Occurrence of mast cells within bundles of myelinated and unmyelinated nerves in the rat tongue

The rat tongue has been the subject of many cytological studies, both purel y descriptive and experimental. To assess the suitability of the organ for additional cytological and histological senior research thesis projects, li ght and transmission electron microscope studies of thin and ultrathin sect ions, respectively, were conducted. Several samples from the anterior dorsa l surface of the tongue of a male rat (Sprague-Dawley) were processed conve ntionally for light and electron microscope study. About 170 sections, each approximately 1 x 1 mm in area and 1.0 mu m thick, collected from 12 adjac ent areas, all including the mucosa, of a tongue were studied in the light microscope. Numerous mast cells were observed scattered throughout the subm ucosal region, adjacent to nerve bundles, blood vessels, and skeletal muscl e, and up to six bundles each consisting of many myelinated and unmyelinate d nerve processes were seen per section. Single, double, and quadruple myel inated nerve processes were also seen. Several of the multiple, mixed nerve bundles contained a mast cell. Mast cells were not found within the endone urium or perineurium of exclusively myelinated processes. Ultrathin section s adjacent to the thin sections containing mast cells within the nerve bund les were sought and studied in the transmission electron microscope to conf irm the identification of these mast cells. Mast cells occur within bundles containing both myelinated and unmyelinated nerves in the rat tongue, and this is an apparently previously unreported event. Furthermore, no clear ev idence has been found in the literature of such specific mast cell distribu tion in other parts of the animal body. Single, double, and quadruple myeli nated nerve processes were noted, but none contained a mast cell. Anat Rec 256:347-353, 1999. (C) 1999 Wiley-Liss, Inc.