Effects of excitatory amino acids, and of their agonists and antagonists on the release of neurotransmitters from the chick retina

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Abstract
Effects of glutamic, aspartic, and cysteic acid, and of kainic acid and N‐methyl aspartate on the release of labeled GABA, glycine, and taurine were examined in isolated, perfused chick retina. Glutamic acid (0.5‐2 mM), increased the release of 3H‐GABA by more than four times and that of 14C‐glycine by about two times. The release of GABA decreased 50% and that of glycine 95% in the presence of the antagonist of glutamic acid receptors, glutamate diethyl ester (300 m̈M). N‐methyl aspartate, used as an agonist of aspartic acid receptors, preferentially increased the release of GABA (seven times) over that of glycine (three times). The stimulatory effect of N‐methyl aspartate was antagonized by D‐α aminoadipate and by Mg. Kainic acid (10 m̈M) induced the release of glycine but not that of GABA. Cysteic acid failed to modify the release of any of the amino acids examined. The efflux of labeled taurine was practically unaffected by all the compounds utilized. The release of GABA by the excitatory amino acids and agonists was Ca‐independent but Na‐dependent, whereas the release of glycine was markedly Ca‐dependent. The evidence presented here suggests that experimental conditions activating receptors of excitatory amino acids differently affect the release of inhibitory amino acids.