Excitatory amino acid analogs evoke release of endogenous amino acids and acetyl choline from chick retina in vitro

There is mounting evidence that excitatory amino acids may play a role in retinal synaptic neurotransmission. In this study, we demonstrate the release of endogenous amino acids and acetylcholine from isolated chick retina in vitro evoked by three excitatory amino acid analogs, kainic acid (K.A). quisqualic acid (Quis), and N-methyl-d,l-aspartic acid (NMDA). The release is dose-dependent and involves putative transmitters from both inner and outer retina. Release from the inner retina is partially Ca²⁺-dependent, while release from the outer retina is Ca²⁺-independent and Na⁺-dependent. Release experiments carried out in the presence of specific excitatory amino acid blocking agents suggest that the release is mediated by two receptors, the kainate receptor and the NMDA receptor. These results are supportive of a role for excitatory amino acids in synaptic neurotransmission in both inner and outer retina.