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.