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Biomedical subjects

M Wakita

Publications and source records attributed to M Wakita.

At least 19 recordsLinked to original sources
PubMed2001

From three-dimensional space vision to prehensile hand movements: the lateral intraparietal area links the area V3A and the anterior intraparietal area in macaques.

The posterior parietal cortex is included in the dorsal cortical visual pathway underlying the three-dimensional (3-D) visual recognition of space and objects. The neurons in the lateral intraparietal area (LIP) respond visually to the three-dimensional objects, whereas those in the anterior intraparietal area (AIP) respond to hand movements to grasp them. LIP receives visual inputs from V3A, whereas AIP projects to the premotor areas; however, it is not known whether the neurons in LIP project to AIP. We herein investigated the connectional substrates that underlie the transformation of three-dimensional vision to prehensile hand movements in the Japanese monkey (Macaca fuscata). After identifying the three-dimensional visually responsive region in the posterior part of LIP by the unit recordings, we injected a bidirectional tracer, wheat germ agglutinin conjugated to horseradish peroxidase, into one of the recording sites. We found that LIP receives neuronal projections from V3A and sends axons to AIP. To confirm our findings, we injected several orthograde tracers into V3A and retrograde tracers into AIP in the same hemispheres. We found that the V3A neurons projecting to LIP terminate in the vicinity of the LIP neurons projecting to AIP. The results suggest that the cortical connections of V3A-LIP-AIP in the lateral bank of the intraparietal sulcus play an important role in the visuomotor transformation for prehensile hand movements.

Animals↗
PubMed2001

The nature and function of mononuclear cells on the resorbed surfaces of bone in the reversal phase during remodeling.

In a reversal phase of bone remodeling many mononuclear cells appear on the resorbed surfaces of bone with characteristic reversal lines as revealed by transmission electron microscopy (TEM). However, these mononuclear cells have been variously hypothesized or reported. The present study examined the TEM features on the resorbed surfaces of three calcified connective tissues, and aimed to clarify the nature and function of the mononuclear cells in a reversal phase. Dentine slices cultured with isolated osteoclasts, human deciduous teeth, and rat mandibles were used in this study. Specimens were fixed, decalcified, and then embedded in Epon 812, and sectioned into 0.1-microm-thick ultrathin sections. The ultrathin sections were stained with uranyl acetate and lead citrate, and then examined by TEM. Many sharply pointed collagen fibrils with striation were observed exposed on the resorbed surfaces of cultured dentine slices, but there were neither cells nor reversal lines. The same features were observed on the root dentine surfaces of human deciduous teeth. Under many mononuclear cells in a reversal phase of remodeling, reversal lines were seen on the resorbed surfaces of rat mandibles, but there were no striated collagen fibrils exposed on the bone surfaces. The alternation of the TEM features on the resorbed surfaces before and after the participation of mononuclear cells in a reversal phase of remodeling suggests the nature and function of these cells: they participate in both degrading the demineralized and disrupted matrix left on the resorbed surfaces and forming reversal lines there.

Animals↗
PubMed2001

A light microscopic study of the attachment mechanism in different kinds of adhesive lines in rat molars.

This study was designed to observe drifting molars of 70-day-old rats by light microscopy, and to elucidate whether there are similar attachment mechanisms at different kinds of adhesive lines in periodontal mineralized tissue of the rat molar region. Three kinds of adhesive lines--cement lines on resorbed alveolar bone, cement lines on resorbed roots, and cemento-dentinal junctions were examined. The two kinds of cement lines showed similar histological and histochemical features, they were proteoglycan-rich and fiber-poor. They appeared to form on the resorbed tissue before principal fiber reattachment. After covering by new bone or by reparative cementum, the cement lines retained the original features. The cemento-dentinal junction showed features very similar to those of the cement lines. Previous studies have suggested that the cemento-dentinal junctions bind the cementum and dentine by adhesion of proteoglycans. Structural similarities suggest that cement lines provide similar links between new bone and resorbed bone and between resorbed root and reparative cementum. In conclusion, this study suggests that there is one attachment mechanism for the different kinds of collagen based hard tissue in the rat molar region.

Animals↗
PubMed2001

Apoptosis and proliferation of myoepithelial cells in atrophic rat submandibular glands.

