The Role of Glutamate Decarboxylase and GABA Transaminase in Post Mortem GABA Increases in Discrete Regions of Rat Brain

Abstract

Preliminary experiments were performed to establish the optimal microwave irradiation time required to protect the brain from post mortem metabolism of GABA. Following this study, the high-energy phosphates, which deplete rapidly during brain ischemia and/or anoxia, were measured along with GABA to further acertain the utilization of the proper irradiation time. The metabolic enzymes in the GABA system are known to be more rapidly destroyed by microwave treatment than those in the high-energy phosphate system. The regional distribution of GABA in discrete regions of the rat brain was then determined and compared for animals sacrificed by decapitation or microwave irradiation (5kW, 1 sec). As generally accepted, the GABA content found in most regions after decapitation was higher than that after microwave irradiation. However, the degree of post mortem GABA increase varied from region to region. For example, the GABA content in the substantia nigra, superior colliculus, inferior colliculus and hypothalamus increased by 86, 112, 119 and 37 percent, respectively, when compared to the control levels obtained with microwave irradiation. In other regions, such as the striatum and the thalamus, the post mortem GABA increase was not significant. The regional distribution of GAD activity paralleled that of the GABA concentration, whereas the regional distribution of GABA-T activity was not necessarily consistent with the GABA concentration and the GAD activity. The correlation between the regional post mortem GABA increase and the GAD and GABA-T activities in the present study, however, indicate that both enzymes may be involved in determining the degree of post mortem GABA increase in individual brain regions.