The localization of GABA-Transaminase in the striato-nigral system

Abstract

The localization of gamma-aminobutyric acid transaminase (GABA-T), the degrading enzyme for γ-aminobutyric acid, was examined in the striatum and substantia nigra using biochemical techniques. Selective destruction of the nigrostriatal dopaminergic system with 6-hydroxydopamine had no effect on the activity of GABA-T in either the striatum or the substantia nigra, although striatal tyrosine hydroxylase activity was reduced by half. Intrastriatal injection of kainic acid in adult rats resulted in a significant dose-dependent decrease in GABA-T activity in both the striatum and the substantia nigra. The decrease in both of these regions was significantly correlated with the decrease in the GABA synthetic enzyme glutamate decarboxylase (GAD). The intrastriatal injection of kainic acid in ten day old rats did not affect striatal GAD or GABA-T activities, although striatal choline acetyl-transferase activity was reduced by half. It is concluded that the GABA-T activity in the striatum is predominantly localized in neuronal elements, although not, apparently, in cholinergic neurons. Some GABA-T activity is also present in the terminals of the striatonigral neurons. However, the dopaminergic nigrostriatal neurons do not appear to contain GABA-T. It is suggested that high GABA-T activity may be characteristic of GABA neurons.