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The influence of the sensory nerve fibers on the differentiation of the Merkel cell was examined in the denervated labial mucosa of adult rabbits. Part of the lower labial mucosa was excised following mental nerve resection. Twenty-one and 50 days later, the regenerated mucosa was examined by electron microscopy with special reference to the distribution and maturation of Merkel cells, and compared with the normal and the denervated intact mucosa. A number of immature Merkel cells appeared in the denervated and regenerated epithelium by 21st day after the operation. The distribution density of the Merkel cells in a unit area of the mucosa did not change much but the percentage of the mature Merkel cells increased significantly until 50 days after the operation. The mature Merkel cells in the denervated and regenerated mucosa showed a normal ultrastructure, though their orientation and location were not uniform, shifting more superficially than the cells in the normal mucosa. In the controlateral intact epithelium of the denervated labial mucosa, no substantial decrease in the population density of Merkel cells was recognized, though the desquamation of Merkel cells was observed. It was conspicuous that the percentage of immature Merkel cells to the total number of the Merkel cells was significantly increased after the denervation in the intact labial mucosa. This study suggests that Merkel cells differentiate independently of sensory nerve fibers, but the latter are requisite to maintain the former in a uniform, basal disposition in the epithelium.

Tooth germ derived from the mandible of newborn mice was used in this study. The enamel organs were dissected and attached directly to coverslips without using the plasma clot. By this method it was possible, for the first time as far as is known, to attain preparations in which the major part of the outgrowth from the explant consisted purely of epithelial-like cells which probably were aneloblasts. Abundant desmosomes and tonofilaments were confirmed by transmission electron microscopy. Under the scanning electron microscope this outgrowth of epithelial cells revealed characteristic intercellular connections which were divided into four types. 1)In the part nearest to the explant, cell boundaries were indicated with a large number of short microvilli. 2)In the zone beyond the first type, the intercellular connection was represented by bridge-like processes firmly combined with each other. 3)In a still further zone, the tips of bridge-like processes were free from the cell connection and extended to the adjacent cells with the advance of cell migration. 4)In the most peripheral part of the explant, the cytoplasmic processes were capable of further expansion. These cells were soon separated from the adjacent cells to migrate as free cells.

Organized mechanoreceptors in mucosae and vermilion borders of rat lower lips were studied by light and electron microscopy. Cholinesterase histochemistry was applied to whole-mount preparations of mucosae for the light and electron microscopic identification of mechanoreceptors. Three types of lamellated corpuscles (a simple corpuscle; a coiled, simple corpuscle; and a Meissner-like corpuscle), and a unique, organized, bush-like assembly of free nerve terminals were identified. The simple corpuscles were found exclusively in the vestibular mucosa facing the incisor teeth. In contrast, bush-like endings were confined to the vestibular mucosa and to the lateral, eminent mucosa that faced the diastema. Furthermore, coiled simple corpuscles and Meissner-like corpuscles were localized in the boundary zone between the vestibular and lateral eminent mucosae and in the vermilion border. From a functional viewpoint, it is of interest that different areas of the rat lip contain different morphological patterns of mechanoreceptors.

Intranuclear inclusions were found in bone marrow cells of miniature pigs, whose ultrastructure and nature were examined by electron microscope and by cytochemical techniques. The inclusions were found predominantly in the granulocyte series and in a megakaryocyte and plasma cell. The inclusions consisted of closely packed, wavy filaments, 20-40 in number. They varied in size from 0.5-1.0 mum in length and 0.2-0.5 mum in width. The largest inclusion extended across the entire length of the nucleus. Occasionally, an inclusion extending toward the nuclear pore was observed. the intranuclear inclusions showed a tendency to appear frequently in immature granulocytes. The experiment on enzyme digestion for the epoxy sections showed that the inclusions were insoluble in RNase, DNase, pepsin, trypsin and protease solutions. These results seem to suggest that the intranuclear inclusions of blood cells differ from filamentous inclusions which have been noted previously in some neurons.