Regional distribution and relative amounts of glutamate decarboxylase isoforms in rat and mouse brain

The levels of the two isoforms of glutamate decarboxylase (GAD) were measured in 12 regions of adult rat brain and three regions of mouse brain by sodium dodecylsulfate-polyacrylamide gel electrophoresis and immunoblotting with an antiserum that recognizes the identical C-terminal sequence in both isoforms from both species. In rat brain the amount of smaller isoform, GAD(65), was greater than that of the larger isoform, GAD(67), in all twelve regions. GAD(65) ranged from 77-89% of total GAD in frontal cortex, hippocampus, hypothalamus, midbrain, olfactory bulb, periaqueductal gray matter, substantia nigra, striatum, thalamus and the ventral tegmental area. The proportion of GAD(65) was lower in amygdala and cerebellum but still greater than half of the total. There was a strong correlation between total GAD protein and GAD activity. In the three mouse brain regions analysed (cerebellum, cerebral cortex and hippocampus) the proportion of GAD(65) (35,47, and 51% of total GAD) was significantly lower than in the corresponding rat-brain regions. The amount of GAD(67) was greater than the amount of GAD(65) in mouse cerebellum and was approximately equal to the amount of GAD(65) in mouse cerebral cortex and hippocampus. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.