Morphological differences among nerve fiber endings in the rat oral mucosa as revealed by methylene blue staining.

The nerve fiber distribution in the oral mucosa of the soft palate and palatoglossal arch of the rat was studied by means of methylene blue supravital staining. It was focused primarily on the dye uptake of intraepithelial nerve fibers. Differences in the morphology of nerve fiber terminations were found between these regions of the oral mucosa. In the soft palate, local accumulations of intraepithelial nerve fibers which branched and showed terminal enlargements were detected. Intra- and perigemmal nerve fibers of chemosensory corpuscles could be stained. In the palatoglossal arch, numerous elongated papillae were seen containing nerve fiber plexus showing a complicated arborization pattern. In part, the collaterals penetrated the epithelium. The soft palate contained only a small number of lower but broader papillae which were covered by a more expanded intraepithelial nerve fiber plexus. In both regions, anastomoses between the branches of single nerve fibers were sometimes seen. Solitary delicate nerve fiber endings were loosely distributed throughout the epithelia. In addition, intrapapillar nerve endings, which were enclosed by a slightly stained capsule, were intensely stained; they showed characteristic lateral protuberances. The Merkel's discs were visualized as the components of a terminal network of nerve fiber branches. The observed differences in the shape and locations of the nerve terminations suggest different functions of these nerve fibers. Due to the low costs of the staining procedure and its ease in handling, it is well-suited for a mapping of the innervation pattern of the whole oral mucosa.