The distribution of somatostatin-containing neurons in mice of both sexes was immunohistochemically examined and compared with that in rats. In radioimmunoassay the relative somatostatin content in the mouse brain was 2-3 times higher than that in the rat. The overall immunohistochemical staining for somatostatin was much stronger and more prominent in the mouse than in the rat. Although the distribution pattern of somatostatin immunoreactivity was basically the same between the two animals, several regions, especially the nucleus anterior hypothalami and the nucleus interpeduncularis, were found to contain large aggregates of somatostatin-immunoreactive neurons in the mouse brain but not in the rat. The electrolytic lesions to the nucleus anterier hypothalami caused a marked decrease in somatostatin immunoreactivity of the outer layer of the median eminence in the mouse. This suggests that the nucleus anterior hypothalami is an additional source of somatostatin for the median eminence in the mouse. The differences recognized between the species are interesting from functional and evolutionary points of view.

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Rabbit polyclonal antibodies against bovine amelogenins and enamelins which did not show any cross-reaction were raised, and ultrathin sections of rat incisors were examined by the protein A-gold and ABC methods.
The immunoreactivity of amelogenins was found in dense granules in the intercellular spaces between preameloblasts, and later over the fine- and coarsetextured material. The immunoreactivity was present over the cell organelles associated with the secretory pathway, as well as pale and dark lysosomes of the presecretory and secretory ameloblasts. Here the enamel was immunolabeled in the intercrystal spaces. The immunoreactivity in multivesicular bodies was stronger in preameloblasts than in secretory ameloblasts. In the region of second ruffle-ended ameloblasts at the maturation stage, the immunolabeling was intense in the ruffled-border, but in the rough endoplasmic reticulum and Golgi apparatus, the immunolabeling was much weaker than at the secretory stage.
The immunolabeling for enamelins showed essentially the same intracellular topographical pattern as that for amelogenins by the secretory stage, but was weaker. The immunoreactivity was found mainly attached to the enamel crystals. Double immunostaining of amelogenins and enamelins revealed that both immunoreactivities were present over the same cell organelles associated with secretion and lysosomal systems. It is suggested that the presecretory and secretory ameloblasts are actively involved in the secretion, degradation and resorption of enamel proteins, and that multivesicular bodies and lysosomes in the cells take part in these processes. Amelobasts are considered to be related to the synthesis of enamelins.

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The sites of interaction between antigenpresenting cells (dendritic cells, macrophages) and lymphocytes in the human palatine tonsil were investigated by pre-embedding immuno-electron microscopy and acid-phosphatase histochemistry. Used in this study were: an S-100 protein antiserum recognizing Langerhans cells and interdigitating cells, OKT6 monoclonal antibody reacting with surface antigens of Langerhans cells, and Leu-3a monoclonal antibody directed to surface antigens of helper-T-cells.
In the stratified squamous epithelium, Langerhans cells with characteristic rod-shaped or racket-shaped Birbeck granules exhibited S-100 protein and OKT6 immunoreactivites, and frequently extended long processes to adjacent lymphocytes. The subepithelial area contained a significant number of macrophages, some of which were closely apposed to interdigitating cells with S-100 protein immunoreactivity. Occasionally, macrophages with acid-phosphatase-positive phagosomes and/or lysosomes extended short processes to neighboring lymphocytes. In the interfollicular area, some interdigitating cells and a few Langerhans cells were seen in proximity to or in contact with lymphocytes stained with the Leu-3a antibody.
These findings support previous in vitro studies suggesting the induction of T-cell activation by antigenpresenting cells. They further indicate that T-cell activation by the individual antigen-presenting cells takes place in different areas of the human palatine tonsil through a variety of cell-to-cell interactions.

