| Research Summary |
| The retina functions over an enormous range of stimulus intensities from dim starlight to bright sunlight. Rod photoreceptors mediate dim light vision, while cones subserve daytime vision. Dopamine, an intrinsic retinal neurochemical, alters retinal information processing by increasing the activity of cone circuits, while suppressing that of rods. The studies of our laboratory are directed at uncovering the cellular mechanisms of dopamine's actions. We showed that the release of dopamine is increased by light and suppressed by prolonged darkness. Dopamine, acting through a D1 receptor coupled to a cAMP-dependent pathway, increases the postsynaptic efficacy of glutamate at the junction between cones and second order retinal neurons. We demonstrated that dopamine also alters the permeability of gap junctions between rod and cone photoreceptors, a mechanism dependent on a D2 dopamine receptor. We also showed that dopamine is one of a host of modulators that alter the properties of intrinsic time- and voltage-dependent currents in retinal neurons. Presently, we are investigating the process of glutamate release by photoreceptors and its dependence on light, voltage, and calcium and exploring the possibility that dopamine can modulate glutamate release. Our overall conclusion is that dopamine is a chemical messenger for light adaptation and it acts through multiple cellular mechanisms.
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| Related Images |
Image 1 | Responses of isolated retinal horizontal cells to glutamate agonists. Horizontal cells were maintained in a whole-cell patch configuration at a holding potential of -60 mV. A train of 20 mV, 500 msec hyperpolarizing pulses presented at 1 Hz was superimposed on the holding potential. AMPA, L-glutamate, kainate, or quisqualate were presented to test cells as pulses from an electronically driven puffer pipette. The timing of the pulse is shown as a short horizontal bar above the trace. All four agonists elicited inward currents associated with a conductance increase. The responses to AMPA and quisqualate were desensitizing; those to glutamate and kainate were sustained. The upward arrows indicate the onset of a wash in normal Ringer's solution. Vertical bar is 100 pA for AMPA, quisqualate, and glutamate and 300 pA for kainate. |
| Research Information |
Research Interests | Dopamine-Induced Modulation of Retinal Function | Research Keywords | cone photoreceptors, dopamine, glutamate horizontal cell, retina, rod photoreceptors, Xenopus |
