Cholinergic Surface Antigen Chol-1 Is Present in a Subclass of VIP-Containing Rat Cortical Synaptosomes

The colocalization of vasoactive intestinal polypeptide (VIP) with the cholinergic specific surface antigen Chol-1 was investigated in synaptosomes derived from the rat cerebral cortex. Immunoaffinity purification of cortical synaptosomes using antisera to Chol-1 resulted in the copurification of VIP and cholinergic nerve terminals. VIP was purified with a yield of 75% of that of choline acetyltransferase (ChAT). These results suggest that approximately 53% of the cortical cholinergic terminals contain VIP, whereas 75% of the cortical VIP content is present in these cholinergic terminals. Both hypotonic lysis and depolarization of the nerve terminals resulted in the differential release of VIP and acetylcholine (ACh), indicating the different compartmentalization in the same nerve terminal. Complement-mediated lysis of cholinergic nerve terminals, using antisera to Chol-1, resulted in the release of 64% of the ChAT, 71% of ACh, and 27% of the VIP. The application of our method enables quantifying and mapping, with a fast, efficient, and specific technique, the coexisting peptides in cholinergic neurons of distinct brain areas.