Postnatal development of the blood vasculature in the rat adrenal gland was examined with scanning electron microscopy (SEM), using a microcorrosion casting method.
The cortical vascular bed on postnatal day 1 (P1) was incipient, consisting of an outer capillary layer and an inner sinusoidal vascular layer of the juxtamedullary zone. The vascular bed grew continuously with clearer zonal differentiation as the maturation proceeded. By P7 the outer capillary layer had differentiated into the vasculature of the glomerular and fascicular zone, while the juxtamedullary sinusoidal vascular layer had reduced its thickness to differentiate into the vasculature of the reticular zone.
The neonatal adrenal vasculature consisted only of the cortico-medullary system. The medullary arteries and the medullary capillary bed were first observed on P14. The adrenomedulla thus came to receive a twofold blood supply by this time. Before the establishment of the medullary arterial system, the medulla appeared to receive its blood supply partly from the cortical capillaries and partly from the radial sinusoidal vessels passing through the cortical vascular bed. The radial sinusoidal vessels were suggested to differentiate into the cortical capillaries. The medullary arteries may originate from the vessels associated with chromaffin bodies incorporated into the adrenal gland or differentiate from the radial sinusoidal vessels.
Histological changes, including cortical cell involution and hemorrhage occurring during the neonatal period, would seem to have crucial relevance to the remodeing of the adrenal vasculature.

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Rat hind limb buds, aged between prenatal days 14 and 18, were used for electron microscopy and immunocytochemistry of fibronectin, laminin and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling staining indicative of DNA fragmentation.
Fibronectin and laminin were actively synthesized in the rough endoplasmic reticulum of epidermal cells in the apical ectodermal ridge between prenatal days 14 and 15, but most cells underwent apoptosis after prenatal day 15. As the regression of the apical ectodermal ridge progressed, mesenchymal cells associated with the marginal veins were successively incorporated into the endothelium devoid of the basal lamina. No mitotic figures of endothelial cells were recognized either in the marginal vein or in the surrounding growing capillaries. Extracellular matrix components connected the adjacent mesenchymal cells, with the endothelium of such vessels immunoreacting to fibronectin and laminin. In addition, fibronectin-immunoreactive networks among the interstices of the mesenchymal cell cords developed in the avascular zone between the epidermis and the growing capillaries at prenatal day 15, but became inconspicuous at prenatal day 16.
These results indicate that the apoptosis of the epidermal cells is the major reason for the regression of the apical ectodermal ridge, and that the capillary ingrowth from the marginal veins to the avascular zone is accelerated by transformation of mesenchymal cells to endothelial ones. Fibronectin and laminin seem to play crucial roles in capillary growth, especially in the adhesion between endothelial cells of the pre-existing vessels and mesenchymal cells.

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The three-dimensional (3-D) architecture of the myosalpinx in the sheep was studied by scanning electron microscopy after the removal of interstitial connective tissue with NaOH digestion. In the extramural portion of the tubo-uterine junction, the myosalpynx is made up of densely packed, circularly arranged superficial fibers and of innermost loose fiber bundles following an almost longitudinal course. In the isthmus and ampulla, the myosalpinx is constituted by oblique bundles of variable length, which run around the tube and merge into the surrounding musculature, giving rise to a plexiform arrangement. The present 3-D observations demonstrate that the sheep myosalpinx consists mainly of single muscular fibers and more complex bundles which show a multiple spatial arrangement and a plexiform distribution. Such a muscular architecture is more likely suited for stirring rather than pushing the embryos and gametes through the tube.

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Using specimens from the posterior-superior quadrant of the human tympanic membrane, meatal skin, retroauricular skin and middle ear cholesteatoma, epidermal cell proliferation was studied by cultures in FC43 emulsion containing bromodeoxyuridine (BrdU), and cell death was detected by in situ labeling of nuclear DNA fragmentation (TUNEL staining). The culture of specimens with BrdU revealed labeling in the basal cell layer and/or the layer immediately above it. The counts of BrdU-labeled cells both at and beside the malleus handle and at the annulus were significantly higher than those in the tympanic membrane, meatal skin, retroauricular skin and cholesteatoma, indicating the existence of epidermal proliferation centers in the annulus and malleus handle. TUNEL-positive cells were observed in the uppermost layer of the epidermis, and counts of dying cells did not show any significant differences among specimens from the different areas. From these observations, we conclude that addition of newly proliferated cells at the proliferation center and uniform cell death cause epidermal cell migration over the tympanic membrane and ear canal. In addition, no proliferation center was seen in the epidermis of cholesteatoma, suggesting a disturbance of epidermal cell migration.
Furthermore, BrdU-labeling at the margin of persistently perforated tympanic membranes from patients with chronic otitis media revealed that, at the perforation margin, the counts of BrdU-labeled cells were not higher than those of the normal tympanic membrane. In addition, a few BrdU-labeled cells were observed in the lamina propria and mucosal cell layer, indicating that persistent perforation of the tympanic membrane results from the failure of proliferating cells to increase at the margin of the perforation.

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The existence of Langerhans cells in the stratified squamous epithelium of severely combined immunodeficient (SCID) mice was studied by enzyme histochemistry, immunohistochemistry and electron microscopy. Considerable numbers of ATPase-positive Langerhans cell were observed in the epidermis (ear and hind limb) as well as in the stratified squamous mucosal epithelium (forestomach and tongue) of SCID mice. The cells also expressed Ia antigen. This indicates that, in spite of the lack of functional T and B lymphocytes, the antigen-presenting function of Langerhans cell was retained in SCID mice. In the epidermis, frequency of Ia expressing Langerhans cells was low, but in the forestomach epithelium, 90% of Langerhans cells had strong Ia positivity. In the forestomach epithelium of SCID mice, the regulation of Langerhans cell maturation was affected differently from the epidermis.
As with normal mice, the occurrence of Langerhans cell in female SCID mice was higher than in males; hormonal immuno-regulations may be normal in SCID mice. Under electron microscopy, many Birbeck granules were observed in epidermal Langerhans cells but few in those of the mucosal epithelium.
In SCID mice, Langerhans cell exists constitutively in the epidermis and mucosal epithelium, where the cell may function in a defense system independent from T and B lymphocytes.

