Article,

Segmental organization of hindbrain functional circuits in adult anamniotes
Straka, H; Baker, R; Gilland, E
2007 DEC ;268(12):1138-1139, Journal of morphology
— id: 87179, year: 2007, vol: 268, page: 1138, stat: Journal Article,

Precerebellar hindbrain neurons encoding eye velocity during vestibular and optokinetic behavior in the goldfish
Beck, James C; Rothnie, Paul; Straka, Hans; Wearne, Susan L; Baker, Robert
2006 Sep;96(3):1370-1382, Journal of neurophysiology
Elucidating the causal role of head and eye movement signaling during cerebellar-dependent oculomotor behavior and plasticity is contingent on knowledge of precerebellar structure and function. To address this question, single-unit extracellular recordings were made from hindbrain Area II neurons that provide a major mossy fiber projection to the goldfish vestibulolateral cerebellum. During spontaneous behavior, Area II neurons exhibited minimal eye position and saccadic sensitivity. Sinusoidal visual and vestibular stimulation over a broad frequency range (0.1-4.0 Hz) demonstrated that firing rate mirrored the amplitude and phase of eye or head velocity, respectively. Table frequencies >1.0 Hz resulted in decreased firing rate relative to eye velocity gain, while phase was unchanged. During visual steps, neuronal discharge paralleled eye velocity latency (approximately 90 ms) and matched both the build-up and the time course of the decay (approximately 19 s) in eye velocity storage. Latency of neuronal discharge to table steps (40 ms) was significantly longer than for eye movement (17 ms), but firing rate rose faster than eye velocity to steady-state levels. The velocity sensitivity of Area II neurons was shown to equal (+/- 10%) the sum of eye- and head-velocity firing rates as has been observed in cerebellar Purkinje cells. These results demonstrate that Area II neuronal firing closely emulates oculomotor performance. Conjoint signaling of head and eye velocity together with the termination pattern of each Area II neuron in the vestibulolateral lobe presents a unique eye-velocity brain stem-cerebellar pathway, eliminating the conceptual requirement of motor error signaling
— id: 68818, year: 2006, vol: 96, page: 1370, stat: Journal Article,

Ancestral electrophysiological properties of thalamic neurons in vertebrates
Gamkreilidze GN; Baker R; Llinas R
2006 ;32:?-?, Society for Neuroscience Abstract Viewer & Itinerary Planner
— id: 75343, year: 2006, vol: 32, page: ?, stat: Journal Article,

Conserved co-regulation and promoter sharing of hoxb3a and hoxb4a in zebrafish
Hadrys, Thorsten; Punnamoottil, Beena; Pieper, Mareike; Kikuta, Hiroshi; Pezeron, Guillaume; Becker, Thomas S; Prince, Victoria; Baker, Robert; Rinkwitz, Silke
2006 Sep 1;297(1):26-43, Developmental biology (Orlando)
The expression of zebrafish hoxb3a and hoxb4a has been found to be mediated through five transcripts, hoxb3a transcripts I-III and hoxb4a transcripts I-II, driven by four promoters. A 'master' promoter, located about 2 kb downstream of hoxb5a, controls transcription of a pre-mRNA comprising exon sequences of both genes. This unique gene structure is proposed to provide a novel mechanism to ensure overlapping, tissue-specific expression of both genes in the posterior hindbrain and spinal cord. Transgenic approaches were used to analyze the functions of zebrafish hoxb3a/hoxb4a promoters and enhancer sequences containing regions of homology that were previously identified by comparative genomics. Two neural enhancers were shown to establish specific anterior expression borders within the hindbrain and mediate expression in defined neuronal populations derived from hindbrain rhombomeres (r) 5 to 8, suggesting a late role of the genes in neuronal cell lineage specification. Species comparison showed that the zebrafish hoxb3a r5 and r6 enhancer corresponded to a sequence within the mouse HoxA cluster controlling activity of Hoxa3 in r5 and r6, whereas a homologous region within the HoxB cluster activated Hoxb3 expression but limited to r5. We conclude that the similarity of hoxb3a/Hoxa3 regulatory mechanisms reflect the shared descent of both genes from a single ancestral paralog group 3 gene
— id: 68982, year: 2006, vol: 297, page: 26, stat: Journal Article,

Preservation of segmental hindbrain organization in adult frogs
Straka, Hans; Baker, Robert; Gilland, Edwin
2006 Jan 10;494(2):228-245, Journal of comparative neurology
To test for possible retention of early segmental patterning throughout development, the cranial nerve efferent nuclei in adult ranid frogs were quantitatively mapped and compared with the segmental organization of these nuclei in larvae. Cranial nerve roots IV-X were labeled in larvae with fluorescent dextran amines. Each cranial nerve efferent nucleus resided in a characteristic segmental position within the clearly visible larval hindbrain rhombomeres (r). Trochlear motoneurons were located in r0, trigeminal motoneurons in r2-r3, facial branchiomotor and vestibuloacoustic efferent neurons in r4, abducens and facial parasympathetic neurons in r5, glossopharyngeal motoneurons in r6, and vagal efferent neurons in r7-r8 and rostral spinal cord. In adult frogs, biocytin labeling of cranial nerve roots IV-XII and spinal ventral root 2 in various combinations on both sides of the brain revealed precisely the same rostrocaudal sequence of efferent nuclei relative to each other as observed in larvae. This indicates that no longitudinal migratory rearrangement of hindbrain efferent neurons occurs. Although rhombomeres are not visible in adults, a segmental map of adult cranial nerve efferent nuclei can be inferred from the strict retention of the larval hindbrain pattern. Precise measurements of the borders of adjacent efferent nuclei within a coordinate system based on external landmarks were used to create a quantitative adult segmental map that mirrors the organization of the larval rhombomeric framework. Plotting morphologically and physiologically identified hindbrain neurons onto this map allows the physiological properties of adult hindbrain neurons to be linked with the underlying genetically specified segmental framework. J. Comp. Neurol. 494:228-245, 2006. (c) 2005 Wiley-Liss, Inc
— id: 60893, year: 2006, vol: 494, page: 228, stat: Journal Article,

Morphology and physiology of the cerebellar vestibulolateral lobe pathways linked to oculomotor function in the goldfish
Straka, Hans; Beck, James C; Pastor, Angel M; Baker, Robert
2006 Oct;96(4):1963-1980, Journal of neurophysiology
Intracellular recording and single-cell labeling were combined to investigate the oculomotor circuitry of the goldfish cerebellar vestibulolateral lobe, consisting of the eminentia granularis (Egr) and caudal lobe. Purkinje cells exhibiting highly conserved vertebrate electrophysiological and morphological properties provide the direct output from the caudal lobe to the vestibular nuclei. Biocytin labeling of the Egr distinguished numerous hindbrain precerebellar sources that could be divided into either putative mechano- or vestibulosensitive nuclei based on cellular location and axon trajectories. Precerebellar neurons in a hindbrain nucleus, called Area II, were electrophysiologically characterized after antidromic activation from the Egr (>50% bilateral) and their morphology analyzed after intracellular biocytin labeling (n = 28). Bipolar spindle-shaped somas ranged widely in size with comparably scaled dendritic arbors exhibiting largely closed field configuration. Area II neurons (85%) projected to the ipsilateral Egr with most (93%) sending a collateral through the cerebellar commissure to the contralateral Egr; however, 15% projected to the contralateral Egr by crossing in the ventral hindbrain. Axon terminals in the vestibular nucleus were the only collaterals within the hindbrain. Every Area II neuron received a disynaptic EPSP after contralateral horizontal canal nerve stimulation and a disynaptic IPSP, preceded by a small EPSP (>50%), after ipsilateral activation. Vestibular synaptic potentials were of varying shape/amplitude, unrelated to neuron location in the nucleus, and thus likely a correlate of somadendritic size. The exceptional separation of eye position and eye velocity signals into two separate hindbrain nuclei represents an ideal model for understanding the precerebellar projection to the vestibulocerebellum
— id: 142120, year: 2006, vol: 96, page: 1963, stat: Journal Article,

Evolutionary patterns of cranial nerve efferent nuclei in vertebrates
Gilland, Edwin; Baker, Robert
2005 ;66(4):234-254, Brain behavior & evolution
All vertebrates have a similar series of rhombomeric hindbrain segments within which cranial nerve efferent nuclei are distributed in a similar rostrocaudal sequence. The registration between these two morphological patterns is reviewed here to highlight the conserved vs. variable aspects of hindbrain organization contributing to diversification of efferent sub-nuclei. Recent studies of segmental origins and migrations of branchiomotor, visceromotor and octavolateral efferent neurons revealed more segmental similarities than differences among vertebrates. Nonetheless, discrete variations exist in the origins of trigeminal, abducens and glossopharyngeal efferent nuclei. Segmental variation of the abducens nucleus remains the sole example of efferent neuronal homeosis during vertebrate hindbrain evolution. Comparison of cranial efferent segmental variations with surrounding intrinsic neurons will distinguish evolutionary changes in segment identity from lesser transformations in expression of unique neuronal types. The diversification of motoneuronal subgroups serving new muscles and functions appears to occur primarily by elaboration within and migration from already established segmental efferent pools rather than by de novo specification in different segmental locations. Identifying subtle variations in segment-specific neuronal phenotypes requires studies of cranial efferent organization within highly diverse groups such as teleosts and mammals
— id: 60894, year: 2005, vol: 66, page: 234, stat: Journal Article,

Instrumentation for measuring oculomotor performance and plasticity in larval organisms
Beck, James C; Gilland, Edwin; Baker, Robert; Tank, David W
2004 ;76:385-413, Methods in cell biology
— id: 49301, year: 2004, vol: 76, page: 385, stat: Journal Article,

Quantifying the ontogeny of optokinetic and vestibuloocular behaviors in zebrafish, medaka, and goldfish
Beck, James C; Gilland, Edwin; Tank, David W; Baker, Robert
2004 Dec;92(6):3546-3561, Journal of neurophysiology
We quantitatively studied the ontogeny of oculomotor behavior in larval fish as a foundation for studies linking oculomotor structure and function with genetics. Horizontal optokinetic and vestibuloocular reflexes (OKR and VOR, respectively) were measured in three different species (goldfish, zebrafish, and medaka) during the first month after hatching. For all sizes of medaka, and most zebrafish, Bode plots of OKR (0.065-3.0 Hz, +/-10 degrees/s) revealed that eye velocity closely followed stimulus velocity (gain > 0.8) at low frequency but dropped sharply above 1 Hz (gain < 0.3 at 3 Hz). Goldfish showed increased gain proportional to size across frequencies. Linearity testing with steps and sinusoids showed excellent visual performance (gain > 0.8) in medaka almost from hatching; but zebrafish and goldfish exhibited progressive improvement, with only the largest equaling medaka performance. Monocular visual stimulation in zebrafish and goldfish produced gains of 0.5 versus <0.1 for the eye viewing a moving versus stationary stimulus pattern but 0.25 versus <0.1 in medaka. Angular VOR appeared much later than OKR, initially at only high accelerations (>200 degrees /s at 0.5 Hz), first in medaka followed by larger (8.11 mm) zebrafish; but it was virtually nonexistent in goldfish. Velocity storage was not observed except for an eye velocity build-up in the largest medaka. In summary, a robust OKR was achieved shortly after hatching in all three species. In contrast, larval fish seem to be unique among vertebrates tested in their lack of significant angular VOR at stages where active movement is required for feeding and survival
— id: 47777, year: 2004, vol: 92, page: 3546, stat: Journal Article,

Comparative genomic analysis of vertebrate Hox3 and Hox4 genes
Hadrys, Thorsten; Prince, Victoria; Hunter, Michael; Baker, Robert; Rinkwitz, Silke
2004 Apr 15;302(2):147-164, Journal of experimental zoology. Part B. Molecular & developmental evolution
We used a comparative genomic approach to identify putative cis-acting regulatory sequences of the zebrafish hoxb3a and hoxb4a genes. We aligned genomic sequences spanning the clustered Hoxb1 to Hoxb5 genes from pufferfish, mice, and humans with the zebrafish hoxba and hoxbb cluster sequences. We identified multiple blocks of conserved sequences in non-coding regions within and surrounding the Hoxb3/b4 gene locus; a subset of these blocks are conserved in the zebrafish hoxbb cluster, despite loss of hoxb3/b4 genes. Overall, we find that the architecture of the Hoxb3/b4 loci and of the conserved sequence elements is very similar in teleosts and mammals. Our analyses also revealed two alternative transcripts of the zebrafish hoxb3a gene and an exon sequence unusually located 10 kb upstream of adjacent hoxb4a; an equivalent murine Hoxb3 exon has not yet been confirmed. We show that many of the Hoxb3/b4 conserved non-coding sequences correlate with functional neural enhancers previously described in the mouse. Further, within the conserved non-coding sequences we have identified binding sites for transcription factors, including Kreisler/Valentino, Krox20, Hox, and Pbx, some of which had not been previously described for the mouse. Finally, we demonstrate that the regulatory sequences of zebrafish hoxa3a are divergent with respect to the mouse ortholog Hoxa3, or the paralog hoxb3a. Despite limited conservation of regulatory sequences, zebrafish hoxa3a and hoxb3a genes share very similar expression profiles
— id: 46221, year: 2004, vol: 302, page: 147, stat: Journal Article,

