Substance P nerve fibres in the canine larynx by PAP immunohistochemistry

The distribution of the Substance P (SP) immunoreactive nerve fibres in the canine larynx and laryngeal nerves was studied by PAP immunohistochemistry. Many individual SP immunoreactive nerve fibres with varicosities were observed within the epithelial layer and in the connective tissue below the epithelium of the laryngeal mucosa. Small numbers of SP immunoreactive nerve fibres were also found in the submucosal gland region and some of them appeared to terminate in glandular cells. These findings are consistent with the view that SP might be involved in the laryngeal sensory innervation system and the laryngeal glandular secretion. No SP immunoreactive nerve fibres were found in any intrinsic laryngeal muscles. The recurrent laryngeal nerve and the superior laryngeal nerve contained SP immunoreactive nerve fibres and were considered to lie in the pathway of the SP nerve fibres to the larynx.