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The taste bud in the rat vallate papillae was observed by immunohistochemistry for PGP 9.5 at the light and electron microscope levels; routine transmission electron microscopy was also performed. Immunoreactivity for PGP 9.5, a marker protein of paraneurons, was localized in the cytoplasm of the Type III or gustatory cells. More intensive immunoreactivity occurred in the nerve fibers, though a part of the nerve fibers remained unstained.
The nerve fibers as detected by the immunostaining and by routine electron microscopy formed a coarse subepithelial plexus which issued branches upwards through the basal lamina. In the basal portion of the taste bud, these fibers formed a hitherto unknown intragemmal plexus of dense and delicate meshwork. This plexus, in turn, extended beaded fibers between the taste bud cells, forming synaptic contacts with Type III cells. Some of the immunoreactive nerve fibers were confirmed to reach the taste pore by light microscopy; electron-microscopic examination could not demonstrate their directly being exposed to the space of the taste pore.
This study also deals with the fine structure of the rat taste bud with special reference to the Type III cells and their synapses with nerve fibers, as the rat has recently been rather seldom used in this field of study.

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Transferrin binding protein (TfBP), a glycoprotein, is originally purified from the chicken oviduct. Recently, TfBP has been revealed as a novel transferrin binding protein, structurally related to the chicken heat shock protein 108. The physiological function of this protein, however, has not yet been established. Antiserum to TfBP was found to stain selectively transferrin- and iron-rich oligodendrocytes of the normal chicken brain, suggesting a role for this protein in connection with transferrin and iron storage in these cells. In this study, we further demonstrate a TfBP-immunoreactivity in the chicken respiratory tract mucosa, where transferrin is known to be present and have antioxidant and antibacterial properties. A strong TfBP immunoreactivity was revealed in certain regions of the respiratory tract. In the trachea and bronchi, TfBP-immunoreactive product was localized specifically to the mucous gland cells, whereas ciliated epithelial cells were negative. In the lung, TfBP immunoreactivity was mostly confined to the parabronchi and atria. The immunoreactive products were found in the cytoplasm of the epithelial cells lining the parabronchial and atrial walls. These findings suggest that the presence of TfBP in the airway mucosa may be a necessary condition for transferrin concentration in the extracellular milieu of the respiratory tract.

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Neuromuscular junctions in the posterior cricoarytenoid (PCA) muscle of the adult rat larynx were examined by scanning electron microscopy. Two types of focal junctions were characterized by the nerve endings with terminal varicosities or terminal buttons and by the subneural apparatuses with a group of cuplike depressions (2-5μm in diameter), not labyrinthine gutters. One type of the subneural apparatuses consisted of a large number (more than 20) of depressions with predominantly slit-like junctional folds. The other type was characterized by a small number (about 10) of depressions with a few junctional folds. From the relative proportions of the two types of muscle fibers and subneural apparatuses in the rat PCA muscle, we suggest that the Type II fibers have the apparatus consisting of numerous small depressions with many junctional folds, while that of the Type I fibers consists of a small number of depressions with a smaller number of junctional folds. It is suggested that the structural differences of the subneural apparatus reflect different types of muscle fibers.

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During an experiment on developing rats, we encountered an abnormal rat fetus whose adenohypophysis was not in contact with the brain. This fetus was found and killed on the 21st day of gestation when all types of adenohypophysial hormone-producing cells are already immunohistochemically detectable in the normal gland. When compared with its normal counterpart, this brain-detached adenohypophysis was characterized by: 1) its remarkably small volume, less than 10 percent of the size of the normal gland; 2) the lack of a pars intermedia; 3) far fewer numbers of corticotropes, somatotropes and thyrotropes; and 4) the absence of prolactin cells. These results are consistent with our previous in vitro data which showed that contact between the adenohypophysial primordium and diencephalon is indispensable for the proliferation and differentiation of the adenohypophysial hormone-producing cells. The absence of the pars intermedia indicates that the formation of this part of the hypophysis is dependent on the brain in rats, as already shown for frogs.

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An electron microscopic analysis with specific histochemical stainings for acidic glycoconjugates was carried out to examine the endothelium lining blood vessels of the rat spleen. Histochemical staining performed was the postembedding high or low iron diaminethiocarbohydrazide-silver protein-physical development (HID or LID-TCH-SP-PD) method, with or without prior digestion with acidic glycoconjugate-degrading enzymes, such as heparitinase, testicular hyaluronidase, chondroitinase B and neuraminidase. The results indicated that the acidic glycoconjugates in the basal lamina of the endothelial cells lining the four types of blood vessel (central arteries, arterial capillaries, splenic sinuses and pulp veins) were heparan sulfate, chondroitin sulfate A and/or C, chondroitin sulfate B and sialic acid residues. In the endothelial cells lining the central arteries, arterial capillaries and pulp veins, the surface coat of the luminal plasma membrane included heparan sulfate, chondroitin sulfate A and/or C, chondroitin sulfate B and sialic acid residues, whereas the corresponding ultrastructure of the splenic sinuses was devoid of detectable amounts of acidic glycoconjugates. This suggests that such characteristic histochemical features of the endothelium in the four types of the splenic blood vessel can be related to the possible physiological functions of the spleen.

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