The somites are metameric structures. Although these structures appear uniform, other types of muscles differentiate from them along the rostrocaudal body axis. This study investigated whether the somites are committed to producing level specific muscles by heterotopic transplantations between quail and chick embryos.
Our results were as follows: 1) Cervical somites, when transplanted into the thoracic or lumbar region, produced the ectopic ventral muscle mass characteristic of the cervical region. Cervical somites did not develop ribs or body wall muscles associated with the rib in the thoracic region. 2) Thoracic somites did not produce the ventral muscle mass at the cervical region, but produced ectopic ribs and muscles associated with them. These muscles were invested by graft-derived fasciae, but did not show the lamination of body wall muscles. Thoracic somites produced ectopic ribs in the lumbar region, but muscles associated with ectopic ribs showed normal lumbar lamination. These muscles were invested by host derived fasciae. From these results, we propose that somites are committed to producing the level specific trunk muscles, but that the arrangement of the muscles is determined by the fasciae.

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This study examined the localization of Na/K-ATPase in a specially isolated ciliary epithelial bilayer of the rabbit. This bilayer, harvested by a technique developed in this laboratory, consisted of pigmented epithelial (PE) and non-pigmented epithelial (NPE) cells free of stroma and with a well preserved ultrastructural morphology. Immunocytochemical localization of Na/K-ATPase was performed using goat anti-rabbit Na/K-ATPase with the biotin-streptavidin peroxidase method on fresh as well as fixed preparations. The most prominent immunostaining was found along the basolateral infoldings and interdigitations of both NPE and PE cells. This finding suggests that both ciliary epithelial layers participate in active ion transport and the production of aqueous humor.

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The development of Premaxilla and maxilla in the mouse fetus during secondary palate formation from the 12th to the 16th days of gestation was histochemically assessed. To determine the developmental stages, a classification based on the morphogenesis of the limbs, or the “limb score” (LS) was employed. The stage of LS coincided with the gestational age from the 13th to the 15th days. Early on the 12th day, alkaline phosphatase (ALPase) activity was intense in the mesenchyme lateral to the incisor tooth bud and lateroinferior to the inferior orbital nerve. Subsequently, osteoblasts differentiated at these two sites. The ALPase positive area grew concomitantly with the nasal capsule, the molar tooth germ, and the closure of the secondary palate. The area of bone differentiation contoured the orbital nerve and extended to the rostral part of the secondary palate. At the LS stage -6 (13.52 days), ALPase activity was observed in the mesenchyme medial to, and also surrounding the molar tooth germ. The area of osteogenesis of the secondary palate spread along the medial side of the molar tooth germ, where the formation of the medial alveolar process of the maxilla was completed by the LS stage 3 (15.35 days). The ALPase positive area extended to the horizontal palatal shelves. By late on the 16th day, the palatal process was fully developed. In parallel, bone resorption began on the molar side of the alveolar process.
Acid phosphatase and tartrate-resistant acid phosphatase activities (ACPase and TRACPase activity, respectively) revealed ACPase and TRACPase positive mononuclear cells around the molar tooth germ long before ossification occurred. Our results thus suggest an involvement of the incisor tooth bud and the infraorbital nerve in the initial osteogenesis of the premaxilla and maxilla. Enzyme activities lead to the consideration that osteoclast precursors initiate differentiation around the molar tooth germ. Ostensibly, the mechanical force from the growth of the molar tooth would promote differentiation and activation of osteoclasts located on the alveolar process. Also, the LS classification would improve and simplify future studies of the development of the secondary palate.

