The three-dimensional (3-D) organization of the collagen fibrillar network in rabbit uterus was studied by cell maceration/scanning electron microscopy (SEM) method, both during estrus and after stimulation with 100 I. U. of human chorionic gonadotropin (hCG). The cellular elements of glutaraldehydefixed tissue were effectively removed with 2N-NaOH at 25°C for 5-7 days, followed by rinsing in distilled water. Correlative light microscopy (LM) and transmission electron microscopy (TEM) observations were also made in order to better clarify the natural location and distribution of collagen structures in the uterine layers.
In estrous and ovulatory rabbits the superficial compartment of the endometrial stroma was composed of diffusely organized individual collagen fibrils and thin bundles of fibrils, forming specific supporting structures around the uterine glands. The deeper stroma showed a more condensed lamellar arrangement, particularly in the central part of the endometrial folds (plicae). Two distinct collagen networks, detected in the circular and longitudinal muscle layers of the myometrium, represented plexuses of anastomosing fine sheaths around the individual smooth muscle cells. A condensation of the fibrillar framework was observed around the large blood vessels between these two layers. Little alteration in uterine fibrillar network could be noticed in ovulatory animals 12h after stimulation with hCG. Marked changes indicating collagen reorganization occurred in progestational animals 7.5 days after hCG administration. In this case, the collagen fibrillar network of the endometrium showed an irregular pattern consisting of slender elongations surrounding the labyrinthine spaces of the epithelium and corresponding to numerous, extremely attenuated plicae. Such a rearrangement of fibrils is very likely a response to hormonal stimulation of the uterus. To further identify the location of the blood vessels in the uterine collagen skeleton, vascularcasts were also prepared. The collagen fibrillar network not only provides a mechanical support for the structural components of the uterus but also creates a favourable milieu for their activities.

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The blood vascular bed of the cerebral hypophysis in the adult rat was replicated completely or incompletely by arterial injection of different amounts of methacrylate resin, to be observed with a scanning electron microscope.
Complete replication confirmed our previous findings (MURAKAMI et al., 1987) on the distribution and structure of the vascular beds in and around the hypophysis of the rat. One long major and several minor portal routes (vide infra) were reproduced sufficiently together with the systemic veins of the posterior lobe.
Incomplete replication demonstrated that resin flows: 1) via the long portal vessels from the median eminence and neural stalk to the anterior lobe; 2) via the accessory long portal vessels from the subependyma to the anterior lobe; 3) via the short portal vessels from the posterior lobe to the anterior lobe; 4) via the neurointermedial portal vessels from the posterior lobe to the intermediate lobe; 5) via the intermedio-distal portal vessels from the intermediate lobe to the anterior lobe; and 6) via the tuberal portal vessels from the tuberal lobe to the anterior lobe.
Incomplete replication also demonstrated that resin in the median eminence and neural stalk is drained preferentially into the anterior lobe via the long portal vessels, and that resin in the posterior lobe is drained mainly into the systemic veins. We were unable to demonstrate a retrograde resin flow from the anterior lobe to the median eminence, subependyma, neural stalk, intermediate lobe and posterior lobe, nor an ascending resin flow from the posterior lobe to the median eminence and subependyma. Also failing to be noted were an ascending resin flow from the hypophysis to the hypothalamus and a descending resin flow from hypothalamus to the hypophysis.

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Immunohistochemical characterizations of motilin-immunoreactive cells were examined in gastric and duodenal mucosae of nine species of birds from seven orders using five different region-specific motilin antisera. Motilin-immunoreactive cells appeared as open-type cells in the mucosal epithelium and showed varying immunoreactivities to antisera used in all the birds examined except for the cormorant and penguin, which did not show any kinds of immunoreactivity to motilin. Motilin-immunoreactive cells of the emu duodenum were detected by all the motilin-antisera used. The present results suggest that there is a wide range of heterogeneity between motilin molecules among avian species, or perhaps alternatively the existence of a family of motilin-like peptide. Furthermore, the present results should prove useful for a molecular biological study on the evolution of avian motilin.

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Immunohistochemical localization of basic fibroblast growth factor (bFGF) was studied in the rat pituitary gland at light and electron microscopic levels using a specific monoclonal antibody. In the anterior lobe, bFGF-immunoreactivity was found mostly in a cell population without secretory granules, which was identified as the folliculo-stellate (FS) cell by its ultrastructure and expression of S-100 protein. The subcellular localization of the immunoreactivity in FS cell was strictly nuclear. Besides the FS cell, a minor cell population containing small granules of 60-100nm diameter, which seemed to represent immature endocrine cells, was immunostained in the nuclei with the anti-bFGF antibody. In the intermediate lobe, a subpopulation of the S-100 protein-positive cells lining the pituitary cleft was immunoreactive for bFGF. These results imply that the agranular cell types are the main producer and/or target of rat pituitary bFGF, and that bFGF may play a role in the differentiation of pituitary endocrine cells.

