The T cell population in the intestinal epithelium, comparable in size to the T cell pool in the spleen, is characterized by the predominant distribution of T cells bearing γδ T cell receptors. To determine the functional significance of the intraepithelial lymphocytes, we observed γδ T cells present in the jejunal epithelium in cattle, in which there is predominance of γδ T cells. Immunohistochemistry of frozen sections demonstrated that γδ T lymphocytes were densely distributed in the villous epithelium but there were fewer in the lamina propria and they were not present in the crypt epithelium. Ultrastructurally, intraepithelial γδ T cells were characterized by possessing electron-dense granules and interdigitating with enterocyte cytoplasm. Enterocytes, which were inserted by processes of intraepithelial lymphocytes or contacted by their cell bodies, showed morphologic changes seen in apoptotic cell death, such as elevated electron density of the cytoplasm and condensation of the chromatin. Apoptotic cells and cell debris were found in macrophages, which gathered in the subepithelial region of villus tips. These findings suggest that in the small intestine of cattle, γδ T cells are involved in the renewal of epithelial cells by inducing apoptosis of epithelial cells.

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We unilaterally destroyed the nasal radix of rat embryos on day 15.5 of gestation (E15.5) in utero so as to block the olfactory inputs to the ipsilateral forebrain vesicle. The embryonic brains were examined after 6 days' survival (E21.5). In the deafferented half of the brain, LHRH neurons were significantly reduced in number, indicating the successful blocking of the olfactory input. On the deafferented side, the olfactory bulb failed to develop, and the telencephalic hemisphere, small in size, accompanied various histogenetic retardations in the primary olfactory cortex, in the cortical plate, and in the hippocampal formation. The striatum revealed remarkable structural differences between the ipsilateral and contralateral sides: on the ipsilateral side, the striatum was small in size and displayed numerical reductions of immunoreactive tyrosine hydroxylase (TH) fibers and substance P (SP) neurons in comparison with those in the contralateral one; in the substantia nigra, TH neurons and SP fibers were less numerous on the deafferented side. There were no remarkable differences in the distribution of TH neurons in the hypothalamus. In view of these sequential histogenetic alterations, it can be assumed that the olfactory inputs play a key role in the telencephalic morphogenesis.

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Sections of the retrosplenial cortex from adult and newborn mouse brains were observed with a light microscope. The retrosplenial cortex of the adult animals contained many neurons (10% of the total), including some dark neurons, with perineuronal sulfated proteoglycans detectable with cationic iron colloid and aldehyde fuchsin. The retrosplenial cortex of the adult animals also contained many neurons (10% of the total) with cell surface glycoproteins reactive to lectin Vicia villosa, soybean or Wisteria floribunda agglutinin. Double staining showed that the majority (75%) of the neurons labeled with lectins were stained with cationic iron colloid, and that some (25%) of them were not stained with this colloid. Double staining also showed that some (25%) of the neurons stained with cationic iron colloid were not labeled with lectins. These findings indicate that the perineuronal sulfated proteoglycans are, at least partly, independent from the cell surface glycoproteins. Observations of the sections from the newborn animals revealed that the perineuronal sulfated proteoglycans were produced by the associated satellite astrocytes 3-4 weeks after birth, and that the cell surface glycoproteins were produced by the associated nerve cells at earlier stages, or 2-3 weeks after birth. Dark neurons began to appear 3-4 weeks after birth. These dark neurons or their Golgi complexes were also reactive to lectins, suggesting the production of cell surface glycoproteins.

