Role of glutamate decarboxylase (GAD) isoform, GAD65, in GABA synthesis and transport into synaptic vesicles -: Evidence from GAD65-knockout mice studies

In GAD(65)-knockout mice, lack of GAD(65) expression was confirmed. The expression level of vesicular GABA transporter (VGAT) was upregulated, and no change in the synaptic vesicles (SV)-associated GAD(67) was found. GAD(65)(-/-) SV transported cytosolic GABA much more efficiently than that of the wild type, further supporting our model that there is a structural and functional coupling between GABA synthesis and packaging into SV. Both full-length and truncated forms of GAD(65) could bind to GABAergic SV, indicating the N-terminus is not required for the anchoring of GAD(65) to SV. Although both GAD65(-/-) SV reconstituted with either GAD(65) or GAD(67) could synthesize GABA from [H-3] glutamate and transport this newly synthesized GABA into SV, the combined evidence suggests that GAD(65) plays a major role in GABA transmission in normal physiological condition. However, GAD(67) could serve this role under some pathological conditions. (C) 2007 Elsevier B.V. All rights reserved.