This study was designed to determine whether apoptosis and proliferation of myoepithelial cells occur in atrophic rat submandibular glands. The excretory duct of the right submandibular gland was doubly ligated with metal clips. The atrophic right submandibular glands removed after 1-28 days of duct ligation were investigated using immunohistochemical double staining for actin as a marker for myoepithelial cells and proliferating cell nuclear antigen (PCNA) as a marker for proliferating cells, double staining for actin immunohistochemistry, nick end-labeling (TUNEL) as a marker for apoptotic cells, and transmission electron microscopy (TEM). A few PCNA- and no TUNEL-positive myoepithelial cells were found in the control submandibular glands taken from animals with no operation. In the experimental glands, PCNA-positive myoepithelial cells were common 2 and 3 days after duct ligation and then decreased in number. TUNEL-positive myoepithelial cells appeared at 2 days and were observed most frequently at 5 days. Apoptotic myoepithelial cells were also identified by TEM. These observations suggest that both apoptosis and proliferation of myoepithelial cells occur, especially in the early phase of atrophy, in the rat submandibular gland.

Actins↗
PubMed2000

Two novel first exons in the prolactin receptor gene are transcribed in a tissue-specific and sexual maturation-dependent manner to encode multiple 5'-truncated transcripts in the testis of the chicken.

Cloning and sequencing of the chicken prolactin receptor (PRLR) gene segment from the transmembrane domain to the box 2 motif revealed the presence of the two testis-specific first exons, TSE-1 and TSE-2, encoding the unique 5'-end sequences of the reported and newly identified multiple 5'-truncated PRLR transcripts containing only the cytoplasmic domain in the testis. TSE-1 was located downstream of the exon encoding the transmembrane domain and TSE-2 presented downstream of the exon encoding the box 1 motif. These findings indicate that the box 1-containing 5'-truncated transcripts are generated by the utilization of TSE-1 as the first exon with distinct splicing donor sites to the box 1-containing exon, and that the utilization of TSE-2 as the first exon and its splicing to the box 2-containing exon results in the generation of the box 1-lacking transcript. Three transcription initiation sites for the box 1-containing 5'-truncated transcripts and two transcription initiation sites for the box 1-lacking transcript were detected by the RNase protection assays. Reverse transcription-polymerase chain reaction analysis showed that the expression levels of all these 5'-truncated PRLR transcripts are simultaneously increased during sexual maturation, accompanying the decrease of the amount of the canonical full-length transcript for PRLR.

Animals↗
PubMed2000

Brain-derived neurotrophic factor expands ocular dominance columns in visual cortex in monocularly deprived and nondeprived kittens but does not in adult cats.

Segregation and stabilization of thalamocortical afferents to eye-specific patches, so-called "ocular dominance (OD) columns," in visual cortex are hypothesized to be based on activity-dependent competition for trophic factors such as brain-derived neurotrophic factor (BDNF) between afferents representing the two eyes during the critical period of postnatal development. To test this hypothesis we observed effects of an intracortical infusion of BDNF on OD columns in monocularly deprived kittens and also compared effects between normal kittens and adult cats. BDNF had a hypertrophic action on afferents irrespective of visual inputs so that it desegregated OD columns in the visual cortex of deprived and normal kittens, but this action was not seen in the adults, substantiating its hypothesized trophic role in plasticity of OD columns in the developing visual cortex.

Animals↗
PubMed2000

Some osteocytes released from their lacunae are embedded again in the bone and not engulfed by osteoclasts during bone remodeling.

It is generally accepted that osteocytes derive from osteoblasts that have secreted the bone around themselves. Osteocytes are cells embedded in the lacunae in the bone, and they are characteristically in contact with other cells by many slender cytoplasmic processes in canaliculi. During bone remodeling, many osteocytes in the bone are released from their lacunae by osteoclasts; however it remains unclear what happens to these released osteocytes. The cortical bone of the rat mandibular body was used in this study. Mandibles were fixed, decalcified, and then embedded in Epon 812. Specimens were sectioned in the frontal direction into serial 0.5 microm-thick semithin or 0.1 microm-thick ultrathin sections, and then examined by light or transmission electron microscopy. Cells that fitted in the osteocytic lacunae with canaliculi extending to the bone were identified as osteocytes in this study. Among many osteocytes released by osteoclasts in cutting cones, there were osteocytes half-released from their lacunae. These cells fitted in their lacunae with canaliculi extending to the bone and showed developed cell organelles in the cytoplasm. In closing cones, many osteocytes were situated in the bone away from cement lines; however, there were half-embedded osteocytes in the bone formed on cement lines. These cells fitted in their lacunae with canaliculi extending to the bone formed below cement lines and showed developed cell organelles in the cytoplasm. These results show that half-embedded osteocytes in closing cones derive from half-released osteocytes in cutting cones. Osteocytes encircled by osteoclasts were sometimes observed on one section, but serial sections showed that these osteocytes fitted in their remaining lacunae in the bone on other sections. This shows that not all osteocytes released from their lacunae are engulfed by osteoclasts. Consequently, the present results suggests that some osteocytes released from their lacunae are embedded again in the bone and not engulfed by osteoclasts during bone remodeling.

