SCANNING ELECTRON-MICROSCOPY AND IMMUNOHISTOCHEMICAL OBSERVATIONS OF THE VASCULAR NERVE PLEXUSES IN THE DENTAL-PULP OF RAT INCISOR

Background: The innervation of rat incisors, which are continuously er upting teeth, is quite unique. Although many reports have documented t he neural control of the pulpal blood flow, only a few studies have ex amined the structure and distribution of vascular nerves in the rat in cisors. This study examined the nerve plexuses and the spatial relatio nship of nerve terminals to smooth muscle cells of the pulp vessels of rat incisors. Methods: The innervation of the pulp vessels of rat inc isors was studied using immunohistochemical evaluations of calcitonin gene-related peptide (CGRP) and neuropeptide-Y (NPY). The three-dimens ional ultrastructure of nerve meshworks and terminals on smooth muscle cells of pulp arterioles were examined by scanning electron microscop y (SEM) with a KOH digestion method. Results: The blood vessels were a ssociated with many nerve fibers immunoreactive for CGRP and NPY. Some NPY and frequent CGRP-immunoreactive nerve fibers were observed in th e labial odontoblast layer. Three different morphologies of nerve fibe rs could be distinguished: fine nerve fibers with numerous terminal va ricosities, medium-sized fibers associated with occasional or much sca rcer varicosities, and thick fibers that had no varicosity and sometim es ran apart from blood vessels. The SEM observations identified five vascular segment types: terminal arterioles, precapillary arterioles, capillaries, postcapillary venules, and muscular venules. Nerve meshwo rks were observed around the large terminal arterioles; these meshwork s were very comparable to those revealed by immunohistochemistry. The vascular smooth muscle cells were closely attached by one or more term inal varicosities. Conclusions: It has become evident that the large t erminal arterioles in the rat incisors receive a dense nerve supply an d provide well-developed wall architecture, suggesting an important ro le of neuronal regulation on the vessels. (C) 1998 Wiley-Liss, Inc.