Excitatory amino acid receptors and transmitter release in the retina

Abstract

The effects of excitatory amino acids and some analogues on the release of GABA and ACh from amacrine cells were studied. The release of endogenous GABA from the isolated rat retina was measured by HPLC. When animals were pretreated with γ-vinyl-GABA (GVG), glutamate evoked a large efflux of GABA but kainate, quisqualate and N- methyl- d-aspartate ( NMDA) were relatively ineffective. The glutamate evoked release of GABA was calcium dependent and was blocked by the antagonist, piperidine-dicarboxylic acid (PDA) indicating that activation of excitatory amino acid receptors was involved in the response. The release of [ 3H]ACh from the rabbit retina was strikingly increased by homocysteate and this effect was blocked by NMDA. Since NMDA also blocked the light evoked release of [ 3H]ACh but not the effects of exogenous glutamate or aspartate, it is possible that homocysteate may be a bipolar cell transmitter released onto cholinergic amacrine cells.