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Immunoreactivities for FMRFamide and substance P (SP) in the carotid labyrinth of the bullfrog were detected using the peroxidase-antiperoxidase method, and the results compared with corresponding differential interference-contrast (Nomarski) images. Colocalization of both peptides was determined by the indirect double immunofluorescence method. Immunoreactivities for FMRFamide and SP were found in nerve fibers distributed in the intervascular stroma of the labyrinth. The FMRFamide-immunoreactive fibers were less numerous than the SP-immunoreactive fibers. In the Nomarski image, FMRFamide-fibers were recognized in relief, with most of them located near the walls of blood vessels. All FMRFamide-fibers coexisted with SP. The results suggest that FMRFamide-immunoreactive fibers are also involved in local vascular regulation of the carotid labyrinth.

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The development of the pineal and retinal photoreceptors in the embryonic rainbow trout, Oncorhynchus mykiss was investigated by means of light and electron microscopy. The pineal photoreceptors endowed with photoreceptive outer segments and signaltransmitting synapses appeared first 15 days after fertilization, and well developed by 21 days. In contrast, the retinal photoreceptors appeared as late as 27 days after fertilization (1 day before hatching). This temporal disparity in photoreceptor development has been compared with the photoperiodic formation of otolith increments, which is initiated during an early developmental stage lacking retinal photoreception. It has been suggested that the early development of pineal photoreceptors may be involved in light-dark recognition, establishment of the diel and circadian rhythms, and entrainment to the environmental photoperiod in the embryonic rainbow trout.

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Structural changes in cumulus-oocyte complexes and granulosa cells were induced by administering pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG) to female mice. Three and 9h after hCG administration, dissolution of the germinal vesicle (GVBD) and progression to the second metaphase occurred respectively in oocytes. The number of cumulus cells associated with the granulosa cell layer decreased significantly 1h after hCG administration. Expansion of cumulus cell investment was due to the abundant deposition of intercellular materials in the cumulus-oocyte complexes during oocyte maturation. A strongly negative-charged (colloidal iron-positive) substance was detected in the intercellular spaces of follicular tissue, especially in the cumulus mass. Moreover, cells located where the cumulus mass and granulosa cell layer intertwined became enlarged during the resumption of the meiosis of oocytes. Colloidal iron-positive substances accumulated extensively within the intercellular spaces of the enlarged cells.

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Morphological aspects of the heart conduction system have been studied by various histochemical markers. However, the actual presence of markers in the conduction system and its developmental mode remain controversial. We have shown the anti-Leu-7 antibody to cross-react with cells of the rat embryonic heart conduction system by an immuno-electron microscopic study. A comparison was thus made between the results of Leu-7 immunohistochemistry and those by other markers previously used for studying the development of the conduction system. As a result, Leu-7 immunoreactivity proved the most reliable marker for studying the conduction system of the developing rat heart. Examination of the developmental mode of a rat conduction system was facilitated with the use of this marker. The immunoreactivity for Leu-7 initially appeared in the anterior wall of the bulboventricular region at 10 days of development. The development of three internodal tracts and two atrioventricular nodes was demonstrated in the following stage. These primordial atrioventricular nodes, one of which connects to a bundle of His, fused to form a single distinctive node followed by completion of the conduction system in the 18 day fetus.

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The present study demonstrated the threedimensional microstructure of the rat diaphragm by scanning electron microscopy (SEM) of either intact or alkali-treated tissues, enzyme-histochemistry, and confocal laser scanning microscopy (LSM). The peritoneal and pleural surfaces of the diaphragm were covered with mesothelial cells studded with microvilli. Many round gaps were formed between the mesothelial cells. The submesothelial connective tissue contained voluminous, irregularly shaped lymphatics. Some of these lymphatics extended many funnel-like projections of their endothelia towards the pored region of the mesothelium. On coming into contact with the mesothelium, many of the lymphatic projections were perforated at their ends, thus giving rise to stomata connecting the peritoneal cavity and lymphatic lumen. Some projections ended blindly while plugging the mesothelial pores, thereby making visible some intercellular gaps in this contact. The subperitoneal sheet of the collagen fiber network possessed clusters of foramina which tightly fit the passage of the lymphatic projections. Confocal LSM of the diaphragm after intraperitoneal injection of FITC-dextran demonstrated the tracer both in the lymphatic lumina and in the connective tissue spaces. Our results indicate that peritoneal fluid is allowed to flow into the connective tissue spaces of the diaphragm through intercellular gaps and into lymphatics through stomata.

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