ARE GAD(65) AND GAD(67) ASSOCIATED WITH SPECIFIC POOLS OF GABA IN BRAIN

Brain contains at least two pools of gamma-aminobutyric acid (GABA), t he transmitter pool and the so-called metabolic pool. To a large exten t these pools may reflect the presence of GABA in different intracellu lar compartments, as immunocytochemical studies show that GABA is not localized mainly in terminals but is distributed throughout neurons. A n interesting issue is the extent to which the two major forms of glut amate decarboxylase (GAD(65) and GAD(67)) are specialized to synthesiz e GABA for these pools. Although GAD(65) and GAD(67) differ significan tly in several characteristics, they also have substantial similaritie s and interactions, and the presence of individual forms of GAD in cer tain cell types is consistent with the idea that GAD(65) and GAD(67) c an each synthesize GABA for both pools. Substantial progress has been made in understanding the regulatory properties of GAD, but the availa ble data provide little indication of how differences between the form s might enable each to serve the demands for GABA synthesis in a speci fic pool.