The actual three-dimensional microstructure of the mammalian liver has been reviewed by scanning electron microscopic (SEM) techniques.
Liver lobuli and acini easily revealed their microarchitecture showing interconnected liver plates, sinusoids and hepatocytes. Isolated liver cells appeared as polyhedrons with six or more facets covered by a large number of microvilli where fronting the sinusoidal wall, or relatively smooth where forming the biliary groove. In addition to microvilli, the biliary canalicular wall showed several pits and/or small holes probably related to secretory processes. Bile channels frequently bifurcated on the same side as the isolated liver laminae. Some bile canaliculi, showing lateral diverticula bordered by microvilli and arising from the cortical cytoplasm of the hepatocyte, were considered to be intracellular branches of bile canaliculi. Zones of minimal distance (0.1μm) were often observed between the spaces of Disse and the lumen of the bile canaliculus. These were interpreted as sites of the simple diffusion of substances from bile to blood and—actually representing loci minoris resisteutiae—they could be considered, pathologically, as possible pathways for bile regurgitation. Numerous blebs and laminar evaginations, probably related to phenomena of secretion and/or absorption, were present in the luminal wall of canaliculo-ductular junctions. Further bile ductules and ducts all possessed a variable number of unusual cilia of unknown roles (chemoreceptive and/or motile?).
Endothelial cells in sinusoids showed numerous fenestrations of different size. Small ones (0.1-0.2μm) were arranged in clusters, while others (-1μm) appeared often subdivided by slender strands of cytoplasm and doubled by laminar cellular extensions belonging to adjacent Kupffer cells or subjacent Ito cells located in the space of Disse. Kupffer cells closely resembled macrophages; their cell body showed numerous microvillous projections, blebs, lamellipodia and occasional filopodia. They were mainly located within the lumen of the sinusoids and often anchored to the endothelial wall with their long processes. In some cases, thin evaginations from Kupffer cells penetrated the endothelial gaps, enlarging them even further. As seen topographically, the subendothelial spaces of Disse appeared considerably larger than was generally evident in thin sections. This actually resulted in a continuous three-dimensional labyrinth of intercellular and pericapillary microlacunae in which hepatocytes were suspended. A few collagen fibers, fragments of basal lamina materials and fat storing cells were found in these spaces.
The fetal liver was composed of ramified cords and irregularly shaped hepatocytic laminae closely associated with wide vessels. The hepatoblasts in particular appeared as large cells uniformly covered with short microvilli. In some instances these were linearly distributed on the cellular surface and likely related to the formation of a biliary groove (morphogenetic event for biliary polarity of the cell).
In fetal sinusoids, transitional forms between Kupffer cells and endothelial cells were never found. Megakariocytes and other irregularly shaped cells were observed in the pericapillary spaces and in the sinusoidal lumen. They perhaps represented intermediary stages of the differentiation of Kupffer cells from monocytes and/or local macrophages.

抄録全体を表示

The fine structure of the taste organ in the Rana catesbiana was observed by light and electron microscopy. The taste organ consists of three distinct cell types, the taste, supporting and basal cells as well as nerve elements. The present findings suggest that the taste cell might function not only as a chemoreceptor cell, but also as a paracrine cell. The basal cell also may have a dual function as both mechanoreceptor and paracrine cell.
Furthermore, taste organs have been examined at intervals from 3hrs to 120 days after sectioning of the glossopharyngeal nerves. The taste organs were almost intact throughout the experimental period after denervation and even after ceasing to produce impulses from chemical or mechanical stimuli. The dense-cored vesicles of the taste or basal cells, which may possess a paracrine action, still remain in the taste organ even 120 days after denervation.
It can be concluded that the morphological integrity of the frog taste organ does not absolutely need the presence of the gustatory fibers in contrast to the nerve-dependent nature of the mammalian taste bud.

抄録全体を表示

A human gingival fibroblast cell line was cultured in a DM-153 medium supplemented with 10% bovine serum. The cells in culture showed both intracellular and extracellular ectopic mineralization. Ultrastructurally, mineralization began within the round and irregularly shaped vesicles contained in large cytoplasmic vacuoles of fibroblasts. The first identifiable needle-shaped crystal was deposited on a point of the inner leaflet of the vesicle membrane. With the increase in size of the crystals, the membranous envelopes were gradually lost, and lattice planes (8.2Å) occurred within the crystal thickness. Crystals radiating from each mineralization center formed mineralized spherules in cytoplasmic vacuoles.
The crystal clusters were extruded from the cells through membrane fusion or cellular degeneration in long-term cultures. These liberated clusters formed extracellular mineralizing matrices around the fibroblasts. In extracellular mineral deposition, the initial crystals arose within extracellular matrix vesicles, but were not associated with collagen, elastic fibers, and any other structures.
These findings indicate that mineral accumulation and phase transformation of amorphous mineral to a crystalline form take place within the vesicular structures. This provides additional evidence for the view that the initiation of calcification and mineralization requires a microenvironment limited by a membranous (vesicular) structure derived from cells.

抄録全体を表示

The neural crest cells of hynobius larvae during the morphogenesis of the neural crest were studied with the following methods: the region of the primordial neural crest was first determined by vital stainings, and then the movement of individual neural crest cells was traced with India ink labeling. The cytoarchitecture and the fine structure of neural crest cells were further observed by light, transmission and scanning electron microscopy.
The primordium of the neural crest is located in the area extending from the lateral part of the neural plate to the medial part of the neural fold. RAVEN (1931) suggested that the lateral part of the neural fold was a part of the primordial neural crest. The result of our vital staining shows that it is the primordial epidermal ectoderm.
The morphogenesis of the neural crest was found to proceed as follows: at first both neural folds moved to the dorsal mid line of larva, then contacted and fused to each other. The primordial neural crest cells in the neural folds became polygonal, and these cells from both folds mixed and formed a neural crest cell mass. In this process they lost their junctional apparatuses. When larvae developed at the tail bud stage, the cells in the lateral part of the neural crest extended their cytoplasmic proccsses and began to migrate.

