The theee-dimensional structure of the transverse-axial tubular system, sarcoplasmic retculum (SR) and mitochondria in the extracapsular region of the intrafusal muscle fibers of the rat lumbrical muscle was observed by ultra-high-resolution scanning electron microscopy after removal of the cytoplasmic matrix by the osmium-DMSO-osmium procedure.
Nuclear chain fibers possessed thick to moderately sized column-forming mitochondria with occasional I-band branches. The transverse tubules (T-tubules) running at the level of the A-band side of the A-I junction were sandwiched between two large terminal cisternae for most of their length, forming triads. The sarcotubules arising from the terminal cisternae formed single-layered networks at the A-band level, and well developed, double-layered, three-dimensional networks at the I-band level. Nuclear bag₁ fibers possessed slender column-forming mitochondria devoid of I-band branches. The T-tubules were located at the level of the A-I junction. Both the T- and the axial-tubules were occasionally coupled with small terminal cisternae, forming dyads or triads. At the I-band level, the SR was well developed and formed single layered networks, but at the A-band level only a few longitudinally arranged sarcotubules and axial tubules were observed. Nuclear bag₂ fibers contained medium to large diameter columnforming mitochondria without I-band branches. The T-tubules ran at the level of the A-band adjacent to the A-I junction, and were coupled at some intervals with terminal cisternae of various lengths. Swollen, large terminal cisternae were frequently seen. As a rule, the SR formed single-layered networks at the A-band level and double-layered networks at the I-band level. Broad cistern-like and thick, cylindrically shaped elements of SR were frequently seen both at the A-band and I-band levels.
This study indicates that the structure of the SR in the extracapsular region of the chain and bag₁ fibers is similar to that of the SR in the sleeve region. However, the SR of the extracapsular region of bag₂ fibers frequently exhibited swollen terminal cisternae and cisternal SR, both rarely seen in the sleeve region.

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The indirect immunoperoxidase (PAP) method was used on chicken lung specimens from embryos ranging in age from 6 days to hatching, chicks and adult chickens of up to 6 months. The ontogenesis and distribution of neurons and paraneurons containing immunoreactivities for serotonin (5HT), bombesin, vasoactive intestinal polypeptide (VIP), substance P (SP) and galanin were investigated. Serotonin-immunoreactive paraneurons were first detected in the pulmonary mesenchyma of 8-day-old embryos, while in the 12-day-old embryos the following neurons and paraneurons were first detected in their respective locations: serotonin-immunoreactive paraneurons in the bronchial epithelium; VIP- and galanin-immunoreactive ganglionic cells and SP-immunoreactive nerve fibres in the intrapulmonary ganglia.
At hatching, serotonin-immunoreactive paraneurons in the epithelium of the air capillaries and air sacs, and bombesin-immunoreactive paraneurons in the epithelium of the primary bronchus, VIP-, galanin- and SP-immunoreactive nerve fibres in the lamina propria of the primary and secondary bronchi and in the pulmonary septa could also be shown. Some serotonin-immunoreactive small paraneurons were also found in the intrapulmonary ganglia. In the adult specimens, VIP-, galanin- and SP-immunoreactive nerve fibre networks were observed throughout the primary bronchus wall and in the lung septa. In intrapulmonary ganglia, VIP- and galanin-immunoreactive neurons and serotonin-immunoreactive small paraneurons could be more numerously demonstrated. Moreover, bombesin paraneurons occurred in the epithelium of primary and secondary bronchi, and serotonin-immunoreactive paraneurons were found in the epithelia of the bronchi and air sacs and in some pluricellular bodies in the lamina propria of the air sac ostia.

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Apical Periodontitis was surgically induced in the mandibular first molar of rats and chronological changes in the periapical bone tissue were observed by histochemistry and electron microscopy.
On the second postoperative day (Day 2), tartrateresistant acid phosphatase (TRACPase)-positive cells emerged on the bone surface facing the inferior alveolar nerve, whereas alkaline phosphatase (ALPase)-positive cells proliferated on the bone marrow surface of the mandibular canal wall. On Day 3, the active resorption of the mandibular canal wall appeared on the surface facing the inferior alveolar nerve. The bone of the upper wall of the canal was completely resorbed. On Day 4, however, numerous ALPase-positive cells emerged over the bone surface facing the inferior alveolar nerve intermingled with TRACPase-positive cells. On Day 5, repair of the upper wall of the mandibular canal by new bone progressed. Bone formation was also observed on the bone surface facing the inferior alveolar nerve. On Day 6, the upper wall of the mandibular canal was remodeled by the new bone, whereas TRACPase-positive cells had already migrated over the bone surface in the vicinity of ALPase-positive cells. From Days 2 to 5, active trabecular bone formation continued in the bone marrow cavity close to the mandibular canal, while TRACPase-positive cells were found only on Day 6. These demonstrate that inflammatory stimuli activate bone formation coupled with bone resorption, as well as direct trabecular bone formation without a bone resorption phase. A rapid bone turnover in the early stage of apical periodontitis is also suggested.
We conclude that bone defects in apical periodontitis are not the result of sole bone resorption but rather, active bone remodeling.

