Two types of cholinergic innervation in cortex, one co-localized with vasoactive intestinal polypeptide

Abstract

The existence of cholinergic neuronal cell bodies in mammalian cerebral cortex was long the subject of much controversy (see ref. 1 for review). Recently, however, a specific cholinergic marker, the acetylcholine synthesizing enzyme, choline acetyltransferase (ChAT, E.C.2.3.1.6), was demonstrated by immunohistochemical methods to be present in bipolar neurones in rat cortex^2,3. Here we show that at least 80% of these intrinsic cholinergic neurones also contain immunoreactivity for vasoactive intestinal polypeptide (VIP), a neuroactive peptde found to be present in a subpopulation of cortical neurones⁴. On the other hand, we find that the ChAT-positive cells in the basal forebrain, which are another major source of cholinergic innervation of the cortex^5–8, contain no detectable VIP-immunoreactivity. In addition, we have observed by both light and electron microscopy that some VIP- and some ChAT-positive structures in cortex are closely associated with blood vessels.