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The presence and distribution of glial fibrillary acidic protein, vimentin, neurofilament protein, cytokeratins No. 8 (52Kd), No. 18 (45Kd) and No. 19 (40Kd) and S-100 protein in pituicytes, folliculo-stellate cells, the epithelium of the Rathke's cysts and squamous cell nests of the pars tuberalis were investigated immunohistochemically by the peroxidase-antiperoxidase (PAP) method in eleven normal human pituitary glands. An identical immunostaining pattern was expressed by both folliculo-stellate cells and pituicytes. In both cell types the immunostaining for glial fibrillary acidic protein (GFAP), S-100 protein and vimentin was strongly positive. These results indicate the probable glial origin of the folliculo-stellate cell, and enlarge the group of glial cell types expressing vimentin. The co-expression of cytokeratins No. 8 and 19, both characteristic for simple epithelia, and S-100 protein was evident in the epithelial cells lining the Rathke's cysts and the squamous cell nests of the pars tuberalis. Furthermore, some epithelial cells of the Rathke's cysts co-expressed cytokeratins, S-100 protein and GFAP, a fact seldom reported and only in relation to rare neoplasms. The cytokeratin No. 18, characteristic for glandular epithelia, was not clearly demonstrated. Finally, the neurofilament protein was detected only in axons of the neurohypophysis; no immunopositive cells could be found throughout the adenohypophysis. Similarities in the antigenic patterns of these cell populations and the possible relation with their origin and nature are discussed.

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The haemopoiesis of Sparus auratus is formed by the following series: erythro-thrombopoietic, granulopoietic, lymphoplasmapoietic and monocytes.
All the cells which form these series originate from one cell called the stem-cell, there being a network of reticular cells and melanomacrophage centres amongst these cells.
The erythropoietic series comprises erythroblast, proerythrocytes, polychromatocytes, reticulocytes and erythrocytes. The morphological changes which occur during the maturing process are: heterochromatinization of the nuclei, the gradual decrease of organelles in the cytoplasm and the increase of the haemoglobin. We also observed thrombocytes characterized by the presence of numerous vacuoles and abundant glycogen in the cytoplasm.
In the lymphoplasmapoietic series are seen lymphoblasts, lymphocytes and plasma cells. The lymphocytes are cells of different sizes with small microvilli in the cell surface and scanty cytoplasm. Outstanding in the plasma cell is the well developed granular endoplasmic reticulum. The monocytes are large cells with an indented nucleus and cytoplasm containing numerous vesicles of different sizes and also a few lysosomes.

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The three-dimensional architecture of the subepithelial tissue of the gastric, the small and the large intestinal mucosa of the rat was observed by scanning electron microscopy (SEM) after removal of cellular elements through prolonged osmication followed by ultrasonication (the method by Highison and Low, 1982), or by cell-maceration with a low temperature NaOH solution (the method by Ohtani, 1987). The basal lamina was exposed by the former method, and the collagenous fibrous sheet immediately under the basal lamina was disclosed by the latter.
The surface of the subepithelial tissue is grossly smooth in the pyloric gland and crypts of the small and the large intestine. However, in the fundic glands of the stomach, the surface structure of the subepithelial tissue greatly differs according to glandular location. In the pit of the fundic glands, the surface of both the basal lamina and the sub-basal laminar fibrous sheet is smooth. In the neck region, however, shallow round depressions are seen. The most striking feature of the subepithelial tissue of the fundic glands is the presence of numerous hemispherical concavities in the middle and basal regions of the glands which harbor parietal cells.
On the surface of the small intestinal villi, the basal lamina is elevated by the underlying capillary network and forms a meshwork of ridges that surround shallow basins in which numerous round fenestrations 1-5μm in diameter are seen. The fibrous sheath of the marginal arteriole is observed as a cord-like protuberance on the apical margin of the villi; this suggests its role in the maintenance of the structural integrity of the villi. In the large intestine, well defined round fenestrations are clearly seen, mainly distributed on the upper third of the crypts, and continuing to the lamina propria.

