Activity of L-glutamic acid decarboxylase in different regions of baboon brain.

1. The activity of glutamic acid decarboxylase (GAD), the enzyme synthesizing gamma-aminobutyric acid (GABA), was determined in over one hundred areas and sub-areas of baboon brain. Remarkably higher enzyme activities were found in the substantia nigra, the pallidum, the colliculi and the certain regions of the hypothalamus. These findings agreed with earlier report on fewer numbers of regions in the brains of lower mammals. 2. By careful dissections and determinations, several specified nuclei of extremely small size were also studied and it was found that the bed nucleus of the stria terminalis had enzyme activity equivalent to that in the substantia nigra. Considerable activity was also found in the coordination nuclei in the midbrain, the nucleus basalis and some other restricted regions. 3. The significance of the differences in GAD activities found in the various regions of the brain is discussed.