Margaret E. Rice, Ph.D.

Differential calcium dependence of axonal versus somatodendritic dopamine release, with characteristics of both in the ventral tegmental area
Chen, Billy T; Patel, Jyoti C; Moran, Kimberly A; Rice, Margaret E
2011 ;5:39-39, Frontiers in systems neuroscience
Midbrain dopamine (DA) neurons in the substantia nigra pars compacta (SNc) and ventral tegmental area (VTA) exhibit somatodendritic release of DA. Previous studies indicate a difference between the Ca(2+) dependence of somatodendritic DA release in the SNc and that of axonal DA release in dorsal striatum. Here, we evaluated the Ca(2+) dependence of DA release in the VTA and nucleus accumbens (NAc) shell for comparison with that in the SNc and dorsal striatum. Release of DA was elicited by single-pulse stimulation in guinea-pig brain slices and monitored with subsecond resolution using carbon-fiber microelectrodes and fast-scan cyclic voltammetry. In dorsal striatum and NAc, DA release was not detectable at extracellular Ca(2+) concentrations ([Ca(2+)](o)) below 1 mM; however, a progressive increase in evoked extracellular DA concentration ([DA](o)) was seen with [Ca(2+)](o) >/= 1.5 mM. By contrast, in SNc and VTA, robust increases in [DA](o) could be elicited in 0.25 mM [Ca(2+)](o) that were approximately 60% of those seen in 1.5 mM [Ca(2+)](o). In SNc, a plateau in single-pulse evoked [DA](o) was seen at [Ca(2+)](o) >/= 1.5 mM, mirroring the release plateau reported previously for pulse-train stimulation in SNc. In VTA, however, evoked [DA](o) increased progressively throughout the range of [Ca(2+)](o) tested (up to 3.0 mM). These functional data are consistent with the microanatomy of the VTA, which includes DA axon collaterals as well as DA somata and dendrites. Differences between axonal and somatodendritic release data were quantified using Hill analysis, which showed that the Ca(2+) dependence of axonal DA release is low affinity with high Ca(2+) cooperativity, whereas somatodendritic release is high affinity with low cooperativity. Moreover, this analysis revealed the dual nature of DA release in the VTA, with both somatodendritic and axonal contributions
— id: 134739, year: 2011, vol: 5, page: 39, stat: Journal Article,

Regulation of Substantia Nigra Pars Reticulata GABAergic Neuron Activity by H(2)O(2) via Flufenamic Acid-Sensitive Channels and K(ATP) Channels
Lee, Christian R; Witkovsky, Paul; Rice, Margaret E
2011 ;5:14-14, Frontiers in systems neuroscience
Substantia nigra pars reticulata (SNr) GABAergic neurons are key output neurons of the basal ganglia. Given the role of these neurons in motor control, it is important to understand factors that regulate their firing rate and pattern. One potential regulator is hydrogen peroxide (H(2)O(2)), a reactive oxygen species that is increasingly recognized as a neuromodulator. We used whole-cell current clamp recordings of SNr GABAergic neurons in guinea-pig midbrain slices to determine how H(2)O(2) affects the activity of these neurons and to explore the classes of ion channels underlying those effects. Elevation of H(2)O(2) levels caused an increase in the spontaneous firing rate of SNr GABAergic neurons, whether by application of exogenous H(2)O(2) or amplification of endogenous H(2)O(2) through inhibition of glutathione peroxidase with mercaptosuccinate. This effect was reversed by flufenamic acid (FFA), implicating transient receptor potential (TRP) channels. Conversely, depletion of endogenous H(2)O(2) by catalase, a peroxidase enzyme, decreased spontaneous firing rate and firing precision of SNr neurons, demonstrating tonic control of firing rate by H(2)O(2). Elevation of H(2)O(2) in the presence of FFA revealed an inhibition of tonic firing that was prevented by blockade of ATP-sensitive K(+) (K(ATP)) channels with glibenclamide. In contrast to guinea-pig SNr neurons, the dominant effect of H(2)O(2) elevation in mouse SNr GABAergic neurons was hyperpolarization, indicating a species difference in H(2)O(2)-dependent regulation. Thus, H(2)O(2) is an endogenous modulator of SNr GABAergic neurons, acting primarily through presumed TRP channels in guinea-pig SNr, with additional modulation via K(ATP) channels to regulate SNr output
— id: 131804, year: 2011, vol: 5, page: 14, stat: Journal Article,

A food restriction protocol that increases drug reward decreases tropomyosin receptor kinase B in the ventral tegmental area, with no effect on brain-derived neurotrophic factor or tropomyosin receptor kinase B protein levels in dopaminergic forebrain regions
Pan, Y; Chau, L; Liu, S; Avshalumov, M V; Rice, M E; Carr, K D
2011 Dec 1;197:330-338, Neuroscience
Food restriction (FR) decreases brain-derived neurotrophic factor (BDNF) expression in hypothalamic and hindbrain regions that regulate feeding and metabolic efficiency, while increasing expression in hippocampal and neocortical regions. Drugs of abuse alter BDNF expression within the mesocorticolimbic dopamine (DA) pathway, and modifications of BDNF expression within this pathway alter drug-directed behavior. Although FR produces a variety of striatal neuroadaptations and potentiates the rewarding effects of abused drugs, the effects of FR on BDNF expression and function within the DA pathway are unknown. The primary purpose of the present study was to examine the effect of FR on protein levels of BDNF and its tropomyosin receptor kinase B (TrkB) receptor in component structures of the mesocorticolimbic pathway. Three to four weeks of FR, with stabilization of rats at 80% of initial body weight, did not alter BDNF or TrkB levels in nucleus accumbens, caudate-putamen, or medial prefrontal cortex. However, FR decreased TrkB levels in the ventral tegmental area (VTA), without change in levels of BDNF protein or mRNA. The finding that FR also decreased TrkB levels in substantia nigra, with elevation of BDNF protein, suggests that decreased TrkB in VTA could be a residual effect of increased BDNF during an earlier phase of FR. Voltage-clamp recordings in VTA DA neurons indicated decreased glutamate receptor transmission. These data might predict lower average firing rates in FR relative to ad libitum fed subjects, which would be consistent with previous evidence of decreased striatal DA transmission and upregulation of postsynaptic DA receptor signaling. However, FR subjects also displayed elevated VTA levels of phospho-ERK1/2, which is an established mediator of synaptic plasticity. Because VTA neurons are heterogeneous with regard to neurochemistry, function, and target projections, the relationship(s) between the three changes observed in VTA, and their involvement in the augmented striatal and behavioral responsiveness of FR subjects to drugs of abuse, remains speculative
— id: 141070, year: 2011, vol: 197, page: 330, stat: Journal Article,

Subsecond regulation of striatal dopamine release by pre-synaptic K(ATP) channels
Patel, Jyoti C; Witkovsky, Paul; Coetzee, William A; Rice, Margaret E
2011 Sep;118(5):721-736, Journal of neurochemistry
J. Neurochem. (2011) 118, 721-736. ABSTRACT: ATP-sensitive K(+) (K(ATP) ) channels are composed of pore-forming subunits, typically Kir6.2 in neurons, and regulatory sulfonylurea receptor subunits. In dorsal striatum, activity-dependent H(2) O(2) produced from glutamate receptor activation inhibits dopamine release via K(ATP) channels. Sources of modulatory H(2) O(2) include striatal medium spiny neurons, but not dopaminergic axons. Using fast-scan cyclic voltammetry in guinea-pig striatal slices and immunohistochemistry, we determined the time window for H(2) O(2) /K(ATP) -channel-mediated inhibition and assessed whether modulatory K(ATP) channels are on dopaminergic axons. Comparison of paired-pulse suppression of dopamine release in the absence and presence of glibenclamide, a K(ATP) -channel blocker, or mercaptosuccinate, a glutathione peroxidase inhibitor that enhances endogenous H(2) O(2) levels, revealed a time window for inhibition of 500-1000 ms after stimulation. Immunohistochemistry demonstrated localization of Kir6.2 K(ATP) -channel subunits on dopaminergic axons. Consistent with the presence of functional K(ATP) channels on dopaminergic axons, K(ATP) -channel openers, diazoxide and cromakalim, suppressed single-pulse evoked dopamine release. Although cholinergic interneurons that tonically regulate dopamine release also express K(ATP) channels, diazoxide did not induce the enhanced frequency responsiveness of dopamine release seen with nicotinic-receptor blockade. Together, these studies reveal subsecond regulation of striatal dopamine release by endogenous H(2) O(2) acting at K(ATP) channels on dopaminergic axons, including a role in paired-pulse suppression
— id: 136636, year: 2011, vol: 118, page: 721, stat: Journal Article,

Dopamine release in the basal ganglia
Rice, M E; Patel, J C; Cragg, S J
2011 Dec 15;198:112-137, Neuroscience
Dopamine (DA) is a key transmitter in the basal ganglia, yet DA transmission does not conform to several aspects of the classic synaptic doctrine. Axonal DA release occurs through vesicular exocytosis and is action potential- and Ca(2+) -dependent. However, in addition to axonal release, DA neurons in midbrain exhibit somatodendritic release by an incompletely understood, but apparently exocytotic, mechanism. Even in striatum, axonal release sites are controversial, with evidence for DA varicosities that lack postsynaptic specialization, and largely extrasynaptic DA receptors and transporters. Moreover, DA release is often assumed to reflect a global response to a population of activities in midbrain DA neurons, whether tonic or phasic, with precise timing and specificity of action governed by other basal ganglia circuits. This view has been reinforced by anatomical evidence showing dense axonal DA arbors throughout striatum, and a lattice network formed by DA axons and glutamatergic input from cortex and thalamus. Nonetheless, localized DA transients are seen in vivo using voltammetric methods with high spatial and temporal resolution. Mechanistic studies using similar methods in vitro have revealed local regulation of DA release by other transmitters and modulators, as well as by proteins known to be disrupted in Parkinson's disease and other movement disorders. Notably, the actions of most other striatal transmitters on DA release also do not conform to the synaptic doctrine, with the absence of direct synaptic contacts for glutamate, GABA, and acetylcholine (ACh) on striatal DA axons. Overall, the findings reviewed here indicate that DA signaling in the basal ganglia is sculpted by cooperation between the timing and pattern of DA input and those of local regulatory factors. This article is part of a Special Issue entitled: Function and Dysfunction of the Basal Ganglia
— id: 141696, year: 2011, vol: 198, page: 112, stat: Journal Article,

H2O2: A Dynamic Neuromodulator
Rice, Margaret E
2011 Aug;17(4):389-406, Neuroscientist
Increasing evidence implicates hydrogen peroxide (H(2)O(2)) as an intracellular and intercellular signaling molecule that can influence processes from embryonic development to cell death. Most research has focused on relatively slow signaling, on the order of minutes to days, via second messenger cascades. However, H(2)O(2) can also mediate subsecond signaling via ion channel activation. This rapid signaling has been examined most thoroughly in the nigrostriatal dopamine (DA) pathway, which plays a key role in facilitating movement mediated by the basal ganglia. In DA neurons of the substantia nigra, endogenously generated H(2)O(2) activates ATP-sensitive K(+) (K-ATP) channels that inhibit DA neuron firing. In the striatum, H(2)O(2) generated downstream from glutamatergic AMPA receptor activation in medium spiny neurons acts as a diffusible messenger that inhibits axonal DA release, also via K-ATP channels. The source of dynamically generated H(2)O(2) is mitochondrial respiration; thus, H(2)O(2) provides a novel link between activity and metabolism via K-ATP channels. Additional targets of H(2)O(2) include transient receptor potential (TRP) channels. In contrast to the inhibitory effect of H(2)O(2) acting via K-ATP channels, TRP channel activation is excitatory. This review describes emerging roles of H(2)O(2) as a signaling agent in the nigrostriatal pathway and basal ganglia neurons
— id: 135259, year: 2011, vol: 17, page: 389, stat: Journal Article,

SKF-83566, a D(1) -dopamine receptor antagonist, inhibits the dopamine transporter
Stouffer, Melissa A; Ali, Solav; Reith, Maarten E A; Patel, Jyoti C; Sarti, Federica; Carr, Kenneth D; Rice, Margaret E
2011 Sep;118(5):714-720, Journal of neurochemistry
J. Neurochem. (2011) 118, 714-720. ABSTRACT: Dopamine (DA) is an important transmitter in both motor and limbic pathways. We sought to investigate the role of D(1) -receptor activation in axonal DA release regulation in dorsal striatum using a D(1) -receptor antagonist, SKF-83566. Evoked DA release was monitored in rat striatal slices using fast-scan cyclic voltammetry. SKF-83566 caused a concentration-dependent increase in peak single-pulse evoked extracellular DA concentration, with a maximum increase of approximately 65% in 5 muM SKF-83566. This was accompanied by a concentration-dependent increase in extracellular DA concentration clearance time. Both effects were occluded by nomifensine (1 muM), a dopamine transporter (DAT) inhibitor, suggesting that SKF-83566 acted via the DAT. We tested this by examining [(3) H]DA uptake into LLc-PK cells expressing rat DAT, and confirmed that SKF-83566 is a competitive DAT inhibitor with an IC(50) of 5.7 muM. Binding studies with [(3) H]CFT, a cocaine analog, showed even more potent action of SKF-83566 at the DAT cocaine binding site (IC(50) = 0.51 muM). Thus, data obtained using SKF-83566 as a D(1) DA-receptor antagonist may be confounded by concurrent DAT inhibition. More positively, however, SKF-83566 might be a candidate to attenuate cocaine effects in vivo because of the greater potency of this drug at the cocaine versus DA binding site of the DAT
— id: 136635, year: 2011, vol: 118, page: 714, stat: Journal Article,

