The three-dimensional organization of the mucosa and submucosa of the rat intestine was analysed by scanning electron microscopy (SEM) aided by microdissection methods. New functional aspects raised by the SEM observations were examined by transmission electron microscopy (TEM). Morphogenesis of the intestinal villi was also illustrated three dimensionally.
Removal of the epithelium by osmic acid maceration revealed the presence of many round fenestrations averaging 3μm in diameter over the villous basal lamina. TEM confirmed that they were not artifacts but represented passages or tracks of cells of the immune system such as lymphocytes, eosinophils and macrophages. Penetration of the epithelial processes into the lamina propria was also observed. Close contacts between these free cells and the epithelial cells suggest an intercellular communication between these different cell types. The basal lamina is thus appears as a structure that allows dynamic interaction between the epithelial layer and the lamina propria, though it is generally regarded as a rigid structure acting as a barrier.
Beneath the basal lamina, a cellular reticulum of fibroblast-like cells overlies the capillary network in the villi. These cells are characterized by bundles of actin filaments and contact with each other by gap junctions. This cellular reticulum probably influences the absorption of nutrients from the villi by its contractile ability in addition to its supportive role. A similar cellular network occurs beneath the epithelium of the intestinal glands. These cells may also mechanically support the glandular organization, maintaining the delicate microvascular bed.
The submucosa is considered the skeleton of the intestine. SEM reveals the main framework of the submucosa is as being composed of two sets of collagen fibers running diagonally around the intestinal wall, one set in a clockwise direction, the other, counterclockwise. These fibers—in different arrays—interweave to form a lattice sheet, which presumably provides the tissue with a high resistance to mechanical forces, particularly in respect to radial forces. The diagonal orientation of the collagen fibers is essential for the flexibility of the submucosa in allowing deformation of the intestinal wall during peristalsis. Despite the nonelastic nature of the collagen fibers, the submucosa can adapt to the various shapes of the intestinal lumen by simply changing the angles formed by these fibers.
Structures of the villous microcirculation, the muscularis mucosae and of the submucous plexus are also discussed.

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Histological and cytological changes in the submandibular glands of adult male mice arising during the growth of sarcoma-180 subcutaneous tumors were studied. The submandibular glands of the mice were examined by morphometric analysis at 1, 3, 6, 10, 20, 30 and 64 days after inoculation of the tumor cells. There was a slow increase in the relative cross-sectional area of the granular convoluted tubule (GCT) in the section of the submandibular gland of the animals as the tumors grew. The increased proportional area of the GCT was significantly different from that of the control's from day 30. However, the mean weight of the glands was not increased. The proportional area of the granular cluster in the cells of the GCT of tumor cells in inoculated animals decreased about 5% on the first day and then quickly increased by 16% on the third day in comparison with those of the controls, eventually reaching a maximum of 74% (control, 54%) by day 30. In addition, the average number of granules per GCT cell decreased in the first three days, then increased to normal levels from day 6, going above the normal level from day 20 of the tumor growth. These changes in the glands of tumor-bearing animals disappeared within 20 days after removal of the tumor. These results indicate that the growth of the sarcoma-180 subcutaneous tumor caused morphological changes in the GCT and GCT cells, suggesting an alternation in the requirements of the secretions contained in the granules, such as the epidermal growth factor, during the growth of the tumor.

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The ultrastructure of both the epithelial basement membrane and the subepithelial capillaries in rabbit tonsils was investigated using light and transmission electron microscopy of sections, and scanning electron microscopy of alkali-water macerated tissues. The basement membrane of the crypt epithelium was seen to consist of the lamina lucida, lamina densa and lamina fibroreticularis. The lamina fibroreticularis is made up of both fine and thick collagen fibrils. The basement membrane possesses numerous pores (0.5-20μm in diameter) through which free cells migrate. The basement membrane overlying the follicle protrudes hemispherically towards the crypt lumen, while that over the interfollicular area forms many papillary projections. The capillaries are surrounded by collagen fibrillar sheaths invariably located below the collagen fibrillar sheet of the epithelial basement membrane. The capillaries immediately below the crypt epithelium, including switch-back loops of capillaries in the papillae, are fenestrated sinusoids (20-40μm in diameter). Plasma cells, lymphocytes and macrophages are numerously gathered around the capillaries. Possible functional relations between these free cells and the fenestrated sinusoids are discussed.

