Occurrence of mast cells in relation to the distribution of nerve fibers in the rat larynx.

The distribution of mast cells in the rat larynx was studied at a light microscopic level in relation to nerve fibers showing substance P (SP)- and calcitonin gene-related peptide (CGRP)-like immunoreactivity (-LI) and ultrastructurally in relation to unmyelinated nerve fibers. Connective tissue mast cells (CTMC), demonstrated by staining for avidin-peroxidase and immunohistochemical staining for 5-hydroxytryptamine (5-HT), were localized in the lamina propria. Alcian blue and toluidine blue revealed mast cells in the epithelium and the lamina propria. The mast cells showed similar regional differences in their distribution as fibers showing SP- and CGRP-LI. A large or moderate number of cells was found on the laryngeal side of the epiglottis, in the ventral recess and in the aryepiglottic folds. No mast cells were found in the vocal cords. In addition, a large number of cells showing 5-HT-LI were observed in the subglottic epithelium but not in the supraglottic and the glottic epithelia. Ultrastructurally and by use of SP- and CGRP-immunohistochemistry, nerve fibers were sometimes observed close to the mast cells. These findings may be of importance in the understanding of laryngeal pathophysiological events.