Fine Structure of Taste Buds in the Rat

Abstract

Summary.The taste buds of rat circumvallate papillae contain three distinct types of cells. The type I (dark) cell is characterized by the presence of dense round granules, which are precursor to the dense substance of the taste pore. The granules are discharged into the pore by exocytosis.The type II (light) cell is filled with numerous vesicles and smooth-surfaced endoplasmic reticulum. The type III cell contains in its basal cytoplasm characteristic dark-cored vesicles and masses of clear vesicles, and makes synapse-like contacts with nerve fibers.The fine structure of foliate buds corresponds to that of circumvallate papillae, while fungiform buds differ in their apical regions.In the latter the pore is filled with vesicles alone, and the type I cell contains rod-shaped granules of moderate density.When polysaccharides were examined by means of the periodic acid-silver methenamine and the periodic acid-thiocarbohydrazide methods, slightly positive reactions were found on the dense granules of the type I cell and the dense substance in the pore, whereas the membranes of the pore vesicles, apical cytoplasmic processes and cytoplasmic vesicles in type II cells showed intense reactions.The ultrastructure of the mammalian taste buds was previously studied in rabbits (ENGSTROM and RYTZNER, 1956;TRUJILLO-CENOZ, 1957;DE LORENZO, 1958;NEMETSCHEK-GANSLER and FERNER, 1964;SCALZI, 1967;MURRAY and MURRAY, 1967; MURRAY, MURRAY and FUJIMOTO, 1969;FUJIMOTO and MURRAY, 1970), rats (GRAY and WATKINS, 1965; FARBMAN, 1965a, b;UGA, 1969), guinea pigs (SPOENDLIN, 1970), monkeys (MURRAY and MURRAY, 1960), and men (GRAZIADEI, 1969;MATTHEWS and MARTIN, 1971;TAKEDA, 1972). These studies have shown disagreement with regard to their cellular composition and the function of the individual cells. In particular, it remains to be established what cell type should be designated as the gustatory receptor. FARBMAN (1965a, b) distinguished the taste buds in rat fungiform papillae into four cell types which were called the peripheral, basal, type I (dark) and type II (light) cells. He considered the type I cell as the gustatory receptor.On the other hand, UGA (1969) who examined the rat circumvallate papillae, divided taste bud cells into two types, the light cells and the dark cells. He regarded the light cells as the gustatory element which is synaptically in contact with nerves. MURRAY, MURRAY and FUJIMOTO (1969) reported the third cell type in addition to the dark and the light ones. The cells of this type contained an aggregation of vesicles of a type generally found in synaptic regions in the basal portion of the cytoplasm, and they regarded this type as a gustatory receptor.The three primary areas of the tongue in mammals where the taste buds are commonly found are those of the circumvallate, foliate and fungiform papillae. In the rat tongue, the fungiform papillae are innervated by the chorda tympani nerve, whereas the circumvallate papillae and the posterior folds of the foliate papillae are 395

The Ultrastructure of Taste Buds in the Newborn Pig

“…These two kinds of structures were more frequent in the basal extended parts of the cells which were the sites of contact with nerve endings similar in appearance to those seen in the light cells. The occasional occurrence of dark vesicles in the cytoplasm of receptor cells, observed also in the sheep (Tichy 1992b), was in contrast with the data of some authors (Takeda and Hoshino 1975;Takeda 1977) who found clusters or aggregations of these structures in the close vicinity of the area where a nerve ending contacts with the cell. A likely explanation is that the amount of dark vesicles increases with their involvement in transferring stimuli from the cell to a sensory fibre.…”

“…The ultrastructure of taste buds on the porcine circumvallate papilla, particularly in the areas of the taste pore and below it, was very similar to that described by Takeda and Hoshino (1975) on fungiform papillae or on in the buds the exposed regions of foliate papillae. The deep and relatively narrow taste pore, small amounts of dark granules in the cytoplasm of type I cells, infrequent and small areas of dark matter in the pore and the fact that the terminal parts of both dark and light cells did not project above the surface epithelium indicate that the buds localized in the wall epithelium of circumvallate papillae in the pig are exposed to greater strain than those in the sheep in the same postnatal period (Tichy 1992b).…”

“…The terminal portions of dark cells extending into the taste pore were markedly thinner than the corresponding cell parts in the ovine buds (Tichy 1992b) and were broken into irregular projections. However, the typical microvilli described in other mammaHn species (Murray 1977;Par an et al 1975;Takeda and Hoshino 1975;Takeda 1977) were missing. This may be either due to an incomplete process of differentiation of this cell type or a species-related difference in the shape of this part of the dark cell.…”

“…The ultrastructure of taste bud has been studied and thoroughly described in a number of amphibian and avian species (Farbman and Yonkers 1971;and others), in laboratory mammals (Farbman 1965a;Murray et al 1969Murray et al , 1972Fujimoto and Murray 1970;Takeda and Hoshino 1975;Takeda 1976;and others) and also in man (Takeda 1972;Paran et aI. 1975;etc.…”

“…1975;etc. ) The results of ultrsstructura1 studies of taste buds have revealed considerable differences which are species-specific and also related to the position of the bud in the lingual mucosa (B e i dler 1969;Murray 1971Murray , 1973Mattern and Paran 1974;Takeda and Hoshino 1975;and others). Farbman (1965a, b), Murray and Murray (1967) and others showed the existence of two basic cell types constituting the taste bud, which they called dark and light cells.…”