The emergence, localization and maturation of neurotransmitter systems during development of the retina inXenopus laevis. I. ?-aminobutyric acid

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Abstract
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.