The biosynthesis and content of gamma-aminobutyric acid in the goldifsh retina.

Goldfish retinas incubated with L-glutamate-(14)C (UL) were found to synthesize gamma-aminobutyric acid-(14)C (GABA-(14)C) The accumulation of newly synthesized GABA was enhanced by physiological stimulation of the retina with flashing light; and this increase was directly proportional to the logarithm of the light intensity. The total GABA content was also higher in light-stimulated than in dark-adapted retinas, although the glutamate content remained unchanged No differences were found in the cell-free activities of glutamate decarboxylase (EC 4 1.1 15) and GABA-glutamate transaminase (EC 2.6.1.19) extracted from light-stimulated and dark-adapted retinas. These findings, together with other physiological and morphologcal evidence, suggest that GABA plays a functional role in synaptic transmission in the goldfish retina