The relationship between odontoblasts and class II major histocompatibility complex (MHC) antigen-expressing cells in the process of dentinogenesis was studied in rat lower incisors, employing immunohistochemistry using OX6-monoclonal antibody. The dental pulp contained numerous OX6-immunopositive cells that varied in morphology from dendritic to spindle under physiological conditions. Under the electron microscope, these immunopositive cells shared common cytoplasmic features, i. e., multivesicular bodies and characteristic fine tubulovesicular structures in their cytoplasm. At the early stage of dentinogenesis, OX6-immunopositive cells, presumably of the immature type, were located in the subodontoblastic layer. During active dentin formation, the OX6-immunopositive cells increased in number and appeared in the odontoblast layer, associating intimately with fenestrated capillaries situated close to the predentin. These cells showed a dendritic appearance and possessed various sizes of multivesicular bodies and characteristic fine tubulovesicular structures, but never contained typical phagosomes. On the other hand, immunopositive macrophages characterized by typical phagosomes tended to occupy the central portion of the pulp.
The results suggest that most, if not all, OX6-immunopositive cells situated deep in the odontoblast layer are dendritic cells playing a role in the defense system of the dental pulp against antigenic molecules arriving from the circulation via the fenestrated capillaries. The increasing number of OX6-immunopositive or immunonegative macrophages appearing near the incisal end of the tooth is thought to be involved in the elimination of degenerated odontoblasts.

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Subcutaneous injections of glucocorticoids into postnatal rats resulted in a drastic reduction in the number of amoeboid microglial cells in the corpus callosum as shown by their labelling with the monoclonal antibodies of the OX-series, ED1, lectin and rhodamine isothiocynate (RhIc). In rats receiving 2 or 3 injections of glucocorticoids and killed at the age of 4 or 7 days, between 40 to 60% of the callosal amoeboid microglial cells were depleted when compared with the corresponding control animals. The cells that survived the glucocorticoid treatments became ramified, while those in the controls of the same age group remained round or amoeboidic. In rats killed at 2 or 3 weeks of age, the microglia became extremely ramified with a concomitant diminution in their immunostaining, particularly in the glucocorticoid-injected rats. In rats receiving glucocorticoid injections along with RhIc, the RhIcladen amoeboid microglia appeared round and amoeboidic and were intensely stained with OX-42, suggesting their activation and upregulation of complement type 3 receptors when compared with rats receiving only glucocorticoids. Compared with the control, cellular proliferation continued in rats given glucocorticoid injection as indicated by the occurrence of many bromodeoxyuridine-labelled cells in the corpus callosum at the age of 6 days. Ultrastructural studies confirmed the presence of mitotic cells identified as amoeboid microglia because of their labelling with isolectin. A striking ultrastructural feature in glucocorticoids-in-jected rats was the wide occurrence of amoeboid microglial cells that had ingested a variable number of lectinlabelled cells.
It is concluded from this study that the drastic reduction of amoeboid microglia after glucocorticoid injections can be attributed to the suppression of their precursor cells, monocytes. Another possible explanation is the acceleration of their degeneration process, probably greatly enhanced by glucocorticoids; the degenerating amoeboid microglia were readily eliminated by the surviving amoeboid microglial cells through endocytosis. Glucocorticoids also accelerated the maturation process of the persisting amoeboid microglia to become ramified in form.

