The dissociation of evoked release of [³H]-GABA and of endogenous GABA from chick retina in vitro

The release of prelabeled [³H]-GABA and endogenous GABA evoked by KCl and excitatory amino acid analogs was compared in intact chick retina and retina previously lesioned by the neurotoxins, kainic acid and N-methyl-d,l-aspartic acid. Significant discrepancies were found in the results obtained by the two techniques; and while changes in endogenous GABA release after neurotoxin lesions correlated with retinal glutamate decarboxylase activity, a marker for GABAergic neurons, the release of [³H]-GABA did not. These results call into question the validity of the prelabeling technique for studying GABA release from retina.