Dysregulation of striatal dopamine release in a mouse model of dystonia
Bao, Li; Patel, Jyoti C; Walker, Ruth H; Shashidharan, Pullanipally; Rice, Margaret E
2010 Sep;114(6):1781-91, Journal of neurochemistry
Dystonia is a neurological disorder characterized by involuntary movements. We examined striatal dopamine (DA) function in hyperactive transgenic (Tg) mice generated as a model of dystonia. Evoked extracellular DA concentration was monitored with carbon-fiber microelectrodes and fast-scan cyclic voltammetry in striatal slices from non-Tg mice, Tg mice with a positive motor phenotype, and phenotype-negative Tg littermates. Peak single-pulse evoked extracellular DA concentration was significantly lower in phenotype-positive mice than in non-Tg or phenotype-negative mice, but indistinguishable between non-Tg and phenotype-negative mice. Phenotype-positive mice also had higher functional D2 DA autoreceptor sensitivity than non-Tg mice, which would be consistent with lower extracellular DA concentration in vivo. Multiple-pulse (phasic) stimulation (five pulses, 10-100 Hz) revealed an enhanced frequency dependence of evoked DA release in phenotype-positive versus non-Tg or phenotype-negative mice, which was exacerbated when extracellular Ca(2+) concentration was lowered. Enhanced sensitivity to phasic stimulation in phenotype-positive mice was reminiscent of the pattern seen with antagonism of nicotinic acetylcholine receptors. Consistent with a role for altered cholinergic regulation, the difference in phasic responsiveness among groups was lost when nicotinic receptors were blocked by mecamylamine. Together, these data implicate compromised DA release regulation, possibly from cholinergic dysfunction, in the motor symptoms of this dystonia model
— id: 113651, year: 2010, vol: 114, page: 1781, stat: Journal Article,

Enhanced Striatal Dopamine Transmission and Motor Performance with LRRK2 Overexpression in Mice Is Eliminated by Familial Parkinson's Disease Mutation G2019S
Li, Xianting; Patel, Jyoti C; Wang, Jing; Avshalumov, Marat V; Nicholson, Charles; Buxbaum, Joseph D; Elder, Gregory A; Rice, Margaret E; Yue, Zhenyu
2010 Feb 3;30(5):1788-1797, Journal of neuroscience
PARK8/LRRK2 (leucine-rich repeat kinase 2) was recently identified as a causative gene for autosomal dominant Parkinson's disease (PD), with LRRK2 mutation G2019S linked to the most frequent familial form of PD. Emerging in vitro evidence indicates that aberrant enzymatic activity of LRRK2 protein carrying this mutation can cause neurotoxicity. However, the physiological and pathophysiological functions of LRRK2 in vivo remain elusive. Here we characterize two bacterial artificial chromosome (BAC) transgenic mouse strains overexpressing LRRK2 wild-type (Wt) or mutant G2019S. Transgenic LRRK2-Wt mice had elevated striatal dopamine (DA) release with unaltered DA uptake or tissue content. Consistent with this result, LRRK2-Wt mice were hyperactive and showed enhanced performance in motor function tests. These results suggest a role for LRRK2 in striatal DA transmission and the consequent motor function. In contrast, LRRK2-G2019S mice showed an age-dependent decrease in striatal DA content, as well as decreased striatal DA release and uptake. Despite increased brain kinase activity, LRRK2-G2019S overexpression was not associated with loss of DAergic neurons in substantia nigra or degeneration of nigrostriatal terminals at 12 months. Our results thus reveal a pivotal role for LRRK2 in regulating striatal DA transmission and consequent control of motor function. The PD-associated mutation G2019S may exert pathogenic effects by impairing these functions of LRRK2. Our LRRK2 BAC transgenic mice, therefore, could provide a useful model for understanding early PD pathological events
— id: 106517, year: 2010, vol: 30, page: 1788, stat: Journal Article,

Cell-autonomous alteration of dopaminergic transmission by wild type and mutant (DeltaE) TorsinA in transgenic mice
Page, Michelle E; Bao, Li; Andre, Pierrette; Pelta-Heller, Joshua; Sluzas, Emily; Gonzalez-Alegre, Pedro; Bogush, Alexey; Khan, Loren E; Iacovitti, Lorraine; Rice, Margaret E; Ehrlich, Michelle E
2010 Sep;39(3):318-326, Neurobiology of disease
Early onset torsion dystonia is an autosomal dominant movement disorder of variable penetrance caused by a glutamic acid, i.e. DeltaE, deletion in DYT1, encoding the protein TorsinA. Genetic and structural data implicate basal ganglia dysfunction in dystonia. TorsinA, however, is diffusely expressed, and therefore the primary source of dysfunction may be obscured in pan-neuronal transgenic mouse models. We utilized the tyrosine hydroxylase (TH) promoter to direct transgene expression specifically to dopaminergic neurons of the midbrain to identify cell-autonomous abnormalities. Expression of both the human wild type (hTorsinA) and mutant (DeltaE-hTorsinA) protein resulted in alterations of dopamine release as detected by microdialysis and fast cycle voltammetry. Motor abnormalities detected in these mice mimicked those noted in transgenic mice with pan-neuronal transgene expression. The locomotor response to cocaine in both TH-hTorsinA and TH-DeltaE-hTorsinA, in the face of abnormal extracellular DA levels relative to non-transgenic mice, suggests compensatory, post-synaptic alterations in striatal DA transmission. This is the first cell-subtype-specific DYT1 transgenic mouse that can serve to differentiate between primary and secondary changes in dystonia, thereby helping to target disease therapies
— id: 133766, year: 2010, vol: 39, page: 318, stat: Journal Article,

Glutamatergic signaling by mesolimbic dopamine neurons in the nucleus accumbens
Tecuapetla, Fatuel; Patel, Jyoti C; Xenias, Harry; English, Daniel; Tadros, Ibrahim; Shah, Fulva; Berlin, Joshua; Deisseroth, Karl; Rice, Margaret E; Tepper, James M; Koos, Tibor
2010 May 19;30(20):7105-7110, Journal of neuroscience
Recent evidence suggests the intriguing possibility that midbrain dopaminergic (DAergic) neurons may use fast glutamatergic transmission to communicate with their postsynaptic targets. Because of technical limitations, direct demonstration of the existence of this signaling mechanism has been limited to experiments using cell culture preparations that often alter neuronal function including neurotransmitter phenotype. Consequently, it remains uncertain whether glutamatergic signaling between DAergic neurons and their postsynaptic targets exists under physiological conditions. Here, using an optogenetic approach, we provide the first conclusive demonstration that mesolimbic DAergic neurons in mice release glutamate and elicit excitatory postsynaptic responses in projection neurons of the nucleus accumbens. In addition, we describe the properties of the postsynaptic glutamatergic responses of these neurons during experimentally evoked burst firing of DAergic axons that reproduce the reward-related phasic population activity of the mesolimbic projection. These observations indicate that, in addition to DAergic mechanisms, mesolimbic reward signaling may involve glutamatergic transmission
— id: 134353, year: 2010, vol: 30, page: 7105, stat: Journal Article,

Mitochondria are the source of hydrogen peroxide for dynamic brain-cell signaling
Bao, Li; Avshalumov, Marat V; Patel, Jyoti C; Lee, Christian R; Miller, Evan W; Chang, Christopher J; Rice, Margaret E
2009 Jul 15;29(28):9002-9010, Journal of neuroscience
Hydrogen peroxide (H(2)O(2)) is emerging as a ubiquitous small-molecule messenger in biology, particularly in the brain, but underlying mechanisms of peroxide signaling remain an open frontier for study. For example, dynamic dopamine transmission in dorsolateral striatum is regulated on a subsecond timescale by glutamate via H(2)O(2) signaling, which activates ATP-sensitive potassium (K(ATP)) channels to inhibit dopamine release. However, the origin of this modulatory H(2)O(2) has been elusive. Here we addressed three possible sources of H(2)O(2) produced for rapid neuronal signaling in striatum: mitochondrial respiration, monoamine oxidase (MAO), and NADPH oxidase (Nox). Evoked dopamine release in guinea-pig striatal slices was monitored with carbon-fiber microelectrodes and fast-scan cyclic voltammetry. Using direct fluorescence imaging of H(2)O(2) and tissue analysis of ATP, we found that coapplication of rotenone (50 nM), a mitochondrial complex I inhibitor, and succinate (5 mM), a complex II substrate, limited H(2)O(2) production, but maintained tissue ATP content. Strikingly, coapplication of rotenone and succinate also prevented glutamate-dependent regulation of dopamine release, implicating mitochondrial H(2)O(2) in release modulation. In contrast, inhibitors of MAO or Nox had no effect on dopamine release, suggesting a limited role for these metabolic enzymes in rapid H(2)O(2) production in the striatum. These data provide the first demonstration that respiring mitochondria are the primary source of H(2)O(2) generation for dynamic neuronal signaling
— id: 100678, year: 2009, vol: 29, page: 9002, stat: Journal Article,

Mobilization of calcium from intracellular stores facilitates somatodendritic dopamine release
Patel, Jyoti C; Witkovsky, Paul; Avshalumov, Marat V; Rice, Margaret E
2009 May 20;29(20):6568-6579, Journal of neuroscience
Somatodendritic dopamine (DA) release in the substantia nigra pars compacta (SNc) shows a limited dependence on extracellular calcium concentration ([Ca(2+)](o)), suggesting the involvement of intracellular Ca(2+) stores. Here, using immunocytochemistry we demonstrate the presence of the sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase 2 (SERCA2) that sequesters cytosolic Ca(2+) into the endoplasmic reticulum (ER), as well as inositol 1,4,5-triphosphate receptors (IP(3)Rs) and ryanodine receptors (RyRs) in DAergic neurons. Notably, RyRs were clustered at the plasma membrane, poised for activation by Ca(2+) entry. Using fast-scan cyclic voltammetry to monitor evoked extracellular DA concentration ([DA](o)) in midbrain slices, we found that SERCA inhibition by cyclopiazonic acid (CPA) decreased evoked [DA](o) in the SNc, indicating a functional role for ER Ca(2+) stores in somatodendritic DA release. Implicating IP(3)R-dependent stores, an IP(3)R antagonist, 2-APB, also decreased evoked [DA](o). Moreover, DHPG, an agonist of group I metabotropic glutamate receptors (mGluR1s, which couple to IP(3) production), increased somatodendritic DA release, whereas CPCCOEt, an mGluR1 antagonist, suppressed it. Release suppression by mGluR1 blockade was prevented by 2-APB or CPA, indicating facilitation of DA release by endogenous glutamate acting via mGluR1s and IP(3)R-gated Ca(2+) stores. Similarly, activation of RyRs by caffeine increased [Ca(2+)](i) and elevated evoked [DA](o). The increase in DA release was prevented by a RyR blocker, dantrolene, and by CPA. Importantly, the efficacy of dantrolene was enhanced in low [Ca(2+)](o), suggesting a mechanism for maintenance of somatodendritic DA release with limited Ca(2+) entry. Thus, both mGluR1-linked IP(3)R- and RyR-dependent ER Ca(2+) stores facilitate somatodendritic DA release in the SNc
— id: 99027, year: 2009, vol: 29, page: 6568, stat: Journal Article,

Immunocytochemical identification of proteins involved in dopamine release from the somatodendritic compartment of nigral dopaminergic neurons
Witkovsky, P; Patel, J C; Lee, C R; Rice, M E
2009 Dec 1;164(2):488-496, Neuroscience
We examined the somatodendritic compartment of nigral dopaminergic neurons by immunocytochemistry and confocal microscopy, with the aim of identifying proteins that participate in dopamine packaging and release. Nigral dopaminergic neurons were identified by location, cellular features and tyrosine hydroxylase immunoreactivity. Immunoreactive puncta of vesicular monoamine transporter type 2 and proton ATPase, both involved in the packaging of dopamine for release, were located primarily in dopaminergic cell bodies, but were absent in distal dopaminergic dendrites. Many presynaptic proteins associated with transmitter release at fast synapses were absent in nigral dopaminergic neurons, including synaptotagmin 1, syntaxin1, synaptic vesicle proteins 2a and 2b, synaptophysin and synaptobrevin 1 (VAMP 1). On the other hand, syntaxin 3, synaptobrevin 2 (VAMP 2) and SNAP-25-immunoreactivities were found in dopaminergic somata and dendrites Our data imply that the storage and exocytosis of dopamine from the somatodendritic compartment of nigral dopaminergic neurons is mechanistically distinct from transmitter release at axon terminals utilizing amino acid neurotransmitters
— id: 101614, year: 2009, vol: 164, page: 488, stat: Journal Article,

