The distribution of atrial natriuretic polypeptide (ANP) and atrial specific granules in the myocytes of the atria and ventricles of an experimental animal model, stroke-prone spontaneously hypertensive rats (SHRSP) and a control, Wistar Kyoto rats (WKY), was examined using immunocytochemical and electron microscopic techniques. In the atria of both SHRSP and WKY, ANP-immunoreactivity was recognized in the perinuclear regions of essentially all cardiac myocytes. In the ventricles of WKY, ANP-immunoreactivity was hardly seen except for the impulse-conducting system. However, in the ventricles of SHRSP, almost all cardiac myocytes possessed immunoreaction products which were scattered evenly throughout the cytoplasm; this distribution pattern differed from that of the atrial wall of this strain.

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The blood vascular bed of two human pancreata was replicated partially by arterial perfusion of intentionally reduced amounts of low viscosity methacrylate resin, to be observed with a scanning electron microscope. The findings were compared with those obtained from a pancreas replicated completely by a sufficient amount of resin.
Complete replication confirmed our previous findings (MURAKAMI et al., 1992) that many exocrine lobules contained one or more endocrine islets, which preferentially issued insulo-acinar portal vessels continuous with the lobular capillaries.
Incomplete replication demonstrated that the casting medium filled blood capillaries in the endocrine islets more promptly than those in the exocrine lobules and secretory ducts. Furthermore, islet-containing lobules allowed a more rapid resin flow to the exocrine tissue via the insulo-acinar portal route than did the lobules lacking an islet.
Since the resin medium used had the viscosity of blood and was injected under physiological pressure, the results obtained by the incomplete arterial injections are believed to suggest the physiological state of blood flow in the pancreas.

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The immunohistochemical localization of actin, vimentin and tubulin in adult ovine and bovine seminiferous tubules was studied at both the light and electron microscopical levels, using an improved methodical protocol. α-smooth muscle actin and structural F-actin were found to be present in myoid peritubular cells. Structural F-actin also occurs in Sertoli cells at three localizations; 1) As part of the Sertoli-Sertolijunctions in a stage-dependent manner; 2) where Sertoli cells are in contact with spermatocytes; 3) in ectoplasmic specializations lining the recesses that support elongating spermatid heads. Vimentin is localized in peritubular myoid and fibroblastic cells and in Sertoli cells. In the latter, vimentin is concentrated in a perinuclear position. α-tubulin is observed in the cytoplasm of spermatogonia, in axonema and manchette of spermatids and in Sertoli cells with their abundant microtubules. Since the α-tubulin reaction decorates even the narrowest lateral and apical cell processes, it is an excellent marker to study changes in Sertoli cell shape and size during the seminiferous epithelial cycle in rams and bulls.

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The region between the longitudinal and circular muscle layers of the canine proximal colon was investigated by light and electron microscopy. Unique smooth muscle bundles, referred to as “oblique” muscles, were arranged in branching/anastomosing bundles, forming a network intermeshed with the nerve plexus and vasculature. These smooth muscles were concentrated along the ganglia and primary connectives of the myenteric plexus, thus showing a periodic distribution roughly corresponding to that of the ganglia.
The oblique smooth muscle bundles bridged the distance between the circular and longitudinal muscle layers and blended into the inner aspect of the longitudinal muscle layer and the outer aspect of the circular muscle layer. A few oblique muscle cells occurred within the sheath of the ganglia and primary strands, i. e., perineurium.
Oblique muscles may serve to electrically couple the circular and longitudinal muscle layers, thus explaining the synchronous electrical activities of these muscles. It is possible that the pacemaker activity in the myenteric region is generated by these muscle cells. Oblique muscles may also serve to protect nerve elements and the vasculature from the mechanical stress of peristalsis.

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Immunohistochemistry revealed the presence of tyrosine hydroxylase (TH)-, neuropeptide Y (NPY)-, calcitonin gene-related peptide (CGRP)- and substance P (SP)-immunoreactive nerve fibers and SP-immunoreactive neuronal cell bodies in the pineal gland of the cotton rat (Sigmodon hispidus). Abundant TH- and NPY-immunoreactive fibers were distributed evenly throughout the gland; less numerous CGRP- and SP-immunoreactive fibers were distributed in the superficial pineal and the stalk, but were scarce in the deep pineal. All the immunoreactive fibers were usually found around blood vessels. Since TH- and NPY-immunoreactive fibers in various pineal regions disappeared completely with superior cervical ganglionectomy, these fibers are all considered postganglionic sympathetic fibers. Intrapineal CGRP- or SP-immunoreactive fibers decreased considerably in number following superior cervical ganglionectomy, suggesting that some sympathetic fibers contain CGRP or SP. Bilateral bundles of nerve fibers under the transverse sinuses, corresponding to the nervi conarii, contained TH-, NPY-, CGRP- and SP-immunoreactive fibers, which continued into those distributed in the pineal capsule. In the nervi conarii, fibers immunoreactive for TH and NPY disappeared after superior cervical ganglionectomy, but those immunoreactive for CGRP and SP persisted. Thus, non-sympathetic, CGRP- and SP-immunoreactive fibers, together with sympathetic fibers, are presumed to enter the gland by way of the nervi conarii. Neuronal cell bodies, containing SP-like immunoreactivity and being possibly parasympathetic in nature, occurred occasionally in the superficial pineal.

