Neuropeptides in the facial nerve of the rat

Abstract

The occurrence of peptidergic nerve fibres containing substance P (SP), calcitonin gene-related peptide (CGRP), vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY) in the cerebral arteries and arterioles is well known. NPY is a vasoconstrictor, while SP, CGRP and VIP induce cerebrovascular dilatation. Vascular dysregulation of the vasa nervorum of the facial nerve is believed to be a central factor in the pathogenesis of Bell's palsy. Hilger's theory of the primary and/or secondary oedema which is followed by the vicious circle is generally accepted. It was our aim to describe the occurrence and distribution of neuropeptides in the blood vessels of the facial nerve. We examined the facial nerves of 6 male Wistar rats using the indirect immunofluorescence technique. There is not only a characteristic distribution of the neuropeptides in different parts of the facial nerves, but there are also beaded axons of sensory nerve fibers, which are localised freely in the endoneurium. These SP and CGRP containing beaded axons which densely innervate the nerve in the bony canal, are capable of inducing an oedema by neurogenic inflammation. Our findings suggest that there must be a vascular regulation in the facial nerve which is controlled by various neuropeptides.