Diffusible hydrogen peroxide generated by synaptic activity inhibits axonal dopamine release in striatum
Avshalumov, Marat V; Patel, Jyoti C; Bao, Li; MacGregor, Duncan G; Sidlo, Zsuzsanna; Rice, Margaret E
Beyond the synapse: Cell-cell signaling in synaptic plasticity New York, NY, US: Cambridge University Press, 2008,
(from the book) The chapter considers a less well-known intercellular messenger, hydrogen peroxide, in regulating dopamine release in the striatum. Hydrogen peroxide works together with the traditional neurotransmitters, glutamate, and gamma-aminobutyric acid (GABA), to regulate dopamine release from dorsal striatum. The chapter also considers reactive oxygen species in neuron survival and the important role of glia in releasing antioxidants for neuroprotection. These non-traditional signaling molecules expand beyond the synapse and interact with non-neuronal cells to modulate neurons in normal and pathological conditions.
— id: 5015, year: 2008, vol: , page: 181, stat: Chapter,

AMPA receptor-dependent H2O2 generation in striatal medium spiny neurons but not dopamine axons: one source of a retrograde signal that can inhibit dopamine release
Avshalumov, Marat V; Patel, Jyoti C; Rice, Margaret E
2008 Sep;100(3):1590-1601, Journal of neurophysiology
Dopamine-glutamate interactions in the striatum are critical for normal basal ganglia-mediated control of movement. Although regulation of glutamatergic transmission by dopamine is increasingly well understood, regulation of dopaminergic transmission by glutamate remains uncertain given the apparent absence of ionotropic glutamate receptors on dopaminergic axons in dorsal striatum. Indirect evidence suggests glutamatergic regulation of striatal dopamine release is mediated by a diffusible messenger, hydrogen peroxide (H2O2), generated downstream from glutamatergic AMPA receptors (AMPARs). The mechanism of H2O2-dependent inhibition of dopamine release involves activation of ATP-sensitive K+ (KATP) channels. However, the source of modulatory H2O2 is unknown. Here, we used whole cell recording, fluorescence imaging of H2O2, and voltammetric detection of evoked dopamine release in guinea pig striatal slices to examine contributions from medium spiny neurons (MSNs), the principal neurons of striatum, and dopamine axons to AMPAR-dependent H2O2 generation. Imaging studies of H2O2 generation in MSNs provide the first demonstration of AMPAR-dependent H2O2 generation in neurons in the complex brain-cell microenvironment of brain slices. Stimulation-induced increases in H2O2 in MSNs were prevented by GYKI-52466, an AMPAR antagonist, or catalase, an H2O2 metabolizing enzyme, but amplified by mercaptosuccinate (MCS), a glutathione peroxidase inhibitor. By contrast, dopamine release evoked by selective stimulation of dopamine axons was unaffected by GYKI-52466 or MCS, arguing against dopamine axons as a significant source of modulatory H2O2. Together, these findings suggest that glutamatergic regulation of dopamine release via AMPARs is mediated through retrograde signaling by diffusible H2O2 generated in striatal cells, including medium spiny neurons, rather than in dopamine axons
— id: 93338, year: 2008, vol: 100, page: 1590, stat: Journal Article,

Dopamine spillover after quantal release: rethinking dopamine transmission in the nigrostriatal pathway
Rice, Margaret E; Cragg, Stephanie J
2008 Aug;58(2):303-313, Brain research. Brain research reviews
The predominance of dopamine (DA) receptors at extrasynaptic vs. synaptic sites implies that DA signaling is by diffusion-based volume transmission. In this review, we compare characteristics that regulate extracellular DA behavior in substantia nigra pars compacta (SNc) and striatum, including regional differences in structure (a 40% greater extracellular volume fraction in SNc vs. striatum) and in dynamic DA uptake (a 200-fold greater DA uptake rate in striatum vs. SNc). Furthermore, we test the assumption of diffusion-based volume transmission for SNc and striatum by modeling dynamic DA behavior after quantal release using region-specific parameters for diffusion and uptake at 37 degrees C. Our model shows that DA uptake does not affect peak DA concentration within 1 mum of a release site in either SNc or striatum because of the slow kinetics of DATs vs. diffusion. Rather, diffusion and dilution are the dominant factors governing DA concentration after quantal release. In SNc, limited DAT efficacy is reflected in a lack of influence of uptake on either amplitude or time course of DA transients after quantal release up to 10 mum from a release site. In striatum, the lack of effect of the DAT within 1 mum of a release site means that perisynaptic DATs do not 'gate' synaptic spillover. This contrasts with the conventional view of DA synapses, in which DATs efficiently recycle DA by re-uptake into the releasing axon terminal. However, the model also shows that a primary effect of striatal uptake is to curtail DA lifetime after release. In both SNc and striatum, effective DA radius after quantal release is ~2 mum for activation of low-affinity DA receptors and 7-8 mum for high-affinity receptors; the corresponding spheres of influence would encompass tens to thousands of synapses. Thus, the primary mode of intercellular communication by DA, regardless of region, is volume transmission
— id: 91429, year: 2008, vol: 58, page: 303, stat: Journal Article,

Inhibition of striatal dopamine release by CB1 receptor activation requires nonsynaptic communication involving GABA, H2O2, and KATP channels
Sidlo, Zsuzsanna; Reggio, Patricia H; Rice, Margaret E
2008 Jan;52(1-2):80-88, Neurochemistry international
The main psychoactive component of marijuana, Delta9-tetrahydrocannabinol (THC), acts in the CNS via type 1 cannabinoid receptors (CB1Rs). The behavioral consequences of THC or synthetic CB1R agonists include suppression of motor activity. One explanation for movement suppression might be inhibition of striatal dopamine (DA) release by CB1Rs, which are densely localized in motor striatum; however, data from previous studies are inconclusive. Here we examined the effect of CB1R activation on locally evoked DA release monitored with carbon-fiber microelectrodes and fast-scan cyclic voltammetry in striatal slices. Consistent with previous reports, DA release evoked by a single stimulus pulse was unaffected by WIN55,212-2, a cannabinoid receptor agonist. However, when DA release was evoked by a train of stimuli, WIN55,212-2 caused a significant decrease in evoked extracellular DA concentration ([DA]o), implicating the involvement of local striatal circuitry, with similar suppression seen in guinea pig, rat, and mouse striatum. Pulse-train evoked [DA]o was not altered by either AM251, an inverse CB1R agonist, or VCHSR1, a neutral antagonist, indicating the absence of DA release regulation by endogenous cannabinoids with the stimulation protocol used. However, both CB1R antagonists prevented and reversed suppression of evoked [DA]o by WIN55,212-2. The effect of WIN55,212-2 was also prevented by picrotoxin, a GABAA receptor antagonist, and by catalase, a metabolizing enzyme for hydrogen peroxide (H2O2). Furthermore, blockade of ATP-sensitive K+ (KATP) channels by tolbutamide or glybenclamide prevented the effect of WIN55,212-2 on DA release. Together, these data indicate that suppression of DA release by CB1R activation within striatum occurs via a novel nonsynaptic mechanism that involves GABA release inhibition, increased generation of the diffusible messenger H2O2, and activation of KATP channels to inhibit DA release. In addition, the findings suggest a possible physiological substrate for the motor effects of cannabinoid agonist administration
— id: 78685, year: 2008, vol: 52, page: 80, stat: Journal Article,

H(2)O(2) Signaling in the Nigrostriatal Dopamine Pathway Via ATP-Sensitive Potassium Channels: Issues and Answers
Avshalumov, Marat V; Bao, Li; Patel, Jyoti C; Rice, Margaret E
2007 Feb;9(2):219-231, Antioxidants & Redox Signaling
The role of reactive oxygen species (ROS) as signaling agents is increasingly appreciated. Studies of ROS functions in the central nervous system, however, are only in their infancy. Using fast-scan cyclic voltammetry and fluorescence imaging in brain slices, the authors discovered that hydrogen peroxide (H(2)O(2)) is an endogenous regulator of dopamine release in the dorsal striatum. Given the key role of dopamine in motor, reward, and cognitive pathways, regulation by H(2)O(2) has implications for normal dopamine function, as well as for dysfunction of dopamine transmission. In this review, data are summarized to show that H(2)O(2) is a diffusible messenger in the striatum, generated downstream from glutamate receptor activation, and an intracellular signal in dopamine neurons of the substantia nigra, generated during normal pacemaker activity. The mechanism by which H(2)O(2) inhibits dopamine release and dopamine cell activity is activation of ATP-sensitive K+ (K(ATP)) channels. Characteristics of the neuronal and glial antioxidant networks required to permit H(2)O(2) signaling, yet prevent oxidative damage, are also considered. Lastly, estimates of physiological H(2)O(2) levels are discussed, and strengths and limitations of currently available methods for H(2)O(2) detection, including fluorescence imaging using dichlorofluorescein (DCF) and the next generation of fluorescent probes, are considered
— id: 69283, year: 2007, vol: 9, page: 219, stat: Journal Article,

Regulation of postsynaptic Ca2+ influx in hippocampal CA1 pyramidal neurons via extracellular carbonic anhydrase
Fedirko, Nataliya; Avshalumov, Marat; Rice, Margaret E; Chesler, Mitchell
2007 Jan 31;27(5):1167-1175, Journal of neuroscience
Synchronous neural activity causes rapid changes of extracellular pH (pH(e)) in the nervous system. In the CA1 region of the hippocampus, stimulation of the Schaffer collaterals elicits an alkaline pH(e) transient in stratum radiatum that is limited by extracellular carbonic anhydrase (ECA). When interstitial buffering is diminished by inhibition of ECA, the alkalosis is enhanced and NMDA receptor (NMDAR)-mediated postsynaptic currents can be augmented. Accordingly, the dendritic influx of Ca2+ elicited by synaptic excitation may be expected to increase if ECA activity were blocked. We tested this hypothesis in the CA1 stratum radiatum of hippocampal slices from juvenile rats, using extracellular, concentric pH- and Ca2+-selective microelectrodes with response times of a few milliseconds, as well as Fluo-5F imaging of intracellular Ca2+ transients. Brief stimulation of the Schaffer collaterals elicited an alkaline pH(e) transient, a transient decrease in free extracellular Ca2+ concentration ([Ca2+]e), and a corresponding transient rise in free intracellular Ca2+ concentration ([Ca2+]i). Inhibition of ECA with benzolamide caused a marked amplification and prolonged recovery of the pH(e) and [Ca2+]e responses, as well as the dendritic [Ca2+]i transients. The increase in amplitude caused by benzolamide did not occur in the presence of the NMDAR antagonist APV, but the decay of the responses was still prolonged. These results indicate that ECA can shape dendritic Ca2+ dynamics governed by NMDARs by virtue of its regulation of concomitant activity-dependent pH(e) shifts. The data also suggest that Ca2+ transients are influenced by additional mechanisms sensitive to shifts in pH(e)
— id: 71148, year: 2007, vol: 27, page: 1167, stat: Journal Article,

Dopaminergic modulation of tracer coupling in a ganglion-amacrine cell network
Mills, Stephen L; Xia, Xiao-Bo; Hoshi, Hideo; Firth, Sally I; Rice, Margaret E; Frishman, Laura J; Marshak, David W
2007 Jul-Aug;24(4):593-608, Visual neuroscience
Many retinal ganglion cells are coupled via gap junctions with neighboring amacrine cells and ganglion cells. We investigated the extent and dynamics of coupling in one such network, the OFF alpha ganglion cell of rabbit retina and its associated amacrine cells. We also observed the relative spread of Neurobiotin injected into a ganglion cell in the presence of modulators of gap junctional permeability. We found that gap junctions between amacrine cells were closed via stimulation of a D(1) dopamine receptor, while the gap junctions between ganglion cells were closed via stimulation of a D(2) dopamine receptor. The pairs of hemichannels making up the heterologous gap junctions between the ganglion and amacrine cells were modulated independently, so that elevations of cAMP in the ganglion cell open the ganglion cell hemichannels, while elevations of cAMP in the amacrine cell close its hemichannels. We also measured endogenous dopamine release from an eyecup preparation and found a basal release from the dark-adapted retina of approximately 2 pmol/min during the day. Maximal stimulation with light increased the rate of dopamine release from rabbit retina by 66%. The results suggest that coupling between members of the OFF alpha ganglion cell/amacrine cell network is differentially modulated with changing levels of dopamine
— id: 94439, year: 2007, vol: 24, page: 593, stat: Journal Article,

Hydrogen peroxide as a diffusible messenger : evidence from voltammetric studies of dopamine release in brain slices
Rice, Margaret E; Avshalumov, Marat V; Patel, Jyoti C
Electrochemical methods for neuroscience Boca Raton : CRC Press/Taylor & Francis, 2007,