Plasticity and tuning by visual feedback of the stability of a neural integrator
Major, G; Baker, R; Aksay, E; Mensh, B; Seung, HS; Tank, DW
2004 MAY 18 ;101(20):7739-7744, Proceedings of the National Academy of Sciences of the United States of America
Persistent neural firing is of fundamental importance to working memory and other brain functions because it allows information to be held 'online' following an input and to be integrated overtime. Many models of persistent activity rely on some kind of positive feedback internal to the neural circuit concerned; however, too much feedback causes runaway firing (instability), and too little results in loss of persistence (leak). This parameter sensitivity leads to the hypothesis that the brain uses an error signal (external feedback) to tune the stability of persistent firing by adjusting the amount of internal feedback. We test this hypothesis by manipulating external visual feedback, a putative sensory error signal, in a model system for persistent firing, the goldfish oculomotor neural integrator. Over tens of minutes to hours, electronically controlled visual feedback consistent with a leaky or unstable integrator can drive the integrator progressively more unstable or leaky, respectively. Eye fixation time constants can be reduced >100-fold to <1 s. Normal visual feedback gradually retunes the integrator back to stability. Changes in the phase of the sinusoidal vestibulo-ocular response are consistent with integrator detuning, as are changes in ocular drift following eye position shifts compensating for brief passive head movements during fixations. Corresponding changes in persistent firing of integrator neurons are presented in the accompanying article. The presence, strength, and reversibility of the plasticity demonstrate that, in this system, external visual feedback plays a vital role in gradually tuning the stability of the neural integrator
— id: 46620, year: 2004, vol: 101, page: 7739, stat: Journal Article,

Plasticity and tuning of the time course of analog persistent firing in a neural integrator
Major, G; Baker, R; Aksay, E; Seung, HS; Tank, DW
2004 MAY 18 ;101(20):7745-7750, Proceedings of the National Academy of Sciences of the United States of America
In a companion paper, we reported that the goldfish oculomotor neural integrator could be trained to instability or leak by rotating the visual surround with a velocity proportional to +/- horizontal eye position, respectively. Here we analyze changes in the firing rate behavior of neurons in area I in the caudal brainstem, a central component of the oculomotor neural integrator. Persistent firing could be detuned to instability and leak, respectively, along with fixation behavior. Prolonged training could reduce the time constant of persistent firing of some cells by more than an order of magnitude, to <1 s. Normal visual feedback gradually retuned persistent firing of integrator neurons toward stability, along with fixation behavior. In animals with unstable fixations, approximately half of the eye position-related cells had upward or unstable firing rate drift. In animals with leaky fixations, two-thirds of the eye position-related cells showed leaky firing drift. The remaining eye position-related cells, generally those with lower eye position thresholds, showed a more complex pattern of history-dependent/predictive firing rate drift in relation to eye drift. These complex drift cells often showed a drop in maximum persistent firing rate after training to leak. Despite this diversity, firing drift and the degree of instability or leak in firing rates were broadly correlated with fixation performance. The presence, strength, and reversibility of this plasticity demonstrate that, in this system, visual feedback plays a vital role in gradually tuning the time course of persistent neural firing
— id: 46621, year: 2004, vol: 101, page: 7745, stat: Journal Article,

Correlated Discharge among Cell Pairs within the Oculomotor Horizontal Velocity-to-Position Integrator
Aksay, Emre; Baker, Robert; Seung, HSebastian; Tank, David W
2003 ;23(34):10852-10858, Journal of neuroscience
In the oculomotor system, temporal integration of velocity commands into position signals may depend on synaptic feedback among neurons of a bilateral brainstem cell assembly known as the 'neural integrator.' Both ipsilateral excitatory and contralateral inhibitory projections between eye position-related integrator cells are hypothesized as a substrate for positive feedback supporting integration. Presence of feedback interactions should be evident in cross-correlation functions of neuron pairs. Here, unilateral and bilateral paired recordings were obtained during fixation behavior from neurons in goldfish brainstem area I, a key element of the integrator. During fixations, discharge of most unilateral pairs, composed of cells with eye position sensitivities of the same sign, was positively correlated with lag of 0-10 msec. Typically, a very narrow peak near zero lag was observed. Discharge of bilateral pairs, composed of cells with position sensitivities of the opposite sign, was either negatively correlated with lag of 0-10 msec or not correlated. Troughs in negative correlations always had minima between 3 and 5 msec lag. These results are consistent with the feedback hypothesis of temporal integration, highlighting excitation unilaterally and inhibition bilaterally.
— id: 46442, year: 2003, vol: 23, page: 10852, stat: Journal Article,

History Dependence of Rate Covariation between Neurons during Persistent Activity in an Oculomotor Integrator
Aksay, Emre; Major, Guy; Goldman, Mark S; Baker, Robert; Seung, HSebastian; Tank, David W
2003 ;13(11):1173-1184, Cerebral cortex
(from the journal abstract) Persistent firing in response to a brief stimulus is a neural correlate of short-term memory in a variety of systems. In the oculomotor neural integrator, persistent firing that encodes eye position is maintained in response to transient saccadic eye-velocity commands. To a first approximation, firing rates in the integrator vary linearly with eye position. Thus, viewed across many cells, the pattern of persistent firing in the integrator may be constrained to a unique line of stable states. Here this idea was tested by examining the relationship between firing rates of simultaneously recorded neurons. Paired recordings were obtained in awake goldfish from neurons in hindbrain area I, an essential part of the horizontal eye-position integrator. During spontaneous eye movements consisting of sequential fixations at different horizontal positions, the pair relationship between the majority of cells on the same side of the integrator was not unique: for a given rate of one cell, the rate of the paired cell assumed different values that depended systematically on the preceding saccade history. This finding suggests that the set of persistent firing states that encode eye position is not constrained to a unique line, and that models with stable states restricted to a such a line ...
— id: 46449, year: 2003, vol: 13, page: 1173, stat: Journal Article,

Long duration three-dimensional imaging of calcium waves in zebrafish using multiphoton fluorescence microscopy
Gilland, Edwin; Baker, Robert; Denk, Winfried
2003 Oct;205(2):176-177, Biological bulletin
— id: 42649, year: 2003, vol: 205, page: 176, stat: Journal Article,

Olanzapine's efficacy for relapse prevention in bipolar disorder: A randomized double-blind placebo-controlled 12-month clinical trial
Tohen, M; Bowden, C; Calabrese, J; Chou, J; Jacobs, T; Baker, R; Williamson, D; Evans, A
2003 SEP ;13(8):S212-S213, European neuropsychopharmacology
— id: 55426, year: 2003, vol: 13, page: S212, stat: Journal Article,

Central pathways mediating oculomotor reflexes in an elasmobranch, Scyliorhinus canicula
Graf, Werner; Gilland, Edwin; McFarlane, Matt; Knott, Laura; Baker, Robert
2002 Oct;203(2):236-238, Biological bulletin
— id: 60895, year: 2002, vol: 203, page: 236, stat: Journal Article,

The eyelid levator muscle: servant of two masters
May, Paul J; Baker, Robert G; Chen, Bingzhong
2002 ;17 Suppl 2:S4-S7, Movement disorders
— id: 60904, year: 2002, vol: 17 Suppl 2, page: S4, stat: Journal Article,

The frog as a unique vertebrate model for studying the rhombomeric organization of functionally identified hindbrain neurons
Straka, H; Baker, R; Gilland, E
2002 Feb-Mar;57(3-4):301-305, Brain research bulletin
The segmental organization of cranial nerve efferent, vestibular, and precerebellar neurons of larval ranid frogs is essentially retained in adult frogs, indicating the absence of any substantial postembryonic longitudinal migration of hindbrain neurons in this group. Comparison of the rhombomeric organization of vestibulomotor and branchiomotor pathways across different species suggests that the frog hindbrain blueprint is common to most vertebrates. The unique segmental stability seen in frogs can be, used to create a quantitative stereotactic map of the adult brain that mirrors the embryonic and larval rhombomeric framework. Such a map allows the large number of physiologically identified hindbrain neurons in adult frogs to be linked with their underlying genetic specification. Transgenic reporters and antisense knockdown of gene activities suspected of having necessary functions in patterning neurons within specific rhombomeres may allow direct testing of the proposed map. (C) 2002 Elsevier Science Inc
— id: 27510, year: 2002, vol: 57, page: 301, stat: Journal Article,

In vivo intracellular recording and perturbation of persistent activity in a neural integrator
Aksay, E; Gamkrelidze, G; Seung, HS; Baker, R; Tank, DW
2001 FEB ;4(2):184-193, Nature neuroscience
To investigate the mechanisms of persistent neural activity, we obtained in vivo intracellular recordings from neurons in an oculomotor neural integrator of the goldfish during spontaneous saccades and fixations. Persistent changes in firing rate following saccades were associated with step changes in interspike membrane potential that were correlated with changes in eye position. Perturbation of persistent activity with brief intracellular current pulses designed to mimic saccadic input only induced transient changes of firing rate and membrane potential. When neurons were hyperpolarized below action potential threshold, position-correlated step changes in membrane potential remained. Membrane potential fluctuations were greater during more depolarized steps. These results suggest that sustained changes in firing rate are supported not by either membrane multistability or changes in pacemaker currents, but rather by persistent changes in the rate or amplitude of synaptic inputs
— id: 55154, year: 2001, vol: 4, page: 184, stat: Journal Article,

Vestibuloocular reflex of the adult flatfish. III. A species-specific reciprocal pattern of excitation and inhibition
Graf W; Spencer R; Baker H; Baker R
2001 Sep;86(3):1376-1388, Journal of neurophysiology
In juvenile flatfish the vestibuloocular reflex (VOR) circuitry that underlies compensatory eye movements adapts to a 90 degrees relative displacement of vestibular and oculomotor reference frames during metamorphosis. VOR pathways are rearranged to allow horizontal canal-activated second-order vestibular neurons in adult flatfish to control extraocular motoneurons innervating vertical eye muscles. This study describes the anatomy and physiology of identified flatfish-specific excitatory and inhibitory vestibular pathways. In antidromically identified oculomotor and trochlear motoneurons, excitatory postsynaptic potentials (EPSPs) were elicited after electrical stimulation of the horizontal canal nerve expected to provide excitatory input. Electrotonic depolarizations (0.8-0.9 ms) preceded small amplitude (<0.5 mV) chemical EPSPs at 1.2-1.6 ms with much larger EPSPs (>1 mV) recorded around 2.5 ms. Stimulation of the opposite horizontal canal nerve produced inhibitory postsynaptic potentials (IPSPs) at a disynaptic latency of 1.6-1.8 ms that were depolarizing at membrane resting potentials around -60 mV. Injection of chloride ions increased IPSP amplitude, and current-clamp analysis showed the IPSP equilibrium potential to be near the membrane resting potential. Repeated electrical stimulation of either the excitatory or inhibitory horizontal canal vestibular nerve greatly increased the amplitude of the respective synaptic responses. These observations suggest that the large terminal arborizations of each VOR neuron imposes an electrotonic load requiring multiple action potentials to maximize synaptic efficacy. GABA antibodies labeled axons in the medial longitudinal fasciculus (MLF) some of which were hypothesized to originate from horizontal canal-activated inhibitory vestibular neurons. GABAergic terminal arborizations were distributed largely on the somata and proximal dendrites of oculomotor and trochlear motoneurons. These findings suggest that the species-specific horizontal canal inhibitory pathway exhibits similar electrophysiological and synaptic transmitter profiles as the anterior and posterior canal inhibitory projections to oculomotor and trochlear motoneurons. Electron microscopy showed axosomatic and axodendritic synaptic endings containing spheroidal synaptic vesicles to establish chemical excitatory synaptic contacts characterized by asymmetrical pre/postsynaptic membrane specializations as well as gap junctional contacts consistent with electrotonic coupling. Another type of axosomatic synaptic ending contained pleiomorphic synaptic vesicles forming chemical, presumed inhibitory, synaptic contacts on motoneurons that never included gap junctions. Altogether these data provide electrophysiological, immunohistochemical, and ultrastructural evidence for reciprocal excitatory/inhibitory organization of the novel vestibulooculomotor projections in adult flatfish. The appearance of unique second-order vestibular neurons linking the horizontal canal to vertical oculomotor neurons suggests that reciprocal excitation and inhibition are a fundamental, developmentally linked trait of compensatory eye movement circuits in vertebrates
— id: 60896, year: 2001, vol: 86, page: 1376, stat: Journal Article,

Development of the vertebrate inner ear
Rinkwitz S; Bober E; Baker R
2001 Oct;942(9):1-14, Annals of the New York Academy of Sciences
The inner ear, also called the membranous labyrinth, contains the cochlea, which is responsible for the sense of hearing, and the vestibular apparatus, which is necessary for the sense of balance and gravity. The inner ear arises in the embryo from placodes, which are epithelial thickenings of the cranial ectoderm symmetrically located on either side of hindbrain rhombomeres 5 and 6. Placode formation in mice is first visible at the 12-somite stage and is controlled by surrounding tissues, the paraxial mesoderm and neural ectoderm. Diffusible molecules such as growth factors play an important role in this process. The activity of several genes confers the identity to the placodal cells. Subsequent cellular proliferation processes under influences from the adjacent hindbrain cause the inner ear epithelium to invaginate and form a vesicle called the otocyst. Combinatorial expression of several genes and diffusible factors secreted from the vesicle epithelium and hindbrain control specification of distinct inner ear compartments. Transplantation studies and inner ear in vitro cultures show that each of these compartments is already committed to develop unique inner ear structures. Later developmental periods are principally characterized by intrinsic differentiation processes. In particular, sensory patches differentiate into fully functional sensory epithelia, and the semicircular canals along with the cochlear duct are elaborated and ossified
— id: 26566, year: 2001, vol: 942, page: 1, stat: Journal Article,

