Regional differences in the distribution of nerve fibers showing substance P- and calcitonin gene-related peptide-like immunoreactivity in the rat larynx

Summary The distribution of substance P (SP) — and calcitonin gene-related peptide (CGRP) — containing nerve fibers in the rat larynx was studied using immunohistochemistry. Double-labeling studies revealed a high degree of co-existence of SP- and CGRP-like immunoreactivity (LI) in the nerve fibers in the larynx. There was a considerable regional difference in the number of immunoreactive nerve fibers in the epithelium and lamina propria. Richly supplied sites were the laryngeal side of the epiglottis and the ventral recess, whilst there was no evidence of nerve fibers in the squamous epithelium of the vocal cords. However, where the squamous epithelium of the vocal cords changed into a cuboidal epithelium, a moderate number of nerve fibers was present, and a large number of fibers was seen where the squamous epithelium of the cords was in close contact with cartilage. Nerve fibers showing SP- and CGRP-LI were also observed close to the acini and ducts of the glands, in the blood vessel walls, close to the perichondrium of all the cartilages, and outside the cricothyroid and cricoarytenoid joints. CGRP-LI was detected in epithelial cells facing the lumen of the airway and in cells in the acini and ducts of glands in the subglottic region and trachea. Unilateral sympathectomy did not affect the pattern of SP- and CGRP-innervation in the larynx, whereas after vagotomy, the SP- and CGRP-innervation almost disappeared ipsilaterally in the upper parts of the epiglottis and aryepiglottic folds.