THE BIOSYNTHESIS AND CONTENT OF GAMMA-AMINOBUTYRIC ACID IN THE GOLDFISH RETINA

Goldfish retinas incubated with L-glutamate-¹⁴C (UL) were found to synthesize γ-aminobutyric acid-¹⁴C (GABA-¹⁴C) 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