The innervation of taste buds in the soft palate of the rat as revealed by methylene blue staining.

Light microscopic data on the innervation of taste buds in the soft palate of the rat obtained by methylene blue (MB) supravital staining are presented here for the first time. The taste pore including subpopulations of taste bud cells and nerve fibers were stained. Intragemmal nerve fibers were detected ascending up to the taste pore; this suggests the possibility of additional paracellular pathways in taste transduction directly via nerve fibers. Moreover, relatively large bulbous or laminar enlargements of the intragemmal nerve fibers were found. The branches of these nerve fibers, showing minute spiny protuberances, appeared to anastomose. Some perigemmal nerve fibers were also seen in close apposition to the taste pore. The basal plexus in the vicinity of the taste buds showed enlargements which resembled the Merkel's discs, but were significantly smaller. These structures did not occur in the subgemmal part of the basal plexus. Regarding the oxygen-dependency of the staining reaction, it was speculated that both MB and oxygen were attracted by iron-containing enzymes. Therefore, the strong affinities for MB shown by subpopulations of nerve fibers and taste bud cells were explained by their high requirements for oxygen. Furthermore due to its selectivity for intraepithelial nerve fibers and sensory cells, the method applied here is well-suited for routine use in light microscopy.