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The blood vascular architecture of the rat nasal associated lymphoid tissue (NALT) was studied by scanning electron microscopy of corrosion casts. To examine the correlation of the vasculature with the distribution of lymphocyte subsets, the NALT was also studied by light microscopy of immuno-stained samples. The NALT was supplied by a branch of the inferior nasal artery which arose from the sphenopalatine artery. This branch reached the bottom of the NALT and ramified arterioles to the follicles and the parafollicular regions. These arterioles ascended toward the subepithelial region, giving off capillaries en route to form a coarse plexus within the follicles and the parafollicular regions. The arterioles reached the subepithtelial region and formed a subepithelial capillary network consisting of a single layer of flat meshwork. The follicular, parafollicular and subepithelial capillaries anastomosed one another. The capillaries in each region were gathered into collecting venules, which in turn drained into high endothelial venules (HEVs) in the parafollicular region. The HEVs ran through the parafollicular regions around the follicular perimeters, and flowed into ordinary veins to leave the NALT. Lymphocytes labeled with an anti-T cell antibody were mainly distributed in the parafollicular regions, where HEVs were situated. B cells were mostly observed in the follicular and dome areas. The microvascular structure and its correlation with lymphocyte subset domains in the NALT were essentially similar to those in other mucosa associated lymphoid tissues (MALTs) such as tonsils and Peyer's patches.

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The muscle coat of the upper region of the mouse oviduct undergoes morphological changes in both the muscular and the connective matrix components during pregnancy and the post-partum period. During pregnancy, there is a significant increase in the number of mitochondria and caveolae and in the extension of the smooth endoplasmic reticulum in smooth muscle cells, suggesting the enhancement of their contractile activity. Within two days after delivery, these changes regress completely. The interstitial connective matrix in pregnancy undergoes a de novo genesis of basal lamina-like material and of collagen fibers, which vary in diameter and are irregular in outline. Both these connective components appear in relation to deep, round shaped pits present all along the smooth muscle cell surface. After delivery, characteristic morphological patterns appear associated with the active role which the smooth muscle cells play in resorption and reorganization of the intercellular connective matrix.

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The ultrastructure of the stromal cells, macrophages and lymphoid cells in the head-kidney of the sea bass (Dicentrarchus labrax L.) was studied. Like mammals, stroma cell types here include endothelial and adventitial cells comprising the sinusoidal wall, fibroblast-like reticular cells related to scarce reticular fibres, and macrophage-type reticulum cells, the last probably corresponding to the resident macrophage population of higher vertebrates. Their possible role in the haemopoietic microenvironment is considered. Monocyte-macrophages, macrophages and melano-macrophages, probably corresponding to ontogenic or functional stages of the same cell type were identified and their functional significances are discussed. Scarce, free lymphoid cells or small clusters of lymphocytes but no lymphopoietic islets were recognizable. Large lymphocytes, small lymphocytes and very scarce developing and mature plasma cells were identified. The lymphoid function and defensive role of the head-kidney were analyzed.

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Nerve fibers in the villi of the canine ileum were studied with special reference to their relation to the central lacteal. Immunohistochemically demonstrable nerve fibers containing substance P (SP) and calcitonin gene-related peptide (CGRP) were rather more numerous in the villi of the ileum than in those of the duodenum, as observed in our previous study (ICHIKAWA et al., 1991). They were distributed beneath the epithelium and associated with smooth muscle fibers. Besides these localizations, immunoreactive fibers were gathered, especially at the middle of the hight of the villus, close to the endothelial cells of the central lacteal. This particular distribution of nerves was more evident in the ileum than in the duodenum.
Electron microscope observation indicated beaded fibers containing large cored (peptidergic) and small clear vesicles coursing closely under the lacteal endothelium, partly intercalated by a basement membrane and partly in direct contact. The nerve fibers often penetrated the endothelial cell, being directly surrounded by its cytoplasm. Although the above-described findings essentially coincide with our previous observations in canine duodenum (ICHIKAWA et al., 1991), the present study in the ileum demonstrated occasional nerve fibers protruding into the lacteal lumen with a knob-like swelling.
It is suggested that the SP and CGRP-containing nerves in problem might be sensory in nature, possibly monitoring mechanical information from the lumen and wall of the central lacteal. At the same time, these nerves are suggested to be secretory in nature, releasing the peptides to exert unknown effects upon the lacteal wall and its vicinity, presumably in response to luminal and mural stimuli.

