The distribution of vasoactive intestinal polypeptide (VIP), gastrin-releasing peptide (GRP)/bombesin, somatostatin, vasopressin, neuropeptide Y (NPY) and serotonin was examined immunohistochemically in the suprachiasmatic nucleus (SCN) of male rats genetically deficient for vasopressin (Brattleboro strain). VIP-containing neurons and their varicose fibers were preferentially distributed in large numbers in the ventromedial part of the SCN. GRP/bombesin-containing neurons and their fibers were also gathered in the ventral part of the SCN, particularly in the ventromedical region of the nucleus. Somatostatin-containing neurons and their fibers were prominent in the rostral and middle portions of the SCN, where the highest concentration of immunoreactivity was restricted in their ventromedial part. No vasopressin-immunoreactivity was found at all throughout the SCN. Profuse NPY-containing varicose fibers were observed in the ventrolateral part of the SCN, but no immunoreactive neurons were distributed in this nuclear region. Serotonergic fibers showed a topographic arrangement in the SCN: a serotonin-immunoreactive nerve plexus was predominantly distributed in the ventrolateral part. These findings indicate that the SCN of Brattleboro rats is composed of distinct subdivisions of immunoreactive cell bodies and fibers. The distribution of the five peptides and indoleamine within the SCN in the Brattleboro strain was compared with that in normal Long-Evans rats. Furthermore, both strains of rats were exogeneously administered with arginine-vasopressin, but no conspicuous difference in the regional patterns of immunoreactivity was detected. The possible role of vasopressin in the SCN is discussed.

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Histochemical and immunohistochemical studies of the adrenal gland of bullfrogs gave the following results.
1. The occurrence of two types of cells, intensely and weakly chromaffin cells, was demonstrated by a dichromate-chromate fixation. The former cells corresponded to strongly argentaffin cells in Masson-Hamperl's method and were regarded as noradrenaline-containing cells. The latter cells corresponded to weakly argentaffin cells and were identified as adrenaline-containing cells.
2. Enkephalin- and serotonin-like immunoreactivities were found in the adrenal chromaffin cells. The combination of immunohistochemistry and fluorescence histochemistry indicated three types of cells in the adrenal gland: cells with adrenaline and serotonin; those with noradrenaline and serotonin; and those with adrenaline, enkephalin and serotonin.
3. Varicose nerve fibers with substance P-, calcitonin gene-related peptide (CGRP)-, peptide HI (PHI)- and gastrin releasing peptide (GRP)-like immunoreactivities were found on solitary or small clustered chromaffin cells. The CGRP-fibers were also located among chromaffin cells forming large clusters. Neuropeptide Y (NPY)-immunoreactive fibers, as well as the other four fibers, were seen around the small arteries and arterioles supplying the adrenal gland.
4. Double immunostaining for substance P and CGRP demonstrated the occurrence of nerve fibers with three kinds of immunoreactivities in the adrenal gland: fibers with both substance P- and CGRP-like immunoreactivities; those with substance P-like immunoreactivity without CGRP-like immunoreactivity; and those with CGRP-like immunoreactivity without substance P-like immunoreactivity. Double staining for substance P and CGRP also showed the presence of dorsal root ganglionic neurons which contained the three above-mentioned immunoreactivities. Thus, these neurons are suggested to supply the adrenal gland.
5. In the paravertebral sympathetic ganglia, most small neurons were immunopositive for NPY. These neurons were presumed to supply the small arteries and arterioles in the adrenal gland.

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To study in detail vascularization in the hypothalamo-hypophysial complex in some Japanese elasmobranchs, injection casts of blood vessels were observed by scanning electron microscopy. Materials used were a gummy shark (Mustelus manazo), a cloudy dogfish (Scyliorhinus torazame) and a skate (Raja porosa).
The vascular supply to the hypothalamo-hypophysial region of the elasmobranchs is carried out by the inferior hypothalamic arteries and their branches that originate from the internal carotid artery. In the gummy shark, a pair of inferior hypothalamic arteries send several branches to the median eminence running along the anterolateral sides of the distal adenohypophysis. These branches form the capillary plexus, displaying anastomosis and convolution at the ventral surface of the median eminence. The plexus assumes capillary glomeruli at the lateral region of the posterior median eminence. Numerous branches derived from the plexus are directed backward through the pars distalis, join with the capillary net work (which develop in the neuro-intermediate lobe) and are finally gathered together to form a thick hypophysial vein. The ventral lobe receives several arterial branches from the internal carotid arteries and carotid artery to form a unique vascular bed. Therefore, it is assumed that in elasmobranchs the hypothalamic control of the ventral lobe is weaker than that of adenohypophysial components.

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In order to study the three-dimensional architecture of the cytoskeletal system and its functional properties in the secretory cell, the anterior pituitaries of rats and mice were examined by the quick-freezing deep-etching method.
The cytoplasm of the anterior pituitary cell is occupied by networks of several kinds of fine filaments. For convenience, the filaments which terminate at cytoorganelles, secretory granules, and plasma membrane were classified into three types.
The filaments running away from the complicated networks of fine filaments terminate on the outer surface of the membrane of the cytoorganelles, secretory granules, and small vesicles and on the inner surface of the plasma membrane. These filaments, 4-10nm in diameter, were termed associating filaments by us.
There are direct connections by filaments between adjacent cytoorganelles, or between the cytoorganelle and secretory granule, or between the secretory granule and plasma membrane. These filaments are also 4-10nm in diameter, and were termed connecting filaments by us.
Short filaments, 3-8nm in diameter, link directly at right angles the opposite membranes crossing over the cisterna of the nuclear envelope, of the rough endoplasmic reticulum, of the Golgi apparatus, and the intramitochondrial space and also the intercellular space. We named these linking filaments.
These findings strongly suggest that these filaments are essential elements for supporting, maintaining and organizing the shape and location of all the cytoorganelles in the cell, and that they vary according to cellular function.
The limiting membrane of the secretory granule is bound to the associating filaments and connecting filaments, running radially and at times connecting to the microtubules or plasma membrane. These filaments and microtubules may play a role in the organization and transport of secretory granules toward the plasma membrane.