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The differentiation of the keratinocytes of the human palatine tonsils were studied by means of light and electron microscopy and immunohistochemistry using a polyclonal (K) and two monoclonal antikeratin antibodies (PKK1, PKK2). In the surface epithelium, the basal cells, cuboidal or columnar in shape, undergo progressive terminal differentiation and are transformed into the flattened cells of the upper layers. K reacts with both the basal and spinous layers, while PKK1 and PKK2 mark exclusively the basal layer. In the neck portion of the crypt, cavities containing one or aggregated lymphocytes with amorphous substances are observed in the spinous layer. The cavities are surrounded by elongated cytoplasmic processes of transformed epithelial cells bearing surface microvilli. These transformed epithelial cells display intense PKK1- and PKK2-positive reactions, whereas other conventional polygonal cells in the vicinity remain PKK1- and PKK2- negative as do those in the surface epithelium. In the deep portion of the crypt, where numerous lymphocytes invade the epithelium, the epithelial cells are transformed into star-shaped reticulum cells showing PKK1- and PKK2-positive reactions. The extended and branched cytoplasmic processes interconnect with one another constituting a complex network of reticulum cells, the well known reticulation of the crypt epithelium. Ten-nm filaments are usually oriented parallel to the longitudinal axis of transformed epithelial cells. Our observations suggest that the cell-shape transformation, i. e., from conventional polygonal epithelial cells into epithelial reticulum cells, occurs when the epithelial cells are in close contact with the infiltrating lymphocytes, and that this transformation is accompanied by a change in keratin phenotype.

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Athymic animals are characterized by unusual features in lymph nodes, which are indicative of immunodeficiencies. These features include hypertrophy of follicles, atrophy of the peripheral cortex above the center of deep cortex units, and the formation of lymphocyte clusters at the periphery of these units as well as of compartment replicas in the capsules. Such features were recently observed in some nodes of a minority of aged euthymic animals and we concluded that they probably also reflected immunodeficiencies, since immunodeficiencies may emerge in aging euthymic animals. In an attempt to validate this conclusion, we exposed one-year-old gnotobiotic animals to a conventional milieu, thereby presumably rendering these euthymic animals somewhat immunodeficient, and checked their nodes for unusual features. Nodal unusual features, similar to those encountered in nodes of athymic and of some aged euthymic animals, arose rapidly and the ex-gnotobiotic animals either manifested signs of infections or died. These findings support our previous conclusion that the arising of such features reflects a progressive emergence of a certain state of immunodeficiency with aging.

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The distribution of NADPH-diaphorase positive cells was examined histochemically in the retinae of the pigeon and frog. In the pigeon, three different types of amacrine cells were identified in the inner nuclear layer (INL) on the basis of cell body size and staining intensity. In the frog two types of NADPH-diaphorase positive amacrine cells have been demonstrated in the INL. Therefore, the NADPH-diaphorase method selectively stains several subtypes of amacrine cells in the retina of lower vertebrates. Although the actual function of NADPH-diaphorase activity is unknown, diaphorase histochemistry provides a convenient method for achieving Golgi-like images of amacrine cells in the retina.

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The disappearance and reappearance of rat liver gap junctions with respect to the time elapsed after partial hepatectomy and the location in the liver acinar zones were analysed immunohistochemically and morphometrically using an affinity purified antibody against the rat liver gap junction protein. The specificity of antibody was assessed by comparing the immunofluorescent staining patterns of rat organs with those obtained with an antibody raised against a synthetic peptide having the partial primary structure of the putative cytoplasmic domain of the gap junction protein. At 20h after partial hepatectomy, the population density of gap junctions decreased rapidly in the periportal area of the liver acinus. The disappearance of gap junctions progressed from the periportal area toward the central vein. The mean density of gap junctions reached the minimum, about 10% relative to the zero time value, at 48h after the operation. The reappearance of gap junctions became marked after 72h. No periportal-centrilobular gradient in the distribution of gap junctions was discernible after 96h. The time course of the change in the density of gap junctions was found to take a much longer period than those previously reported. The possible effect of the liver microcirculation on the alteration of gap junctions during the liver regeneration is suggested.