— id: 5839, year: 2007, vol: , page: ?, stat: Chapter,

Limited regulation of somatodendritic dopamine release by voltage-sensitive Ca channels contrasted with strong regulation of axonal dopamine release
Chen, Billy T; Moran, Kimberly A; Avshalumov, Marat V; Rice, Margaret E
2006 Feb;96(3):645-655, Journal of neurochemistry
The mechanism underlying somatodendritic release of dopamine (DA) appears to differ from that of axon-terminal release. Specifically, somatodendritic DA release in the substantia nigra pars compacta (SNc) persists in low extracellular Ca2+ concentrations that are insufficient to support axonal release in striatum, suggesting that limited Ca2+ entry is necessary to trigger somatodendritic release. Here, we compared the role of voltage-dependent Ca2+ channels in mediating DA release in striatum versus SNc using specific blockers of N-, P/Q-, T-, R- and L-type Ca2+ channels individually and in combination. Release of DA evoked by a single stimulus pulse in the dorsal striatum and SNc of guinea-pig brain slices was monitored in real time using carbon-fiber microelectrodes with fast-scan cyclic voltammetry. Single-pulse evoked DA release was shown to be independent of regulation by concurrently released glutamate or GABA acting at ionotropic receptors in both regions. Under these conditions, striatal DA release was completely prevented by an N-type channel blocker, omega-conotoxin GVIA (100 nm), and was decreased by 75% by the P/Q-type channel blocker omega-agatoxin IVA (200 nm). Blockade of T-type channels with Ni2+ (100 microm) or R-type channels with SNX-482 (100 nm) decreased axonal release in striatum by 25%, whereas inhibition of L-type channels with nifedipine (20 microm) had no effect. By contrast, none of these Ca2+-channel blockers altered the amplitude of somatodendritic DA release in the SNc. Even a cocktail of all blockers tested did not alter release-signal amplitude in the SNc, although the duration of the release response was curtailed. The limited involvement of voltage-dependent Ca2+ channels in somatodendritic DA release provides further evidence that minimal Ca2+ entry is required to trigger the release process, compared with that required for axon-terminal release
— id: 63071, year: 2006, vol: 96, page: 645, stat: Journal Article,

Endogenous hydrogen peroxide regulates the excitability of midbrain dopamine neurons via ATP-sensitive potassium channels
Avshalumov, Marat V; Chen, Billy T; Koos, Tibor; Tepper, James M; Rice, Margaret E
2005 Apr 27;25(17):4222-4231, Journal of neuroscience
ATP-sensitive K+ (K(ATP)) channels link metabolic state to cell excitability. Here, we examined regulation of K(ATP) channels in substantia nigra dopamine neurons by hydrogen peroxide (H2O2), which is produced in all cells during aerobic metabolism. Blockade of K(ATP) channels by glibenclamide (100 nM) or depletion of intracellular H2O2 by including catalase, a peroxidase enzyme, in the patch pipette increased the spontaneous firing rate of all dopamine neurons tested in guinea pig midbrain slices. Using fluorescence imaging with dichlorofluorescein to visualize intracellular H2O2, we found that moderate increases in H2O2 during partial inhibition of glutathione (GSH) peroxidase by mercaptosuccinate (0.1-0.3 mM) had no effect on dopamine neuron firing rate. However, with greater GSH inhibition (1 mM mercaptosuccinate) or application of exogenous H2O2, 50% of recorded cells showed K(ATP) channel-dependent hyperpolarization. Responsive cells also hyperpolarized with diazoxide, a selective opener for K(ATP) channels containing sulfonylurea receptor SUR1 subunits, but not with cromakalim, a selective opener for SUR2-based channels, indicating that SUR1-based K(ATP) channels conveyed enhanced sensitivity to elevated H2O2. In contrast, when endogenous H2O2 levels were increased after inhibition of catalase, the predominant peroxidase in the substantia nigra, with 3-amino-1,2,4-triazole (1 mM), all dopamine neurons responded with glibenclamide-reversible hyperpolarization. Fluorescence imaging of H2O2 indicated that catalase inhibition rapidly amplified intracellular H2O2, whereas inhibition of GSH peroxidase, a predominantly glial enzyme, caused a slower, smaller increase, especially in nonresponsive cells. Thus, endogenous H2O2 modulates neuronal activity via K(ATP) channel opening, thereby enhancing the reciprocal relationship between metabolism and excitability
— id: 56143, year: 2005, vol: 25, page: 4222, stat: Journal Article,

Partial mitochondrial inhibition causes striatal dopamine release suppression and medium spiny neuron depolarization via H2O2 elevation, not ATP depletion
Bao, Li; Avshalumov, Marat V; Rice, Margaret E
2005 Oct 26;25(43):10029-10040, Journal of neuroscience
Mitochondrial dysfunction is a potential causal factor in Parkinson's disease. We show here that acute exposure to the mitochondrial complex I inhibitor rotenone (30-100 nM; 30 min) causes concentration-dependent suppression of single-pulse evoked dopamine (DA) release monitored in real time with carbon-fiber microelectrodes in guinea pig striatal slices, with no effect on DA content. Suppression of DA release was prevented by the sulfonylurea glibenclamide, implicating ATP-sensitive K+ (KATP) channels; however, tissue ATP was unaltered. Because KATP channels can be activated by hydrogen peroxide (H2O2), as well as by low ATP, we examined the involvement of rotenone-enhanced H2O2 generation. Confirming an essential role for H2O2, the inhibition of DA release by rotenone was prevented by catalase, a peroxide-scavenging enzyme. Striatal H2O2 generation during rotenone exposure was examined in individual medium spiny neurons using fluorescence imaging with dichlorofluorescein (DCF). An increase in intracellular H2O2 levels followed a similar time course to that of DA release suppression and was accompanied by cell membrane depolarization, decreased input resistance, and increased excitability. Extracellular catalase markedly attenuated the increase in DCF fluorescence and prevented rotenone-induced effects on membrane properties; membrane changes were also largely prevented by flufenamic acid, a blocker of transient receptor potential (TRP) channels. Thus, partial mitochondrial inhibition can cause functional DA denervation via H2O2 and KATP channels, without DA or ATP depletion. Furthermore, amplified H2O2 levels and TRP channel activation in striatal spiny neurons indicate potential sources of damage in these cells. Overall, these novel factors could contribute to parkinsonian motor deficits and neuronal degeneration caused by mitochondrial dysfunction
— id: 59526, year: 2005, vol: 25, page: 10029, stat: Journal Article,

The glial antioxidant network and neuronal ascorbate: protective yet permissive for H2O2 signaling
Avshalumov, Marat V; MacGregor, Duncan G; Sehgal, Lilly M; Rice, Margaret E
2004 Nov;1(4):365-376, Neuron glia biology
Increasing evidence implicates reactive oxygen species, particularly hydrogen peroxide (H2O2), as intracellular and intercellular messengers in the brain. This raises the question of how the antioxidant network in the brain can be sufficiently permissive to allow messages to be conveyed yet, at the same time, provide adequate protection against oxidative damage. Here we present evidence that this is accomplished in part by differential antioxidant compartmentalization between glia and neurons. Based on the rationale that the glia-to-neuron ratio is higher in guinea-pig brain than in rat brain, we examined the neuroprotective role of the glial antioxidant network by comparing the consequences of elevated H2O2 in guinea-pig and rat brain slices. The effects of exogenously applied H2O2 on evoked population spikes in hippocampal slices and on edema formation in forebrain slices were assessed. In contrast to the epileptiform activity observed in rat hippocampal slices after H2O2 exposure, no pathophysiology was seen in guinea-pig hippocampal slices. Similarly, elevated H2O2 caused edema in rat brain slices, whereas this did not occur in guinea-pig brain tissue. The resistance of guinea-pig brain tissue to H2O2 challenge was lost, however, when glutathione (GSH) synthesis was inhibited (by buthionine sulfoximine), GSH peroxidase activity was inhibited (by mercaptosuccinate), or catalase was inhibited (by 3-amino-1,2,4,-triazole). Strikingly, exogenously applied ascorbate, a predominantly neuronal antioxidant, was able to compensate for loss of any other single component of the antioxidant network. Together, these data imply significant roles for glial antioxidants and neuronal ascorbate in the prevention of pathophysiological consequences of the endogenous neuromodulator, H2O2
— id: 93965, year: 2004, vol: 1, page: 365, stat: Journal Article,

DAncing past the DAT at a DA synapse
Cragg, Stephanie J; Rice, Margaret E
2004 May;27(5):270-277, Trends in neurosciences
— id: 45310, year: 2004, vol: 27, page: 270, stat: Journal Article,

Nicotine amplifies reward-related dopamine signals in striatum
Rice, Margaret E; Cragg, Stephanie J
2004 Jun;7(6):583-584, Nature neuroscience
Reward-seeking behaviors depend critically on dopamine signaling--dopamine neurons encode reward-related information by switching from tonic to phasic (burst-like) activity. Using guinea pig brain slices, we show that nicotine, like cocaine and amphetamine, acts directly in striatum where it enhances dopamine release during phasic but not tonic activity. This amplification provides a mechanism for nicotine facilitation of reward-related dopamine signals, including responses to other primary reinforcers that govern nicotine dependence in smokers
— id: 45309, year: 2004, vol: 7, page: 583, stat: Journal Article,

Glutamate-dependent inhibition of dopamine release in striatum is mediated by a new diffusible messenger, H2O2
Avshalumov, Marat V; Chen, Billy T; Marshall, Sarah P; Pena, Dianna M; Rice, Margaret E
2003 Apr 1;23(7):2744-2750, Journal of neuroscience
How glutamate regulates dopamine (DA) release in striatum has been a controversial issue. Here, we resolve this by showing that glutamate, acting at AMPA receptors, inhibits DA release by a nonclassic mechanism mediated by hydrogen peroxide (H(2)O(2)). Moreover, we show that GABA(A)-receptor activation opposes this process, thereby enhancing DA release. The influence of glutamate and GABA on DA release was assessed in striatal slices using carbon-fiber microelectrodes and fast-scan cyclic voltammetry. Modulation by both transmitters was prevented by H(2)O(2)-metabolizing enzymes. In addition, the influence of GABA(A)-receptor activation was lost when AMPA receptors were blocked with GYKI-52466. Together, these data show that modulation of DA release by glutamate and GABA depends on H(2)O(2) generated downstream from AMPA receptors. This is the first evidence that endogenous glutamate can lead to the generation of reactive oxygen species under physiological conditions. We also show that inhibition of DA release by H(2)O(2) is mediated by sulfonylurea-sensitive K(+) channels: tolbutamide blocked DA modulation by glutamate and by GABA. The absence of ionotropic glutamate or GABA receptors on DA terminals indicates that modulatory H(2)O(2) is generated in non-DA cells. Thus, in addition to its known excitatory actions in striatum, glutamate mediates inhibition by generating H(2)O(2) that must diffuse from postsynaptic sites to inhibit presynaptic DA release via K(+)-channel opening. These findings have significant implications not only for normal striatal function but also for understanding disease states that involve DA and oxidative stress, including disorders as diverse as Parkinson's disease and schizophrenia
— id: 39252, year: 2003, vol: 23, page: 2744, stat: Journal Article,

Activation of ATP-sensitive K+ (K(ATP)) channels by H2O2 underlies glutamate-dependent inhibition of striatal dopamine release
Avshalumov, Marat V; Rice, Margaret E
2003 Sep 30;100(20):11729-11734, Proceedings of the National Academy of Sciences of the United States of America
In many cells, ATP-sensitive K+ channels (KATP channels) couple metabolic state to excitability. In pancreatic beta cells, for example, this coupling regulates insulin release. Although KATP channels are abundantly expressed in the brain, their physiological role and the factors that regulate them are poorly understood. One potential regulator is H2O2. We reported previously that dopamine (DA) release in the striatum is modulated by endogenous H2O2, generated downstream from glutamatergic alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-receptor activation. Here we investigated whether H2O2-sensitive KATP channels contribute to DA-release modulation by glutamate and gamma-aminobutyric acid (GABA). This question is important because DA-glutamate interactions underlie brain functions, including motor control and cognition. Synaptic DA release was evoked by using local electrical stimulation in slices of guinea pig striatum and monitored in real time with carbon-fiber microelectrodes and fast-scan cyclic voltammetry. The KATP-channel antagonist glibenclamide abolished the H2O2-dependent increase in DA release usually seen with AMPA-receptor blockade by GYKI-52466 [1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine hydrochloride] and the decrease in DA release seen with GABA-type-A-receptor blockade by picrotoxin. In contrast, 5-hydroxydecanoate, a mitochondrial KATP-channel blocker, was ineffective, as were sulpiride, a D2-receptor antagonist, and tertiapin, a G protein-coupled K+-channel inhibitor. Diazoxide, a sulfonylurea receptor 1 (SUR1)selective KATP-channel opener, prevented DA modulation by H2O2, glutamate, and GABA, whereas cromakalim, a SUR2-selective opener, did not. Thus, endogenous H2O2 activates SUR1-containing KATP channels in the plasma membrane to inhibit DA release. These data not only demonstrate that KATP channels can modulate CNS transmitter release in response to fast-synaptic transmission but also introduce H2O2 as a KATP-channel regulator
— id: 39064, year: 2003, vol: 100, page: 11729, stat: Journal Article,

