The emergence, localization and maturation of neurotransmitter systems during development of the retina in Xenopus laevis. I. γ‐aminobutyric acid

The high‐affinity uptake, biosynthesis and release of GABA have been studied in the retina of Xenopus laevis. In the mature retina, [³H]‐GABA is accumulated predominantly by horizontal cells. A second population of cells located in the inner nuclear layer (possibly a type of amacrine cell) also showed a specific GABA uptake. In addition, this retina contains significant activities of L‐glutamic acid decarboxylase and also releases [³H]‐GABA in response to increasing K⁺ concentrations in the medium. We have followed the appearance and maturation of these GABA‐ergic properties during embryonic development of this retina. Our results indicate that these properties emerge in a precise temporal pattern during retinal differentiation: the specific neuronal uptake of GABA synthesis which is followed by K⁺‐stimulated GABA release.