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In the early phase of heart development, the endocardial cells migrate into the truncal swellings and atrioventricular (AV) cushions, and become mesenchymal cells. Vitronectin is a glycoprotein which is thought to mediate cell migration. The present study demonstrates by immunohistochemistry the distribution of vitronectin in order to elucidate its contribution to endocardial cell migration in the developing chick heart.
At HAMBURGER and MAMILTON'S stage 23, the network of fibrillar material filled the extracellular space of both truncal swellings and AV cushions. The fibrillar network has been thought to be a matrix for endocardial cell migration. The network was stained with the anti-vitronectin antibody. At stage 29, the swellings and cushions were packed with mesenchymal cells, though immunoreactivity to the antibody was still observed in the extracellular matrix. The myocardium facing the AV cushions reacted to the antibody, but the myocardium surrounding the truncus arteriosus did not. The intensity of the immunohistochemical staining of the myocardium facing the AV cushions increased and reached a peak at stages 24 to 26, and then became weak by stage 29. The endocardial sheet, aortico-pulmonary septum and developing tunica media of the great arteries were not stained by the antibody at any stage.
These results strongly suggest that vitronectin is involved in the migration of endocardial cells, and that the myocardium facing the AV cushions produces vitronectin.

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The distribution of melanin pigment-containing cells in the bones of both young and adult silky fowls was observed. Melanin pigment was detected not only in melanocytes which were mainly distributed in the periosteum, but also in all the other types of cells in the periosteum and bone. The continuity of the number of pigment granules in melanocytes and that in the other pigment-containing cells could not be recognized because the granules in the latter cells were much fewer than those in the former. In young fowls, the pigmentcontaining cells were distributed in all layers of the periosteum and bone, but their number was low. On the other hand, in aged fowls, most of the cells in the periosteum had pigment granules. In the bone, however, pigment granules were observed only in osteocyte situated near the surface. These findings suggest that the pigment granules which are observed in osteocytes have been transferred from melanocytes to osteogenic cells or osteoblasts before they differentiate to osteocytes, where they are presumed to be digested.

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Parietal bones from mice 1-20 weeks of age were histochemically stained for detection of acid-phosphatase activity and then observed by the light microscope to evaluate the distribution and shape of osteoclasts on the inner surface of their bones. After microscopic examination, the same bones were macerated by NaOCl to both remove organic materials and expose the mineralized surface. The inner surface was then examined by scanning electron microscopy and the observations were compared with the light micrographs of the areas where osteoclasts were located. The bone resorption areas were identified as well-demarcated rough areas, and corresponded to the areas where osteoclasts were distributed. In young mice, osteoclasts observed in the bone resorption areas, which were composed of accumulations of irregular concavities, were mainly polygonal or round in shape. In adult mice, elongated osteoclasts with longer or shorter cytoplasmic processes were predominant; the bone concavities were also elongated and gathered in a flame-like pattern. The findings suggest that osteoclasts change shape according to their resorptive activities and that the activities differ between growing bones and those where growth has ceased, probably in relation to the modeling and remodeling of the bone.

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Guinea pig taste buds were observed by transmission electron microscopy with special reference to cell types and innervation. The taste bud comprised four distinct cell types: basal, type I, type II, and type III cells. Basal cells, residing at the baso-lateral region of the taste bud without extending to the taste pore, were considered precursors of the other types of cells. The rest were all spindle-shaped cells reaching apically to the taste pit.
Type I cells were characterized by the darkest appearance of the cytoplasm, apically possessing large, electron-dense granules and basally enveloping intragemmal nerves. This cell type, intervening between the other types of cells, was postulated to be sustentacular in nature.
Type II cells, the largest and lightest cells in the taste bud, possessed a conspicuous stack of smooth endoplasmic reticulum above the nucleus. Due to their intimate and specialized relationships with nerves, the type II cells were presumed to receive an efferent innervation.
Type III cells made synaptic contacts with nerves and contained dense-cored vesicles, which accumulated in the synaptic areas. This finding strongly suggests a gustatory function for the cells. The occurrence of such numerous peptidergic-type granules gathering to gustatory synapses as demonstrated in this report has not been recorded in previous papers on mammalian taste buds. The nerve terminals on the type III cell also contained synaptic vesicles, thus suggesting a reciprocal synapse here.
The taste bud often included degenerating cells which were demonstrated to be phagocytosed by extrinsic cells identified as macrophages.

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Using a monoclonal antibody against human erythropoietin, its immunoreactivity was localized in the endothelial cells of peritubular blood vessels in the anemic mouse kidney. Other cell components of the kidney including glomeruli and tubules were negative. The non-anemic, normal kidney failed to reveal erythropoietin immunoreactivity.

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