Genetic variation in brain L-glutamate decarboxylase activity from two inbred strains of mice

Two inbred strains of mice, C57BL/6Bg and DBA/1Bg, were compared for genetic varaition in brain L-glutamate decarboxylase (GAD) activity. Although no large difference was found between the strains in whole brain GAD activity at adult age (27--45 days postnatally), regional examination revealed a difference in GAD activity in the cerebral cortex (15% higher in DBA); subcellular examination revealed a difference in synaptosomal fraction (21% higher in DBA). When GAD activity was measured in synaptosomal fractions prepared from dissected cerebral cortex, DBA was 34% higher than C57BL. In addition, differences in GAD activity between the two strains could be observed even in the whole brain (10--15% higher in DBA) during earlier development (15--23 days postnatally). These data indicate that at adult age, genetic difference in GAD activity between the two strains exists mainly in nerve terminals of the cerebral cortex. It is postulated that the difference may be due to a genetically mediated mechanism regulating GAD in the presynaptic terminals of GABA neurons of the cerebral cortex.