The use of gabaculine-induced accumulation of GABA for an index of synthesis of GABA in the retina

The characteristics of accumulation of gamma-aminobutyric acid (GABA) in the retina after an intravitreal injection of the GABA-T inhibitor, gabaculine, have been studied in rats. The accumulation of GABA after injection of gabaculine was both dosage- and time-dependent. In both dark- and light-adapted-retinas, GABA continued to increase linearly for at least 90 min after an injection of gabaculine and this increase (3-fold) was similar in dark- and light-adapted rats. The GABA agonist, muscimol, and the GABA antagonist, bicuculline methiodide, significantly inhibited and facilitated, respectively, the gabaculine-induced increase in GABA levels. Previous studies have shown that accumulation of GABA following the irreversible inhibition of GABA-T was useful for measuring the rate of synthesis of GABA in the central nervous system, and these studies suggest that this technique may also be useful in the retina.