Rhombomeric organization of vestibular pathways in larval frogs
Straka, H; Baker, R; Gilland, E
2001 AUG 13 ;437(1):42-55, Journal of comparative neurology
Rhombencephalic subnuclei and projection pathways related to vestibular function were mapped in larval ranid frogs. The retention of overt postembryonic rhombomeres (r) allowed direct visualization of the locations of neurons retrogradely labeled with fluorescent dextran amines from the midbrain oculomotor complex, cerebellum, vestibular nuclei, and spinal cord. Oculomotor projecting vestibular neurons were mainly located in bilateral r1/2, ipsilateral r3, and contralateral r5-8, and spinal projecting vestibular neurons mainly in ipsilateral r4 and contralateral r5. Vestibular commissural neurons were located in r1-3 and r5-7 and were largely excluded from r4. Cerebellar projecting neurons included contralateral inferior olivary neurons in r8 and vestibular neurons in bilateral r6/7 and contralateral r1/2. Mapping these results onto adult anuran vestibular organization indicates that the superior vestibular nucleus derives from larval r1/2, the lateral vestibular nucleus from r3/4, and the major portions of the medial and descending vestibular nuclei from r5-8. The lateral vestibulospinal tract projects from an origin in r4, whereas a possible ascending tract of Deiters arises in r3. Rhombomere 5 contains a nuclear group that appears homologous to the tangential nucleus of fish, reptiles, and birds and thus likely serves gravistatic and linear vestibulomotor reflexes. Comparisons between frogs and other vertebrates suggest that vestibular neurons performing similar computational roles during head movements originate from the same segmental locations in different species. (C) 2001 Wiley-Liss, Inc
— id: 54955, year: 2001, vol: 437, page: 42, stat: Journal Article,

Anatomy and discharge properties of pre-motor neurons in the goldfish medulla that have eye-position signals during fixations
Aksay, E; Baker, R; Seung, HS; Tank, DW
2000 AUG ;84(2):1035-1049, Journal of neurophysiology
Previous work in goldfish has suggested that the oculomotor velocity-to-position neural integrator for horizontal eye movements may be confined bilaterally to a distinct group of medullary neurons that show an eye-position signal. To establish this localization, the anatomy and discharge properties of these position neurons were characterized with single-cell Neurobiotin labeling and extracellular recording in awake goldfish while monitoring eye movements with the scleral search-coil method. All labeled somata (n = 9) were identified within a region of a medially located column of the inferior reticular formation that was similar to 350 mu m in length, similar to 250 mu m in depth, and similar to 125 mm in width. The dendrites of position neurons arborized over a wide extent of the ventral half of the medulla with especially heavy ramification in the initial 500 mu m rostral of cell somata (n = 9). The axons either followed a well-defined ventral pathway toward the ipsilateral abducens (n = 4) or crossed the midline (n = 2) and projected toward the contralateral group of position neurons and the contralateral abducens. A mapping of the somatic region using extracellular single unit recording revealed that position neurons (n > 120) were the dominant eye-movement-related cell type in this area. Position neurons did not discharge below a threshold value of horizontal fixation position of the ipsilateral eye. Above this threshold, firing rates increased linearly with increasing temporal position [mean position sensitivity = 2.8 (spikes/s)/degrees, n = 44]. For a given fixation position, average rates of firing were higher after a temporal saccade than a nasal one (n = 19/19); the magnitude of this hysteresis increased with increasing position sensitivity. Transitions in firing rate accompanying temporal saccades were overshooting (n = 43/44), beginning, on average, 17.2 ms before saccade onset (n = 17). Peak firing rate change accompanying temporal saccades was correlated with eye velocity (n = 36/41). The anatomical findings demonstrate that goldfish medullary position neurons have somata that are isolated from other parts of the oculomotor system, have dendritic fields overlapping with axonal terminations of neurons with velocity signals, and have axons that are capable of relaying commands to the abducens. The physiological findings demonstrate that the signals carried by position neurons could be used by motoneurons to set the fixation position of the eye. These results are consistent with a role for position neurons as elements of the velocity-to-position neural integrator for horizontal eye movements
— id: 54548, year: 2000, vol: 84, page: 1035, stat: Journal Article,

Imaging of multicellular large-scale rhythmic calcium waves during zebrafish gastrulation
Gilland E; Miller AL; Karplus E; Baker R; Webb SE
1999 Jan 5;96(1):157-161, Proceedings of the National Academy of Sciences of the United States of America
Oscillations of cytosolic free calcium levels have been shown to influence gene regulation and cell differentiation in a variety of model systems. Intercellular calcium waves thus present a plausible mechanism for coordinating cellular processes during embryogenesis. Herein we report use of aequorin and a photon imaging microscope to directly observe a rhythmic series of intercellular calcium waves that circumnavigate zebrafish embryos over a 10-h period during gastrulation and axial segmentation. These waves first appeared at about 65% epiboly and continued to arise every 5-10 min up to at least the 16-somite stage. The waves originated from loci of high calcium activity bordering the blastoderm margin. Several initiating loci were active early in the wave series, whereas later a dorsal marginal midline locus predominated. On completion of epiboly, the dorsal locus was incorporated into the developing tail bud and continued to generate calcium waves. The locations and timing at which calcium dynamics are most active appear to correspond closely to embryonic cellular and syncytial sites of known morphogenetic importance. The observations suggest that a panembryonic calcium signaling system operating in a clock-like fashion might play a role during vertebrate axial patterning
— id: 57035, year: 1999, vol: 96, page: 157, stat: Journal Article,

Structure and function of vestibular and visual pathways controlling horizontal eye movements in the African cichlid fish, Haplochromis burtoni
Gilland, E; Rinkwitz, S; Baker, R
1999 Oct 23-28;25(1-2):1401-1401, Abstracts (Society for Neuroscience)
— id: 15845, year: 1999, vol: 25, page: 1401, stat: Journal Article,

Abducens internuclear and ascending tract of deiters inputs to medial rectus motoneurons in the cat oculomotor nucleus: synaptic organization
Nguyen LT; Baker R; Spencer RF
1999 Mar 8;405(2):141-159, Journal of comparative neurology
Abducens internuclear and ascending tract of Deiters (ATD) inputs to medial rectus motoneurons in the oculomotor nucleus are important for conjugate horizontal movements. In the present study, the organization of these separate populations of neurons and their synaptic connections with medial rectus motoneurons in the cat oculomotor nucleus have been examined by light and electron microscopy by using retrograde and anterograde axonal tracers. Consistent with the patterns of retrograde horseradish peroxidase labeling, the abducens internuclear projection is predominantly, if not exclusively, contralateral, whereas the ATD projection is exclusively ipsilateral, as demonstrated by anterograde autoradiographic and biocytin labeling. Both populations of synaptic endings contain spheroidal synaptic vesicles and establish synaptic contacts with modest postsynaptic densifications. In addition, ATD synaptic endings frequently are associated with subjunctional dense bodies and subsurface cisternae. The two populations of excitatory inputs differ, however, in their soma-dendritic distribution. The majority of abducens internuclear synaptic endings contact distal dendrites, whereas the majority of ATD synaptic endings contact proximal dendrites or somata. Abducens internuclear synaptic endings furthermore have a higher density of mitochondria than ATD synaptic endings. The more proximal location of ATD synaptic endings is consistent with the faster rise time and earlier reversal to polarizing currents of ATD excitatory postsynaptic potentials in comparison to those evoked by the abducens internuclear pathway as determined electrophysiologically. Given the differences in the physiologic signals conveyed by the abducens internuclear (eye velocity and eye position) and ATD (head velocity) pathways, the findings in this study suggest that the soma-dendritic stratification of the two inputs to medial rectus motoneurons may provide a means for the separate control of visuomotor and vestibular functions, respectively
— id: 57061, year: 1999, vol: 405, page: 141, stat: Journal Article,

Otolith ocular reflex function of the tangential nucleus in teleost fish
Suwa H; Gilland E; Baker R
1999 May 28;871:1-14, Annals of the New York Academy of Sciences
In teleost fish, the tangential nucleus can be identified as a compact, separate cell group lying ventral to the VIIIth nerve near the middle of the vestibular complex. Morphological analysis of larval and adult hindbrains utilizing biocytin and fluorescent tracers showed the tangential nucleus to be located entirely within rhombomeric segment 5 with all axons projecting into the contralateral MLF. Combined single-cell electrophysiology and morphology in alert goldfish found three classes of neurons whose physiological sensitivity could be readily correlated with rotational axes about either the anterior (45 degrees), posterior (135 degrees), or horizontal (vertical axis) semicircular canals. Tangential neurons could be distinguised from those in semicircular-canal specific subnuclei by an irregular, spontaneous background of 10-15 sp/s and sustained static sensitivity after +/- 4 degrees head displacements. Each axis-specific tangential subtype terminated appropriately onto oculomotor subnuclei responsible for either vertical, torsional, or horizontal eye movements and, in a few cases, axon collaterals descended in the MLF toward the spinal cord. We hypothesize, therefore, that the tangential nucleus consists of 3 axis-specific phenotypes that process gravitoinertial signals largely responsible for controlling oculomotor function, but that also in part, maintain body posture
— id: 11986, year: 1999, vol: 871, page: 1, stat: Journal Article,

From genes to behavior in the vestibular system
Baker R
1998 Sep;119(3):263-275, Otolaryngology, head & neck surgery
The central nervous system of all vertebrate embryos is derived from a series of conspicuous segments, called neuromeres, that are particularly visible in the midbrain and hindbrain areas, giving rise to the brain stem sensory and motor nuclei. This article focuses on a series of eight embryonic rhombomeric segments whose progeny can be identified in adults by the locations of iteratively homologous reticulospinal neurons and cranial motor nuclei IV through XII. Evidence shows that these rhombomeric units represent domains of gene expression, lineage restriction, and accordingly, individual vestibular neuronal phenotypes with unique oculomotor and spinal projections. Preliminary electrophysiologic and behavioral correlates of a few vestibulo-oculomotor subgroups are used as examples to illustrate the hypothesis that homologous vestibular phenotypes likely exist in all taxa because the genetic prepattern is already well established in primitive vertebrates. Finally, the segmented hindbrain arrangement responsible for the longitudinally arranged column of vestibular subnuclei is placed in perspective with genetic and molecular approaches that will eventually permit a causal reconstruction of the signaling mechanisms responsible for the development of unique vestibular subgroups
— id: 7496, year: 1998, vol: 119, page: 263, stat: Journal Article,

Rhombomeric organization of brainstem motor neurons in larval frogs
Straka H; Gilland E; Baker R
1998 Oct;195(2):220-222, Biological bulletin
— id: 7812, year: 1998, vol: 195, page: 220, stat: Journal Article,

Mossy and climbing fiber pathways play different roles in oculomotor performance and adaptation
Baker, R
1997 FEB 28 ;11(3):3792-3792, FASEB journal
— id: 53265, year: 1997, vol: 11, page: 3792, stat: Journal Article,

Neurobiology/sensory biology - Discussion
Bass, AH; Highstein, SM; Morris, CE; Kawasaki, M; Baker, R; Atema, J; Barlow, R
1997 FEB ;192(1):161-163, Biological bulletin
— id: 53271, year: 1997, vol: 192, page: 161, stat: Journal Article,

Excitatory and inhibitory vestibular pathways to the extraocular motor nuclei in goldfish
Graf W; Spencer R; Baker H; Baker R
1997 May;77(5):2765-2779, Journal of neurophysiology
Electrophysiological, ultrastructural, and immunohistochemical techniques were utilized to describe the excitatory and inhibitory vestibular innervation of extraocular motor nuclei in the goldfish. In antidromically activated oculomotor motoneurons, electrical stimulation of the intact contralateral vestibular nerve produced short-latency, variable amplitude electrotonic excitatory postsynaptic potentials (EPSPs) at 0.5-0.7 ms followed by chemical EPSPs at 1.0-1.3 ms. Stimulation of the ipsilateral vestibular nerve produced small amplitude membrane hyperpolarizations at a latency of 1.3-1.7 ms in which equilibrium potentials were slightly more negative than resting potentials. The inhibitory postsynaptic potentials (IPSPs) reversed with large amplitudes after the injection of chloride ions suggesting a proximal soma-dendritic location of terminals exhibiting high efficacy inhibitory synaptic conductances. In antidromically identified abducens motoneurons and putative internuclear neurons, electrical stimulation of the contralateral vestibular nerve produced large-amplitude, short-latency electrotonic EPSPs at 0.5 ms followed by chemical depolarizations at 1.2-1.3 ms. Stimulation of the ipsilateral vestibular nerve evoked IPSPs at 1.4 ms that were reversed after injection of current and/or chloride ions. gamma-Aminobutyric acid (GABA) antibodies labeled inhibitory neurons in vestibular subdivisions with axons projecting into the ipsilateral medial longitudinal fasciculus (MLF). Putative GABAergic terminals surrounded oculomotor, but not abducens, motoneurons retrogradely labeled with horseradish peroxidase. Hence the spatial distribution of GABAergic neurons and terminals appears highly similar in the vestibuloocular system of goldfish and mammals. Electron microscopy of motoneurons in the oculomotor and abducens nucleus showed axosomatic and axodendritic synaptic endings containing spheroidal synaptic vesicles establishing chemical, presumed excitatory, synaptic contacts with asymmetric pre- and/or postsynaptic membrane specializations. The majority of contacts with spheroidal vesicles displayed gap junctions in which the chemical and electrotonic synapses were either en face to dissimilar or adjacent to one another on the same soma/dendritic profiles. Another separate set of axosomatic synaptic endings, presumed to be inhibitory, contained pleiomorphic synaptic vesicles with symmetric pre- and/or postsynaptic membrane specializations that never included gap junctions. Excitatory and inhibitory synaptic contacts appeared equal in number but were more sparsely distributed along the soma-dendritic profiles of oculomotor as compared with abducens motoneurons. Collectively these data provide evidence for both disynaptic vestibular inhibition and excitation in all subdivisions of the extraocular motor nuclei suggesting the basic vestibulooculomotor blueprint to be conserved among vertebrates. We propose that unique vestibular neurons, transmitters, pathways, and synaptic arborizations are homologous structural traits that have been essentially preserved throughout vertebrate phylogeny by a shared developmental plan
— id: 60897, year: 1997, vol: 77, page: 2765, stat: Journal Article,

