IMMUNOHISTOCHEMICAL, ELECTROPHYSIOLOGICAL, AND ELECTRON-MICROSCOPIC STUDY OF RAT FUNGIFORM TASTE-BUDS AFTER REGENERATION OF CHORDA TYMPANI THROUGH THE NON-GUSTATORY LINGUAL NERVE

The sensory innervation of fungiform papillae on the rat dorsal tongue is derived from branches of two cranial nerves: the lingual branch of the trigeminal nerve which provides somatosensory innervation and the chorda tympani (CT) branch of the facial nerve, which provides innerv ation to the taste buds. Removal of the CT results in degeneration of the taste buds. Removal of both nerves results in reduction in size of fungiform papillae and an altered pattern of keratinization in its ep ithelium. Regeneration of nerves to the epithelium restores the pre-op erative condition. Thus, in addition to their sensory functions, both the CT and lingual seem to exert trophic effects on the phenotypic exp ression of epithelial cells in the fungiform papillae. We severed both the CT and lingual nerves in rats and sutured the proximal stump of t he CT to the distal stump of the lingual to promote regeneration of th e CT along the lingual nerve pathway. At the same time, we prevented t he proximal stump of the lingual from regenerating into the tongue. Ou r purpose was to determine whether and how the innervation pattern of the regenerated taste bud might be different from normal under these e xperimental conditions. We found that reinnervation by the CT through the lingual nerve occurs, that this restores the anatomical and functi onal integrity of the fungiform taste buds and papillae, and that some papillae, but not all, were richly innervated with subgemmal, extrage mmal, and perigemmal neuron-specific enolase, calcitonin gene-related peptide, substance P, and neurokinin A-positive fibers. Moreover, resp onses to taste stimuli were recorded electrophysiologically from the C T. (C) 1996 Wiley-Liss, Inc.