Heterogeneity of glutamatergic and gabaergic release machinery in cerebral cortex

We investigated whether cortical glutamatergic and GABAergic release machineries can be differentiated on the basis of the proteins they express, by studying the degree of co-localization of synapsin (SYN) I and II, synaptophysin (SYP) I and II, synaptosomal-associated protein (SNAP)-25 and SNAP-23 in vesicular glutamate transporter (VGLUT) 1-, VGLUT2- and vesicular GABA transporter (VGAT)-positive puncta in the rat cerebral cortex. Co-localization studies showed that SYNI and II were expressed in similar to 90% of VGLUT1+, similar to 30% of VGLUT2+ and 30-50% of VGAT+ puncta; SYPI was expressed in similar to 95% of VGLUT1 +, 30% of VGLUT2+, and 45% of VGAT+ puncta; SYPII in similar to 7% of VGLUT1+, 3% of VGLUT2+, and 20% of VGAT+ puncta; SNAP-25 in similar to 94% of VGLUT1+, 5% of VGLUT2+, and 1% of VGAT+ puncta, and SNAP-23 in similar to 3% of VGLUT1+, 86% of VGLUT2+, and 22% of VGAT+ puncta. Since SYPI, which is considered ubiquitous, was expressed in about half of GABAergic axon terminals, we studied its localization electron microscopically and in immunoisolated synaptic vesicles: these studies showed that similar to 30% of axon terminals forming symmetric synapses were SYPI-negative, and that immunoisolated VGAT-positive synaptic vesicles were relatively depleted of SYPI as compared with VGLUT1 + vesicles. Overall, the present investigation shows that in the cerebral cortex of rats distinct presynaptic proteins involved in neurotransmitter release are differentially expressed in GABAergic and in the two major types of glutamatergic axon terminals in the cerebral cortex of rats. (C) 2007 IBRO. Published by Elsevier Ltd. All rights reserved.