Neurobiology/sensory biology - Discussion
Kawasaki, M; Fetcho, JR; Wiederhold, M; Baker, R; Eaton, RC; Baxter, DA; Bass, AH; Morris, CE; Barlow, R; Highstein, SM; Sack, FD
1997 FEB ;192(1):154-156, Biological bulletin
— id: 53270, year: 1997, vol: 192, page: 154, stat: Journal Article,

Normal and adapted visuooculomotor reflexes in goldfish
Marsh E; Baker R
1997 Mar;77(3):1099-1118, Journal of neurophysiology
Under normal physiological conditions, whole field visual motion generally occurs in response to either active or passive self-motion. In the laboratory, selective movement of the visual surround produces an optokinetic response (OKR) that acts primarily to support the vestibuloocular reflex (VOR). During visual world motion, however, the OKR can be viewed as operating independently over frequency and amplitude ranges insufficient for vestibular activation. The goal of the present study was to characterize this isolated behavior of the OKR in goldfish as an essential step for studying central neuronal correlates of visual-vestibular interactions and the mechanisms underlying oculomotor adaptation. After presentation of either binocular sinusoidal or step visual stimuli, conjugate eye movements were elicited with an amplitude and phase profile similar to that of other vertebrates. An early and a delayed component were measured with different dynamics that could be altered independently by visual training. The ensuing visuomotor plasticity was robust and exhibited five major characteristics. First, the gain of both early and delayed components of the OKR increased > 100%. Second, eye velocity decreased 0.5-2.0 s before the change in direction of stimulus velocity. Third, on lengthening the duration of a constant velocity visual stimulus (e.g., from 8 to 16 s), eye velocity decreased toward 0 degrees/s. This behavior was correlated with the direction and period as opposed to the frequency of the visual stimulus ('period tuning'). Fourth, visual stimulus training increased VOR eye velocity with a ratio of 0.6 to 1 to that measured for the OKR. Fifth, the OKR adaptation, eye velocity consistently oscillated in a conjugate, symmetrical fashion at 2.4 Hz in the light, whereas in the dark, a rhythmical low-amplitude eye velocity occurred at the visual training frequency. We conclude that the frequency and amplitude of visual stimuli for eliciting the goldfish OKR are well suited for complementing the VOR. Unlike most mammals, OKR adaptive modifications significantly alter VOR gain, whereas the effects of VOR training are much less on OKR gain. These observations suggest that both distributed circuits and discrete neuronal populations control visuo- and vestibulomotor performance. Finally, the existence of a rhythmic, 'period tuned' visuomotor behavior provides a unique opportunity to examine the neuronal mechanisms of adaptive plasticity
— id: 56968, year: 1997, vol: 77, page: 1099, stat: Journal Article,

Signal processing by brainstem neurons during spontaneous and nystagmic eye movements in the goldfish
Pastor, M; delaCruz, RR; Baker, R
1996 MAY ;493P(7):S14-S15, Journal of physiology
— id: 52860, year: 1996, vol: 493P, page: S14, stat: Journal Article,

Dendritic morphology of projection neurons in the cat pretectum
Schmidt, M; Lehnert, G; Baker, RG; Hoffmann, KP
1996 JUN 10 ;369(4):520-532, Journal of comparative neurology
The distribution and dendritic morphology of neurons in the cat pretectal nuclear complex were analyzed with respect to their projection to the ipsilateral dorsal lateral geniculate nucleus (LGNd) and the ipsilateral inferior olive (IO). Single and double retrograde tracing techniques were combined with intracellular injections of either horseradish peroxidase into electrophysiologically identified pretectal neurons or Lucifer Yellow into retrogradely labeled somata. Pretectal cells afferent to the LGNd were located in the nucleus of the optic tract (NOT), adjacent dorsal terminal nucleus of the accessory optic system (DTN), and posterior pretectal nucleus (NPP). Cells projecting to the IO were also distributed throughout the NOT-DTN and dorsal part of the NPP. Separate tracer injections (fluorogold and horseradish peroxidase [HRP] or granular blue) into the LGNd and the IO showed considerable overlap of labeled neurons in the NOT and dorsal NPP. Double-labeled neurons, however, were not-observed after double tracer injections into LGNd and IO. Partial topographical segregation of the two populations was observed along the dorsoventral axis because LGNd-projecting neurons exhibited maximum density ventral to that of IO neurons. Pretectal cells to the LGNd had cell body diameters between 16 and 48 mu m. Somatic shapes varied between fusiform and multipolar with considerable overlap between these two morphological appearances. Neurons projecting to the IO exhibited similar cell body sizes and their morphology also varied from fusiform to multipolar. Quantitative analysis of dendritic field size and orientation, number and order of dendritic arborizations, and symmetry of the dendritic tree revealed no statistically significant difference between the two neuronal populations. Hence, neurons of the two populations cannot be unequivocally identified just from the dendritic morphology. By contrast, dendritic morphology was correlated with the topographical location of either cell type within the pretectal nuclei rather than projection. Thus, the morphological appearance of neurons located dorsally predominantly was fusiform while neurons located ventrally mostly were multipolar. (C) 1996 Wiley-Liss, Inc
— id: 52893, year: 1996, vol: 369, page: 520, stat: Journal Article,

Segmental organization of vestibular and reticular projections to spinal and oculomotor nuclei in the zebrafish and goldfish
Suwa, H; Gilland, E; Baker, R
1996 OCT ;191(2):257-259, Biological bulletin
— id: 52732, year: 1996, vol: 191, page: 257, stat: Journal Article,

EFFECT OF TEMPERATURE ON THE NORMAL AND ADAPTED VESTIBULO-OCULAR REFLEX IN THE GOLDFISH
MCELLIGOTT, JG; WEISER, M; BAKER, R
1995 OCT ;74(4):1463-1472, Journal of neurophysiology
1. The vestibule-ocular reflex, a sensorimotor process, operates in a similar manner for homeothermic (mammals) and poikilothermic (fish) animals. However, individual physiological, biochemical, and/or pharmacological thermolabile processes that underlie the operation of this reflex could alter the operation of this reflex in a poikilotherm. The object of this study was to determine what aspects of the vestibule-ocular reflex are affected by temperature changes naturally experienced by a poikilothermic animal, the goldfish. 2. Experiments were conducted on the visuovestibulo-(Vis-VOR) and vestibule-ocular reflex (VOR) during normal operation as well as during the acquisition (learning) and retention (memory) phases of adaptive gain change. These studies were carried out at temperatures to which goldfish had been acclimated over several weeks and after rapid (<5 min) shifts from this acclimation temperature. 3. Normal sinusoidal Vis-VOR and VOR gains before adaptation were found to be independent of the acclimation temperature over a wide range. Acute temperature changes of up to 10 degrees C either above or below a 20 degrees C acclimation temperature (Ac degrees C = 20 degrees C) did not significantly modify normal visual and/or vestibular oculomotor reflex gains. 4. Surprisingly, slight reductions in temperature, as small as 2.5 degrees C, noticeably reduced Vis-VOR and VOR gain adaptations. Both short (3 h) and intermediate (up to 48 h) term reflex modifications were affected. Loss of adaptation was observed 10 degrees C below the acclimation temperature (Ac-10 degrees C); however, return to the original temperature immediately restored most (60-100%) of the previously acquired Vis-VOR and VOR gain changes. In contrast, elevation of temperature up to 10 degrees C above the acclimation temperature (Ac+10 degrees C) did not alter either increases or decreases in the adapted Vis-VOR or VOR gain. 5. A decrease in temperature reduced the magnitude of an adapted VOR gain increase and elevated the magnitude of an adapted gain decrease, thus returning the VOR gain back toward its normal control gain before adaptation. Because both increases and decreases in VOR gain were affected by the same temperature reduction, the cold effect was not a generalized reflex suppression, but inactivation of a process responsible for maintaining VOR adaptation. 6. During the acquisition phase, the time course and magnitude of adaptive VOR gain increases at temperatures acutely set 8-10 degrees C below the acclimation temperature were similar to those obtained at the acclimation temperature. Because the same temperature decrease inactivated retention of adapted VOR gain changes, the neuronal processes underlying the acquisition and the retention phases of Vis-VOR or VOR adaptation are suggested to differ qualitatively. 7. With the use of velocity step stimuli, both the adapted dynamic (<100 ms) and sustained (>100 ms) components of VOR adaptation were reduced by cooling. This effect on the dynamic component demonstrates an alteration in the shortest latency pathway through the vestibular nucleus and indicates that one thermosensitive site resides in the brain stem. 8. These results also show that, over a wide range of temperatures (20 +/- 10 degrees C), the neuronal processing that is responsible for the normal operation of the visuovestibulo- and/or vestibule-ocular reflex and for the retention of reflex adaptation functions by separate physiological processes within the same brain stem and cerebellar circuitry. 9. We conclude that temperature exhibits a unique, and unexpected, state-dependent effect on sensorimotor regulation and adaptation for periods up to 48 h. Temperature does not alter normal VOR or the acquisition phase of an adapted gain change. However, because it inactivates retention of adaptive VOR gain changes reversibly, we propose that thermolability of an adapted VOR gain change reflects the alteration of a separate ligand and/or current related membrane event. As a result, visual-vestibular oculomotor learning is masked, but only temporarily as the complete memory trace or engram is actually never lost
— id: 86683, year: 1995, vol: 74, page: 1463, stat: Journal Article,

VOCAL-ACOUSTIC PATHWAYS IN A TELEOST FISH
BASS, AH; MARCHATERRE, MA; BAKER, R
1994 JUL ;14(7):4025-4039, Journal of neuroscience
Many teleost fish generate acoustic signals for vocal communication by the synchronized, high-frequency contraction of skeletal, sonic muscles. In midshipman, eight groups of brainstem neurons were distinguished after biocytin application to the sonic nerve that, we propose, represent the entire vocal motor circuit. Biocytin-filled terminals were ubiquitous within all areas containing labeled neurons and, together with ultrastructural evidence, suggested a serial, transneuronal transport at synaptic sites between at least three neuronal groups. The most intensely labeled neurons were positioned in the caudal brainstem and included a previously characterized pacemaker-motoneuron circuit and a newly recognized ventral medullary nucleus that itself gave rise to extensive commissural and lateral brainstem bundles linking the pacemaker circuitry to the rostral brainstem. Five additional groups formed a column rostrally within the medial brainstem adjacent to eighth nerve (octaval)-recipient nuclei largely presumed to be acoustic. This column extended dorsally up to the ventricular cell layer and as far anterior as midbrain isthmal levels. The best-defined group was in the octaval efferent nucleus that directly innervates the sacculus that is considered the auditory division of the inner ear. Saccular afferents and neurons throughout the medial column were also filled after biocytin application to the saccular nerve. This vocal-acoustic network overlaps low-threshold, electrical stimulation sites in the rostral brainstem that elicit vocalizations. The medial column must therefore be the origin of the descending pathway controlling activation of the vocal pacemaker circuitry and likely forms the basis for acoustically elicited vocalizations. We suggest this network, together with input from the pacemaker circuitry, is also the origin of a vocal-related, corollary discharge to acoustic nuclei. Direct links between vocal and acoustic brain regions are thus traits common to aquatic and terrestrial vertebrates
— id: 52389, year: 1994, vol: 14, page: 4025, stat: Journal Article,

Cerebellar role in adaptation of the goldfish vestibuloocular reflex
Pastor AM; de la Cruz RR; Baker R
1994 Sep;72(3):1383-1394, Journal of neurophysiology
1. The time course of eye velocity responses elicited by head velocity steps was compared in normal, adapted, and cerebellectomized goldfish. Vestibuloocular reflex (VOR) adaptation was induced by combined visual and vestibular stimulation that altered the ratio of eye to head velocity (VOR gain) toward values either higher or lower than the control amplitude. The velocity step consisted of alternating periods of head rotation at a constant velocity of 16 degrees/s zero-to-peak around the vertical axis. 2. The VOR produced by head velocity steps consisted of an early acceleration-related component, the dynamic response, separated from a sustained period of constant velocity, the plateau, by a sag that occurred around 125-150 ms. Latency of the VOR averaged 18 ms for the adducting eye and 20 ms for abducting eye independent of the initial VOR gain. Adapted dynamic VOR responses diverged from the control records at the earliest detectable latency after both high and low VOR gain training. This result demonstrates modification in the shortest latency brain stem VOR pathway, presumably, the three-neuron reflex arc. 3. After acute cerebellectomy the adapted dynamic response was unaltered for approximately 50 ms in the low-gain and 70 ms in the high-gain VOR states. Not less than 30% of the altered velocity was retained throughout the remaining dynamic and sustained component. These results demonstrate that the vestibulocerebellum is not necessary for the maintenance of the earliest adapted eye velocity. Hence brain stem pathways are sufficient for the expression of the modified VOR. 4. Purkinje cells identified by simple and complex spikes were recorded extracellularly in the area of the vestibulocerebellum, where electrical stimulation produced conjugate ipsiversive horizontal eye movements. Independent eye and head velocity sensitivities were determined in response to visual world motion and VOR suppression, respectively. The two signals either added, canceled, or were both present in Purkinje cells throughout the range of eye velocity induced by vertical axis visual-vestibular stimulation. 5. Latency of Purkinje cell discharge to either a vestibular or visual velocity step exhibited means of 43 and 70 ms, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)
— id: 65784, year: 1994, vol: 72, page: 1383, stat: Journal Article,