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In order to clarify the contraversial structure that CAJAL (1889, 1893, 1911) called “interstitial cells” in the intestine, we have compared the descriptions by CAJAL with our recent findings.
CAJAL defined three groups of interstitial cells in the intestine: those in the mucosa, the deep muscular plexus, and the myenteric plexus. In the deep muscular plexus, he described cells with small perikarya and long, branching processes. Neither glial cells nor ZIO positive fibroblast-like cells, the only cell types seen in the numbers and location necessary to support CAJAL's observations, conformed with the morphology he described. CAJAL might have described a composite cell, or chimera, the cell body being that of a glial (or perhaps a fibroblast-like) cell and the processes being simultaneously stained neurites that ran in close association with the cell.
In the myenteric plexus, staining with S-100 protein for glial cells and ZIO for fibroblast-like cells reveal cells between the external muscle layers. Cells stained with S-100 protein resemble the drawings and also his description of the interstitial cells, although these cells appear to be less frequent than CAJAL's drawings indicate. There are numerous glial cells in the ganglia and primary strands of the plexus which were not included in CAJAL's publications. Conversely, the fibroblast-like cells are incidentally associated with nerve fibers. Although they lie in the same plane, the fibroblast-like cells form a pattern distinct from that of the nerve fibers of the tertiary component of the myenteric plexus. These cells occur in the distribution and numbers of the interstitial cells described by CAJAL. They are stained by ZIO and also immunoreactive for gamma-aminobutyric acid. They can be identified by scanning electron microscopy.
In the mucosa, Golgi staining reveals a pattern of nerve fiber bundles that is indistinguishable from CAJAL's drawings. Glial cell bodies frequently occur at the intersections of these bundles and appear as cell nuclei surrounded by a cytoplasm which is actually the stained nerve fiber bundles. What CAJAL depicted as interstitial cells were composite structures consisting of glial cells and contiguous nerve fiber bundles.
We conclude that the structures which CAJAL called interstitial cells in the intestine do not originate from one cell type. Nevertheless, two groups of fibroblast-like cells, those lying parallel and close to the nerve strands of the deep muscular plexus and those of the myenteric plexus, can be recognized by ZIO staining and scanning electron microscopy. These should be called interstitial cells in conformity with general usage and the numbering system adopted by THUNEBERG (1982), i. e., ICC-I for those at the level of the myenteric plexus, and ICC-III for those associated with the deep muscular plexus.

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The chromogranins are large acidic proteins contained in secretion granules of adrenal medullary cells. These proteins are also presumed to be regular constituents of other endocrine cells, e. g., pancreatic endocrine cells. In our previous immunohistochemical studies performed in the endocrine pancreas of 10 mammalian species, only canine endocrine cells lacked any immunoreactivity for chromogranin A. Therefore, this problem was reinvestigated in the present study. Antisera against bovine and rat chromogranin A, B, and C (=secretogranin II) were applied under various conditions of the immunohistochemical protocol. Upon meeting certain requirements, chromogranin-immunoreactivities were found also in canine pancreatic B- (insulin), PP- (pancreatic polypeptide), and EC- (enterochromaffin) cells. The immunohistochemical data suggest that canine chromogranins partially differ structurally or immunologically from bovine chromogranins and completely from rat chromogranins. In addition, the present findings confirm our previous findings about both interspecies differences in the cellular localization of chromogranins in the endocrine pancreas and the peculiar localization of secretogranin II to pancreatic PP-cells.
Finally, the present methodological studies have shown that even the buffer used in the immunohisto-chemical protocol may be decisive for a false-positive or false-negative immunostaining.

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Mouse epididymides were examined by light and electron microscopy 6, 12, 24h, 1.5, 2, 3, and 5 days after efferent duct cutting when the mice were 60 days of age. Six hours after operation, the principal cells in the initial segment of the epididymal duct began to degenerate following the disappearance of intraluminal spermatozoa. The degenerated cells increased rapidly and reached their greatest number 24h, and then decreased to smaller numbers until 48h. These degenerative changes were followed by the appearance of macrophages in the epithelium, which were first seen 12h after operation, becoming very frequent at one and 1.5 days, and then decreasing to become rare at 3 and 5 days. The macrophages phagocytosed the degenerated principal cells. The degenerated principal cells were also ingested and digested by undegenerated principal cells and basal cells. The intraepithelial mitotic figures had almost disappeared at 24h but were frequently observed at 2 days and more so at 3 days. They returned to normal numbers at 5 days. The volume of the initial segment was decreased to one third until the third day. The principal cells in this segment became similar in both light-microscopic appearance and ultrastructures to the cells in the next segment 5 days after efferent duct cutting. The changes were localized only in the initial segment.

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Transitory cystic cavities, associated with the subependymal region of the aqueduct in the midbrain of postnatal rats aged 1-15 days, were studied by light and scanning electron microscopy. The walls of these cysts, as observed in scanning electron microscopy, were lined by a dense feltwork of nerve fibres. Two types of cells were identified in the cysts: smaller glioblasts and larger amoeboid microglial cells. The glioblasts were characterized by a smoother cell body with radiating long processes. The amoeboid microglial cells showed blebs and pseudopodia on their surface. They either adhered to the walls or floated freely in the lumen. It is postulated that the formation of the subependymal cysts in the developing brain resulted following the cleavage or breakdown of the nervous tissue due to the expansion of the aqueduct and the brain as a whole. The amoeboid microglial cells in the cysts were probably derived from the extravasated blood monocytes in response to the physical damage ensuing during the formation of the cysts.

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