Age-related changes in sensory and secretomotor nerve endings in the larynx of F344/N rat.

The aim of the present study was to define the age-related changes in sensory and secretomotor nerve endings in the larynx of F344/N rats. For this purpose, laryngeal tissue sections obtained from 12-, 24- and 35-month-old F344/N rats were compared with respect to the density, distribution and morphology of various types of sensory and secretomotor nerve endings immunoreactive for protein gene product 9.5 (PGP 9.5), calcitonin gene-related peptide (CGRP) and substance P (SP). Two distinct forms of PGP 9.5-immunoreactive motor end-plates were noted; the large sized motor end-plates localized in thyroarytenoid and cricoarytenoid muscles were degenerated in aged rats, while the small sized motor end-plates, localized predominantly in vocal muscles, did not show any age-related changes. CGRP- and SP-immunoreactive nerve fibres of the laryngeal glands did not show any age-related changes. Subepithelial laminar nerve endings immunoreactive to PGP 9.5 showed degeneration with ageing. Aggregates of terminal arborisations in the subepithelial region were smaller in aged animals. PGP 9.5-immunostained taste cells and well-developed subgemmal network were abundant in 12- and 24-month-old rats, but only a few were noted in aged rats. The total number of taste buds decreased significantly with ageing. CGRP- and SP-immunostained taste bud-nerve endings were noted in 12- and 24-month-old rats, but only rarely in 35-month-old rats. The laryngeal epithelium contained PGP 9.5-, CGRP- and SP-immunoreactive thin free nerve endings with many varicosities; their number and distribution were similar between 12- and 24-month-old rats, while only a few endings were observed in 35-month-old rats. Our results indicated that ageing is associated with the reduction of laryngeal sensory and secretomotor nerve endings.