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Three-dimensional structures of the capitulum and first mitochondria in the neck region of the hamster spermatozoa, were observed with transmission (TEM) and scanning electron microscope (SEM). Some capitula revealed a variable contour even in the caudal epididymis, but most finally developed to form a typical wagonette shape. The final shape of the capitulum is probably produced by the aid of apical protrusion of the right, pyramidal mitochondrium. The right and left first mitochondria were triangular pyramids in contour, while the dorsal and ventral ones were rod-like in shape. The mutual transformations between the capitulum and the first mitochondria are discussed in relation to the completion of the neck region.

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The transitional portion in human eccrine sweat glands was observed by transmission electron microscope (TEM). The transitional portion, consisting of columnar epithelial cells (columnar cells) and basal cells, formed a very short segment about 25 to 50μm in length. The portion was abruptly connected to the secretory segment, and shifted to the excretory duct without marked ultrastructural changes. The columnar cells were morphologically characterized by small apical vesicles as reported in previous reports. Considering the frequency of the mitosis of the columnar cells, the transitional portion seemed to be one of the areas of cell proliferation in the gland.
Basal cells were sparse in the region connecting the secretory segment, but dense near the duct. Basal cells in the secretory segment side of the transitional portion, containing thin microfilament-bundles in the infranuclear cytoplasm, were considered to be immature myoepithelial cells. On its ductal side, however, the basal cells showed morphological profiles similar to ductal peripheral cells. These findings suggest that the differentiation of myoepithelial cells occurs in the transitional portion of eccrine sweat glands.

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An immunohistochemical study using a streptavidin-biotin method demonstrated the extensive distribution of neuropeptide Y (NPY)-like immunoreactivity in the brain of the white sturgeon, Acipenser transmontanus, with the highest density in the basal telencephalon and diencephalon. Two labeled cell groups were found in the telencephalon, in mediobasal and dorsocaudal locations. Labeled fibers were considerably dense in the ventral area. The epithalamus displayed dense networks of varicose fibers in the ganglion habenulae, but only a few fibers were seen in the organon subcommissurale. In the thalamus, two groups of labeled cells were discerned in the periventricular gray matter: an anteroventral group largely composed of cerebrospinal fluid (CSF)-contacting neurons, and a dorsocaudal group consisting of non-CSF-contacting large neurons. The hypothalamus also contained a number of CSF-contacting neurons in the periventricular areas including the nucleus lobi inferioris, the nucleus lateralis tuberis and the nucleus recessus posterioris. Labeled varicose fibers were closely associated with the hypothalamo-hypophyseal complex, the organon vasculosum hypothalami, and the saccus vasculosus. Immunoreactive cells and fibers were also detected in the dorsal region of the adenohypophysis. These results suggest that NPY or a related molecule is involved in the hypothalamic neuroendocrine mechanisms of this primitive bony fish.

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Acute inflammatory reactions in different respiratory regions were studied in a lipopolysaccharide (LPS) instilled rat model. Rats were sacrificed at 1, 2, 4, 8, 12, 24 and 48h after administration of Escherichia coli LPS to the lumen of the trachea, and changes in the trachea, bronchioles and alveoli were observed by light and electron microscopy.
In the trachea, neutrophils were markedly increased in subepithelial connective tissue and between tracheal epithelial cells, from 2h on, showing a peak at 8h. The number of tracheal mast cells increased at 4 and 8h. Different structural features of secretory granules between mast cells in the tracheal epithelium and subepithelium were noticed, and the possible involvement of mast cells in airway acute inflammation is discussed.
In the bronchioles, Clara cells showed characteristic morphological alterations. At 8 to 12h, Clara cells revealed well-developed smooth and rough endoplasmic reticula and many free ribosomes, possibly for enhanced synthesis of secretory substances. Many Clara cells possessed a large apocrine-like protrusion filled with an amorphous substance, likely indicating an apocrine secretion of the cells. At 24h, Clara cells were observed to take on a pseudostratified arrangement, suggesting enhanced proliferation of progenitor cells and their differentiation into Clara cells.
In the alveoli, neutrophils infiltrated alveolar walls and pulmonary venules at 4h and disappeared at 12h. Prior to morphological changes in bronchioles and alveolar walls at 2h, the macrophages with well-developed filopodia and free-ribosomes appeared in alveolar sacs and ducts. They may contribute to histological changes especially at the initial stage of acute inflammation in alveoli.

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