Neurotransmitter-specific identification and characterization of neurons in the all-cone retina of Anolis carolinensis, I: Gamma-aminobutyric acid

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Abstract
The inhibitory amino-acid neurotransmitter, gamma-aminobutyric acid (GABA), was localized in the pure cone retina of the lizard Anolis carolinensis by autoradiographic and immunocytochemical techniques. Uptake of [3H]-GABA labeled horizontal cells, amacrine cells, numerous cells in the ganglion cell layer, both plexiform layers, and the nerve fiber layer. Label in the inner plexiform layer showed distinct lamination.The pattern of GABA immunoreactivity was similar to the pattern of [3H]-GABA uptake, although some differences, particularly in labeling of amacrine and ganglion cells, were observed. Immunocytochemistry revealed endogenous stores of GABA in a set of horizontal cells, amacrine cells, and cells in the ganglion cell layer. Both plexiform layers were labeled by the GABA antisera. Labeling in the inner plexiform layer (IPL) was highly stratified and GABA-immunoreactive strata were present in both sublaminae a and b. Six subtypes of conventionally placed GABA-immunoreactive amacrine cells and one displaced amacrine cell subtype were identified. Three of the six conventional amacrine cell subtypes were of pyriform morphology and three subtypes were of multipolar morphology. GABA-immunoreactive interstitial cells also were observed.Under certain conditions the GABA antiserum labeled the cones. Etching the resin eliminated cone labeling, suggesting that GABA in the cones is present in a labile pool, unlike GABA in horizontal or amacrine cells, or the observed labeling was not due to endogenous GABA. Cones did not demonstrate [3H]-GABA uptake.