Scanning electron microscopic observations of the periodontal ligament fibers and cells in rat molar teeth.

The periodontal ligament of rat molar teeth was observed with scanning electron microscopy (SEM) using two different methods: NaOH maceration and KOH-collagenase treatments. Rat jaws with molar teeth were fixed, demineralized with 10% EDTA, and cut into several pieces. After maceration with 5% NaOH for 5 days at room temperature, the cellular elements were completely removed and the periodontal ligament fibers appeared as bundles of collagen fibrils. The fibers branched and anastomosed but did not spread fibrils randomly. In some regions near the alveolar bone, collagen fibrils circularly binding the fibers were found. When treated with 30% KOH for 7 to 10 minutes at 60 degrees C and with 0.1% collagenase, the periodontal ligament fibers were removed and the cells appeared as spindle and stellate shapes, and combined with the irregular cell processes of each other. Thus, the interaction between the periodontal ligament fibers and cells were three-dimensionally visualized by using the two different methods.     

Scanning electron microscopic surface morphology of isolated hepatocytes from normal and premalignant rat liver.

Scanning electron microscopy was performed on hepatocytes isolated after collagenase perfusion of livers from rats fed 2-acetylaminofluorene (AAF) in the diet for 6--8 weeks and on hepatocytes from control rats. The premalignant AAF-cells showed a greater variation in cell size and shape. They also exhibited a reduced number of microvilli and more blebs and other protrusions on the surface than hepatocytes from control animals.     

Scanning electron microscopic observations of normal and regenerating nerve roots in the cat

The surface morphology of normal and regenerated nerve roots was studied using correlated scanning and transmission electron microscopic methods. Nerve roots of the cauda equina were either cut and rejoined or crossed from a segment above to a segment below. Good regeneration was observed in both experimental procedures. The regenerated nerve root sheath had alterations in surface structure created by extensive growth of collagen. Despite this collagen formation, regenerated axons crossed the anastomotic site with relative ease. Surface features of the regenerated axons were similar in appearance to those of the normal axon. Schwann cells were easily recognized, as were the collagen fibers of the endoneurium, although the endoneurium was more prominent and occupied more of the interaxonal space. Macrophages were identified as round structures with a laminated surface or as a honeycomb structure. Internal features of the regenerating axons were more difficult to identify, but mitochondria and a fibrous network were observed. These studies have demonstrated the application of scanning electron microscopic methods to visualize surface structures and cells in regenerated nerve roots.     

Scanning electron microscopic study of fourDiphyllobothrium species

Three-dimensional observation was carried out on plerocercoids and adults ofDiphyllobothrium dendriticum, D. ditremum, D. latum, andD. vogeli using scanning electron microscopy. The species-specific differences between plerocercoids were recognized in the shapes of the whole body, scolex, and bothrium and the wrinkle pattern on the body surface. The differences between adult worms were also observed in the shapes of the scolex, neck, and genital papillae around the genital pore and the pattern on the egg surface. The significance of species specificity in the three-dimensional morphology of diphyllobothriid cestodes is briefly discussed.     

Scanning electron microscopic study of follicular lymphoma

Nine cases of follicular lymphoma were studied by scanning electron microscopy. The morphological findings by this method emphasizes the heterogeneity of the cellular composition of the follicles, even in the cases not labelled as mixed type, and the degree to which the anatomy of a normal secondary follicle is mimicked. Large nonlymphoid cells, presumably dendritic, are present in the follicles. There are no differences in the surface features of the follicular and interfollicular lymphoid cells.     

Scanning electron microscopic determination of quantitative parameters of villi in the rat jejunum

In rat jejunum, the number of epithelial cells per villus and the villus surface area were measured directly on the scanning electron micrograph. The villus height and the number of epithelial cells of the same villus were measured on the histological sections under a light microscope. Both the number of epithelial cells per villus and the villus surface area correlated well with the villus height and with the number of epithelial cells per villus sections. In the normal rat jejunum, the approximate values of the number of epithelial cells per villus surface and villus surface area may be estimated from the villus height or the number of epithelial cells per villus section.     

