The innervation of taste buds in the soft palate and circumvallate papilla of the rat as revealed by the zinc iodide-osmium tetroxide technique.

The taste buds in the soft palate and the circumvallate papillae of the rat were investigated by the zinc iodide-osmium tetroxide technique. In addition, electron micrographs of taste buds stained with this method were presented for the first time. Differences in taste bud structures were found between the examined regions. The taste buds of the soft palate showed a complicated plexus of intragemmal nerve fibers. Some fibers exhibited terminal polymorphic swellings. Single branches could be traced close to the space of the taste pore. In the soft palate, the taste bud cells remained unstained, whereas in the circumvallate papillae of the tongue, a subpopulation of taste bud cells could be selectively stained and the intragemmal nerve fibers were characterized by large varicosities. The morphological dissimilarities between the taste buds of the investigated regions might be explained by their functional characteristics, or possibly their varying affinities to the taste qualities. Electron microscopic investigation of the stained circumvallate papillae revealed that the electron-dense reaction product had primarily accumulated in a subpopulation of light cells. Dark cells exhibited only a slight labelling. In detail, the precipitate was found loosely distributed in the cytoplasm as well as the nuclei of the cells, and particularly concentrated at the membranes of light vacuoles, this probably being profiles of dilated endoplasmic reticulum. A few roundish accumulations of precipitate were seen in the cytoplasm of taste bud cells, which showed no intensive light microscopic staining. Labelled material was also found within the taste pores outside the apical processes of the cells. The present findings indicate that the zinc iodide-osmium tetroxide technique is applicable to neuroanatomical studies of taste buds.