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

Macrophages are known to be phagocytes in the olfactory epithelium of adult rats. The participation of other cell types in phagocytosis in association with the cell death process was examined in the olfactory epithelium after unilateral bulbectomy of neonatal mice. The terminal deoxynucleotidyl transferase (TdT)-mediated biotinylated dUTP nick end-labeling (TUNEL) method revealed that the process of olfactory cell death consists of acute and chronic periods. The number of apoptotic cell profiles on the operated side peaked at 1 day, and the percentage of labeled cell profiles was 13.6%. The number of dying cells rapidly decreased at 3 days and decreased further at 5 days. Only 3% of the cells were labeled at 5 days. The percentage of dying cells increased again at the end of first postoperative week and remained two- to four-fold higher than control values for 2 months (4.7-5.3%). Electron micrographs of sections from early postbulbectomy stages (1-7 days) showed that as many as 30% of supporting cell profiles contained apoptotic bodies, cellular debris and phagosomes in the cytoplasm. The number of supporting cell profiles containing phagosomes declined to a plateau 2 weeks following bulbectomy and remained at 8-12% of the supporting cell population for 2 months. The results indicate that supporting cells in the olfactory epithelium play a significant role in phagocytosis in both acute and chronic of cell death after bulbectomy in newborn mice. However, supporting cells are not the exclusive phagocytic cell type in the bulbectomized epithelium; a small number of macrophages was also observed. Moreover, the phagocytosis by supporting cells was observed in unperturbed epithelium in the early stages during postnatal development.

Summary.Taste buds of the mouse circumvallate papillae were studied by electron microscopy to elucidate the innervation involving the adrenergic nerve supply. Typical afferent synaptic contacts, with increased density of the membranes and aggregations of synaptic vesicles in the cytoplasm adjacent to the nerve endings, were demonstrated between the type III cells and the nerve endings.Along the regions of contact between the type II cells and the nerve endings, cisternae of endoplasmic reticulum were often seen beneath the cell membrane, and the nerve endings contained relatively many synaptic-sized vesicles.Such an innervation seems to be efferent in nature. For the detection of the adrenergic nerve supply, 5-hydroxydopamine (5-OH-DA) was injected after pretreatment with L-DOPA and nialamide. The mice showed numerous adrenergic nerve fibers in the connective tissue underlying the taste buds. On very few occasions, the adrenergic nerves penetrated the basal lamina of the taste buds and came into contact with the bud cells. Some adrenergic nerves were distributed among the epithelial cells around the taste buds. The reaction product from acetylcholine esterase activity was found around the adrenergic nerve fibers labeled with 5-OH-DA.Although the fine structures of the mammalian taste buds have been described by a number of authors (ENGSTROM and

The olfactory epithelium of mice after axotomy was investigated to clarify the stem cells of olfactory cells by double immunostaining using antikeratin (MA903) and anti-bromodeoxyuridine (BrdU) antibodies and by conventional electron microscopy. When a single dose of BrdU was given to mice 9 days after axotomy, immunostaining for BrdU was found in the globose basal cells which were negative for MA903, but not in the basal cells proper which were positive for MA903. The BrdU-immunoreactive cells increased 3- to 6-fold over the number of these cells in the controls, indicating active cell proliferation. At other postoperative days (4 and 14 days), fewer BrdU-immunoreactive cells were found. Furthermore, three pulses of BrdU resulted in numerous BrdU-immunolabelings in the globose basal cells and a few in the basal cells proper. There was no detectable difference in the number of labeled basal cells proper in operated and unoperated mice. In the electron micrographs 9 days after axotomy, the basal cells proper, flat-shaped in unoperated mice, appeared cylindrical or pyramidal in shape and the globose basal cells often lay between the basal cells proper. In unoperated controls, the globose basal cells were located above the flat-shaped basal cells proper. The results suggest that the stem cells of the olfactory cells are globose basal cells and not basal cells proper, and that the shape of basal cells proper changes in relation to the active proliferation of stem cells.

No abstract