Three dimensional observation of the nerve fibers along the cerebral blood vessels.

Three dimensional observation of the nerve fibers along the cerebral blood vessels was investigated by scanning electron microscopy. Electron probe X-ray microanalysis was also performed in the cerebral blood vessels treated with peroxidase-antiperoxidase immunohistochemistry intensified by nickel ammonium sulfate. Nerve fibers (2-8 microns in diameter) formed a plexus on the outer surface of the adventitia. After branching, the nerve fibers penetrated the blood vessel adventitia. Substance P-immunoreactive nerve fibers showed a meshwork pattern in the outer layer of the adventitia, and vasoactive intestinal polypeptide (VIP)-immunoreactive nerve fibers revealed a spiral running pattern in the inner layer of the adventitia. Taken together with previous studies, these findings suggest that substance P nerve fibers in the cerebral arteries may not be related to arterial dilatation or constriction, but VIP nerve fibers may be vasodilative.