The identification and some functions of GABAergic neurons in the proximal retina of the catfish

Putative GABAergic neurons in the inner retina of the Texas channel catfish, Ictalurus punctatus, were studied using autoradiographic, biochemical and electrophysiological techniques. A pyriform amacrine cell, ramifying predominantly in sublamina b of the inner plexiform layer, was found to accumulate exogenous GABA in the dark. GABA could be released from these cells with high K+ Ringers solution and the release was blocked by Co2+. These data suggest that a class of catfish amacrine cells are GABAergic. To substantiate this, extracellular recordings were made from ganglion cells during the superfusion of the GABA blocking agent bicuculline methochloride. This agent modified the responses of ganglion cells in a manner consistent with the notion that GABAergic amacrine cells are a major source of input to on-center ganglion cells. There also appeared to be an indirect GABAergic influence on a subclass of off-center ganglion cell.