Animals↗
PubMed2000

Apoptosis and mitosis of parenchymal cells in the duct-ligated rat submandibular gland.

Apoptosis and proliferation of parenchymal cells during atrophy of rat submandibular gland induced by double duct ligation were investigated using immunohistochemistry for proliferating cell nuclear antigen (PCNA), terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-digoxigenin nick end labelling (TUNEL) and transmission electron microscopy (TEM). At 2 and 3 days after ligation, increased PCNA positive cells and mitoses were seen in ducts; thereafter PCNA positive cells decreased in number. At 3 and 4 days, the acinar cell population rapidly decreased, with many remaining TUNEL positive acinar cells. During this period, TEM showed typical apoptotic acinar cells that were phagocytosed by adjacent acinar cells or intraepithelial macrophages. After 7 days, most acinar cells had disappeared, leaving prominent residual ducts; a few acinar cells remained, especially at the lobule periphery. Submandibular gland duct ligation thus induced marked depletion of acinar cell by apoptosis and a concurrent short-lived cycle of duct cell proliferation.

Animals↗
PubMed2000

Ultrastructural study of the root dentine surface resuming resorption on human deciduous teeth.

Resorption of deciduous teeth is not continuous, but alternates with periods of repair or rest. Dentine surfaces in periods of rest or repair resume resorption by odontoclasts during physiological root resorption of the deciduous teeth. However, no observations of such dentine surfaces have been shown. The characteristic feature of the dentine surfaces resuming resorption remains unknown. Tartrate-resistant acid phosphatase activity (TRAP) was detected on human deciduous teeth. The root resorbing surfaces on these teeth were photographed with a whole-mount light microscope, and the photographed areas were serially sectioned into 0.5 micron semithin sections. Preodontoclasts and odontoclasts were three-dimensionally reconstructed. On root resorbing surfaces, areas with small scattered TRAP-positive cells were observed among areas with many TRAP-positive resorbing odontoclasts and TRAP-negative areas. The sections showed that areas with small scattered TRAP-positive cells have features similar to those of TRAP-negative areas, but there were three kinds of characteristic TRAP-positive cells: preodontoclasts, odontoclasts forming small lacunae, and preodontoclasts, and odontoclasts with cytoplasmic processes extending to the dentine surface, which is covered with cells. These results suggest that the areas with small scattered TRAP-positive cells could be at the stage of resuming resorption, and show that the presence of preodontoclasts and odontoclasts with cytoplasmic processes extending to the covered dentine surface is a characteristic feature of the dentine surface at this stage.

Acid Phosphatase↗
PubMed2000

The structure of the cemento-dentinal junction in rat molars.

The cemento-dentinal junction was observed in the acellular and cellular cementum of rat molars by light and scanning electron microscopy. Scanning electron microscopy, combined with NaOH maceration, was used to observe the fibrous architecture directly in this region. Light microscopy revealed that the cemento-dentinal junction contains fewer collagen fibrils and more proteoglycans than the cementum and dentin. Scanning electron microscopy also showed that fibril intermingling is found only in some regions of the fibril-poor junction in macerated specimens. Prolonged maceration breaks down the cemento-dentinal junction in spite of the fibril intermingling. Only macerated specimens showed detachment here. It was established that NaOH maceration removes interfibrillar substances effectively, and does not damage the fibril structure or architecture. This suggests that the adhesion of proteoglycans is more important than fibril intermingling for preserving the cemento-dentinal attachment in the rat molar.

Animals↗
PubMed2000

Light and electron microscopic study of the initial attachment of principal fibers to the alveolar bone surface in rat molars.

This study was designed to observe the principal fibers and alveolar bone in various developmental stages in rat molars using light and transmission electron microscopy and to elucidate the mechanism of initial principal fiber attachment to the alveolar bone surface. Maxillary alveolar bone between the 2nd and 3rd molars of 20- and 25-day-old rats was used. A proteoglycan-rich, fiber-poor, and electron dense layer formed on the alveolar bone surface before the principal fiber organization. This layer was not seen before principal fibers had started to develop. Principal fibers first contacted and then became embedded in this layer. With further development, new bone deposited on this layer and around already attached principal fibers. These findings suggest that this electron dense, proteoglycan-rich layer may act as an adhesive factor to mediate the initial attachment of principal fibers to the alveolar bone surface.

