The Formation of Glutamate, Aspartate and Gaba in the Rat Retina; Glucose and Glutamine as Precursors

The distribution of the neuroactive amino acids taurine, GABA, glycine, glutamate and aspartate, together with glutamine, have been studied in the rat retina. Peak levels of taurine were found in photoreceptor cells and of GABA and glycine in a retinal fraction enriched in amacrine cells and, synaptic terminals. In vitro, GABA formation from [3H]glutamine and [14C]glucose was also most prominent in this fraction; at 500 μm [3H]glutamine was the better precursor. Observations on metabolism in the photoreceptor cell layer of the tissue suggest an active turnover of glutamate, aspartate and GABA, and show that glutamine may serve as an alternative substrate to glucose here, perhaps via the GABA bypath.