CHOLINERGIC INNERVATION OF THE VASCULAR W ALL

The wall of blood vessels involved in both peripheral and extracerebra l circulations is innervated by parasympathetic cholinergic fibers. Th ese fibers induce an endothelium-dependent relaxation which involves s ynthesis and release by endothelial cells of nitric oxide (NO), a diff usible agent acting as a muscular relaxant. Nerves capable of NO synth esis are present on extracerebral arteries and seem to release NO via a nicotinic-mediated pre-synaptic stimulation. In the cerebral cortex, intraparenchymal microvessels are in intimate relationship with choli nergic nerve terminals that are either intrinsic or that originate fro m the basal forebrain. This neurovascular apposition includes an inter vening glial leaflet suggesting that astrocytes are involved in the re gulatory mechanisms by which the brain controls its blood supply and t he blood brain barrier. Thus, a neuronal-glial-vascular signalling mec hanism is probably involved in the regulation of cortical microcircula tion.