EYE POSITION AND EYE VELOCITY INTEGRATORS RESIDE IN SEPARATE BRAIN-STEM NUCLEI
PASTOR, AM; DELACRUZ, RR; BAKER, R
1994 JAN 18 ;91(2):807-811, Proceedings of the National Academy of Sciences of the United States of America
Two types of central nervous system integrators are critical for oculomotor performance. The first integrates velocity commands to create position signals that hold fixation of the eye. The second stores relative velocity of the head and visual surround to stabilize gaze both during and after the occurrence of continuous self and world motion. We have used recordings from single neurons to establish that the ''position'' and ''velocity'' integrators for horizontal eye movement occupy adjacent, but nonoverlapping, locations in the goldfish medulla. Lidocaine inactivation of each integrator results in the eye movement deficits expected if horizontal eye position and velocity signals are processed separately. These observations also indicate that each brainstem compartment generates and stores these signals. Consequently, each integrator exhibits functional autonomy. Therefore, we propose that the intrinsic electrophysiological properties of the constituent neurons in each brainstem subnucleus may be sufficient for producing integrator rhythmicity
— id: 52606, year: 1994, vol: 91, page: 807, stat: Journal Article,

DEVELOPMENTAL RELATIONS BETWEEN 6TH NERVE MOTOR-NEURONS AND THEIR TARGETS IN THE CHICK-EMBRYO
WAHL, CM; NODEN, DM; BAKER, R
1994 OCT ;201(2):191-202, Developmental dynamics
The developmental relations between abducens (VI) nerves and their targets, the lateral rectus, quadratus, and pyramidalis muscles, have been examined in the chick embryo from early neural tube stages through 10 days of incubation. Sites of myoblast origins were determined by microinjection of replication-incompetent retroviruses containing the LacZ reporter into paraxial mesoderm corresponding to somitomeres 3-5. Motor neurons and axons were identified by Bodian staining, immunocytochemistry, and application of DiI and DiO to dissected peripheral nerves, Anlage of the dorsal oblique originate in somitomere 3, close to the ventrolateral margin of the mid-to-caudal mesencephalon. Precursors of the lateral rectus arise deep within somitomere 4, beside the future metencephalon (rhombomere ''A''). Quadratus and pyramidalis precursors are located between and partially segregated from these other two anlage. VIth nerve axons exit rhombomeres 5 and 6 via multiple median roots, fasciculate, and by stage 17 have elongated rostrally beneath the hindbrain. Immediately caudal to a mesenchymal pre-muscle condensation located deep to rhombomere 2, the VIth nerve separates into two branches. One branch enters the rostral portion of the condensation, from which quadratus and pyramidalis muscles will segregate. This branch projects exclusively from rhombomere 5 and is the accessory abducens nerve. The other branch enters the caudal, presumptive lateral rectus, region of the condensation. This is the abducens nerve, and it projects from cell located in both rhombomeres 5 and 6. These findings indicate that specific matching of motor nerves with their presumptive targets begins prior to the differentiation and segregation of myogenic populations, and that spatial organization of developing eye muscles is initiated well before they interact with connective tissue precursors derived from the neural crest. (C) 1994 Wiley-Liss, Inc
— id: 52315, year: 1994, vol: 201, page: 191, stat: Journal Article,

Conservation of neuroepithelial and mesodermal segments in the embryonic vertebrate head [published erratum appears in Acta Anat (Basel) 1994;149(2):164]
Gilland E; Baker R
1993 ;148(2-3):110-123, Acta anatomica
The organization of embryonic efferent cranial nerves is addressed here by interspecies comparison of segmentally patterned neuromeres, efferent neuronal populations and early mesodermal sources of target muscles. The segmental constancy of these three structural patterns is evaluated for elasmobranch, teleost, reptile, bird and mammal embryos and compared with the segmentally restricted expression patterns of Hox genes. A conserved series of hindbrain neuroepithelial segments (rhombomeres) is present in all of these taxa. Dye-labeling experiments demonstrate that the segmental locations of efferent neurons projecting through individual cranial nerves are likewise highly conserved. Notable segmental variation is however shown in the location of the VI and IX-XII motoneurons, suggesting the likelihood of homeotic-like changes in relations between rhombomere and neuronal 'identity' during vertebrate evolution. Since experimentally induced shifts in expression borders of Hox genes appear to be correlated with alterations in segment identity and/or neuronal phenotype, the need for further examination of segmental locations of specific neuronal groups and the segmental expression patterns of Hox genes between species is emphasized. Comparison of early cranial mesodermal subdivisions in elasmobranchs with descriptions of somitomeres in amniotes suggests that a series of axially unique mesodermal populations may also be conserved throughout vertebrates. The possibility is raised that common mechanisms of axial specification may underlie the initial appearance of segmental patterning in both neural and mesodermal layers during gastrulation. Implications of these conserved patterns for understanding the phylogenetic origin of the vertebrate head are briefly discussed
— id: 7884, year: 1993, vol: 148, page: 110, stat: Journal Article,

LONGITUDINAL AND TANGENTIAL MIGRATION OF CRANIAL NERVE EFFERENT NEURONS IN THE DEVELOPING HINDBRAIN OF SQUALUS-ACANTHIAS
GILLAND, E; BAKER, R
1992 OCT ;183(2):356-358, Biological bulletin
— id: 54406, year: 1992, vol: 183, page: 356, stat: Journal Article,

ANATOMICAL ORGANIZATION OF THE BRAIN-STEM OCTAVOLATERALIS AREA OF THE OYSTER TOADFISH, OPSANUS-TAU
HIGHSTEIN, SM; KITCH, R; CAREY, J; BAKER, R
1992 MAY 22 ;319(4):501-518, Journal of comparative neurology
Anatomical studies were undertaken to analyze the brainstem organization of the auditory, vestibular, and lateral line nuclei in a teleost, the oyster toadfish, Opsanus tau. Neuronal cytoarchitectonics and horseradish peroxidase label of cranial nerves were utilized to delineate the borders of the five octavus and two lateralis brainstem nuclei. Each of the eight octavolateralis nerves were labeled individually to compare and contrast their central projections. Projections of the three semicircular canals were found to be largely overlapping. Terminal fields were observed within the eminentia granularis and in each of the octavus nuclei. The nucleus anterior octavus was reciprocally innervated by the semicircular canals and the saccule. The canals terminated heavily in the ventral portions of the anterior octavus, whereas the saccule terminated extensively in the dorsal nuclear portions. The saccule also distributed terminals throughout the octavus cell column, including a light terminal field within the dorsal, medial, and anterior portions of the descending octavus nucleus, a region densely innervated by this end-organ in other species. These results suggest that the anterior octavus nucleus may have a dual function. The dorsal portions may be an auditory relay nucleus, whereas the ventral portions may subserve vestibular function. Utriclar and lagenar afferents also terminated throughout the octavus cell column. Afferents of the anterior and posterior lateral lines ended within the eminentia granularis and the lateral line nuclei. Semicircular canal afferents and lateral line afferents appeared completely segregated within the eminentia. The above results are useful as an aid in the understanding of an ongoing, comprehensive functional analysis of auditory and vestibular mechanisms in toadfish and complement previous work on the efferent vestibular and sound-producing motor systems. Examination of toadfish contributes to a more general and complete overview of the octavolateralis area of teleosts and the eventual identification of primitive and derived patterns of octaval organization. Additionally, this work may permit the further demonstration of species-typical characters that may indicate adaptations to particular behavioral repertoires
— id: 51958, year: 1992, vol: 319, page: 501, stat: Journal Article,

CRANIAL EFFERENT NEURONS EXTEND PROCESSES THROUGH THE FLOOR PLATE IN THE DEVELOPING HINDBRAIN
MARSH, E; UCHINO, K; BAKER, R
1992 OCT ;183(2):354-356, Biological bulletin
— id: 54405, year: 1992, vol: 183, page: 354, stat: Journal Article,

Characterization and adaptive modification of the goldfish vestibuloocular reflex by sinusoidal and velocity step vestibular stimulation
Pastor AM; de la Cruz RR; Baker R
1992 Dec;68(6):2003-2015, Journal of neurophysiology
1. The normal and adapted vestibuloocular reflex (VOR) of goldfish was characterized by means of sinusoidal, velocity step, and position step head rotations about the vertical axis. VOR adaptation was induced by short-term, 1- to 4-h, presentation of visual and vestibular stimuli that altered the ratio of eye to head velocity. 2. The VOR response measured with sinusoidal oscillations in the dark was close to ideal compensatory values over 2 decades (1/32-2 Hz). Gain approximated unity, and phase, in relation to the head, was nearly 180 degrees. The VOR was linear within the range of head velocity tested (4-64 degrees/s). 3. Head velocity steps from 1/8 to 1 Hz produced steplike eye velocity profiles that could be divided into an early acceleration-related 'dynamic' component and a later constant-velocity 'sustained' period frequently separated by a sag at approximately 0.1-0.15 s from the initiation of eye movement. The sustained response exhibited no decay during the constant-velocity component of the step. 4. Higher temporal resolution of the dynamic response showed the adducting eye movement to have a shorter latency, faster rise time, and larger peak gain than the abducting eye movement. The characteristics of this directional asymmetry were similar for position steps and electrical stimulation of the vestibular nerve. However, the asymmetry was not observed during sinusoidal head rotation, the sustained component of the step response, or after electrical stimulation of the VIth and IIIrd nerves. We conclude that this directional asymmetry is of central origin and may be largely due to the parallel vestibular and abducens internuclear neuron pathways onto medial rectus motoneurons. 5. The VOR adaptation process for both higher and lower eye velocity exhibited an exponential time course with time constants of 55 and 45 min, respectively. After continuous sinusoidal training for 4 h, VOR gain reached an asymptotic level 5% away from perfect suppression in the low-gain training, but 19% away from the actual performance in the high-gain paradigm. The time constant for VOR gain reversal was 5 h, and an asymptotic level 40% less than performance was reached within 10 h. 6. Adapted VOR gain was symmetrical for both directions of eye movement measured either during sinusoidal rotation or the sustained part of the velocity step. VOR adaptation also produced a comparable gain change in the nasal and temporal directions of the dynamic component, but this reflected the asymmetric characteristics observed in the preadapted condition.(ABSTRACT TRUNCATED AT 400 WORDS)
— id: 65792, year: 1992, vol: 68, page: 2003, stat: Journal Article,

GABA AND GLYCINE AS INHIBITORY NEUROTRANSMITTERS IN THE VESTIBULOOCULAR REFLEX
SPENCER, RF; BAKER, R
1992 MAY 22 ;656(7):602-611, Annals of the New York Academy of Sciences
— id: 51895, year: 1992, vol: 656, page: 602, stat: Journal Article,

THE PATHWAYS AND FUNCTIONS OF GABA IN THE OCULOMOTOR SYSTEM
SPENCER, RF; WANG, SF; BAKER, R
1992 JUN ;90(6):307-331, Progress in brain research
— id: 51939, year: 1992, vol: 90, page: 307, stat: Journal Article,

EVOLUTION OF HOMOLOGOUS VOCAL CONTROL TRAITS
Bass, A; Baker, R
1991 Oct-Nov;38(4-5):240-254, Brain behavior & evolution
Evolutionary neurobiolocists want to know how neuronal properties (or traits) have been modified to subserve adaptive changes in behavioral phenotypes. Homology can provide a conceptual framework to distinguish the separate contributions of phylogenetic factors and current adaptive modifications to extant traits and behaviors. In this essay, a suite of nine vocal/sonic motor traits are compared in two orders of teleost fishes, the Batrachoidiformes and Scorpaeniformes. Only three of the traits are modified among Scorpaeniformes, the more advanced group. The large number of conserved characters among the study species suggests their sonic motor systems are homologs. This conclusion is consistent with the known phylogeny of teleosts and further implies that homologous sonic motor traits are more extensively modified among more recently evolved members (in this case the Scorpaeniformes) of the teleostean lineage. Since homology implies a common ontogenetic history for any trait, modifications thereof can potentially be linked to changes in identifiable developmental events, which themselves are homologs. Several hypotheses are proposed to account for the origins of modified sonic traits. The further demonstration that modified traits of the sonic motor system are in fact adaptations sets the stage for behavioral ecological studies that attempt to understand why the modified traits underlie behavioral changes that increase an individual's fitness
— id: 32141, year: 1991, vol: 38, page: 240, stat: Journal Article,