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The dendritic morphology and retinal distribution of substance P (SP)-immunoreactive neurons was determined in two Australian lizard species Pogona vitticeps and Varanus gouldii, by using immunohistochemistry on retinal wholemounts and sectioned materials. In both species, two classes of SP-immunoreactive neurons were described in the inner nuclear layer (INL) and classified as amacrine cells (types A and B). Type A amacrine cells had large somata and wide-field, bistratified dendrites branching in sublaminas 1 and 5 of the inner plexiform layer (IPL). Their morphology and retinal distribution differed between the two species. Type B amacrine cells in both species had small somata and small-field dendritic branching. A population of SP-immunoreactive neurons with classical ganglion cell morphology were identified in the ganglion cell layer (GCL). Immunostained ganglion cells occurred in larger numbers in Varanus gouldii than in Pogona vitticeps.
In both species type B SP cells were the most numerous and were estimated to be about 60, 000-70, 000. They were distributed non-uniformly with a high density band across the horizontal meridian of the retina, from where the density decreased towards the dorsal and ventral retinal margins. In both species type A amacrine cells occurred in small numbers distributed sparsely in the peripheral retina. The faint immunostaining of SP-immunoreactive neurons in the GCL, did not allow us to reliably determine their numbers and retinal distribution. The functional significance of SP-immunoreactive amacrine and ganglion cells in the lizard retina remains to be determined.

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Ruffini endings in the periodontal ligament of rodents are ensheathed by a special type of terminal Schwann cell with a particularly developed rough endoplasmic reticulum and Golgi apparatus, and further enveloped by a characteristic multi-layered structure. In order to reveal the functional significance of the structures, localization of a laminin molecule in the periodontal Ruffini endings of rats was immunohistochemically investigated at the levels of light and electron microscopy.
Immunostaining using an anti-laminin serum clearly demonstrated the profiles of the Ruffini endings as well as those of the blood vessels. Ultrastructurally, reaction products for laminin were deposited in the entire thickness of the multi-layered structure, supporting the idea that this structure is derived from the basal lamina. The basal lamina, immunoreacting with laminin antiserum, was penetrated by periodontal collagen fibers, possibly serving as an adhesive device between the Ruffini endings and surrounding collagen fibers. The laminin immunoreactive materials were also recognized in the vesicles and caveolae of the terminal Schwann cells which tended to gather at the interstitial surface of the cells. The terminal Schwann cells are therefore believed to be directly involved in the formation of the multilayered basal lamina through the active production of its materials.

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Pancreatic endocrine cells of Caiman latirostris were investigated by electron microscopy using conventional and immunocytochemical methods. Ultrastructurally, four types of endocrine cells were classified according to the morphology of their secretory granules. Three types of endocrine cells were identified as either glucagon, insulin or somatostatin cells by the presence of such characteristic granules well established in mammals. The remaining endocrine cell type could not be classified by its ultrastructural features alone.
Immunocytochemical observations confirmed the ultrastructural classification of glucagon, insulin and somatostatin cells. In addition, endocrine cells immunoreactive for either pancreatic polypeptide (PP) or motilin were identified. Morphometric analysis of PP -and motilin-immunoreactive granules demonstrated that they were the most polymorphous and smallest granules among the pancreatic endocrine cell granules. Although both PP and motilin granules closely resemble each other, motilin granules were smaller in size and more spherical in shape than PP granules.

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Motilin-immunoreactive cells in the duodenum, pyloric stomach and pancreas of Caiman latirostris and Caiman crocodilus were investigated using region specific antisera for porcine and canine motilin molecules. Motilin-immunoreactive cells were found in the duodenum, pyloric stomach and pancreas of both caiman species. These cells were primarily open-type endocrine ones in the epithelium of the duodenum and pyloric stomach. Motilin-immunoreactive cells were observed in both the exocrine and endocrine portions of the pancreas, and frequently exhibited one or more cytoplasmic processes of variable length. Since motilin-immunoreactive cells do not cross-react with serotonin or any of the other pancreatic and gut hormones, they are considered to be cell type independent from any of the other known pancreatic or gut endocrine cells. The molecular similarity between caiman motilin and porcine and canine motilins and the heterogeneity of the motilin molecule in the caiman digestive system is discussed.

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