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Mammalian gonadotrope (Gn-) cells producing FSH and LH show great variability in their cytological characteristics. To gain a closer view of the corresponding phenotypes, Gn-cells of male rats were investigated by various methods including immunocytochemistry on serial semithin sections, quantitative immunocytochemistry, three-dimensional reconstructions, sequential semithin-/thin-section technique, routine electron microscopy, and immuno-electron microscopy. Gn-cells were immunostained with FSH and LH antisera and with antibodies raised against synthetic N- and C-terminal sequences of chromogranin A (CgA) and secretogranin II (SgII), and four phenotypes of Gn-cells could be identified. The great majority of Gn-cells were densely immunoreactive for both gonadotropins and both chromogranins and accordingly classified as “typical” gonadotropes; a second type was less immunoreactive for LH and therefore was termed “LH-poor”. The two remaining phenotypes showed ultrastructures suggesting an increased synthetic activity. One of them was characterized as a “FSH/CgA-poor” gonadotrope. The other, also poor in CgA, morphologically corresponded to “signet-ring” cells previously known only in gonadectomized animals. The two types of secretory granules present in male rat Gn-cells showed a strict segregation of chromogranin immunoreactivities: CgA was confined to the large, less opaque granules, whereas SgII, to the small, electron-dense granules. Consequently the two “CgA-poor” Gn-cell subtypes exhibited only a very few large-sized secretory granules. A correlation was suggested between high cellular activity and a decrease in CgA in Gn-cells. The reasons for the morphological and functional heterogeneity of Gn-cells remain enigmatic. Presumably, they either differ in the susceptibility for GnRH and testosterone or are differently regulated by paracrine factors.

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Isolated collagen fibrils from the bovine cornea and sclera were investigated by atomic force microscopy (AFM) in a non-contact mode. AFM imaging visualized the surface topography of both corneal and scleral collagen fibrils with quantitative information on their height and width. The corneal collagen fibrils had a height of 15.6±1.5nm and a D-periodicity of 63.9±0.5nm. On the other hand, the height and D-periodicity of scleral collagen fibrils were 74.2±55.7nm and 65.4±0.7nm, respectively. A periodic banding pattern of grooves and ridges was found in individual fibrils, although the groove depth was 2.81±0.29nm in the cornea and 5.47±0.66nm in the sclera. When collagen fibrils were treated with acetic acid, they swelled and untwisted into subfibrils. The AFM is useful to analyze surface morphology of collagen fibrils and their subfibrils at high resolution with quantitative information.

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Our pervious electron microscopic studies indicated that Merkel cells (MCs) in the gerbil palatine mucosa were polymorphic, possibly reflecting different function. In order to verify and extend this evidence, the shape of and the innervation to MCs in the palatine mucosa of six different species of rodents including the Mongolian gerbil and the rat were examined by immunohistochemistry and transmission electron microscopy.
Immunohistochemistry using anti-cytokeratin 20 (CK20) antibody revealed that in the gerbil palatine mucosa, approximately half of MCs were dendritic. Confocal laser scanning microscopy after double labeling with anti-cytokeratin and anti-PGP 9.5 or anti-Na⁺/K⁺-ATPase β1 subunit antibodies indicated that most of the dendritic MCs (DMCs) in these mucosae were free of innervation. Electron microscopy showed that all species of rodents examined contained abundant dendritic MCs as well as roundish (oval to round) MCs (RMCs) with typical innervation. Secretory granules of the RMCs were usually concentrated at the synaptic site, whereas those of the DMCs tended to accumulate in the tips of the cytoplasmic processes and in the cytoplasm facing the basal lamina. Some MCs showed features intermediate between those of the RMC and DMC.
These results indicate that MCs in rodent palatine mucosae are consistently polymorphic, and that DMCs may represent a distinctive subset with specific, presumably including endocrine and paracrine, functions different from those of RMCs.