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Morphological characteristics of TSH-immunoreactive cells (TSH-like cells) in the pars tuberalis (PT) of intact adult male rats were studied by light and electrom microscopic immunocytochemistry. TSH-like cells in the rat PT can be classified into three types by light microscopy: 1) cells diffusely stained thronghout the cytoplasm, 2) diffusely weak stained cells containing a strongly stained spot in the paranuclear region; 3) cells with a strongly stained spot in the paranuclear region without diffuse reaction. We call the latter two cell types “spot cells”. Electron microscopic immunocytochemistry revealed that the latter two cells reacted very strongly in the Golgi apparatus. The spot cells were localized throughout the PT from rostral to caudal extremities as well as the ventral surface area of the pars distalis (PD) which was connected to the PT. The cytoplasm of the TSH-cells in the PD proper was strongly and diffusely stained with anti-TSH serum, while there was no spot-like staining in any cells. The spot cells demonstrated by electron microscopy contained a well developed Golgi apparatus, many microvesicles and a few secretory granules. These immunocytochemical results clearly showed two apparently distinct types of TSH-immunoreactive cells between the PT and PD in the intact adult male rat adenohypophysis. This morphological distinction of TSH-immunoreactive cells suggests functional differences in these cells.

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The ultrastructure of water-clear cells has been described in human hyperplastic parathyroid glands. However, previous studies have failed to demonstrate this type of cell in normal human or other vertebrate parathyroid glands. Upon recently recongnizing water-clear cells in the parathyroid glands of the golden hamster, we intended to examine the occurrence of these cells in other animals. In the present study the parathyroid glands of about one-year-old rabbits were observed by electron microscopy. Water-clear cells containing numerous vacuoles were demonstrated dispersed among the chief cells. The cells were generally situated close to the basal lamina of perivascular space which lay against the capillary vessel and were attached by desmosomes to the chief cells. Irregularly shaped vacuoles in the water-clear cells resembled dilated cisternae of the granular endoplasmic reticulum in the chief cells. Several ribosomes could be seen attached to the membrane of some of the irregularly shaped vacuoles. It is conceivable that the water-clear cells are transformed from the chief cells.

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Light and electron microscopic studies were made on pulpal nerve fibers in mouse lower incisors, typical continuously growing teeth. Serial sections, from the apex of the odontogenic sheath to the incisal edge of the apical foramen, were examined by light microscopy to identify myelinated fibers passing through the apical foramen. The fine structure of the pulpal nerves was examined by electron microscopy at three sites: 1) the level at the incisal edge of the apical foramen; 2) a level 5mm incisal from the apex of the odontogenic sheath; and 3) the level where the incisor comes out of the alveolar bone.
No myelinated fibers were found passing through the apical foramen; they were also lacking at the three levels of the pulp. At level 2, unmyelinated axons were seen in close contact with smooth muscle fibers of arterioles. At level 3, nerve fibers were difficult to distinguish from processes of fibroblasts and odontoblasts. Degenerating axons were present in Schwann cells, and fine unmyelinated axons running through the odontoblast cell layer were seen.
Various types of unmyelinated axons were observed in the apical region (level 1). These axons were classified into 6 types on the basis of their fine structures: Type I, bundles of unmyelinated axons completely or partly ensheathed by Schwann cell cytoplasm (mature type); Type II, bundles of unmyelinated axons in a space formed by a Schwann cell membrane (regenerating type); Type III, bundles of unmyelinated axons ensheathed not by a Schwann cell, but merely by a basal lamina (regenerating type); Type IV, single axons in direct contact with the basal lamina (regenerating or terminal type); Type V, naked, electron-dense axons with many vesicles and mitochondria (growth cone-like type); and Type VI, electron opaque axons, due to loss of axonal organellae (degenerating type). The significance of these structures is discussed in relation to the continuous growth of the rodent incisor.