Brain edema induced by in vitro ischemia: causal factors and neuroprotection
MacGregor, Duncan G; Avshalumov, Marat V; Rice, Margaret E
2003 Jun;85(6):1402-1411, Journal of neurochemistry
Decreased cerebral blood flow, hence decreased oxygen and glucose, leads to ischemic brain injury via complex pathophysiological events, including excitotoxicity, mitochondrial dysfunction, increased intracellular Ca2+, and reactive oxygen species (ROS) generation. Each of these could also contribute to cerebral edema, which is the primary cause of patient mortality after stroke. In vitro brain slices are widely used to study ischemia. Here we introduce a slice model to investigate ischemia-induced edema. Significant water gain was induced in coronal slices of rat brain by 5 min of oxygen and glucose deprivation (OGD) at 35 degrees C, with progressive edema formation after return to normoxic, normoglycemic medium. Edema increased with increasing injury severity, determined by OGD duration (5-30 min). Underlying factors were assessed using glutamate-receptor antagonists (AP5/CNQX), blockade of mitochondrial permeability transition [cyclosporin A (CsA) versus FK506], inhibition of Na+/Ca2+ exchange (KB-R7943), and ROS scavengers (ascorbate, Trolox, dimethylthiourea, Tempol). All agents except KB-R7943 and FK506 significantly attenuated edema when applied after OGD; KB-R7943 was effective when applied before OGD. Significantly, complete prevention of ischemia-induced edema was achieved with a cocktail of AP5/CNQX, CsA and Tempo applied after OGD, which demonstrates the involvement of multiple, additive mechanisms. The efficacy of this cocktail further shows the potential value of combination therapies for the treatment of cerebral ischemia
— id: 39209, year: 2003, vol: 85, page: 1402, stat: Journal Article,

NMDA receptor activation mediates hydrogen peroxide-induced pathophysiology in rat hippocampal slices
Avshalumov, Marat V; Rice, Margaret E
2002 Jun;87(6):2896-2903, Journal of neurophysiology
Endogenous reactive oxygen species (ROS) can act as modulators of neuronal activity, including synaptic transmission. Inherent in this process, however, is the potential for oxidative damage if the balance between ROS production and regulation becomes disrupted. Here we report that inhibition of synaptic transmission in rat hippocampal slices by H2O2 can be followed by electrical hyperexcitability when transmission returns during H2O2 washout. As in previous studies, H2O2 exposure (15 min) reversibly depressed the extracellular population spike (PS) evoked by Schaffer collateral stimulation. Recovery of PS amplitude, however, was typically accompanied by mild epileptiform activity. Inclusion of ascorbate (400 microM) during H2O2 washout prevented this pathophysiology. No protection was seen with isoascorbate, which is a poor substrate for the stereoselective ascorbate transporter and thus remains primarily extracellular. Epileptiform activity was also prevented by the N-methyl-D-aspartate (NMDA) receptor antagonist, DL-2-amino-5-phosphonopentanoic acid (AP5) during H2O2 washout. Once hyperexcitability was induced, however, AP5 did not reverse it. When present during H2O2 exposure, AP5 did not alter PS depression by H2O2 but did inhibit the recovery of PS amplitude seen during pulse-train stimulation (10 Hz, 5 s) in H2O2. Inhibition of glutamate uptake by l-trans-2,4-pyrrolidine dicarboxylate (PDC; 50 microM) during H2O2 washout markedly enhanced epileptiform activity; coapplication of ascorbate with PDC prevented this. These data indicate that H2O2 exposure can cause activation of normally silent NMDA receptors, possibly via inhibition of redox-sensitive glutamate uptake. When synaptic transmission returns during H2O2 washout, enhanced NMDA receptor activity leads to ROS generation and consequent oxidative damage. These data reveal a pathological cycle that could contribute to progressive degeneration in neurological disorders that involve oxidative stress, including cerebral ischemia
— id: 32481, year: 2002, vol: 87, page: 2896, stat: Journal Article,

Modulation of somatodendritic dopamine release by endogenous H(2)O(2): susceptibility in substantia nigra but resistance in VTA
Chen, Billy T; Avshalumov, Marat V; Rice, Margaret E
2002 Feb;87(2):1155-1158, Journal of neurophysiology
We showed previously that dopamine (DA) release in dorsal striatum is inhibited by endogenously generated hydrogen peroxide (H(2)O(2)). Here, we examined whether endogenous H(2)O(2) can also modulate somatodendritic DA release in the substantia nigra pars compacta (SNc) and the ventral tegmental area (VTA), with companion measurements in DA terminal regions. Evoked DA release was monitored in brain slices using carbon-fiber microelectrodes with fast-scan cyclic voltammetry. Exogenous H(2)O(2) decreased DA release by 50-60% in SNc and VTA but only by 35% in nucleus accumbens. Whether endogenous H(2)O(2) also modulated somatodendritic release was examined using the glutathione peroxidase inhibitor, mercaptosuccinate (MCS), which should increase stimulation-evoked H(2)O(2) levels. In the presence of MCS, DA release was suppressed by 30-40% in SNc as well as in dorsal striatum and nucleus accumbens. In striking contrast, DA release in the VTA was unaffected by MCS. These data are consistent with stronger H(2)O(2) regulation or lower H(2)O(2) generation in VTA than in the other regions. Importantly, oxidative stress has been linked causally to Parkinson's disease, in which DA cells in SNc degenerate, but VTA cells are spared. The present data suggest that differences in oxidant regulation or generation between SNc and VTA could contribute to this
— id: 27280, year: 2002, vol: 87, page: 1155, stat: Journal Article,

Synaptic regulation of somatodendritic dopamine release by glutamate and GABA differs between substantia nigra and ventral tegmental area
Chen, Billy T; Rice, Margaret E
2002 Apr;81(1):158-169, Journal of neurochemistry
Midbrain dopamine (DA) cells of the substantia nigra pars compacta (SNc) and the ventral tegmental area (VTA) exhibit somatodendritic release of DA. To address how somatodendritic release is regulated by synaptic glutamatergic and GABAergic input, we examined the effect of ionotropic-receptor antagonists on locally evoked extracellular DA concentration ([DA]o) in guinea pig midbrain slices. Evoked [DA]o was monitored with carbon-fiber microelectrodes and fast-scan cyclic voltammetry. In SNc, evoked [DA]o was 160% of control in the presence of the AMPA-receptor antagonist, GYKI-52466, or the NMDA-receptor antagonist, AP5. Similar increases were seen with the GABAA-receptor antagonist, picrotoxin, or the GABA(B)-receptor antagonist, saclofen. The increase seen with GYKI-52466 was prevented when both picrotoxin and saclofen were present, consistent with normal, AMPA-receptor mediated activation of GABAergic inhibition. The increase with AP5 persisted, however, implicating NMDA-receptor mediated activation of another inhibitory circuit in SNc. In the VTA, by contrast, evoked [DA]o was unaffected by GYKI-52466 and fell slightly with AP5. Neither picrotoxin nor saclofen alone or in combination had a significant effect on evoked [DA]o. When GABA receptors were blocked in the VTA, evoked [DA]o was decreased by 20% with either GYKI-52466 or AP5. These data suggest that in SNc, glutamatergic input acts predominantly on GABAergic or other inhibitory circuits to inhibit somatodendritic DA release, whereas in VTA, the timing or strength of synaptic input will govern whether the net effect on DA release is excitatory or inhibitory
— id: 39628, year: 2002, vol: 81, page: 158, stat: Journal Article,

Role of the antioxidant ascorbate in hibernation and warming from hibernation
Drew, K L; Toien, O; Rivera, P M; Smith, M A; Perry, George; Rice, M E
2002 Dec;133(4):483-492, Comparative biochemistry & physiology. CBP. Toxicology & pharmacology
Ground squirrels tolerate up to 90% reductions in cerebral blood flow during hibernation as well as rapid reperfusion upon periodic arousal from torpor without apparent neurological damage. Thus, hibernation is studied as a model of tolerance to cerebral ischemia and other types of brain injury. Metabolic suppression likely plays a primary adaptive role that allows hibernating species to tolerate dramatic fluctuations in blood flow. Several other aspects of hibernation physiology are also consistent with tolerance to ischemia and reperfusion suggesting that multiple neuroprotective adaptations may work in concert during hibernation. The purpose of the present work is to review evidence for enhanced antioxidant defense systems during hibernation, with a focus on ascorbate, and discuss potential roles of these antioxidants during hibernation. In concert with dramatic decreases in blood flow, nutrient and oxygen delivery, plasma concentrations of the antioxidant ascorbate [(Asc)p] increase 3-5-fold during hibernation. In contrast, during re-warming, [Asc]p declines at a relatively rapid rate that peaks at the time of maximal O(2) consumption. This peak in O(2) consumption also coincides with a brief rise in plasma urate concentration consistent with a surge in reactive oxygen species production. Overall, data suggest that elevated concentration of plasma ascorbate is poised for distribution to metabolically active tissues during the surge in oxidative metabolism that accompanies re-warming during hibernation. This pool of ascorbate, as well as increased expression of other antioxidant defense systems, may protect vulnerable tissues from oxidative stress during hibernation and re-warming from hibernation. Better understanding of the role of ascorbate in hibernation may guide use of ascorbate and other antioxidants in treatment of stroke, head trauma and neurodegenerative disease
— id: 145567, year: 2002, vol: 133, page: 483, stat: Journal Article,

Brain antioxidant regulation in mammals and anoxia-tolerant reptiles: balanced for neuroprotection and neuromodulation
Rice, M E; Forman, R E; Chen, B T; Avshalumov, M V; Cragg, S J; Drew, K L
2002 Dec;133(4):515-525, Comparative biochemistry & physiology. CBP. Toxicology & pharmacology
Reactive oxygen species (ROS) generated by mitochondrial respiration and other processes are often viewed as hazardous substances. Indeed, oxidative stress, defined as an imbalance between oxidant production and antioxidant protection, has been linked to several neurological disorders, including cerebral ischemia-reperfusion and Parkinson's disease. Consequently, cells and organisms have evolved specialized antioxidant defenses to balance ROS production and prevent oxidative damage. Research in our laboratory has shown that neuronal levels of ascorbate, a low molecular weight antioxidant, are ten-fold higher than those in much less metabolically active glial cells. Ascorbate levels are also selectively elevated in the CNS of anoxia-tolerant reptiles compared to mammals; moreover, plasma and CSF ascorbate concentrations increase markedly in cold-adapted turtles and in hibernating squirrels. Levels of the related antioxidant, glutathione, vary much less between neurons and glia or among species. An added dimension to the role of the antioxidant network comes from recent evidence that ROS can act as neuromodulators. One example is modulation of dopamine release by endogenous hydrogen peroxide, which we describe here for several mammalian species. Together, these data indicate adaptations that prevent oxidative stress and suggest a particularly important role for ascorbate. Moreover, they show that the antioxidant network must be balanced precisely to provide functional levels of ROS, as well as neuroprotection
— id: 39362, year: 2002, vol: 133, page: 515, stat: Journal Article,

H(2)o(2) is a novel, endogenous modulator of synaptic dopamine release
Chen BT; Avshalumov MV; Rice ME
2001 Jun;85(6):2468-2476, Journal of neurophysiology
Recent evidence suggests that reactive oxygen species (ROS) might act as modulators of neuronal processes, including synaptic transmission. Here we report that synaptic dopamine (DA) release can be modulated by an endogenous ROS, H(2)O(2). Electrically stimulated DA release was monitored in guinea pig striatal slices using carbon-fiber microelectrodes with fast-scan cyclic voltammetry. Exogenously applied H(2)O(2) reversibly inhibited evoked release in the presence of 1.5 mM Ca(2+). The effectiveness of exogenous H(2)O(2), however, was abolished or decreased by conditions that enhance Ca(2+) entry, including increased extracellular Ca(2+) concentration ([Ca(2+)](o); to 2.4 mM), brief, high-frequency stimulation, and blockade of inhibitory D(2) autoreceptors. To test whether DA release could be modulated by endogenous H(2)O(2), release was evoked in the presence of the H(2)O(2)-scavenging enzyme, catalase. In the presence of catalase, evoked [DA](o) was 60% higher than after catalase washout, demonstrating that endogenously generated H(2)O(2) can also inhibit DA release. Importantly, the Ca(2+) dependence of the catalase-mediated effect was opposite to that of H(2)O(2): catalase had a greater enhancing effect in 2.4 mM Ca(2+) than in 1.5 mM, consistent with enhanced H(2)O(2) generation in higher [Ca(2+)](o). Together these data suggest that H(2)O(2) production is Ca(2+) dependent and that the inhibitory mechanism can be saturated, thus preventing further effects from exogenous H(2)O(2). These findings show for the first time that endogenous H(2)O(2) can modulate vesicular neurotransmitter release, thus revealing an important new signaling role for ROS in synaptic transmission
— id: 21190, year: 2001, vol: 85, page: 2468, stat: Journal Article,

Novel Ca2+ dependence and time course of somatodendritic dopamine release: substantia nigra versus striatum
Chen BT; Rice ME
2001 Oct 1;21(19):7841-7847, Journal of neuroscience
Somatodendritic release of dopamine (DA) in midbrain represents a novel form of intercellular signaling that inherently differs from classic axon-terminal release. Here we report marked differences in the Ca(2+) dependence and time course of stimulated increases in extracellular DA concentration ([DA](o)) between the substantia nigra pars compacta (SNc) and striatum. Evoked [DA](o) was monitored with carbon-fiber microelectrodes and fast-scan cyclic voltammetry in brain slices. In striatum, pulse-train stimulation (10 Hz, 30 pulses) failed to evoke detectable [DA](o) in 0 or 0.5 mm Ca(2+) but elicited robust release in 1.5 mm Ca(2+). Release increased progressively in 2.0 and 2.4 mm Ca(2+). In sharp contrast, evoked [DA](o) in SNc was nearly half-maximal in 0 mm Ca(2+) and increased significantly in 0.5 mm Ca(2+). Surprisingly, somatodendritic release was maximal in 1.5 mm Ca(2+), with no change in 2.0 or 2.4 mm Ca(2+). Additionally, after single-pulse stimulation, evoked [DA](o) in striatum reached a maximum (t(max)) in <200 msec, whereas in SNc, [DA](o) continued to rise for 2-3 sec. Similarly, the time for [DA](o) to decay to 50% of maximum (t(50)) was 12-fold longer in SNc than striatum. A delayed t(max) in SNc compared with striatum persisted when DA uptake was inhibited by GBR-12909 and D(2) autoreceptors were blocked by sulpiride, although these agents eliminated the difference in t(50). Together, these data implicate different release mechanisms in striatum and SNc, with minimal Ca(2+) required to trigger prolonged DA release in SNc. Coupled with limited uptake, prolonged somatodendritic release would facilitate DA-mediated volume transmission in midbrain
— id: 26654, year: 2001, vol: 21, page: 7841, stat: Journal Article,