BEHAVIOR OF CAT ABDUCENS MOTONEURONS FOLLOWING THE INJECTION OF TOXIC RICIN INTO THE LATERAL RECTUS MUSCLE
Delacruz, RR; Baker, R; Delgadogarcia, JM
1991 Mar 29;544(2):260-268, Brain research
The aim of this investigation was to study the behaviour of identified abducens motoneurons in the chronic cat following a single injection of toxic ricin into the lateral rectus muscle. Lateral rectus electromyographic potentials induced by VIth nerve stimulation disappeared, and abducens antidromic field potentials decreased by 90% 3 days following ricin injection. Several abnormalities and a significant decrease in eye position and velocity sensitivities were observed in motoneuron activity up to 8-10 days following ricin injection. Contrary to a previous report for axotomized abducens motoneurons, no functional sign of recovery was observed. Histological analysis showed a survival of 10-15% of the abducens motoneuron population 10 days following ricin injection. From this time on, recorded motoneurons behaved like controls, but showed a specific retraction signal suggesting an exclusive projection onto the retractor bulbi muscle. Although intermingled in the nucleus with motoneurons, no recorded abducens internuclear interneuron was affected by the ricin during one month following the injection
— id: 32185, year: 1991, vol: 544, page: 260, stat: Journal Article,

RESPONSE OF ADULT CAT ABDUCENS INTERNUCLEAR INTERNEURONS TO SELECTIVE REMOVAL OF THEIR TARGET MOTONEURONS
Delacruz, RR; Baker, R; Delgadogarcia, JM
1991 Apr;84(1):167-172, Experimental brain research
The morphological and physiological integrity of abducens internuclear interneurons was evaluated following chemical removal of their almost exclusive target, i.e. the contralateral medial rectus motoneuron population. Motoneuron death was induced by toxic ricin injection into the ipsilateral medial rectus muscle. The main advantage of this method is that target removal is not associated with presynaptic axon damage. The activity of identified abducens internuclear interneurons was recorded before and after target removal during spontaneous eye movements in the chronic cat preparation. Several abnormalities and a remarkable decrease in eye position and velocity sensitivities were observed in the discharge pattern of these neurons for a period of 15-20 days following target removal. After that time all recorded interneurons behaved normally. A parallel morphological study showed the absence of any abducens internuclear interneuron death. These results indicate that, after a critical period, the abducens internuclear interneuron population recovers its normal behavior following target removal with no evidence of neuronal loss
— id: 32188, year: 1991, vol: 84, page: 167, stat: Journal Article,

Influence of temperature on adaptive changes of the vestibuloocular reflex in the goldfish
McElligott JG; Weiser M; Baker R
1991 ;627:375-377, Annals of the New York Academy of Sciences
— id: 65749, year: 1991, vol: 627, page: 375, stat: Journal Article,

SEXUAL DIMORPHISMS IN THE VOCAL CONTROL-SYSTEM OF A TELEOST FISH - MORPHOLOGY OF PHYSIOLOGICALLY IDENTIFIED NEURONS
Bass, AH; Baker, R
1990 Dec;21(8):1155-1168, Journal of neurobiology
— id: 31825, year: 1990, vol: 21, page: 1155, stat: Journal Article,

BEHAVIOR OF ACCESSORY ABDUCENS AND ABDUCENS MOTONEURONS DURING EYE RETRACTION AND ROTATION IN THE ALERT CAT
Delgadogarcia, JM; Evinger, C; Escudero, M; Baker, R
1990 Aug;64(2):413-422, Journal of neurophysiology
— id: 32052, year: 1990, vol: 64, page: 413, stat: Journal Article,

Neuronal adaptation accompanying metamorphosis in the flatfish
Graf W; Baker R
1990 Oct;21(7):1136-1152, Journal of neurobiology
Flatfish provide a natural paradigm to investigate adaptive changes in the central nervous system of vertebrates. During their metamorphosis, the animals undergo a 90 degrees tilt to one side or the other to become the bottom-adapted adult flatfish. The eye on the down side is pushed over to the up side. Thus, vestibular and oculomotor coordinate systems rotate 90 degrees relative to each other. As a result, during swimming movements different types of compensatory eye movements are produced before and after metamorphosis by the same vestibular stimulation. Intracellular staining of central neurons with horseradish peroxidase revealed that in postmetamorphic flatfish second-order horizontal canal neurons contact vertical eye muscle motoneuron pools on both sides of the brain via pathways that are absent in all other vertebrates studied. These unique connections provide the necessary and sufficient connectivity to adapt the flatfish's eye movement system to the animals' postmetamorphic existence. Although the adult fish has a bilaterally asymmetric appearance, the central nervous connectivity reestablishes symmetry in the vestibulo-oculomotor system
— id: 60898, year: 1990, vol: 21, page: 1136, stat: Journal Article,

Synaptic organization of tectal-facial pathways in cat. II. Synaptic potentials following midbrain tegmentum stimulation
May PJ; Vidal PP; Baker R
1990 Aug;64(2):381-402, Journal of neurophysiology
1. The organization of the synaptic pathways underlying midbrain tegmentum influence over the facial musculature was studied with the use of an acute electrophysiological approach in the cat. Under pentobarbital sodium anesthesia, synaptic potentials were recorded intracellularly in antidromically identified facial motoneurons following electrical stimulation of the paralemniscal zone. The cells of origin and the pathways responsible for the potentials evoked from the paralemniscal zone were defined with the use of retrograde transport of horseradish peroxidase (HRP). The putative role of the paralemniscal zone with regard to the production of disynaptic, tectally evoked potentials in facial motoneurons was investigated both by inactivating this nucleus with injections of lidocaine and by making acute brain stem lesions to sever the paralemniscal-facial and other afferent pathways. 2. Following paralemniscal stimulation, monosynaptic, excitatory postsynaptic potentials (EPSPs) with latencies ranging from 0.6 to 0.9 ms, steep rising phases, and amplitudes in excess of 4.0 mV were recorded in motoneurons of the temporal and auriculoposterior subdivisions, which supply the pinna muscles. Smaller amplitude EPSPs (less than 1.0 mV) with monosynaptic latencies were observed in the zygomatic subdivision. Polysynaptic EPSPs with latencies ranging from 1.0 to 1.8 ms were also observed in all three of these subdivisions. However, only long-latency EPSPs, arriving at 2.0 ms or later, were present in ventral subdivision motoneurons. 3. Inhibitory postsynaptic potentials (IPSPs) were also frequently recorded in facial motoneurons after paralemniscal stimulation. Monosynaptic IPSPs with latencies ranging from 0.8 to 1.2 ms and amplitudes in excess of 4.0 mV were recorded in facial motoneurons of the temporozygomatic and auriculoposterior subdivisions, as were polysynaptic IPSPs with latencies ranging from 1.2 to 1.8 ms. IPSPs were sometimes observed in combination with a smaller, shorter latency EPSPs. Only long-latency IPSPs of greater than 2.0 ms were recorded in ventral subdivision motoneurons. In all cases, both the EPSPs and the IPSPs were graded in character and could be augmented by multiple stimuli. 4. The contralateral paralemniscal zone and the supraoculomotor area, bilaterally, represented the two most prominent afferent sources labeled after HRP injection of the facial nucleus. The superior colliculus and numerous reticular formation regions were also identified as facial nucleus afferents by the presence of retrogradely labeled cells. The retrogradely labeled cells in the paralemniscal zone exhibited heterogeneous soma size. HRP-labeled axons of the paralemniscal-facial pathway were observed to cross the midline by traveling ventral to the brachium conjunctivum in the caudal mesencephalon.(ABSTRACT TRUNCATED AT 400 WORDS)
— id: 60905, year: 1990, vol: 64, page: 381, stat: Journal Article,

REGENERATION AND SOMA SIZE CHANGES FOLLOWING AXOTOMY OF THE TROCHLEAR NERVE
Murphy, EH; Brown, J; Iannuzzelli, PG; Baker, R
1990 May 22;295(4):685-697, Journal of comparative neurology
— id: 31875, year: 1990, vol: 295, page: 685, stat: Journal Article,

REGENERATION AND SOMA SIZE CHANGES FOLLOWING AXOTOMY OF THE TROCHLEAR NERVE
Murphy, EH; Brown, J; Iannuzzelli, PG; Baker, R
1990 Feb 22;292(4):524-536, Journal of comparative neurology
— id: 31889, year: 1990, vol: 292, page: 524, stat: Journal Article,

EVIDENCE FOR GLYCINE AS AN INHIBITORY NEUROTRANSMITTER OF VESTIBULAR, RETICULAR, AND PREPOSITUS HYPOGLOSSI NEURONS THAT PROJECT TO THE CAT ABDUCENS NUCLEUS
Spencer, RF; Wenthold, RJ; Baker, R
1989 Aug;9(8):2718-2736, Journal of neuroscience
— id: 31626, year: 1989, vol: 9, page: 2718, stat: Journal Article,

BEHAVIOR OF NEURONS IN THE ABDUCENS NUCLEUS OF THE ALERT CAT .3. AXOTOMIZED MOTONEURONS
DELGADOGARCIA, JM; DELPOZO, F; SPENCER, RF; BAKER, R
1988 JAN ;24(1):143-160, Neuroscience
— id: 41854, year: 1988, vol: 24, page: 143, stat: Journal Article,

Synaptic organization of the tectal-facial pathways in the cat. I. Synaptic potentials following collicular stimulation
Vidal PP; May PJ; Baker R
1988 Aug;60(2):769-797, Journal of neurophysiology
1. The synaptic pathways underlying tectal influence over pinna movements were studied using an acute electrophysiological approach. Under pentobarbital anesthesia, postsynaptic potentials were recorded intracellularly in antidromically identified, cat facial motoneurons following electrical stimulation of the superior colliculus. How collicular topography is reflected in these synaptic potentials was examined using multiple stimulation sites. The pathways responsible for tectally evoked synaptic potentials were studied by making acute brain stem lesions and by intra-axonal horseradish peroxidase (HRP) staining. 2. Monosynaptic excitatory potentials (EPSPs) with latencies ranging from 0.7 to 1.1 ms and amplitudes that were always less than 1 mV were recorded in motoneurons following stimulation of the contralateral superior colliculus. Larger disynaptic EPSPs ranging in latency from 1.2 to 2.0 ms were recorded both in isolation and in association with monosynaptic EPSPs. In addition, disynaptic inhibitory synaptic potentials (IPSPs) with latencies ranging from 1.5 to 2.5 ms were observed, often in combination with monosynaptic EPSPs. Both disynaptic EPSPs and IPSPs were graded, augmented by multiple stimuli and found in all categories of motoneurons. 3. Stimulation of the ipsilateral superior colliculus produced nearly the same spectrum of potentials and latencies as did contralateral tectal stimulation. Occlusion between ipsi- and contralaterally evoked IPSPs suggests there might be a common element in the inhibitory disynaptic pathways. 4. More discrete populations of facial motoneurons were investigated. Specifically, motoneurons innervating the platysma and orbicularis oculi muscles, the intrinsic ear muscles, and muscles that move the vibrissae all displayed tectally elicited mono- and di-synaptic potentials. Collicular input was not restricted to motoneurons involved in orienting the pinnae. 5. The presence, polarity, and amplitude of the synaptic potentials evoked in individual facial motoneurons exhibited variations that were related to the site of stimulation in either the ipsi- or contralateral colliculus. These variations are compatible with the idea that the collicular input to facial motoneurons is topographically organized. 6. Acute lesions at the level of the superior olive indicated that the pathway producing the contralateral monosynaptic EPSPs runs, near the midline, ipsilateral to the target facial nucleus, whereas the contralateral disynaptic and the ipsilateral mono- and disynaptic pathways lie further lateral.(ABSTRACT TRUNCATED AT 400 WORDS)
— id: 11010, year: 1988, vol: 60, page: 769, stat: Journal Article,

EYE-MOVEMENT REPERTOIRE OF THE CABAZON SCULPIN, SCORPAENICHTHYS-MARMORATUS
Weiser, M; Bass, A; Mcelligott, JG; Baker, R
1988 Oct;175(2):308-308, Biological bulletin
— id: 31428, year: 1988, vol: 175, page: 308, stat: Journal Article,

Extra- and intracellular HRP analysis of the organization of extraocular motoneurons and internuclear neurons in the guinea pig and rabbit
Evinger C; Graf WM; Baker R
1987 Aug 15;262(3):429-445, Journal of comparative neurology
The distribution of extraocular motoneurons and abducens and oculomotor internuclear neurons was determined in guinea pigs by injecting horseradish peroxidase (HRP) into individual extraocular muscles, the abducens nucleus, the oculomotor nucleus, and the cerebellum. Motoneurons in the oculomotor nucleus innervated the ipsilateral inferior rectus, inferior oblique, medial rectus, and the contralateral superior rectus and levator palpebrae muscles. Most motoneurons of the trochlear nucleus projected to the contralateral superior oblique muscle although a small number innervated the ipsilateral superior oblique. The abducens and accessory abducens nuclei innervated the ipsilateral rectus and retractor bulbi muscles, respectively. The somata of abducens internuclear neurons formed a cap around the lateral and ventral aspects of the abducens nucleus. The axons of these internuclear neurons terminated in the medial rectus subdivision of the contralateral oculomotor nucleus. At least two classes of guinea pig oculomotor internuclear interneurons exist. One group, located primarily ventral to the oculomotor nucleus, innervated the abducens nucleus and surrounding regions. The second group, lying mainly in the dorsal midline area of the oculomotor nucleus, projected to the cerebellum. Intracellular staining with HRP demonstrated similar soma-dendritic organization for oculomotor and trochlear motoneurons of both guinea pigs and rabbits. Dendrites of oculomotor motoneurons radiated symmetrically from the soma to cover approximately one-third of the entire nucleus, and each motoneuron sent at least one dendrite into the central gray overlying the oculomotor nucleus. In both species, a small percentage of oculomotor motoneurons possessed axon collaterals that terminated both within and outside of the nucleus. The dendrites of trochlear motoneurons extended into the medial longitudinal fasciculus and the reticular formation lateral to the nucleus. Our data on the topography of motoneurons and internuclear neurons in the guinea pig and soma-dendritic organization of motoneurons in the guinea pig and rabbit show that these species share common organizational and morphological features. In addition, comparison of these data with those from other mammals reveals that dendritic complexity (number of dendrites per motoneuron) of extraocular motoneurons exhibits a systematic increase with animal size
— id: 60899, year: 1987, vol: 262, page: 429, stat: Journal Article,

