A GABA antagonist, bicuculline, exerts its uncoupling action on external horizontal cells through dopamine cells in carp retina.

External horizontal cells in isolated retinas of the carp (Cyprinus carpio) were intracellularly recorded and marked with the fluorescent dye Lucifer Yellow (LY). These cells are electrically coupled via gap junctions, so that the injected dye normally diffused to neighboring cells. A GABA antagonist, bicuculline (Bcc, 20 microM), applied to the vitreous fluid beneath the isolated retina, altered the spatial properties of light-induced responses, by increasing the amplitude of responses to central spots and decreasing that of those to distant spots. Bcc also restricted to injected dye to single recorded cells. These uncoupling actions of Bcc were similar to those of amphetamine (20 microM) or dopamine (10-20 microM) and were abolished by the presence of a dopaminergic blocker, haloperidol (20-40 microM). Both the actions of Bcc and amphetamine were not observed when applied to retinas deprived of dopaminergic cells by prior destruction with 6-hydroxydopamine. Therefore, Bcc exerts its uncoupling actions on external horizontal cells indirectly through the dopaminergic system in the carp retina.