Scanning electron microscopic examination of reversible hyperplasia of the rat urinary bladder.

Urinary bladder damage caused by surgical incision, freeze-ulceration, or formalin instillation in male Fischer 344 rats was studied by light and scanning electron microscopy. The first two methods resulted in focal ulceration of the urinary bladder; the last induced diffuse mucosal damage. With each method, the damage was followed by regenerative hyperplasia and repair, the bladder mucosa returning to normal in 3-4 weeks. Epithelial cells in the hyperplastic areas had ropy microridges and uniform short microvilli on their luminal surfaces as observed by scanning electron microscopy. When the hyperplasia was marked, with nodular and papillary formation, occasional epithelial cells had pleomorphic microvilli on their surfaces. Rats treated either by surgical incision or freeze-ulceration had normal bladders after a 2-year observation period. Combined with results from previous experiments, pleomorphic microvilli are not a marker of neoplasia or irreversibility but appear with marked or prolonged mucosal proliferation even if reversible.     

Scanning electron microscopic studies of reticular framework in the rat mesenteric lymph node

Background: The reticular framework in the lymph node has in the past been studied mainly by light microscopy of silver-impregnated specimens. The aim of the present study is to understand three-dimensionally the ultrastructure and organization of the reticular framework better than before. Methods: The mesenteric lymph nodes of the rat were prepared either an alkali-water maceration method or a conventional method and were observed in a scanning electron microscope (SEM). Results: The SEM study of alkali-water macerated tissues visualized directly the reticular fiber network in the lymph node. The reticular fibers consisted of thin bundles of collagem fibrils. They were continuous with the collagen fibriliar sheaths of blood vessels and lymphatic sinuses as well as with the fibrous capusule, thus acting as a skeleton of the lymph node. The arrangement of the reticulum was variable, depending on individual compartments. The SEM study of conventionally treated tissues, on the other hand, clarified the shape of reticular cells and their relationship with the reticular fibers. The sinus reticular cells connected with the sinus lining cells but separated from the parenchymal reticular cells, indicating that the former two originate from lymphatic endothelial cells. The parenchymal reticular cells varied in shape depending on their locations but essentially shared features with fibroblasts. Conclusions: The arrangements of the reticular fibers in the parenchyma were closely related to the associated reticular cells, showing the possibility that the reticular cells maintain the shape of the reticular framework suitable for each compartment of the lymph node. © 1995 Wiley-Liss, Inc.     

Scanning and transmission electron microscopic study of visceral and parietal peritoneal regions in the rat

The visceral peritoneum of intraabdominal organs (spleen, stomach, liver, small intestine), omentum majus and the parietal peritoneum of the anterior abdominal wall and the diaphragm were studied in adult Wistar rats by combined scanning and transmission electron microscopy (SEM, TEM). In general, the peritoneal surface consisted of a mesothelium composed of cubic, flat or intermediate cell types delimited by a basal lamina. Cubic mesothelial cells predominated in parenchymal organs (spleen, liver) and were characterized by prominent and indentated nuclei, a cytoplasm richly supplied with organelles, a dense microvillous coat, basal invaginations and elaborate intercellular contacts. Flat mesothelial cells were observed in the intestinal, omental and parietal peritoneum (tendinous diaphragm, abdominal wall) and showed elongated nuclei, scant cytoplasm, a poorly developed organelle apparatus and sparsely distributed microvilli. An intermediate mesothelial cell type was described within the gastric peritoneum characterized by a central cytoplasmic protrusion at the nuclear region containing most of the cytoplasmic organelles and by thin finger-like cytoplasmic processes. The submesothelial connective tissue layer was composed of collagen fiber bundles, fibroblasts and free cells (macrophages, granulocytes, mast cells) and contained blood and lymphatic vessels. In the spleen, elastic fibers formed a membranous structure with intercalated smooth muscle cells. Mesothelial openings were observed as tunnel-like invaginations within the hepatic peritoneum and as clusters of peritoneal stomata within the parietal peritoneum of the anterior abdominal wall and the muscular diaphragm. The round or oval openings of the peritoneal stomata were frequently occluded by overlapping adjacent mesothelial cells and their microvillous coat or obstructed by cellular material. At the side of the peritoneal stomata the mesothelial cell layer was interrupted to allow a direct access to the underlying submesothelial lymphatic system. The mesothelium and lymphatic endothelium shared a common basal lamina. The endothelial cells were discontinuous and displayed valve-like plasmalemmatic interdigitations facilitating an intercellular transport of fluids and corpuscular elements from the peritoneal cavity to the submesothelial lymphatic lacunae. The findings underline the morphological heterogeneity of the peritoneum in visceral and parietal regions, suggesting different functional implications, and further support the presence of extra-diaphragmatic peritoneal stomata.     

