Effects of GABA antagonists on spectral responses of horizontal cells in the carp retina

Abstract

Previous experiments have shown that, in the carp retina, a GABA-mediated feedback from horizontal cells to cones is involved in neural mechanisms of color opponency. In this article, we investigated effects of GABA antagonists, picrotoxin and bicuculline, on spectral responses of horizontal cells. These chemicals caused selective suppression of responses to long wavelength, probably because the feedback was blocked. In particular, a biphasic spectral response curve in the H2 cell turned into almost monophasic. The presence of feedback in the carp retina was further supported by the fact that depolarizing synaptic potentials were detected in cones at the center, when horizontal cells were hyperpolarized by a peripheral annulus illumination.