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This study describes ultrastructural and morphometric changes in the arginine vasopressin (AVP)-like immunoreactive and oxytocin (OT)-like immunoreactive neurons in the hypothalamic paraventricular nuclei (PVN) and supraoptic nuclei (SON) of streptozotocin-induced diabetic rats at 1-12 months post-diabetes. At 1-6 months post diabetes, both AVP-immunoreactive and OT-immunoreactive neuronal somata were hypertrophied in the PVN and SON. These neuronal somata contained highly dilated rough endoplasmic reticulum in the cytoplasm. The reaction product for AVP as well as OT localization was dispersed throughout the cytoplasm and cell nucleus, but not within the nucleolus. Moreover, the reaction product appeared to be studded onto the ribosomes on dilated cisterns of the endoplasmic reticulum. At 9-12 months post-diabetes, both AVP-immunoreactive and OT-immunoreactive dendrites contained dilated endoplasmic reticulum, autophagic vacuoles, lipid bodies, microtubules, membranous bodies and occasionally swollen mitochondria. Labelled hypertrophied axonal profiles containing neurosecretory granules, autophagic vacuoles, membranous bodies and tubulovesicular elements were also observed in the neuropil. Morphometric study showed that both AVP-immunoreactive and OT-immunoreactive neuronal somata of the PVN and SON in the diabetic rats were markedly hypertrophied at all the time intervals examined. It is concluded that the morphometric changes observed represent hyperactivity of both AVP- and OT-immunoreactive neurons, while the concurrent ultrastructural changes observed at later stages may be indicative of degeneration.

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Nerve endings in the canine tracheal muscle were examined by light microscopy after immunohistochemical staining with an antibody against neurofilament protein, and by transmission electron microscopy. The endings were found to consist of accumulations of ramified axon terminals. The endings ranged from 100-400μm in maximal length to 30-80μm in minimal length. Most of the endings were arranged parallel to the smooth muscle strands, with 80-90% located in the membranous wall and densely distributed in the cranial region of the trachea. The endings were covered with a connective tissue sheath that contained fine elastic fibers.
Ultrastructural examination revealed that axon terminals were derived from myelinated axons, and were located in a connective tissue sheath among the smooth muscle cells. Each axon terminal contained large numbers of mitochondria, lysosomes, neurofilaments, glycogen granules and synaptic vesicles. Incomplete coverage by Schwann cells and multiple layers of basal lamina were observed around the axon terminals.
Surgical denervation revealed that the endings were of vagal origin. The access pathway to the endings in about one-third of the cranial region of the trachea appeared to be the cranial laryngeal nerve, while in about two-thirds of the caudal region, this appeared to be the tracheal branches derived from the recurrent laryngeal nerve and/or from the vagosympathetic trunk.

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While Ricinus communis agglutinin 1(RCA-1) can be used as a specific marker to study the development and differentiation of microglial cells in human embryogenesis, little is known about the structural heterogeneity and nature of RCA-1⁺ cells. To analyse the structural peculiarities of RCA-1⁺ cells, we have used primary dissociated cultures of human embryonic brain. These have been used as models for investigating many of the aspects of central nervous system (CNS) HIV infection. We have shown that primary dissociated cultures from human embryos as young as 10 weeks gestation contain RCA-1⁺ cells. The RCA-1⁺ cells exist in two forms, those without (type I) and those with (type II) processes. The former have a poorly developed ultrastructure, while the latter have well developed ultrastructural features, such as rough endoplasmic reticulum with short cisternae, abundant ribosomes, mitochondria, lysosomes and vacuoles. Furthermore, some of these cells with processes have well developed cytoskeletal features. In this paper, the classfication of RCA-1⁺ cells of embryonic human brain is considered and their morphology compared to micro-glia identified in rodent CNS.

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Regions of the visual cortex and the deep layers of the superior colliculus (SC) have been suggested to be functionally linked via an ‘indirect’ pathway through the basal ganglia. The present report demonstrates projections from the striate (area 17) and extrastriate (areas 18 and 18a) visual cortex in Long-Evans hooded rats to the striatum (ST) and SC with anterograde (biocytin) and retrograde (WGA-HRP and fluorescent dyes) tracers. Biocytin injections into each cortical area produced markedly different patterns of labeling in ST and SC. Injections into area 17 resulted in a dense labeling in the superficial layers of SC, with little labeling present in the deep layers of SC or ST. In contrast, injections into area 18a, which produced marked labeling in the deep layers of SC with moderate in the superficial layers, resulted in dense labeling in the caudal two-thirds of the dorsal region of ST; injections into area 18 produced numerous terminals mainly in the deep layers of SC and in the rostral two-thirds of the dorsal aspect of ST. WGA-HRP injections into ST resulted in numerous retrogradely labeled pyramidal neurons in areas 18 and 18a, but only a few labeled neurons were observed in area 17.
Corticostriatal neurons in extrastriate visual cortex were distributed predominantly in layer V, with smaller numbers in layers II and III, whereas corticotectal neurons were located only in layer V of both the striate and extrastriate visual cortex. Although corticostriatal and corticotectal neurons were intermingled in layer V, no double-labeled neurons were observed following injections of different fluorescent dyes into ST and SC. It appears, therefore, that: 1) the major source of visual input to both ST and the deep layers of SC in the rat arises not from the primary visual cortex but from extrastriate visual areas; and that 2) the projections from the extrastriate visual area to ST and SC originate from different populations of corticofugal neurons.