Immunohistochemical and electron microscopic characterization of brush cells of the rat cecum

Brush cells (BCs) are relatively rare cells that are sparsely distributed throughout the mammalian digestive and respiratory systems. BCs have been identified in the rodent large intestine, but these cells have not been characterized by immunocytochemistry or electron microscopy. We previously demonstrated that rat bile duct BCs had strong immunoreactivity for six proteins that function in HCO(3)(-) secretion and thus assumed that BCs secrete NaHCO(3). It is well known that the gastrointestinal (GI) tract secretes NaHCO(3), but it is not known whether BCs of the GI tract also express proteins related to HCO(3)(-) secretion. Thus, in the present study, using double immunostaining for cytokeratin 18, a specific marker for BCs, we investigated protein expression in BCs from the rodent GI tract. We show that BCs from the GI tract express six proteins related to HCO(3)(-) secretion: cystic fibrosis transmembrane conductance regulator (CFTR), Cl(-)/HCO(3)(-) exchanger, Na(+)/HCO(3)(-) cotransporter, carbonic anhydrase II, Na(+)/H(+) exchanger (NHE) 1, and NHE3. These results suggest that BCs from the GI tract secrete NaHCO(3). In addition, we examined BCs from the rat cecum using electron microscopy (EM). Transmission EM (TEM) showed that BCs have long microvilli, a well-developed tubulovesicular system, and an abundant cytoskeleton. Scanning EM revealed that BCs were scattered on the luminal surface of the cecum and had numerous long microvilli.     

Scanning electron microscopic study of spinal arachnoid plaques

Calcified or ossified plaques within the spinal arachnoid membranes are often reported at autopsy and are occasionally incriminated as the cause of neurological symptoms in patients undergoing surgery. Histological studies of plaques have been done, but to our knowledge no studies using the scanning electron microscope (SEM) have been reported. In this study, portions of the spinal cord with plaques were removed from adult human cadavers in the dissecting laboratory and processed for SEM and energy-dispersive x-ray analysis (EDAX). The surfaces of the plaques appeared to be fibrous in some areas, studded with irregularly shaped projections or nodules in others, and smooth in yet other areas. Cells were seen in lacunae-like depressions on the surfaces of some plaques and EDAX revealed the presence of calcium on and near the cells. In some areas calcium and phosphorus were both detected, but not in the ratios seen in bone. No calcium was seen on smooth or fibrous areas. It is suggested that the plaques sampled in this study were composed largely of fibrous tissue encrusted in some areas with calcium salts. There was no evidence that any of the plaques contained bone.     