Dopamine-mediated volume transmission in midbrain is regulated by distinct extracellular geometry and uptake
Cragg SJ; Nicholson C; Kume-Kick J; Tao L; Rice ME
2001 Apr;85(4):1761-1771, Journal of neurophysiology
Somatodendritic release of dopamine (DA) in midbrain is, at least in part, nonsynaptic; moreover, midbrain DA receptors are predominantly extrasynaptic. Thus somatodendritic DA mediates volume transmission, with an efficacy regulated by the diffusion and uptake characteristics of the local extracellular microenvironment. Here, we quantitatively evaluated diffusion and uptake in substantia nigra pars compacta (SNc) and reticulata (SNr), ventral tegmental area (VTA), and cerebral cortex in guinea pig brain slices. The geometric parameters that govern diffusion, extracellular volume fraction (alpha) and tortuosity (lambda), together with linear uptake (k'), were determined for tetramethylammonium (TMA(+)), and for DA, using point-source diffusion combined with ion-selective and carbon-fiber microelectrodes. TMA(+)-diffusion measurements revealed a large alpha of 30% in SNc, SNr, and VTA, which was significantly higher than the 22% in cortex. Values for lambda and k' for TMA(+) were similar among regions. Point-source DA-diffusion curves fitted theory well with linear uptake, with significantly higher values of k' for DA in SNc and VTA (0.08--0.09 s(-1)) than in SNr (0.006 s(-1)), where DA processes are sparser. Inhibition of DA uptake by GBR-12909 caused a greater decrease in k' in SNc than in VTA. In addition, DA uptake was slightly decreased by the norepinephrine transport inhibitor, desipramine in both regions, although this was statistically significant only in VTA. We used these data to model the radius of influence of DA in midbrain. Simulated release from a 20-vesicle point source produced DA concentrations sufficient for receptor activation up to 20 microm away with a DA half-life at this distance of several hundred milliseconds. Most importantly, this model showed that diffusion rather than uptake was the most important determinant of DA time course in midbrain, which contrasts strikingly with the striatum where uptake dominates. The issues considered here, while specific for DA in midbrain, illustrate fundamental biophysical properties relevant for all extracellular communication
— id: 32227, year: 2001, vol: 85, page: 1761, stat: Journal Article,

Ascorbate dynamics and oxygen consumption during arousal from hibernation in Arctic ground squirrels
Drew, K L; Chao, M L; Rice, M E
2001 Aug;281(2):R572-R583, American journal of physiology. Regulatory, integrative, & comparative physiology
During hibernation in Arctic ground squirrels (Spermophilus parryii), O(2) consumption and plasma leukocyte counts decrease by >90%, whereas plasma concentrations of the antioxidant ascorbate increase fourfold. During rewarming, O(2) consumption increases profoundly and plasma ascorbate and leukocyte counts return to normal. Here we investigated the dynamic interrelationships among these changes. Plasma ascorbate and uric acid (urate) concentrations were determined by HPLC from blood samples collected at approximately 15-min intervals via arterial catheter; leukocyte count and hematocrit were also determined. Body temperature, O(2) consumption, and electromyographic activity were recorded continuously. Ascorbate, urate, and glutathione contents in body and brain samples were determined during hibernation and after arousal. During rewarming, the maximum rate of plasma ascorbate decrease occurred at the time of peak O(2) consumption and peak plasma urate production. The ascorbate decrease did not correlate with mouth or abdominal temperature; uptake into leukocytes could account for only a small percentage. By contrast, liver and spleen ascorbate levels increased significantly after arousal, which could more than account for ascorbate clearance from plasma. Brain ascorbate levels remained constant. These data suggest that elevated concentrations of ascorbate [(Asc)] in plasma [(Asc)(p)] provide an antioxidant source that is redistributed to tissues during the metabolic stress that accompanies arousal
— id: 134949, year: 2001, vol: 281, page: R572, stat: Journal Article,

Neuroprotective adaptations in hibernation: therapeutic implications for ischemia-reperfusion, traumatic brain injury and neurodegenerative diseases
Drew, K L; Rice, M E; Kuhn, T B; Smith, M A
2001 Sep 1;31(5):563-573, Free radical biology & medicine
Brains of hibernating mammals are protected against a variety of insults that are detrimental to humans and other nonhibernating species. Such protection is associated with a number of physiological adaptations including hypothermia, increased antioxidant defense, metabolic arrest, leukocytopenia, immunosuppression, and hypocoagulation. It is intriguing that similar manipulations provide considerable protection as experimental treatments for central nervous system injury. This review focuses on neuroprotective mechanisms employed during hibernation that may offer novel approaches in the treatment of stroke, traumatic brain injury, and neurodegenerative diseases in humans
— id: 145568, year: 2001, vol: 31, page: 563, stat: Journal Article,

HEPES prevents edema in rat brain slices
MacGregor DG; Chesler M; Rice ME
2001 May 11;303(3):141-144, Neuroscience letters
Brain slices gain water when maintained in bicarbonate-buffered artificial cerebro-spinal fluid (ACSF) at 35 degrees C. We previously showed that this edema is linked to glutamate receptor activation and oxidative stress. An additional factor that may contribute to swelling is acidosis, which arises from high CO(2) tension in brain slices. To examine the role of acidosis in slice edema, we added N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) to osmotically balanced ACSF (HEPES-ACSF), thereby increasing buffering capacity beyond that provided by bicarbonate/CO(2). Water gain was markedly inhibited in HEPES-ACSF. After 3 h incubation in HEPES-ACSF at 35 degrees C, water gain was limited to that of fresh slices after 1 h recovery in ACSF at room temperature. The effect of HEPES in decreasing slice water gain was concentration dependent from 0.3 to 20 mM. The inhibition of water gain by HEPES suggests that tissue acidosis is a contributing factor in brain slice edema
— id: 20706, year: 2001, vol: 303, page: 141, stat: Journal Article,

Mice transgenic for exon 1 of the Huntington's disease gene display reduced striatal sensitivity to neurotoxicity induced by dopamine and 6-hydroxydopamine
Petersen, A; Hansson, O; Puschban, Z; Sapp, E; Romero, N; Castilho, R F; Sulzer, D; Rice, M; DiFiglia, M; Przedborski, S; Brundin, P
2001 Nov;14(9):1425-1435, European journal of neuroscience
Huntington's disease is an autosomal dominant hereditary neurodegenerative disorder characterized by severe striatal cell loss. Dopamine (DA) has been suggested to play a role in the pathogenesis of the disease. We have previously reported that transgenic mice expressing exon 1 of the human Huntington gene (R6 lines) are resistant to quinolinic acid-induced striatal toxicity. In this study we show that with increasing age, R6/1 and R6/2 mice develop partial resistance to DA- and 6-hydroxydopamine-mediated toxicity in the striatum. Using electron microscopy, we found that the resistance is localized to the cell bodies and not to the neuropil. The reduction of dopamine and cAMP regulated phosphoprotein of a molecular weight of 32 kDa (DARPP-32) in R6/2 mice does not provide the resistance, as DA-induced striatal lesions are not reduced in size in DARPP-32 knockout mice. Neither DA receptor antagonists nor a N-methyl-d-aspartate (NMDA) receptor blocker reduce the size of DA-induced striatal lesions, suggesting that DA toxicity is not dependent upon DA- or NMDA receptor-mediated pathways. Moreover, superoxide dismutase-1 overexpression, monoamine oxidase inhibition and the treatment with the free radical scavenging spin-trap agent phenyl-butyl-tert-nitrone (PBN) also did not block DA toxicity. Levels of the antioxidant molecules, glutathione and ascorbate were not increased in R6/1 mice. Because damage to striatal neurons following intrastriatal injection of 6-hydroxydopamine was also reduced in R6 mice, a yet-to-be identified antioxidant mechanism may provide neuroprotection in these animals. We conclude that striatal neurons of R6 mice develop resistance to DA-induced toxicity with age
— id: 145569, year: 2001, vol: 14, page: 1425, stat: Journal Article,

Ascorbate regulation and its neuroprotective role in the brain
Rice ME
2000 May;23(5):209-216, Trends in neurosciences
Ascorbic acid (vitamin C) occurs physiologically as the ascorbate anion: a water-soluble antioxidant that is found throughout the body. However, despite the high, homeostatically regulated levels of brain ascorbate, its specific functions in the CNS are only beginning to be elucidated. Certainly, it acts as part of the intracellular antioxidant network, and as such is normally neuroprotective. There is also evidence that it acts as a neuromodulator. A possibly unique role it might have is as an antioxidant in the brain extracellular microenvironment, where its concentration is modulated by glutamate-ascorbate heteroexchange at glutamate uptake sites. Ongoing studies of ascorbate and glutamate transporters should lead to rapid progress in understanding ascorbate regulation and function
— id: 11737, year: 2000, vol: 23, page: 209, stat: Journal Article,

Distinct regional differences in dopamine-mediated volume transmission
Rice ME
2000 ;125(4):277-290, Progress in brain research
— id: 39511, year: 2000, vol: 125, page: 277, stat: Journal Article,

Dependence of dopamine calibration factors on media Ca2+ and Mg2+ at carbon-fiber microelectrodes used with fast-scan cyclic voltammetry
Kume-Kick J; Rice ME
1998 Oct 1;84(1-2):55-62, Journal of neuroscience methods
Carbon-fiber microelectrodes and voltammetric methods have been used extensively for the detection of dopamine in brain tissue in vivo and in vitro. Voltammetric microelectrodes are often calibrated in non-physiological media, like phosphate-buffered saline, rather than in oxygenated physiological media. Here, we determined dopamine calibration factors (nA microM-1) in several defined solutions for two types of carbon-fiber electrode used with fast-scan cyclic voltammetry. For both electrode types, dopamine calibration factors, and thus electrode sensitivities, were 2-3-fold higher in phosphate- or HEPES-buffered saline than in a bicarbonate-based artificial CSF (ACSF) that reflected that normal ionic composition of brain extracellular fluid. Removal of Ca2+ and Mg2+ from ACSF eliminated this difference. Because extracellular Ca2+ concentration ([Ca2+]o) can fall under stimulation conditions used to elicit dopamine release, we also evaluated the size of stimulated [Ca2+]o shifts in guinea pig midbrain slices using ion-selective microelectrodes. The [Ca2+]o decreases were less than 100 microM, which was well below the mM decreases observed to alter DA sensitivity. Consequently, calibration data obtained in normal physiological solutions should be valid under conditions of mild stimulation. Moreover, calibration in divalent cation-free media will cause calculated DA levels to be underestimated and should be avoided, unless appropriate for a given experimental paradigm
— id: 7377, year: 1998, vol: 84, page: 55, stat: Journal Article,

Differential compartmentalization of brain ascorbate and glutathione between neurons and glia
Rice ME; Russo-Menna I
1998 Feb;82(4):1213-1223, Neuroscience
Compartmentalization of brain ascorbate and glutathione between neurons and glia has been a source of controversy. To address this question, we determined the ascorbate and glutathione contents of brain tissue with defined, but varying, densities of neurons and glia. In developing rat cortex and hippocampus, glutathione content rose during gliogenesis, while ascorbate fell. By contrast, ascorbate, but not glutathione, increased markedly during granule cell proliferation and maturation in the developing cerebellum. Similarly, in tissue from adult cerebral cortex of species with distinct neuron densities, ascorbate content increased linearly with increasing neuron density in the order: human<rabbit<guinea-pig<rat<mouse, whereas glutathione was relatively constant. These data suggest that ascorbate predominates in neurons, whereas glutathione is slightly predominant in glia. Quantitative analysis of ascorbate and glutathione contents in these studies combined with appropriate intra- and extracellular volume fraction data permitted calculation of concentrations of ascorbate in neurons (10 mM) and glia (0.9 mM), and glutathione in neurons (2.5 mM) and glia (3.8 mM). The relative accuracy of these values was confirmed by their use in a model that reliably predicted changes in ascorbate and glutathione levels in rat cortex during the first three postnatal weeks and into adulthood. These findings not only provide new information about the intracellular composition of neurons and glia, but also have implications for understanding the roles of ascorbate and glutathione in normal brain function, as well as neuron and glia involvement in disease states linked to oxidative stress
— id: 7757, year: 1998, vol: 82, page: 1213, stat: Journal Article,