抄録全体を表示

A new method for causing excessive liquid intake was developed as the condition opposite to dehydration, and the effect of this copious drinking for 2, 4 and 6 days on the pars intermedia of the hypophysis was evaluated by quantitative electron microscopy in mice.
Free access to 5% glucose solution and concurrent food deprivation resulted in the development of polydipsic mice. Drinking volume was 18.9±1.1ml/10g BW on day 2, 20.8±1.2 on day 4 and 24.1±1.3 on day 6, respectively, while remaining at 2.2±0.2ml/10g BW in the control.
Copious drinking was found to elicit secretory activity of the pars intermedia cells. The cytoplasmic volume percentage of rough endoplasmic reticulum (rER) and the numerical density of Golgi granules increased significantly on day 2 reaching a peak on day 4. Contrarily, secretory granules decreased in number, indicating that the granule release exceeded the activated granule formation. The rise in the activity of the gland was followed by a slight fall after 6 days, which was probably due to a malnutritional condition by food deprivation. Neither 20% glucose drinking nor food deprivation for 4 days enhanced the pars intermedia cells. Thus, excessive water intake seems to be a plausible reason for stimulating secretory activity in cells of the pars intermedia of the hypophysis in mice.

抄録全体を表示

Liver, kidney, spleen and other organs of the rat were fixed with glutar-aldehyde, substituted with absolute ethanol or dimethyl sulfoxide (DMSO), freeze-fractured in liquid nitrogen, stained by the rapid tannin-osmium thiocarbohydrazide-osmium (TaOTO) method (staining with each agent for 10min), critical-point-dried with liquid carbon dioxide, and observed with the scanning electron microscope. The absolute ethanol or DMSO freeze-fracture method provided flat fracture surfaces (without regard to cell boundaries) of the samples and allowed a good visualization of their inner structures. The fracture surfaces were suitably stained by the rapid TaOTO method, and could be scanned with no charging. Neither maked damage nor undesired dislocation of tissue elements was noted on the freeze-fractured and TaOTO-stained surfaces. This procedure, freeze-fracture prior to conductive staining, has an advantage of eliminating the bulk charging effects that tend to occur in specimens fractured after staining. When substituted with 75% DMSO aqueous solution, the samples spontaneously fractured without any need for razor blades. Fracture planes in this spontaneous fracture sometimes ran along the cell boundaries and allowed a clear visualization in the SEM of the enfaced surfaces of closely associated cells such as hepatocytes.

抄録全体を表示

The tooth plates in the living Holocephalan, Chimaera phantasma were studied by various techniques. They consisted of osteodentin and hypermineralized pleromin (kosmin). The degree of mineralization on the latter was as much as in the enameloid of Chondrichthyes and Osteichthyes. Scanning electron microscope observation indicated that the pleromin consisted of large and granular crystals. X-ray powder diffractometry, electron microprobe analysis and analytical electron microscopy revealed that the inorganic constituent of pleromin included, as an essential element, a β-Ca₃(PO₄)₂ (whitlockite) structure containing a small amount of Mg.

抄録全体を表示

Reciprocal interaction between the hemopoietic organ stromal cells and the cells of the granulocytic, megakaryocytic and erythrocytic series in the human liver obtained from 109 embryos 28 to 49 days after ovulation and 76 fetuses from 8 to 22 weeks of gestation were investigated by light and electron microscopy.
The close association of stromal cells with immature cells of the three series was confirmed under the electron microscope and a presumptive HIM (hemopoietic inductive microenvironment) was visualized. A majority of immature erythroblasts intruded into the cytoplasm of the hepatocytes, so the presumptive hemopoietic stem cell types II and IV are undoubtedly differentiated into cells of the erythroid line by contact with hepatocytes at a certain stage of maturation. Granulopoiesis developed among the reticular cells around the ductus venosus—or large arteries in hepatic parenchyma—and the cells of the granulocytic series were enclosed by thin cytoplasmic projections of mesenchymal cells. Neither erythropoiesis nor megakaryopoiesis was noted here. Therefore the compartments composed of one or more reticular cells around the ductus venosus or large arteries seem to have a capacity to regulate the differentiation of the presumptive hemopoietic stem cells type IV into cells of the granulocytic series. This differentiation of presumptive hemopoietic stem cell types II and IV into the megakaryocytic series is belived to be induced by the presence of the microenvironments that consist of foci of a few reticular cells in the hepatic parenchyma, as immature cells of megakaryocytic lineage were encircled by the cytoplasmic projection of one or more reticular cells among hepatocytes.
Erythroblastic islets are concluded to be a kind of HIM, where erythroblasts loosely adhere to the central macrophages and undergo mitoses and maturation.

抄録全体を表示

Chloride cells in gill filaments in the fresh-water catfish (Parasilurus asotus) were examined by electron microscopy, using a tannic acid-glutaraldehyde fixative before osmification. This method allows clear demarcation of the cell surfaces through enhanced contrast and electron density. In the cytoplasm of chloride cells, only those tubules continuous with the cell surfaces—especially the outer leaflet of their membranes—remarkably increase in electron density. The cytoplasm of cells other than chloride cells, however, remains unaffected by the tannic acid treatment. The present study suggests that the use of tannic acid is advantageous for selective demonstration of the cell surfaces and their cytoplasmic derivatives.

抄録全体を表示