Relationship between light adaptation, dopamine release and coupling of horizontal cells in the mudpuppy (Necturus maculosus) retina.

Abstract

The relationship between light adaptation, dopamine release and coupling of horizontal cells was studied in the retina of an amphibian, the mudpuppy, Necturus maculosus. Intracellular recordings were made from horizontal cells in the mudpuppy eyecup preparation. Changes in coupling between horizontal cells under different testing conditions were measured by comparing the changes in horizontal cell responses to stimulation of the center and surround portions of the receptive field. Dopamine caused a decrease in horizontal cell coupling and was more effective in relatively dark-adapted retinas. Both the selective D1 receptor antagonist SCH23390 and 2-amino-4-phosphonobutyrate (APB), a glutamate analog which blocks responses of On-center but not Off-center bipolar cells, caused an increase in coupling and were more effective in relatively light-adapted retinas. On the other hand, cis-2,3-piperidine dicarboxylate (PDA), a glutamate receptor antagonist which blocks responses of Off-center but not On-center bipolar cells, had little effect on coupling. In dark-adapted retinas, exposure to an adapting light caused a decrease in coupling; this effect of light was blocked in the presence of SCH23390 or APB. These results suggest that (1) dopamine regulates horizontal cell coupling via an action at D1 receptors in the mudpuppy retina; (2) the release of dopamine is decreased in dark-adapted retinas and is stimulated by light; (3) the effect of light on dopamine release is mainly via On-center bipolar cells.