Characteristics of electrically evoked somatodendritic dopamine release in substantia nigra and ventral tegmental area in vitro
Rice ME; Cragg SJ; Greenfield SA
1997 Feb;77(2):853-862, Journal of neurophysiology
Somatodendritic dopamine (DA) release from neurons of the midbrain represents a nonclassical form of neuronal signaling. We assessed characteristics of DA release during electrical stimulation of the substantia nigra pars compacta (SNc) in guinea pig midbrain slices. With the use of parameters optimized for this region, we compared stimulus-induced increases in extracellular DA concentration ([DA]o) in medial and lateral SNc, ventral tegmental area (VTA), and dorsal striatum in vitro. DA release was monitored directly with carbon-fiber microelectrodes and fast-scan cyclic voltammetry. Detection of DA in SNc was confirmed by electrochemical, pharmacological, and anatomic criteria. Voltammograms of the released substance had the same peak potentials as those of DA obtained during in vitro calibration, but different from those of the indoleamine 5-hydroxytryptamine. Similar voltammograms were also obtained in the DA-rich striatum during local electrical stimulation. Contribution from the DA metabolite 3,4-dihydroxyphenylacetic acid to somatodendritic release was negligible, as indicated by the lack of effect of the monoamine oxidase inhibitor pargyline (20 microM) on the signal. Lastly, DA voltammograms could only be elicited in regions that were subsequently determined to be positive for tyrosine hydroxylase immunoreactivity (TH-ir). The frequency dependence of stimulated DA release in SNc was determined over a range of 1-50 Hz, with a constant duration of 10 s. Release was frequency dependent up to 10 Hz, with no further increase at higher frequencies. Stimulation at 10 Hz was used in all subsequent experiments. With this paradigm, DA release in SNc was tetrodotoxin insensitive, but strongly Ca2+ dependent. Stimulated [DA]o in the midbrain was also site specific. At the midcaudal level examined, DA efflux was significantly greater in VTA (1.04 +/- 0.05 microM, mean +/- SE) than in medial SNc (0.52 +/- 0.05 microM), which in turn was higher than in lateral SNc (0.35 +/- 0.03 microM). This pattern followed the apparent density of TH-ir, which was also VTA > medial SNc > lateral SNc. This report has introduced a new paradigm for the study of somatodendritic DA release. Voltammetric recording with electrodes of 2-4 microns tip diameter permitted highly localized, direct detection of endogenous DA. The Ca2+ dependence of stimulated release indicated that the process was physiologically relevant. Moreover, the findings that somatodendritic release was frequency dependent across a range characteristic of DA cell firing rates and that stimulated [DA]o varied markedly among DA cell body regions have important implications for how dendritically released DA may function in the physiology and pathophysiology of substantia nigra and VTA
— id: 8432, year: 1997, vol: 77, page: 853, stat: Journal Article,

Enhanced oxidative stress in female rat brain after gonadectomy
Kume-Kick J; Ferris DC; Russo-Menna I; Rice ME
1996 Oct 28;738(1):8-14, Brain research
Oxidative stress, assessed by tissue ascorbate loss following ischemia, is greater in male than female rat brain. The factors mediating this gender difference are unclear. The goal of the present studies was to determine the influence of gonadal sex hormones on this difference. Three weeks prior to experiment, adult Long-Evans male and female rats were gonadectomized for comparison with controls. Ascorbate and glutathione levels were determined in brain and plasma under basal conditions and in brain after one-hour decapitation ischemia, using liquid chromatography with electrochemical detection. Basal ascorbate levels in brain were 6-9% higher in males than in females, whereas plasma levels were 100% higher in males. After gonadectomy, the gender difference in plasma ascorbate levels was lost, while the effect on basal brain levels depended upon region. Ischemia-induced losses in brain ascorbate were three-fold greater in control males compared to control females. Significant losses occurred in frontal cortex, hippocampus, and cerebellum in males during ischemia, whereas loss in females was significant in cerebellum only. After gonadectomy, increased ascorbate loss was seen in all female brain regions, indicating enhanced oxidative stress. This increase eliminated the gender difference in loss; male ascorbate loss was comparatively unaffected by gonadectomy. Glutathione levels and loss were unaffected by either gender or gonadectomy, indicating differences in regulation from that of ascorbate. These findings provide evidence for the hypothesis that protection against oxidative stress is afforded by ovarian sex hormones, thus decreasing the potential for oxidative cell damage in females compared to males
— id: 8312, year: 1996, vol: 738, page: 8, stat: Journal Article,

Long distance pathways of diffusion for dextran along fibre bundles in brain. Relevance for volume transmission
Bjelke, B; England, R; Nicholson, C; Rice, M E; Lindberg, J; Zoli, M; Agnati, L F; Fuxe, K
1995 May 9;6(7):1005-1009, Neuroreport
Texas Red-labelled dextran with a mol. wt of 3000 g mol-1, a marker for the extracellular space, was injected unilaterally into the neostriatum of adult rats (0.3-30 micrograms microliter-1) and its distribution evaluated 1 min to 5 h later. Diffusion in the neuropil was observed with clearance starting after 30 min. After 10-15 min strong labelling along the myelinated fibre bundles was observed in the entire neostriatum. After about 20 min the labelling along the fibres reached into the corpus callosum and the overlaying deep layers of the cerebral cortex. A marked cellular uptake and accumulation of labelled dextran was found in putative perivascular pericytes. Thus, in the living brain preferential extracellular fluid pathways for diffusion exist, especially along fibre bundles, which allow the exchange of chemical signals between two distant regions. These may represent extracellular fluid pathways for volume transmission
— id: 145559, year: 1995, vol: 6, page: 1005, stat: Journal Article,

High levels of ascorbic acid, not glutathione, in the CNS of anoxia-tolerant reptiles contrasted with levels in anoxia-intolerant species
Rice ME; Lee EJ; Choy Y
1995 Apr;64(4):1790-1799, Journal of neurochemistry
Ascorbic acid and glutathione (GSH) are antioxidants and free radical scavengers that provide the first line of defense against oxidative damage in the CNS. Using HPLC with electrochemical detection, we determined tissue contents of these antioxidants in brain and spinal cord in species with varying abilities to tolerate anoxia, including anoxia-tolerant pond and box turtles, moderately tolerant garter snakes, anoxia-intolerant clawed frogs (Xenopus laevis), and intolerant Long-Evans hooded rats. These data were compared with ascorbate and GSH levels in selected regions of guinea pig CNS, human cortex, and values from the literature. Ascorbate levels in turtles were typically 100% higher than those in rat. Cortex, olfactory bulb, and dorsal ventricular ridge had the highest content in turtle, 5-6 mumol g-1 of tissue wet weight, which was twice that in rat cortex (2.82 +/- 0.05 mumol g-1) and threefold greater than in guinea pig cortex (1.71 +/- 0.03 mumol g-1). Regionally distinct levels (2-4 mumol g-1) were found in turtle cerebellum, optic lobe, brainstem, and spinal cord, with a decreasing anterior-to-posterior gradient. Ascorbate was lowest in white matter (optic nerve) in each species. Snake cortex and brainstem had significantly higher ascorbate levels than in rat or guinea pig, although other regions had comparable or lower levels. Frog ascorbate was generally in an intermediate range between that in rat and guinea pig. In contrast to ascorbate, GSH levels in anoxia-tolerant turtles, 2-3 mumol g-1 of tissue wet weight, were similar to those in mammalian or amphibian brain, with no consistent pattern associated with anoxia tolerance. GSH levels in pond turtle CNS were significantly higher (by 10-20%) than in rat for several regions but were generally lower than in guinea pig or frog. GSH in box turtle and snake CNS were the same or lower than in rat or guinea pig. The distribution GSH in the CNS also had a decreasing anterior-to-posterior gradient but with less variability than ascorbate: levels were similar in optic nerve, brainstem, and spinal cord. The paradoxically high levels of ascorbate in turtle brain, which has a lower rate of oxidative metabolism than mammalian, suggest that ascorbate is an essential cerebral antioxidant. High levels may have evolved to protect cells from oxidative damage when aerobic metabolism resumes after a hypoxic dive
— id: 6726, year: 1995, vol: 64, page: 1790, stat: Journal Article,

Origin of the apparent tissue conductivity in the molecular and granular layers of the in vitro turtle cerebellum and the interpretation of current source-density analysis
Okada, Y C; Huang, J C; Rice, M E; Tranchina, D; Nicholson, C
1994 Aug;72(2):742-753, Journal of neurophysiology
1. We determined the origin of the apparent tissue conductivity (sigma 2) of the turtle cerebellum in vitro. 2. Application of a current with a known current density (J) along the longitudinal axis of a conductivity cell produced an electric field in the cerebellum suspended in the cell. The measured electric field (E) perpendicular to the cerebellar surface indicated a significant inhomogeneity in sigma a (= J/E) with a major discontinuity between the molecular layer (0.25 +/- 0.05 S/m, mean +/- SD) and granular layers (0.15 +/- 0.03 S/m) (n = 39). 3. This inhomogeneity was more pronounced after anoxic depolarization. The value of sigma a decreased to 0.11 +/- 0.03 and 0.040 +/- 0.008 S/m in the molecular and granular layers, respectively. The ratio of sigma a S in the two layers increased from 1.67 in the normoxic condition to 2.75 after anoxic depolarization. 4. This difference in sigma a across the two layers was present within the range of frequencies (DC to 10 kHz) studied where the phase of sigma a was small (less than +/- 2 degrees) and therefore sigma a was ohmic. 5. The inhomogeneity in sigma a was in part due to an inhomogeneity in the extracellular conductivity (sigma e) as determined from the extracellular diffusion of ionophoresed tetramethylammonium. Like sigma a, the value of sigma e was also higher in the molecular layer (0.165 S/m) than in the granular layer (0.097 S/m). The inhomogeneity in sigma e was due to a smaller tortuosity and a larger extracellular volume fraction in the molecular layer compared with the granular layer. 6. sigma a was, however, consistently higher, by approximately 50%, than sigma e. A core conductor model of the cerebellum indicated that these discrepancies between sigma a and sigma e were attributable to additional conductivity produced by a passage of the longitudinal applied current through the intracellular space of Purkinje cells and ependymal glial cells, with the glial compartment playing the dominant role. Cells with a long process and a short space constant such as the ependymal glia evidently enhance the effective 'extracellular' conductivity by serving as intracellular conduits for the applied current. The result implies that the effective sigma e may be larger than sigma e for neuronally generated currents in the turtle cerebellum because the space constant for Purkinje cells is several times greater than that for the ependymal glia and consequently Purkinje cell-generated currents travel over a long distance relative to the space constant of glial cells.(ABSTRACT TRUNCATED AT 400 WORDS)
— id: 145560, year: 1994, vol: 72, page: 742, stat: Journal Article,

Direct monitoring of dopamine and 5-HT release in substantia nigra and ventral tegmental area in vitro
Rice ME; Richards CD; Nedergaard S; Hounsgaard J; Nicholson C; Greenfield SA
1994 ;100(3):395-406, Experimental brain research
Fast-scan cyclic voltammetry with carbon fibre microelectrodes was used to detect endogenous dopamine (DA) and 5-hydroxytryptamine (5-HT) release from three distinct regions of guinea-pig mid-brain in vitro: rostral and caudal substantia nigra (SN) and the ventral tegmental area (VTA). Previous electrophysiological studies have demonstrated that cells of the caudal SN and the VTA have similar characteristics, whereas cells in the rostral SN have distinctly different properties. In the present study, we confirmed that each region has tyrosine hydroxylase-positive neurons and determined, using high-performance liquid chromatography, that DA levels were similar in rostral and caudal SN, but lower in SN than in VTA. In each region, application of veratrine, which was shown by intracellular recordings to have a reversible depolarising action, evoked a signal attributable to DA and distinguishable from that of 5-HT. Release signals were monitored every 250 ms with a spatial resolution of less than 50 microns.l DA release was calcium-dependent and was not detectable in a catecholamine-poor area such as the cerebellum, or in mid-brain tissue pre-treated with reserpine. Within the normal mid-brain, the amount of DA released was correlated with tissue content in that it was higher in the VTA than in either region of SN. It is concluded that DA released from somato-dendritic parts of mid-brain neurons exhibits site-specific variation. This is the first report of direct monitoring of DA and 5-HT release from these regions with in situ electrodes and demonstrates the utility of fast-scan cyclic voltammetry to investigate the mechanisms and possible non-classical functions of somato-dendritic DA release
— id: 6727, year: 1994, vol: 100, page: 395, stat: Journal Article,

Transient extracellular volume reduction in neural lobe of rat hypophysis in response to neural stalk stimulation in vitro and its relationship to extracellular potassium
Armstrong, W E; Rice, M E
1993 Apr;69(4):1363-1367, Journal of neurophysiology
1. Using ion-sensitive microelectrodes, a transient reduction in the local volume of neural lobe extracellular space was found to accompany the elevation in extracellular potassium induced by stimulation of the neural stalk. The volume decrease and potassium increase had similar stimulus-response curves when stimulus frequency was varied from 1 to 40 Hz, with maximal response at 20 Hz. The curves for stimulus duration diverged, as a near maximal potassium response was reached in 4-16 s with a 20-Hz stimulus, while the extracellular volume decrease was maximal at 64 s. 2. The volume decrease, but not the potassium increase, was strongly inhibited by lowering bath temperature and moderately inhibited by furosemide and by lowering extracellular chloride concentration. Both the volume and the potassium response were enhanced by ouabain. 3. In conclusion, shrinkage of the local extracellular space in neural lobe during nerve activity is mediated by a metabolically active process which is only partially dependent upon extracellular chloride concentration and anion-cation co-transport, but is relatively independent of Na(+)-K+ pump activity. A transient shrinkage in extracellular space during increased neurohypophysial nerve activity would be expected to play a role in hormone diffusion, ion buffering, and extracellular current flow
— id: 145558, year: 1993, vol: 69, page: 1363, stat: Journal Article,

