The retinal dopamine network alters the adaptational properties of retinal ganglion cells in the cat.
1. Single-unit extracellular recordings of optic tract fibers were used to study ganglion cell (GC) response properties of the intact cat eye before and after the intravitreal injection of haloperidol or SCH23390, dopamine-specific antagonists. Nearly all of the dopaminergic cells in the cat retina are amacrine cells (ACs); thus the dopamine antagonists are thought to primarily block the postsynaptic effects of these dopaminergic amacrine cells. All GCs encountered were subjected to a battery of receptive-field (RF) tests, including classification as X or Y, and as ON or OFF. 2. The effects of haloperidol were greatest in the light-adapted OFF-center pathways and especially in the OFF-center Y-cell. Within 30 min of haloperidol injection, both the spontaneous and light-evoked activity of the OFF-center Y-cell fell to zero, but when the same cell was exposed to lower levels of steady-state background illumination (scotopic levels), the response of the cell once again became robust. 3. OFF-Center Y-cells that had partially recovered from the drug effects and OFF-center X-cells recorded when the drug effect was maximal both possessed intensity-response curves that were shifted to the right of normal. 4. Recovery from the drug effects reflect supranormal responses after the initial response reductions and may be due to haloperidol's action on the dopamine autoreceptor. 5. Of the ON-center cells, only the Y-cells showed response alterations; possessing higher spontaneous activities and slightly reduced amplitudes to RF center (RFC) illumination. 6. The effects of SCH23390 paralleled those of haloperidol except that the onset was faster and the duration of the action of SCH23390 was much shorter, and no supranormal responses followed the initial effects. 7. Dark-adaptation functions of OFF-center GCs revealed a normal rod-cone shift; however, SCH23390 eliminated the rod-cone break, and threshold quickly fell to that of the rod mechanism. 8. The dopaminergic neurons of the cat retina appear to play an important role in regulating the activity of retinal OFF-center pathways in the photopically adapted eye, and one of its functions may be to control the relative contributions of the rod and cone systems to the response properties of light-adapted OFF-center GCs. 9. It is argued that dopamine is released in the light and enhances cone pathway activity, perhaps in the outer retina at bipolar and horizontal cells, and suppresses rod pathway activity, perhaps in the inner retina at amacrine cells.
Maguire
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Sensory Sciences Center, Graduate School of Biomedical Sciences, University of Texas, Houston 77030.
Hamasaki
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DI
D000221:Adaptation, Ocular / Q000502:physiology*; D000818:Animals; D002415:Cats; D004298:Dopamine / Q000502:physiology*; D005074:Evoked Potentials, Visual / Q000502:physiology; D009415:Nerve Net / Q000502:physiology*; D009900:Optic Nerve / Q000502:physiology; D017447:Receptors, Dopamine D1 / Q000502:physiology; D012165:Retinal Ganglion Cells / Q000502:physiology*; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology*
D017447:Receptors, Dopamine D1; D004298:Dopamine