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 erupting teeth, is quite unique. Although many reports have documented the neural control of the pulpal blood flow, only a few studies have examined the structure and distribution of vascular nerves in the rat incisors. This study examined the nerve plexuses and the spatial relationship of nerve terminals to smooth muscle cells of the pulp vessels of rat incisors. Methods: The innervation of the pulp vessels of rat incisors was studied using immunohistochemical evaluations of calcitonin gene-related peptide (CGRP) and neuropeptide-Y (NPY). The three-dimensional ultrastructure of nerve meshworks and terminals on smooth muscle cells of pulp arterioles were examined by scanning electron microscopy (SEM) with a KOH digestion method. Results: The blood vessels were associated with many nerve fibers immunoreactive for CGRP and NPY. Some NPY and frequent CGRP-immunoreactive nerve fibers were observed in the labial odontoblast layer. Three different; morphologies of nerve fibers could be distinguished: fine nerve fibers with numerous terminal varicosities, medium-sized fibers associated with occasional or much scarcer varicosities, and thick fibers that had no varicosity and sometimes ran apart from blood vessels The SEM observations identified five vascular segment types: terminal arterioles, precapillary arterioles, capillaries, postcapillary venules, and muscular venules. Nerve meshworks were observed around the large terminal arterioles; these meshworks were very comparable to those revealed by immunohistochemistry. The vascular smooth muscle cells were closely attached by one or more terminal varicosities. Conclusions: It has become evident that the large terminal arterioles in the rat incisors receive a dense nerve supply and provide well-developed wall architecture, suggesting an important role of neuronal regulation on the vessels.