Effects of GABA on neuronal activities in the distal retina of the carp.

When a transient depolarization was evoked in horizontal cells by a transretinal current pulse, a small hyperpolarizing deflection (probably IPSP) was detected in cones. The IPSP was abolished by superfusion of the retina with GABA-containing Ringer solution, which also hyperpolarized the cones. These results suggest that, in the dark, a GABA-mediated negative feedback was operating from horizontal cells to cones, and terminated in the light. Application of GABA also caused remarkable changes in spectral response curves of horizontal cells, mainly because of suppression of responses to monochromatic lights of longer wavelengths. Therefore, it was concluded that the feedback plays an important role in mechanisms of conversion from the trichromatic process in cones to the opponent color process in horizontal cells.