[Immunohistochemical studies on the peptidergic nerve distribution in hard palate mucosa and gingiva of the rat. 2. Responses of calcitonin gene-related peptide (CGRP)-containing nerve fibers on wound healing of the mucosa].

This study investigated morphological changes of CGRP-containing nerve fibers during wound healing of the rat oral mucosa following resection of the transverse palatine ridge and gingivectomy. The tissue was immunohistochemically examined at 0, 3, 7, 14, 21, 28 and 70 days after surgical injury. The following results were obtained. 1) The Transverse Palatine Ridge. At shorter survival periods (0 and 3 days), CGRP-containing nerve fibers adjacent to the surgical defect degenerated and decreased in number. By 7 days, tissue repair had advanced and the defect had been filled with granulation tissue. Thin nerve fibers were found in and around the granulation tissue, especially nearby newly proliferating blood vessels. At 14 days, extensive regeneration of thin nerve fibers was observed in the repaired tissue. Many of them were found singularly in deeper layers of the repaired tissue, and some in bundles reaching the base of the epithelium. Some of these sprouts appeared to have existed only transiently because their number somewhat reduced by 21 days. The defect was filled with scar tissue at 28 days and mucous structure did not return to normal even at 70 days. Nerve fibers neither regenerated to regain the original density nor formed subepithelial plexuses. 2) The Gingiva. At 0 and 3 days, CGRP-containing nerve fibers near the cut surface of gingiva degenerated and their number decreased. At 7 days, a few thin regenerating fibers were found entering the epithelium on the oral side. Sprouts were also seen around small blood vessels deep in the granulation tissue. By 14 days, the nerve fibers had gradually increased with progress of tissue repair. However, rapid, transient increase in number of fibers, like that observed for the palatine ridge, was not noted. By 21 days, the junctional epithelium had regenerated, and regenerating fibers had redistributed into and beneath the sulcal epithelium. At 28 and 70 days, the repaired marginal gingiva were indistinguishable from normal (and control) marginal gingiva as regards the histology and CGRP-innervation. There were, however, a few exceptions in which junctional epithelium did not fully recover. In these animals, regeneration of CGRP-containing fibers was barely discernible in or around the sulcal epithelium.