Anisotropic and heterogeneous diffusion in the turtle cerebellum: implications for volume transmission
Rice ME; Okada YC; Nicholson C
1993 Nov;70(5):2035-2044, Journal of neurophysiology
1. Measurements of extracellular diffusion properties were made in three orthogonal axes of the molecular and granular layers of the isolated turtle cerebellum with the use of iontophoresis of tetramethylammonium (TMA+) combined with ion-selective microelectrodes. 2. Diffusion in the extracellular space of the molecular layer was anisotropic, that is, there was a different value for the tortuosity factor, lambda i, associated with each axis of that layer. The x- and y-axes lay in the plane parallel to the pial surface of this lissencephalic cerebellum with the x-axis in the direction of the parallel fibers. The z-axis was perpendicular this plane. The tortuosity values were lambda x = 1.44 +/- 0.01, lambda y = 1.95 +/- 0.02, and lambda z = 1.58 +/- 0.01 (mean +/- SE). By contrast, the granular layer was isotropic with a single tortuosity value, lambda Gr = 1.77 +/- 0.01. 3. These data confirm the applicability of appropriately extended Fickian equations to describe diffusion in anisotropic porous media, including brain tissue. 4. Heterogeneity between the molecular and granular layer was revealed by a striking difference in extracellular volume fraction, alpha, for each layer. In the molecular layer alpha = 0.31 +/- 0.01, whereas in the granular layer alpha = 0.22 +/- 0.01. 5. Volume fraction and tortuosity affected the time course and amplitude of extracellular TMA+ concentration after iontophoresis. This was modeled by the use of the average parameters determined experimentally, and the nonspherical pattern of diffusion in the molecular layer was compared with the spherical distribution in the granular layer and agarose gel by computing isoconcentration ellipsoids. 6. One functional consequence of these results was demonstrated by measuring local changes in [K+]o and [Ca2+]o after microiontophoresis of a cerebellar transmitter, glutamate. The ratios of ion shifts in the x- and y-axes in the granular layer were close to unity, with a ratio of 1.04 +/- 0.08 for the rise in [K+]o and 1.03 +/- 0.17 for the decrease in [Ca2+]o. In contrast, ion shifts in the molecular layer had an x:y ratio of 1.44 +/- 0.14 for the rise in [K+]o and 2.10 +/- 0.42 for the decrease in [Ca2+]o. 7. These data demonstrate that the structure of cellular aggregates can channel the migration of substances in the extracellular microenvironment, and this could be a mechanism for volume transmission of chemical signals. For example, the preferred diffusion direction of glutamate along the parallel fibers would help constrain an incoming excitatory stimulus to stay 'on-beam.'
— id: 6495, year: 1993, vol: 70, page: 2035, stat: Journal Article,

Extracellular dopamine concentration in the retina of the clawed frog, Xenopus laevis
Witkovsky P; Nicholson C; Rice ME; Bohmaker K; Meller E
1993 Jun 15;90(12):5667-5671, Proceedings of the National Academy of Sciences of the United States of America
Dopamine reaches targets in the outer retina of the clawed frog (Xenopus laevis) by diffusion from a network of dopaminergic cells and processes located predominantly at the junction of inner nuclear and inner plexiform layers. We obtained values for the steady-state release, uptake, and extracellular concentration of dopamine in the retina by a combination of HPLC (with electrochemical detection), scintillation spectroscopy, and fast-scan cyclic voltammetry. Vitreal concentrations of dopamine varied from 564 +/- 109 nM in light-adapted eyes near the time of subjective dawn to 156 +/- 12 nM in dark-adapted eyes. The data are consistent with a simple model for steady-state dopamine diffusion from an appropriately sited thin-sheet source. This model was used to generate a profile of extracellular dopamine concentration as a function of retinal depth. The model predicted an increase in the dopamine concentration from the vitreous to the layer of dopaminergic cells, remaining constant from that layer to the distal tips of the photoreceptors. This prediction was borne out by comparing fast-scan voltammetric measures of dopamine at the distal tips of the receptors with the vitreal concentrations determined by HPLC using electrochemical detection
— id: 13131, year: 1993, vol: 90, page: 5667, stat: Journal Article,

Diffusion characteristics and extracellular volume fraction during normoxia and hypoxia in slices of rat neostriatum
Rice ME; Nicholson C
1991 Feb;65(2):264-272, Journal of neurophysiology
1. Diffusion properties of submerged, superfused slices from the rat neostriatum were measured by quantitative analysis of concentration-time profiles of tetramethylammonium (TMA+) introduced by iontophoresis. TMA+ was sensed at an ion-selective microelectrode (ISM) positioned 100-150 microns from the source pipette. Slice viability was assessed from the extracellular field potentials evoked by intrastriatal electrical stimulation. 2. Under normoxic conditions the extracellular volume fraction (alpha) was 0.21 (range 0.18-0.24), and the tortuosity (lambda) was 1.54, in slices with good field potentials. In slices with poor field potentials, alpha was 0.09-0.16. Extraction of correct alpha and lambda in the slice required evaluation of nonspecific uptake, k', which was 1 x 10(-2) s-1. 3. Slices were made hypoxic by superfusing physiological saline equilibrated with 95% N2-5% CO2 for 10-30 min. Synaptic components of field potentials were inhibited after 3-4 min in hypoxic media. In some experiments extracellular K+ concentration [( K+]o) was monitored with ISMs. During hypoxia, [K+]o rose from an average baseline of 5.1 mM to 7-10 mM. After reoxygenation, [K+]o transiently fell below the original level. 4. The average value for alpha during hypoxia was 0.13 (a 38% decrease), which was significantly different from control (P less than 0.001) and increased progressively during hypoxic exposure. In contrast, tortuosity and k' were unchanged by this treatment. 5. These data represent the first characterization of the diffusion properties of the rat striatal slice and of changes in extracellular volume fraction during hypoxia in a brain slice preparation.(ABSTRACT TRUNCATED AT 250 WORDS)
— id: 14132, year: 1991, vol: 65, page: 264, stat: Journal Article,

Glutamate- and aspartate-induced extracellular potassium and calcium shifts and their relation to those of kainate, quisqualate and N-methyl-D-aspartate in the isolated turtle cerebellum
Rice, M E; Nicholson, C
1990 ;38(2):295-310, Neuroscience
Ion-selective microelectrodes can be used to evaluate the characteristics and laminar distribution of excitatory amino acid agonist-induced K+ and Ca2+ shifts in the extracellular environment of brain cells. This report describes the pattern of K+ increases and Ca2+ decreases elicited by glutamate and aspartate at 100 microns intervals in the isolated turtle cerebellum. These responses were compared to ion shifts evoked by kainate, quisqualate and N-methyl-D-aspartate. Glutamate and aspartate produced indistinguishable laminar patterns of ion shifts, with the greatest [K+]o and [Ca2+]o shifts in the granular layer. The average maximum granular and molecular layer increases in [K+]o were, respectively, 130% and 24% larger than the increase in the Purkinje cell layer. Kainate-induced increases in [K+]o also followed this granular greater than molecular greater than Purkinje cell layer pattern; however, the corresponding [Ca2+]o decreases were smaller and more variable. Quisqualate-evoked ion shifts in the molecular layer closely mimicked the shape of glutamate- and aspartate-induced responses. In the granular layer, however, quisqualate caused little ion change during iontophoresis followed by large [K+]o and [Ca+]o shifts after the end of the pulse. The minimal ion shifts induced during quisqualate application in the granular layer gave this agonist the distinction of being the only agent tested to have its greatest direct effect in the molecular layer. N-Methyl-D-aspartate caused large, two-phase [K+]o and [Ca2+]o shifts in the granular layer, only small [K+]o rises in the Purkinje cell and ventral molecular layers, and no response in the dorsal molecular layer. The lack of similarity between glutamate- and aspartate-induced ion shifts in the granular layer and those of any one agonist demonstrate the mixed agonist action of glutamate and aspartate in the cerebellum. These studies provide new information about the dynamics of excitatory amino acid receptor activation that is complementary to autoradiographic receptor mapping data and to single cell electrophysiological studies
— id: 145561, year: 1990, vol: 38, page: 295, stat: Journal Article,

Volume and ion regulation in both intracellular and extracellular compartments determined by diffusion, gravimetric and ion analysis
Nicholson, C; Cserr, H F; Rice, M E; DePasquale, M; Patlak, C S
1989 ;582:24-24, Acta physiologica Scandinavica. Supplementum
— id: 145563, year: 1989, vol: 582, page: 24, stat: Journal Article,

Measurement of nanomolar dopamine diffusion using low-noise perfluorinated ionomer coated carbon fiber microelectrodes and high-speed cyclic voltammetry
Rice, M E; Nicholson, C
1989 Sep 1;61(17):1805-1810, Analytical chemistry
Several improvements in the fabrication and use of carbon fiber voltammetric microelectrodes (CFVMs) are described. These procedures did not involve oxidative treatment, but resulted in sensitivities and selectivities approaching those of treated CFVMs, without the inherent slow response times associated with the latter electrodes. To accomplish this we reduced CFVM noise by (1) improving the adhesive seal between the 8 microns o.d. carbon fiber and the glass insulation using vacuum, (2) snapping rather than cutting or beveling the fiber to be flush with the glass, and (3) using a concentrated electrolyte solution to make electrical contact with the fiber. System noise was reduced by digital smoothing and signal averaging. Selectivity of the CFVMs for dopamine over ascorbate was enhanced to better than 2000:1 by coating with Naflon, a perfluorinated cation exchange polymer, using a low (+0.5 V vs Ag/AgCl) electroplating potential. This low voltage also prevented electrode surface oxidation. To demonstrate the performance of our CFVMs, we used them in conjunction with high-speed cyclic voltammetry to accurately measure the diffusion coefficient of iontophoretically released dopamine at concentrations as low as 35 nM over distances of less than 200 microns in agarose gel
— id: 145562, year: 1989, vol: 61, page: 1805, stat: Journal Article,

Calcium diffusion in the brain cell microenvironment
Nicholson, C; Rice, M E
1987 May;65(5):1086-1091, Canadian journal of physiology & pharmacology
A review of some of the literature on Ca2+ diffusion in free media and a variety of nervous tissues is presented. In the majority of tissue studies the apparent diffusion coefficient of Ca2+ is three to nine times smaller than that in a free aqueous medium. The methodology of using pressure microejection and Ca2+ ion-selective microelectrodes to measure Ca2+ diffusion is discussed. Our ongoing studies of Ca2+ diffusion in the cerebral cortex of the rat, using these methods, also confirm that Ca2+ diffusion is mainly influenced by the tortuosity of the tissue rather than other factors such as binding to extracellular charge sites or uptake
— id: 145565, year: 1987, vol: 65, page: 1086, stat: Journal Article,

Interstitial ascorbate in turtle brain is modulated by release and extracellular volume change
Rice, M E; Nicholson, C
1987 Oct;49(4):1096-1104, Journal of neurochemistry
The isolated turtle cerebellum was used as a model system to study effects of depolarizing conditions on interstitial ascorbic acid concentration. The depolarizing stimulus was Leao's spreading depression, which is characterized by transient negative extracellular potentials, high potassium levels (20-60 mM), and local depression of neuronal activity. Interstitial concentrations of ascorbate (200-400 microM) and other electroactive species were monitored voltammetrically, using graphite fiber microelectrodes. Total tissue ascorbate (1,810 nmol/g tissue wet weight) was similar to mammalian levels and was several orders of magnitude higher than catecholamine and indoleamine content. During spreading depression, a large (up to 200 microM) increase in concentration of interstitial electroactive species was monitored. Use of Nafion- and ascorbate oxidase-coated electrodes and uricase confirmed that ascorbate was the only substance detected. Simultaneous monitoring of ascorbate, extracellular potential, and extracellular volume (using tetramethylammonium and ion-selective microelectrodes) indicated that (a) the ascorbate increase began with the decrease in extracellular volume during spreading depression, and (b) much of the increase was the result of extracellular volume decrease. In sucrose-substituted medium, in which volume changes are eliminated, a 50 microM increase in interstitial ascorbate, caused by release from intracellular stores, was also seen. The ascorbate concentration increase was prolonged in sucrose medium, suggesting that an uptake process involving sodium may further regulate interstitial ascorbate concentration
— id: 145564, year: 1987, vol: 49, page: 1096, stat: Journal Article,

The migration of substances in the neuronal microenvironment
Nicholson, C; Rice, M E
1986 ;481:55-71, Annals of the New York Academy of Sciences
— id: 145566, year: 1986, vol: 481, page: 55, stat: Journal Article,