A Light and Electron Microscopic Immunohistochemical Study of Vasoactive Intestinal Polypeptide— And Substance P-Containing Nerve Fibers along the Cerebral Blood Vessels: Comparison with Aminergic and Cholinergic Nerve Fibers

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Abstract
Vasoactive intestinal polypeptide (VIP)– and substance P–containing nerve fibers were observed in the cerebral blood vessels using an immunohistochemical technique. VIP-containing nerve fibers distributed in a spiral pattern, similar to that of muscle cells. Under electron microscopic observation, VIP-immunoreactive terminals lay close to a muscle cell in the inner layer of the adventitia. In contrast, substance P–containing nerve fibers showed a meshwork pattern in the outer layer of the adventitia. Using both acetylcholinesterase (AChE) staining and VIP immunohistochemistry, AChE-positive and VIP-immunoreactive nerve fibers revealed almost the same distribution in the same specimen. The present data suggest that VIP-containing nerve fibers may play a role in the smooth muscle control of the blood vessels, whereas substance P–containing nerve fibers may not take part in muscle control.