Immunohistochemical study of the innervation of the boundary area of the hard and soft palates of the rat.

The palatal mucosa plays an important role for patients using full dentures. The posterior ridge of the denture is designed to fit on the border between the hard and soft palates; accordingly, this boundary area is of importance when the outline of the denture is designed. In the present study, a rich supply of nerve fibers was found in the mucosa of the boundary area of the hard and soft palates of the rat. An immunocytochemical examination revealed nerve fibers containing protein gene product 9.5 (PGP 9.5), calcitonin gene-related peptide (CGRP), substance P (SP), pituitary adenylate cyclase-activating peptide, vasoactive intestinal polypeptide (VIP), C-terminal flanking peptide of neuropeptide Y (c-PON), or nitric oxide synthase (NOS). Thin nerve fibers with PGP 9.5, CGRP, or SP penetrated into the epithelium, reaching beneath the cornified layer and terminated as free nerve endings. VIP-, c-PON- and NOS-containing nerve fibers were distributed in the connective tissue. Many of the VIP- and c-PON-containing nerve fibers were associated with blood vessels. In addition, nerve fibers containing PGP 9.5, CGRP, SP and c-PON were observed around, and penetrating into, the taste buds in the boundary area.