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The ileofibularis muscle of the turtle Trionyx sinensis was examined by light and electron microscopy. Acetylcholinesterase staining showed an “en grappe” type of terminal. The muscle showed succinic dehydrogenase activity with three different types of fibers. The fibers appeared fibrillar type under the electron microscope. Neuromuscular junctions showed the presynaptic portion containing clear vesicles and mitochondria, whereas the postjunctional portion showed only few junctional folds.

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Organized mechanoreceptors in mucosae and vermilion borders of rat lower lips were studied by light and electron microscopy. Cholinesterase histochemistry was applied to whole-mount preparations of mucosae for the light and electron microscopic identification of mechanoreceptors. Three types of lamellated corpuscles (a simple corpuscle; a coiled, simple corpuscle; and a Meissner-like corpuscle), and a unique, organized, bush-like assembly of free nerve terminals were identified. The simple corpuscles were found exclusively in the vestibular mucosa facing the incisor teeth. In contrast, bush-like endings were confined to the vestibular mucosa and to the lateral, eminent mucosa that faced the diastema. Furthermore, coiled simple corpuscles and Meissner-like corpuscles were localized in the boundary zone between the vestibular and lateral eminent mucosae and in the vermilion border. From a functional viewpoint, it is of interest that different areas of the rat lip contain different morphological patterns of mechanoreceptors.

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Intra-arterially injected low viscosity methacrylate filled the lymphatic system in the muscularis externa of the young rat. Scanning electron microscopy of the corrosion casts revealed that between the inner and outer muscular coat there was a lymphatic network made up of polygonal meshes. The initial lymphatics, about 15μm diameter drained into the thicker lymphatics, about 20-80μm diameter. These lymphatics ran along the muscular fibers of either inner or outer layers and formed polygonal (most often rectangular) meshes. The casts of the thicker lymphatics possessed notches indicative of valve locations.
The myenteric nervous plexus was also replicated between the inner and outer muscular coats. The plexus consisted of flat astral structures with primary and secondary, and occasionally tertiary, processes which interconnected with neighboring ones. It is suggested that the enteric neurons are confined in an interconnected channel system.

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The plasma membrane of the Ito cell in the normal rat liver was studied by freeze-fracture electron microscopy. Ito cells appeared to adhere to endothelial cells or to be embedded in the microvilli of hepatocytes. Ramified processes with a few microvilli of the cell extended along the endothelial cells. Caveolae were constantly seen on the plasma membrane, but their numbers varied among cells. Two different patterns of intramembranous particles were found on the plasma membrane of the Ito cells: most cells showed an even distribution of the particles, but the others, aggregates of them. Particle-free domains were seen on the plasma membrane in some Ito cells. Piles of concave or convex sheets were sometimes seen in the freeze-fractured lipid droplets.

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The synaptic interactions between catecholaminergic terminals and luteinizing hormone releasing hormone (LHRH)-containing neurons in the medial preoptic area of the rat was studied by electron microscopy using LHRH immunocytochemistry combined with 5-hydroxydopamine labeling or autoradiography after injection of ³H-dopamine or ³H-noradrenaline in the same tissue section.
Axon terminals labeled with 5-hydroxydopamine, ³H-dopamine or ³H-noradrenaline were found to make synapse-like contacts with LHRH-immunoreactive nerve cell bodies and fibers in the medial preoptic area and also 5-hydroxydopamine-labeled terminals made synaptic contacts with the same LHRH-immunoreactive nerve fibers with unlabeled terminals.
These findings suggest that catecholaminergic neurons may innervate LHRH-containing neurons to regulate LHRH secretion via synapses with other unknown neurons in the medial preoptic area of the rat.

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The mechanism of follicle-like cavity formation from a monolayer of porcine thyroid cells grown in a collagen sandwich was studied. When porcine thyroid cells cultured in a monolayer on the type I collagen gel are overlaid with a second layer of collagen, changes occur in the polarity and arrangement of the cells. After 1 day of culture in the collagen sandwich, some cells in the monolayer proliferate, migrate and form two cell layers. The cell surfaces in contact with the upper or lower collagen gels always show basal characteristics. The primitive follicle lumen sealed by the zonula occludens first appears between two adjacent cells in a monolayer, or between the cells of the upper layer and those of the lower layer. Within 2 days of incubation, the cultured thyroid cells form rather flattened follicle-like cavities, even in the absence of TSH.
Proliferation of the cells surrounding the lumen and luminal fusion would contribute to the development of such cavities. Bundles of numerous filaments are located along the apical and basal plasma membranes, and microtubules are markedly developed in the cytoplasm. The formation of the follicle-like cavities is inhibited by colchicine, suggesting the involvement of microtubules in the lumen-forming process. Immunohistochemistry shows that thyroid cells cultured in the collagen gel preserve the ability for thyroglobulin synthesis and basal lamina formation.

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