MOTONEURONAL INNERVATION AND MECHANICAL-PROPERTIES OF EXTRAOCULAR-MUSCLES IN THE CATFISH, (ICTALURUS-PUNCTATUS)
LENNERSTRAND, G; BAKER, R
1987 NOV ;131(3):361-369, Acta physiologica Scandinavica
— id: 41660, year: 1987, vol: 131, page: 361, stat: Journal Article,

Morphology and distribution of serotoninergic and oculomotor internuclear neurons in the cat midbrain
May PJ; Baker H; Vidal PP; Spencer RF; Baker R
1987 Dec 8;266(2):150-170, Journal of comparative neurology
Serotoninergic fibers have been reported in both the abducens and facial nuclei of the cat. Furthermore, serotoninergic dorsal raphe and oculomotor internuclear neurons occupy similar locations in the periaqueductal gray overlying the oculomotor and trochlear motor nuclei. To resolve the issue of whether these two populations of neurons overlap, serotoninergic fibers were assayed in the abducens and facial nucleus; then the morphologies and distributions of identified serotoninergic neurons and oculomotor internuclear neurons were determined. Both the abducens and facial nuclei contained varicosities labelled with antibody to serotonin, but a much higher density of immunoreactive fibers was present in the latter, especially in its medial aspect. Distinct synaptic profiles labelled with antibodies to serotonin were observed in both nuclei. In both cases, terminal profiles contained numerous small, predominantly spheroidal, synaptic vesicles as well as a few, large, dense-core vesicles. These profiles made synaptic contacts onto dendritic and, in the facial nucleus, somatic profiles that occasionally displayed asymmetric, postsynaptic, membrane densifications. Following injection of horseradish peroxidase into either the abducens or facial nuclei, double-label immunohistochemical techniques demonstrated that the serotoninergic and oculomotor internuclear neurons form two distinct cell populations. The immunoreactive serotoninergic cells were distributed within the dorsal raphe nucleus, predominantly caudal to the retrogradely labelled oculomotor internuclear neurons. The latter were located in the oculomotor nucleus along its dorsal border and in the adjacent supraoculomotor area. Intracellular injection of horseradish peroxidase revealed that oculomotor internuclear neurons have multipolar somata with up to ten long, tapering dendrites that bifurcate approximately five times. Their dendritic fields were generally contained within the nucleus and adjacent supraoculomotor area. In contrast, putative serotoninergic neurons were often spindle-shaped and exhibited far fewer primary dendrites. Many of these long, narrow, sparsely branched dendrites crossed the midline and extended to the surface of the cerebral aqueduct. In the vicinity of the aqueduct they branched repeatedly to form a dendritic thicket. The axons of the intracellularly stained serotoninergic neurons emerged either from the somata or the end of a process with dendritic morphology, and in some cases they produced axon collaterals within the periaqueductal gray. Thus the oculomotor internuclear and serotoninergic populations differ in both distribution and morphology.(ABSTRACT TRUNCATED AT 400 WORDS)
— id: 11295, year: 1987, vol: 266, page: 150, stat: Journal Article,

ANATOMY AND PHYSIOLOGY OF INTRACELLULARLY LABELED OMNIPAUSE NEURONS IN THE CAT AND SQUIRREL-MONKEY
Strassman, A; Evinger, C; Mccrea, RA; Baker, RG; Highstein, SM
1987 Jul;67(2):436-440, Experimental brain research
— id: 31155, year: 1987, vol: 67, page: 436, stat: Journal Article,

BRAIN-STEM NEURONS ARE PECULIAR FOR OCULOMOTOR ORGANIZATION
BAKER, R
1986 JUN 11 ;64(2):257-271, Progress in brain research
— id: 41389, year: 1986, vol: 64, page: 257, stat: Journal Article,

BEHAVIOR OF NEURONS IN THE ABDUCENS NUCLEUS OF THE ALERT CAT .1. MOTONEURONS
DELGADOGARCIA, JM; DELPOZO, F; BAKER, R
1986 APR ;17(4):929-&, Neuroscience
— id: 41595, year: 1986, vol: 17, page: 929, stat: Journal Article,

BEHAVIOR OF NEURONS IN THE ABDUCENS NUCLEUS OF THE ALERT CAT .2. INTERNUCLEAR NEURONS
DELGADOGARCIA, JM; DELPOZO, F; BAKER, R
1986 APR ;17(4):953-&, Neuroscience
— id: 41596, year: 1986, vol: 17, page: 953, stat: Journal Article,

MOTONEURONS AND INTERNUCLEAR NEURONS OF THE MOUSE ABDUCENS NUCLEUS
SHAW, MD; BAKER, R
1986 MAR ;214(3):A120-A120, Anatomical record
— id: 41488, year: 1986, vol: 214, page: A120, stat: Journal Article,

HISTOCHEMICAL-LOCALIZATION OF ACETYLCHOLINESTERASE IN RELATION TO MOTOR NEURONS AND INTERNUCLEAR NEURONS OF THE CAT ABDUCENS NUCLEUS
SPENCER, RF; BAKER, R
1986 APR ;15(2):137-154, Journal of neurocytology
— id: 41588, year: 1986, vol: 15, page: 137, stat: Journal Article,

AN INTRACELLULAR HRP-STUDY OF CAT TENSOR TYMPANI MOTONEURONS
FRIAUF, E; BAKER, R
1985 ;57(3):499-511, Experimental brain research
— id: 41247, year: 1985, vol: 57, page: 499, stat: Journal Article,

The vestibuloocular reflex of the adult flatfish. I. Oculomotor organization
Graf W; Baker R
1985 Oct;54(4):887-899, Journal of neurophysiology
The flatfish species constitute a natural paradigm for investigating adaptive changes in the vertebrate central nervous system. During metamorphosis all species of flatfish experience a 90 degree change in orientation between their vestibular and extraocular coordinate axes. As a result, the optic axes of both eyes maintain their orientation with respect to earth horizontal, but the horizontal semicircular canals become oriented vertically. Since the flatfish propels its body with the same swimming movements when referenced to the body as a normal fish, the horizontal canals are exposed to identical accelerations, but in the flatfish these accelerations occur in a vertical plane. The appropriate compensatory eye movements are simultaneous rotations of both eyes forward or backward (i.e., parallel), in contrast to the symmetric eye movements in upright fish (i.e., one eye moves forward, the other backward). Therefore, changes in the extraocular muscle arrangement and/or the neuronal connectivity are required. This study describes the peripheral and central oculomotor organization in the adult winter flounder, Pseudopleuronectes americanus. At the level of the peripheral oculomotor apparatus, the sizes of the horizontal extraocular muscles (lateral and medial rectus) were considerably smaller than those of the vertical eye muscles, as quantified by fiber counts and area measurements of cross sections of individual muscles. However, the spatial orientations and the kinematic characteristics of all six extraocular muscles were not different from those described in comparable lateral-eyed animals. There were no detectable asymmetries between the left and the right eye. Central oculomotor organization was investigated by extracellular horseradish peroxidase injections into individual eye muscles. Commonly described distributions of extraocular motor neurons in the oculomotor, trochlear, and abducens nuclei were found. These motor neuron pools consisted of two contralateral (superior rectus and superior oblique) and four ipsilateral populations (inferior oblique, inferior rectus, medial rectus, and lateral rectus). The labeled cells formed distinct motor neuron populations, which overlapped little. As expected, the numbers of labeled motoneurons differed in horizontal and vertical eye movers. The numerical difference was especially prominent in comparing the abducens nucleus with one of the vertical recti subdivisions. Nevertheless, there was bilateral symmetry between the motoneurons projecting to the left and right eyes.(ABSTRACT TRUNCATED AT 400 WORDS)
— id: 60901, year: 1985, vol: 54, page: 887, stat: Journal Article,

The vestibuloocular reflex of the adult flatfish. II. Vestibulooculomotor connectivity
Graf W; Baker R
1985 Oct;54(4):900-916, Journal of neurophysiology
The peripheral and central oculomotor organization of the adult flatfish presents no morphological substrates that suffice to explain adaptive changes in its vestibuloocular reflex system. The necessity for an adaptation occurs because of a 90 degrees displacement of the vestibular with respect to the extraocular coordinate axes during metamorphosis. Since a reorganization of vestibuloocular pathways must be hypothesized (12), the location and termination of electrophysiologically identified secondary vestibular neurons with focus on the horizontal canal system was studied with the intracellular horseradish peroxidase method in adult winter flounders. Pseudopleuronectes americanus. The oculomotor target sites of vertical canal related neurons were similar to those described in mammals. Presumed excitatory anterior canal neurons bifurcated after the main axon had crossed the midline. The descending branch headed toward the spinal cord. The ascending branch reached the oculomotor nucleus via the contralateral medial longitudinal fasciculus and terminated in the superior rectus and inferior oblique subdivisions. Presumed inhibitory posterior canal neurons ascended ipsilaterally in the medial longitudinal fasciculus and terminated mainly in the superior rectus and inferior oblique subdivisions. Horizontal canal neurons exhibited characteristics distinctly different from mammalian ones. Two types of second-order neurons were observed. In the first case, cell bodies were located in the anterior portion of the vestibular nuclear complex. After crossing the midline, the axon ascended in the contralateral medial longitudinal fasciculus. Major termination sites were found in the inferior oblique and superior rectus subdivisions of the oculomotor nucleus. Axonal branches then recrossed the midline and terminated in identical locations on the ipsilateral side. In the second case, cell bodies were located in the descending vestibular nucleus. Their axons crossed the midline and also ascended in the contralateral medial longitudinal fasciculus. Major termination sites were in the trochlear nucleus and in the inferior rectus subdivision of the oculomotor nucleus. As in the first case, axonal branches also recrossed the midline and terminated in identical motoneuron pools on the ipsilateral side. The above target sites were exactly those expected to be used in a reciprocal excitatory-inhibitory fashion during compensatory eye movements. Head-down movement would be excitatory for the lower horizontal canal producing contractions of both superior recti and inferior obliques as well as relaxation of the antagonistic inferior recti and superior obliques.(ABSTRACT TRUNCATED AT 400 WORDS)
— id: 60900, year: 1985, vol: 54, page: 900, stat: Journal Article,

ANATOMICAL CONNECTIONS OF THE NUCLEUS PREPOSITUS OF THE CAT
MCCREA, RA; BAKER, R
1985 ;237(3):377-407, Journal of comparative neurology
— id: 41218, year: 1985, vol: 237, page: 377, stat: Journal Article,

CYTOLOGY AND INTRINSIC ORGANIZATION OF THE PERIHYPOGLOSSAL NUCLEI IN THE CAT
MCCREA, RA; BAKER, R
1985 ;237(3):360-376, Journal of comparative neurology
— id: 41217, year: 1985, vol: 237, page: 360, stat: Journal Article,

MORPHOLOGY OF MOTONEURONS IN A MIXED MOTOR POOL OF THE CAT FACIAL NUCLEUS THAT INNERVATE ORBICULARIS OCULIS AND QUADRATUS LABII SUPERIORIS, STAINED INTRACELLULARLY WITH HORSERADISH-PEROXIDASE
SHAW, MD; BAKER, R
1985 ;14(2):627-643, Neuroscience
— id: 41243, year: 1985, vol: 14, page: 627, stat: Journal Article,

TOADFISH SONIC MOTOR SYSTEM .2. MORPHOLOGY
Weiser, M; Bennett, NT; Bennett, MVL; Baker, R
1985 ;169(2):556-557, Biological bulletin
— id: 30823, year: 1985, vol: 169, page: 556, stat: Journal Article,

BLINKING AND ASSOCIATED EYE-MOVEMENTS IN HUMANS, GUINEA-PIGS, AND RABBITS
EVINGER, C; SHAW, MD; PECK, CK; MANNING, KA; BAKER, R
1984 ;52(2):323-339, Journal of neurophysiology
— id: 41061, year: 1984, vol: 52, page: 323, stat: Journal Article,

"SYNAPTIC POTENTIALS IN ANTIDROMICALLY IDENTIFIED OCULOMOTONEURONS IN THE WINTER FLOUNDER, PSEUDOPLEURONECTES-AMERICANUS"
GRAF, W; BAKER, R
1984 ;167(2):527-527, Biological bulletin
— id: 40880, year: 1984, vol: 167, page: 527, stat: Journal Article,

Adaptive changes of the vestibulo-ocular reflex in flatfish are achieved by reorganization of central nervous pathways
Graf W; Baker R
1983 Aug 19;221(4612):777-779, Science
Flatfish provide a natural model for the study of adaptive changes in the vestibulo-ocular reflex system. During metamorphosis their vestibular and oculomotor coordinate systems undergo a 90 degree relative displacement. As a result, during swimming movements different types of compensatory eye movements are produced before and after metamorphosis by the same vestibular stimulation. Intracellular staining of central nervous connections in the flatfish with horseradish peroxidase revealed that in postmetamorphic fish secondary horizontal semicircular canal neurons contact vertical eye muscle motoneuron pools on both sides of the brain via pathways that are absent in all other vertebrates studied
— id: 60902, year: 1983, vol: 221, page: 777, stat: Journal Article,