Scanning electron microscopic studies of the vascular smooth muscle cells and pericytes in the rat heart

The cytoarchitecture of smooth muscle cells and pericytes in the rat cardiac vessels was studied by scanning electron microscopy after the removal of connective tissue matrices using a modified KOH-collagenase digestion method. The initial stem of the coronary arteries had groups of smooth muscle cells which ran in various directions on the outermost layer of the media. Although smooth muscle cells in coronary arteries of more than 100 microm in the outer diameter were arranged in a rough circle around the vessel axis, oblique and/or longitudinal muscle bundles were often present in the medio-adventitial border of the vessels. The presence of irregularly oriented muscular bundles is probably connected with resistance against the stretching force induced by the beating of the heart. As the vessel size decreased toward the periphery, almost all of the smooth muscle cells became spindle-shaped with several tiny processes and ran circularly or helicaly to the vessel axis. In the precapillary arterioles (6-12 microm), smooth muscle cells acquired various cytoplasmic processes which helicaly surrounded endothelial cells. Unmyelinated nerves were often associated with arterioles. Blood capillaries were morphologically divided into three segments: arterial capillaries which had pericytes with wide and circularly oriented processes, true capillaries whose pericytes extended long and thin primary processes bilaterally along the vessel axis, and venous capillaries surrounded irregularly and loosely by wide pericytic processes. The stellate pericytes in the postcapillary venules (10-30 microm) gradually changed into flat tape-like smooth muscle cells, which ran circularly in the collecting venules and veins (30-200 microm). The large collecting veins were finally overwhelmed by superficial thin layer of the myocardium, their own smooth muscle cells being very sparse. This suggests that large veins have poor ability to contract by themselves but are influenced by the surrounding myocardial cells.     

Scanning electron microscopic study of the human auditory ossicles

The human mallei, incudes and stapedes from 34 cadavers were examined using scanning electron microscope (SEM) to compare the bone surface type among different regions of auditory ossicles for males and females. On the malleus of both males and females, almost all of the surfaces showed a smooth fibrous appearance, characteristic of resting surface. Limited bone-forming or resorbing surfaces were identified on the malleus. As compared with the malleus, the percentage area of the resorbing surface and the vascular canal openings were higher on the incus and stapes, especially on the long process (Crus longum) of the incus and the neck of the stapes for both males and females. The percentage area occupied by the resorbing surface of the long process of the incus and the neck of the stapes correlated with that of the vascular canal openings. We consider that the malleus maintained the stable condition, while the long process of the incus and the neck of the stapes demonstrated marked bone resorption. We suppose that the bone erosion may be related to the vascularization in these regions. Though the percentage area of the resorbing surface and the vascular canal openings had the tendency to be high in females, we did not find any significant differences between the males and females. There was no significant correlation between the age and the area of resorbing surface or vascular canal openings.     

Scanning electron microscopic studies on the subepithelial tissue of the gastrointestinal mucosa of the rat

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 1-5 microns 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.     

Cytoarchitecture of the normal rat olfactory epithelium: light and scanning electron microscopic studies

The three-dimensional cytoarchitecture of the normal rat olfactory epithelium was examined by scanning electron microscopy (SEM) of KOH digested tissues as well as by light and transmission electron microscopy of plastic sections. Observations specimens from the lateral side of the olfactory epithelium allowed identification of four cell types by their surface structure: olfactory neurons, supporting cells, basal cells, and duct cells of the Bowman's gland. The olfactory neurons were characterized by the presence of a thick apical process (i.e., dendrite) and a thin basal process (i.e., axon). These olfactory neurons tended to be aligned along the vertical axis of the epithelium. Immature olfactory neurons were present at the basal part of the epithelium and had a pear-shaped cell body with a thin and long axon and a short dendrite which failed to reach the epithelial surface. Supporting cells were roughly columnar in shape and occupied the full length of the epithelium. They became thinner in the basal two thirds of their length but had branched foot processes spreading on the basal surface of the epithelium. Basal cells located in the basal epithelial region were oval, round or cuboidal and present among the foot processes of the supporting cells. The ducts of the Bowman's gland entered the epithelium from the lamina propria and took straight, perpendicular courses within the epithelium. These intraepithelial ducts were composed of several slender cells. The acinar cells are sometimes present in the epithelium and appeared as a globular bulge of the duct at the basal part of the epithelium. SEM observation of the basal surface of the olfactory epithelium also clearly showed that axon bundles were surrounded by the sheet-like processes of Schwann cells, the investment being found at the base of the epithelium just before axon bundles leave the epithelium.