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Neuronal circuitry between the inferior mesenteric ganglion (IMG) and the distal colon as well as the rectum, forming the intestino-intestinal reflex pathway, was investigated in the dog using immunohistochemistry combined with retrograde tract tracing and denervation experiments. Virtually all IMG neurons were tyrosine hydroxylase (TH)-immunoreactive. Of these ganglionic neurons, about 64% were also immunoreactive for calbindin (Calb), some 35% for neuropeptide Y (NPY), and 2% for vasoactive intestinal peptide (VIP). The retrograde tracer experiments revealed that both Calb/TH neurons and NPY/TH neurons projected to the distal colon and the rectum. In these intestinal walls, Calb/TH positive varicose fibers were found in the myenteric and submucous ganglia as well as in the longitudinal muscle layer, while NPY/TH positive fibers were mainly distributed around the vascular walls. Around Calb/TH neurons of the IMG, abundant varicose nerve fibers immunoreactive for VIP, dynorphin (DYN), calcitonin gene-related peptide (CGRP), enkephalin (ENK), substance P (SP) and bombesin (BOM) were distributed. These immunoreactive fibers disappeared after the total denervation of the IMG. After the application of Fast Blue into the IMG or distal stumps of transected lumbar colonic and hypogastric nerves, retrogradely labeled neurons occurred in the myenteric plexus with increasing density along the distal colon and rectum, and were immunoreactive for VIP, DYN, CGRP, ENK, SP or BOM. Double immunostaining of nerve fibers in the distal stumps of the ligated colonic and hypogastric nerves revealed the presence of viscerofugal fibers containing VIP with DYN and/or CGRP and those containing ENK with SP and/or BOM. These results demonstrate for the first time that the efferent limb of the canine intestinointestinal reflex arch via the IMG consists of Calb-immunoreactive ganglion neurons projecting to thelongitudinal muscles in addition to the enteric plexus of the lower intestine and also of NPY-immunoreactive ganglion neurons projecting to the intestinal blood vessels, and that the afferent limb is composed of at least two discrete groups with different peptide contents, i. e., myenteric neurons containing VIP with DYN and/or CGRP and those containing ENK with SP and/or BOM.

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Thin-section studies of the sino-auricular border region in the hearts of 20 species of teleost fish revealed the cardiac Internuncial cell (CIC), hitherto known only in Misgurnus, to occur also in 8 species (Acheilognathus lanceolatus, Carassius auratus longsdorffii, Cyprinus carpio, Girella punctata, Kareius bicoloratus, Rhodeus ocellatus ocellatus, Rhyncopelates oxyrhynchus, Tilapia nilotica), but to be absent in the other 12 species. There was an indication that the CIC was close in nature to myocardial cells because of the findings of Z band-like structures, especially myosin-like thick filaments (ca. 15nm thick) in the cytoplasm. However, the myosin-like thick filaments were not associated with the actin-like thin filaments (ca. 5nm thick) or Z band-like structures. Interestingly, the thick filaments showed considerable variation in their occurrence among individuals of a species (Carassius auratus longsdorfii); they were scarce in all of the CICs (Type I) observed in 12 out of 15 individuals studied, and very numerous in all of the CICs (Type II) in the remaining 3 individuals. All of the CICs in Kareius bicoloratus, Girella punctata, Rhodeus ocellatus ocellatus and Rhyncopelates oxyrhynchus were likely to be Type I and all of the CICs in Acheilognathus lanceolatus, Cyprinus carpio and Tilapia nilotica, Type II.

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Transmission-electron microscopy of cat taste buds confirmed that, as in other mammals, each taste bud comprised four distinct types of cells: Type I, Type II, Type III (gustatory), and Type IV (basal) cells. Gustatory cells made synaptic contacts with nerves to which synaptic vesicles were gathered. The following are the main findings on the cat gustatory cells:
1) The synaptic vesicles of gustatory cells were essentially all dense-cored in type; small clear vesicles, which usually are intermingled in other mammals, could not be found.
2) The vesicles were accumulated not only in the synaptic area but also in the basal cytoplasm. This implies endocrine and paracrine functions.
3) On the basis of the fine structure of the vesicles, two subtypes of gustatory cells were discriminated. A large part of the cells contained vesicles measuring about 180nm in diameter, while a small part had smaller ones of about 100nm in diameter. This is the first demonstration of a dual population of gustatory cells in mammals, suggesting different messenger substances utilized.

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