NITROXIDERGIC INNERVATION OF GUINEA-PIG CEREBRAL-ARTERIES

The presence and distribution of nitric oxide synthase (NOS)-immunorea ctive nerve fibers associated with the guinea pig major cerebral arter ies was studied by means of immunohistochemical, histochemical and ult rastructural techniques. Anterior arteries of the circle of Willis rec eived a rich supply of perivascular nerve fibers containing NOS immuno reactivity while posteriorly localized arteries presented a moderate t o sparse innervation. A double immunofluorescence staining technique r evealed that NOS was localized in nerve fibers distinct from those dis playing substance P or tyrosine hydroxylase. Combined immunofluorescen ce and histochemical staining of the same preparation indicated that N OS immunoreactivity was localized in putative cholinergic nerve fibers (identified by their acetylcholinesterase content) and that NADPH-dia phorase activity (a marker for NOS-containing neurons) was found in ne rves which also possessed VIP immunoreactivity. The ultrastructural st udy revealed that NOS immunoreactivity was present in numerous nerve v aricosities at the adventitial-medial border. These results suggest th at NO and VIP co-exist in putative parasympathetic nerve fibers supply ing the guinea pig cerebral arteries and may be release together in re sponse to nervous stimulation.