Vasoactive intestinal polypeptide (VIP) as a cholinergic co-transmitter: some recent results.

The neuropeptide vasoactive intestinal polypeptide (VIP) copurifies with mammalian brain cholinergic synaptosomes when these are separated from the total brain synaptosome fraction by an immunoadsorption procedure based on an antiserum to a cholinergic-specific antigen. VIP must therefore be reckoned to be a cholinergic co-transmitter in brain. In electromotor and myenteric neurones the two transmitters are differently packaged. The frequency-dependence and pharmacology of release show that the intracellular dynamics of the storage and release processes are quite different for the two neurotransmitters. However in the ileum a portion of the vesicle-bound acetylcholine is recovered in the VIP-storing particles and this might indicate a precursor-product relationship for the two types of vesicle in this system analogous to that which has been proposed for electron-dense and electron-translucent vesicles in noradrenergic nerves.