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Enamel tufts were exposed after decalcification of the enamel matrix and their fine structures and immunocytochemical characteristics were examined. Under the binocular microscope and the scanning electron microscope (SEM), enamel tufts appeared as corrugated ribbon-like structures located on the dentine parallel to the tooth axis. SEM observation disclosed enamel tufts as bundles of well extended tubular structures with cross striations attributable to hypocalcified enamel sheaths. Plate-like structures were observed at the center of enamel tufts, where they ran parallel to the enamel tufts. Under the transmission electron microscope (TEM), the plates of tufts revealed their origin in the superficial layer of the dentine, penetrating the hypercalcified zone adjacent to the dentineenamel (D-E) junction, and then reaching the tuft region. The plates of tufts ran mainly along the enamel sheaths and partially across the prisms in the tuft region. The protein-A-gold technique revealed an intense immunoreactivity for amelogenin over the superficial layer of the dentine, but over the enamel prisms in the tufts nor over the plates of tufts. The immunoreactivity for 13-17kd protein was detected over the filamentous structures closely associated with the enamel sheaths in the enamel tuft. Thus our study disclosed that enamel tufts consist of both well extended hypocalcified enamel prisms and plates of tufts. The major organic component of the enamel tufts is suggested to be 13-17kd protein rather than amelogenin.

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Omeprazole, an inhibitor of gastric acid secretion, was administered to rats at a dosage of 20mg/kg/day for 14 and 35 days, and subsequent changes in subcellular structures of parietal cells were analyzed using morphometry and immunocytochemistry. Plasma gastrin levels were also examined, showing two times higher levels in the experimental groups than in the non-treated control. The volume and surface densities significantly decreased in tubulovesicles of the cells in the experimental rats. In the long term treatment of omeprazole (35 days), the volume density of microvilli on the membranes of secretory canaliculi in the cells also decreased significantly, whereas that of lysosomes clearly increased. By electron microscopy, many dense bodies of various shapes often appeared in the cytoplasm of parietal cells after the omeprazole treatment. Immunocytochemistry revealed that large granular immunodeposits for cathepsin B increase in the epithelial cells of the gastric glands after omeprazole treatment. These results suggest that omeprazole induces quantitatively significant decreases in both tubulovesicles and canalicular microvilli. The decreases in these membrane structures may possibly be ascribed to the degradation of the membrane in lysosomes; the proton pump on the membranes bound irreversibly with omeprazole is believed destined to be degraded in lysosomes.

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The cellular composition and relative frequency of the occurrence of pancreatic endocrine cells were studied immunohistochemically in a primitive eutherian and arboreal folivore, the three-toed sloth, since previous histochemical and ultrastructural studies on the endocrine pancreas of the sloth have detected only a single islet cell type, the A cell.
In the sloth pancreas, four types of endocrine cells immunoreactive for glucagon, insulin, somatostatin and serotonin (5-hydroxytriptamine) were found as reported in the pancreas of human and common experimental mammals, but pancreatic polypeptide-immunoreactive cells were not detected by either avian- or bovine-pancreatic polypeptide antiserum.
The endocrine cells were distributed mainly in the islets and partly also in the exocrine tissue including the pancreatic ducts. Larger or smaller clusters consisting of glucagon- and insulin-immunoreactive cells were also found frequently in the interlobular connective tissue. In the islets, glucagon- and insulin-immunoreactive cells were the most prominent cell type, while somatostatin- and serotonin-immunoreactive cells were sparse. The most striking feature in the sloth pancreas is the high frequency of glucagon-immunoreactive cells, because these cells are by far less in number than insulin-immunoreactive cells in the islets of human and common experimental mammals. This appears to be an intriguing characteristic of the sloth pancreas in a possible relation to the animal's unique metabolic system and the phylogenetical position.

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The distribution of macrophages in the lingual periodontal ligament of rat incisors was surveyed by histochemical and immunohistochemical methods. Numerous macrophages showing intense ACPase reactions were located primarily in the shear zone of the periodontal ligament. Immunostaining with an ED1-monoclonal antibody that recognizes various subpopulations of macrophages revealed plentiful positive cells showing flamelike profiles throughout the periodontal ligament, in addition to regular macrophages associated with sinusoidal blood vessels. A similar distribution of flamelike cells expressing Ia antigens was demonstrable with immunostaining using an OX6-monoclonal antibody. A consecutive staining of sections for ACPase histochemistry followed by immunoreactions for Ia antigens revealed the presence of two types of the flamelike cells in the periodontal ligament: one with and the other without distinct ACPase activity, corresponding to the macrophage and the dendritic cell, respectively. Either type of flamelike cells was located in the bone-related and shear zones, whereas only dendritic cells without ACPase activity were restricted to the tooth-related zone. OX6-immunonegative cells showing ACPase reactions were also found in the periphery of the sinusoidal blood vessels.
Our data are the first to demonstrate the abundance of macrophages and dendritic cells expressing Ia antigens throughout the lingual periodontal ligament of rat incisors. In addition to regular macrophages, an exclusive localization of macrophages with flamelike extensions has been demonstrated in the bone-related and shear zones of the ligament. The region-specific arrangement of macrophages and dendritic cells with various histochemical and immunological features suggests that the periodontal ligament of rat incisor is a useful model for analyzing the process of differentiation of antigen-presenting cells.

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