In vivo influence of light or darkness on the GABA system in the retina of the frog ( Rana pipiens)

An investigation of glutamate, γ-aminobutyric acid (GABA) and related enzyme systems in the frog retina has shown that adaptation to light and darkness has little or no effect on the content or localization of retinal glutamate. However, GABA levels are decreased by more than 40% in both the bipolar and ganglion cell layers of the dark-adapted frog retina. A decrease of glutamic carboxyl-lyase was also observed. GABA is concentrated in the frog retina primarily within cell layers which are rich in amacrine cells. The temporal decrease of retinal GABA and the decrease in threshold excitability during dark adaptation suggests a correlation between these two phenomena. Our observations are in agreement with the hypothesis that GABA in the frog retina is functionally related to inhibitory neural mechanisms.