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Neurons in the human visual cortex were demonstrated to possess an intensely negatively charged surface coat which was stained with cationic iron colloid and aldehyde fuchsin.
Digestion with hyaluronidase eliminated both the iron colloid and fuchsin stainings of the coats. Treatment with chondroitinase ABC, heparitinase and keratanase eliminated the iron colloid staining of the coats, but did not interfere with the fuchsin staining.
Electron microscopy of ultrathin sections revealed that the cationic iron particles were preferentially deposited in the perineuronal tissue spaces. These findings indicate that the surface coats consist of sulfated proteoglycans, which, as an extracellular matrix, occupy the perineuronal tissue spaces.
This study further demonstrates that neurons with such surface coats are identical with neurons labeled with lectin Vicia villosa agglutinin. The cell surface glycoproteins reactive to this lectin may not be the structural elements of the sulfated coats since the lectin labeling was not interrupted by the hyaluronidase digestion.

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Intracytoplasmic ciliated cysts were observed in the human oviduct epithelium. Transmission electron microscopy demonstrated the occurrence and fine structure of those cysts, clarifying the process of their opening to the oviduct lumen. When located apically in the epithelial layer, the cists moved upwards and expanded into the oviduct lumen, leaving a thin cytoplasmic layer, until they broke into the oviduct lumen. In contrast, basally-lying cysts did not move but were approached by an invagination of the epithelial surface which extended toward the cell base. The cysts were then broken onto the bottom of the invagination and consequently opened into the oviduct lumen. Although the intracytoplasmic ciliated cysts have previously been considered to be formed by abnormal ciliogenesis, the present study indicates that, at least in the human oviduct, they contribute to the formation of the normal ciliated border of the epithelium.

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The binding site of gurmarin, a peptide inhibiting the sweet-taste sensation, was studied in taste buds in rat circumvallate papillae by means of a histochemical technique. Frozen sections of tongues were incubated with gurmarin conjugated with biotin and thereafter examined with a light microscope. Positive reactivity for the peptide was localized to the taste hairs, the apical projections of taste bud cells. The reaction appeared in about 10% of the circumvallate taste buds examined. As electrophysiological studies indicate that gurmarin suppresses the sweet-taste sensation at the level of reception, the present study suggests that the receptor for sweet taste is located on the taste hairs and, furthermore, is present only in a certain, limited number of the taste buds.

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The localization of vacuolar H⁺-ATPase (V-ATPase) in osteoclasts of rat tibiae was examined immunohistochemically using antibodies to 57kD and 72kD subunits of V-ATPase, with confocal laser scanning microscopy and transmission electron microscopy. The two antibodies showed similar immunoreactivities in osteoclasts. We distinguished three patterns of immunoreactivity in osteoclasts: The first pattern was that immunoreactivity was diffusely detected in cytoplasm of osteoclasts; The second one was that osteoclasts showed intense immunoreactivity in their regions contacting with bone surface; and the last was that little immunoreactivity was seen in osteoclasts. Post-embedding methods with protein A-gold complex revealed that the subunits of V-ATPase were localized not only on the membranes of the ruffled borders of osteoclasts, but also around the Golgi apparatus and accumulated tubular lysosomes.
These findings suggest that: 1) immunoreactive patterns for V-ATPase in osteoclasts reflect the polarity and activity of osteoclasts; and 2) V-ATPase on ruffled borders may be transported through tubular lysosomes.

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