Morphology of posterior canal related secondary vestibular neurons in rabbit and cat
Graf W; McCrea RA; Baker R
1983 ;52(1):125-138, Experimental brain research
The morphology of secondary vertical vestibular neurons was investigated by injection of horseradish peroxidase (HRP) into cells connected to the posterior canal system in rabbits (lateral-eyed animals) and cats (frontal-eyed animals). Vestibular neurons were identified by stimulation with bipolar electrodes implanted into the ampullae of the anterior and posterior (PC) semicircular canals of pigmented rabbits; in the cat, these cells were identified by natural and electrical stimulation. Axons monosynaptically activated by PC stimulation were injected with HRP in the medial longitudinal fasciculus (MLF). These were later reconstructed by light microscopy after the brains had been processed with a DAB-CoCl2 method. In the rabbit the majority of the axons bifurcated after crossing the midline with one branch ascending and the other descending in the MLF. The ascending branches gave rise to collaterals that terminated in both the trochlear nucleus and the inferior rectus subdivision of the oculomotor nucleus. In addition some axons also sent collaterals into the paramedian pontine reticular formation, the periaqueductal grey and the interstitial nucleus of Cajal. The descending branches were followed to the caudal part of the medulla in the MLF and gave rise to collaterals terminating in the vestibular nuclei, the medullary reticular formation, the perihypoglossal nuclei, the abducens nucleus, and the facial nucleus. In another cell type axons crossed the midline without giving off any collaterals and proceeded caudally in the caudal MLF. The synaptic effects of the two types of cells were concluded to be excitatory and inhibitory, respectively. Cell bodies of contralaterally projecting neurons were located in either the medial or ventro-lateral vestibular nuclei. In the cat we observed two neuron classes, with contralaterally projecting axons, whose synaptic effects are presumably excitatory. Their cell somata were located in the medial vestibular nucleus. Termination patterns were similar to both the trochlear and oculomotor nuclei, but neither projected to the abducens nucleus. One class of neurons was almost identical to that found in the rabbit with the main axon bifurcating in the MLF. The second type lacked a descending branch in the MLF. Axon collaterals of the latter type crossed the midline within the oculomotor nucleus after terminating in the inferior rectus subdivision to reach a similar portion of the ipsilateral oculomotor nucleus. Collaterals of these axons also terminated bilaterally in the supraoculomotor region between trochlear and oculomotor nucleus, the interstitial nucleus of Cajal and prerubral loci (including the fields of Forel). In similarity to the rabbit, presumed inhibitory vestibular neurons were found with axons directed caudally in the MLF without brain stem collaterals.(ABSTRACT TRUNCATED AT 400 WORDS)
— id: 60903, year: 1983, vol: 52, page: 125, stat: Journal Article,

DIRECT PROJECTIONS FROM VESTIBULAR NUCLEI TO FACIAL NUCLEUS IN CATS
SHAW, MD; BAKER, R
1983 ;50(6):1265-1280, Journal of neurophysiology
— id: 41127, year: 1983, vol: 50, page: 1265, stat: Journal Article,

THE LOCATIONS OF STAPEDIUS AND TENSOR TYMPANI MOTONEURONS IN THE CAT
Shaw, MD; Baker, R
1983 ;216(1):10-19, Journal of comparative neurology
— id: 30655, year: 1983, vol: 216, page: 10, stat: Journal Article,

COMPARISON OF THE MORPHOLOGY OF PHYSIOLOGICALLY IDENTIFIED ABDUCENS MOTOR AND INTER-NUCLEAR NEURONS IN THE CAT - A LIGHT MICROSCOPIC STUDY EMPLOYING THE INTRACELLULAR INJECTION OF HORSERADISH-PEROXIDASE
HIGHSTEIN, SM; KARABELAS, A; BAKER, R; MCCREA, RA
1982 ;208(4):369-381, Journal of comparative neurology
— id: 40397, year: 1982, vol: 208, page: 369, stat: Journal Article,

NEURONAL-ACTIVITY IN PREPOSITUS NUCLEUS CORRELATED WITH EYE- MOVEMENT IN THE ALERT CAT
Lopezbarneo, J; Darlot, C; Berthoz, A; Baker, R
1982 ;47(2):329-352, Journal of neurophysiology
— id: 30332, year: 1982, vol: 47, page: 329, stat: Journal Article,

Electron microscopic observations of axon collateral synaptic endings of cat oculomotor motoneurons stained by intracellular injection of horseradish peroxidase
Spencer RF; Evinger C; Baker R
1982 Feb 25;234(2):423-429, Brain research
Motoneurons in the cat oculomotor nucleus have been identified electrophysiologically and stained by intracellular injection of horseradish peroxidase. Axon collateral arborizations with preterminal and terminal boutons identified by light microscopy corresponded to synaptic endings observed by electron microscopy. Despite variations in size and shape, synaptic endings showed similar ultra-structural features and established asymmetrical predominantly axodendritic synaptic contacts usually characterized by the presence of subjunctional dense bodies underlying the postsynaptic membrane densification
— id: 63143, year: 1982, vol: 234, page: 423, stat: Journal Article,

SOME THOUGHTS ABOUT THE 3 NEURONS IN THE VESTIBULAR OCULAR REFLEX
BAKER, R; EVINGER, C; MCCREA, RA
1981 ;374(NOV):171-188, Annals of the New York Academy of Sciences
— id: 40303, year: 1981, vol: 374, page: 171, stat: Journal Article,

DIFFERENTIAL LOCALIZATION OF ACETYLCHOLINESTERASE (ACHE) IN CAT ABDUCENS MOTO-NEURONS AND INTER-NUCLEAR NEURONS
SPENCER, RF; BAKER, R
1981 ;199(3):A243-A243, Anatomical record
— id: 40238, year: 1981, vol: 199, page: A243, stat: Journal Article,

Synaptic organization of cat accessory abducens nucleus
Baker R; McCrea RA; Spencer RF
1980 Mar;43(3):771-791, Journal of neurophysiology
— id: 63139, year: 1980, vol: 43, page: 771, stat: Journal Article,

MORPHOLOGICAL AND PHYSIOLOGICAL IDENTIFICATION OF EXCITATORY PONTINE RETICULAR NEURONS PROJECTING TO THE CAT ABDUCENS NUCLEUS AND SPINAL-CORD
Grantyn, R; Baker, R; Grantyn, A
1980 ;198(1):221-228, Brain research
— id: 27973, year: 1980, vol: 198, page: 221, stat: Journal Article,

EYE-MOVEMENT RELATED ACTIVITY AND MORPHOLOGY OF 2ND ORDER VESTIBULAR NEURONS TERMINATING IN THE CAT ABDUCENS NUCLEUS
Mccrea, RA; Yoshida, K; Berthoz, A; Baker, R
1980 ;40(4):468-473, Experimental brain research
— id: 27940, year: 1980, vol: 40, page: 468, stat: Journal Article,

LOCALIZATION AND MORPHOLOGY OF CAT RETRACTOR BULBI MOTO-NEURONS
Spencer, RF; Baker, R; Mccrea, RA
1980 ;43(3):754-770, Journal of neurophysiology
— id: 27923, year: 1980, vol: 43, page: 754, stat: Journal Article,

MORPHO-PHYSIOLOGICAL STUDY OF THE CAT ACCESSORY ABDUCENS NUCLEUS
Baker, R; Mccrea, R; Spencer, RF
1979 ;193(3):474-475, Anatomical record
— id: 30140, year: 1979, vol: 193, page: 474, stat: Journal Article,

AXON COLLATERALS OF CAT MEDIAL RECTUS MOTO-NEURONS
Evinger, C; Baker, R; Mccrea, RA
1979 ;174(1):153-160, Brain research
— id: 30084, year: 1979, vol: 174, page: 153, stat: Journal Article,

VESTIBULAR PROJECTIONS TO MEDIAL RECTUS SUBDIVISION OF OCULOMOTOR NUCLEUS
Baker, R; Highstein, SM
1978 ;41(6):1629-1646, Journal of neurophysiology
— id: 29655, year: 1978, vol: 41, page: 1629, stat: Journal Article,

EXCITATORY TERMINATION OF ABDUCENS INTER-NUCLEAR NEURONS ON MEDIAL RECTUS MOTONEURONS - RELATIONSHIP TO SYNDROME OF INTER- NUCLEAR OPHTHALMOPLEGIA
Highstein, SM; Baker, R
1978 ;41(6):1647-1661, Journal of neurophysiology
— id: 29656, year: 1978, vol: 41, page: 1647, stat: Journal Article,

Monosynaptic excitation of trochlear motoneurons following electrical stimulation of the prepositus hypoglossi nucleus
Baker R; Berthoz A; Delgado-Garcia J
1977 Jan 31;121(1):157-161, Brain research
— id: 63142, year: 1977, vol: 121, page: 157, stat: Journal Article,

RESPONSES OF CAT PREPOSITUS HYPOGLOSSI NEURONS TO HORIZONTAL ANGULAR-ACCELERATION
Blanks, RHI; Volkind, R; Precht, W; Baker, R
1977 ;2(3):391-403, Neuroscience
— id: 29533, year: 1977, vol: 2, page: 391, stat: Journal Article,

2 PROJECTIONS OF OCULOMOTOR INTERNUCLEAR NEURONS
Maciewicz, RJ; Romagnano, MA; Baker, R; Highstein, SM
1977 ;187(4):642-643, Anatomical record
— id: 29609, year: 1977, vol: 187, page: 642, stat: Journal Article,

Internal organization of the cat inferior olive
Baker R; Llinas R; Sotelo C
1975 ;21(S1):16-16, Journal of postgraduate medicine
— id: 55762, year: 1975, vol: 21, page: 16, stat: Journal Article,

Blockage of inhibition by ammonium acetate action on chloride pump in cat trochlear motoneurons
Llinas R; Baker R; Precht W
1974 May;37(3):522-532, Journal of neurophysiology
— id: 9998, year: 1974, vol: 37, page: 522, stat: Journal Article,

Electronic coupling between inferior olive neurons in the cat
Llinas R; Baker R; Sotelo C
1974 ;37:2-2, Electroencephalography & clinical neurophysiology
— id: 55734, year: 1974, vol: 37, page: 2, stat: Journal Article,

Electrotonic coupling between neurons in cat inferior olive
Llinas R; Baker R; Sotelo C
1974 May;37(3):560-571, Journal of neurophysiology
— id: 9996, year: 1974, vol: 37, page: 560, stat: Journal Article,

Blockage of chloride pump in trochlear motoneurons by ammonium acetate
Llinas R; Precht W; Baker R
1974 ;347(Suppl):R29-R29 abstract #58, Pflugers archiv = European journal of physiology
— id: 55735, year: 1974, vol: 347, page: R29, stat: Journal Article,

Structural study of inferior olivary nucleus of the cat: morphological correlates of electrotonic coupling
Sotelo C; Llinas R; Baker R
1974 May;37(3):541-559, Journal of neurophysiology
— id: 9997, year: 1974, vol: 37, page: 541, stat: Journal Article,

Electrical transmission between cells in the inferior olive of the cat
Llinas R; Baker R; Sotelo C
1973 ;3:156-156, Abstracts (Society for Neuroscience)
— id: 55747, year: 1973, vol: 3, page: 156, stat: Journal Article,

Cerebellar modulatory action on the vestibulo-trochlear pathway in the cat
Baker R; Precht W; Llinas R
1972 ;15(4):364-385, Experimental brain research
— id: 10011, year: 1972, vol: 15, page: 364, stat: Journal Article,

Mossy and climbing fiber projections of extraocular muscle afferents to the cerebellum
Baker R; Precht W; Llinas R
1972 Mar 24;38(2):440-445, Brain research
— id: 10010, year: 1972, vol: 38, page: 440, stat: Journal Article,

A chloride-dependent inhibitory postsynaptic potential in cat trochlear motoneurons
Llinas R; Baker R
1972 Jul;35(4):484-492, Journal of neurophysiology
— id: 10007, year: 1972, vol: 35, page: 484, stat: Journal Article,

Intracellular potentials evoked in trochlear motoneurones by vestibular nerve activation
Baker R; Precht W; Llinas R
1971 ;30:A105-A105, Federation Proceedings (Federation of American Societies for Experimental Biology)
— id: 55707, year: 1971, vol: 30, page: A105, stat: Journal Article,

Electrotonic coupling between neurones in the rat mesencephalic nucleus
Baker, R; Llinas, R
1971 Jan;212(1):45-63, Journal of physiology
— id: 10018, year: 1971, vol: 212, page: 45, stat: Journal Article,

Cerebellar control of ipsilateral vestibular inhibition of trochlear motoneurons
Precht W; Baker R; Llinas R
1971 ;9:460-460, Proceedings of the International Union of Physiological Sciences
— id: 55724, year: 1971, vol: 9, page: 460, stat: Journal Article,

Electronic coupling between neurons in the mesencephalic root of the Vth nerve in the rat
Baker R; Llinas R
1970 ;10:64A-64A, Abstracts (Biophysical Society)
— id: 55730, year: 1970, vol: 10, page: 64A, stat: Journal Article,