Alveolar Process↗
PubMed1999

cDNA cloning and developmental alterations in gene expression of the two Pit-1/GHF-1 transcription factors in the chicken pituitary.

Pit-1/GHF-1 (Pit-1) transcription factors promote the gene expressions for growth hormone (GH), prolactin (PRL), and the beta chain of thyroid-stimulating hormone in vertebrate pituitary glands. The present study analyzed the nature of chicken Pit-1s (cPit-1s) and their developmental expressions in the pituitary. Chicken pituitary expressed two cPit-1 mRNAs encoding cPit-1alpha and cPit-1gamma composed of 335 and 327 amino acid residues, respectively. They possessed different N-terminal regions and the common C-terminal regions containing a POU-specific domain and a POU homeodomain. Northern blot analysis revealed the pituitary-specific expressions of these Pit-1 mRNAs, and the Pit-1alpha mRNA expressions were two to three times higher than those for Pit-1gamma in both cephalic and caudal lobes of the pituitary. The cPit-1alpha and gamma mRNA expressions simultaneously increased after hatching until 4 weeks and then slightly decreased at 5 weeks. Similar gene expression profiles were observed for GH and PRL during the posthatch developmental period.

Amino Acid Sequence↗
PubMed1999

Changing myoepithelial cell distribution during regeneration of rat parotid glands.

The distribution of the myoepithelial cells during regeneration of the rat parotid gland after atrophy induced by one week of parotid duct ligation was investigated by immunohistochemistry for actin and transmission electron microscopy (TEM). Immunohistochemically, residual ducts were surrounded by actin-positive cells when clips were removed from the duct. Three days later, most of the newly formed acini originating from the residual ducts were also embraced by actin-positive cells. After 10 days, actin-positivity tended to be seen as dots around acini that decreased in number day by day. On day 21 actin-positive cells mainly surrounded intercalated ducts with only a few positive reactions identified at the acinar periphery. Electron microscopically, residual ducts and newly formed acini were peripherally embraced by myoepithelial cells before day 5. After day 7, shift of myoepithelial cells from the periphery of acini to the duct-acinar junctional region was identified. Then few myoepithelial cells were identified at the periphery of acini. These observations indicate that myoepithelial cells migrate from the acinar periphery to the duct-acinar junctional region during rat parotid regeneration, and that such behaviour is closely related to that seen during rat parotid development.

Actins↗
PubMed1999

The structure and function of the cemento-dentinal junction in human teeth.

The structure and function of the cemento-dentinal junction were studied in human molars by light and electron microscopy. The cemento-dentinal junction was an approximately 1-3-micron-thick layer full of proteoglycans with mucopolysaccharides but containing fewer collagen fibrils than the root dentin and cementum. In places, cemental fibrils crossed the cemento-dentinal junction. These fibrils appeared to intermingle with dentinal fibrils. By enzymatic treatment of decalcified specimen with hyaluronidase and trypsin, the cemento-dentinal junction decreased or lost staining affinity to toluidine blue. Prolonged treatment caused the separation of cementum from the root dentin during routine histological processes. These data suggest that the adhesion of proteoglycans is more important than the intermingling of dentinal and cemental fibrils for the cemento-dentinal attachment.

Adolescent↗
PubMed1998

Constitutive expression of a heterologous Eubacterium ruminantium xylanase gene (xynA) in Butyrivibrio fibrisolvens.

An Eubacterium ruminantium xylanase gene (xynA) was inserted into pYK4, a shuttle vector replicable in both Escherichia coli and Butyrivibrio fibrisolvens, and the resultant chimeric plasmid (pYK4XT) was electroporated into B. fibrisolvens OB156C in an attempt to obtain a more xylanolytic B. fibrisolvens. Electrotransformants were screened by the development of erythromycin resistance, followed by an activity staining and Southern hybridization. The presence of mRNA from xynA in the transformant, B. fibrisolvens NO4, was confirmed by Northern hybridization. Xylanase activity of the transformant NO4 was apparently enhanced regardless of carbon sources in the medium. When grown on glucose or cellobiose. NO4 had approximately 5-6 times higher intracellular activity than the parent OB156C on a culture volume basis as well as protein basis. The transformant showed extracellular xylanase activity much higher (between 7- and 10(4)-fold) than the parent. Transformant NO4 recorded the highest activity when grown on xylan. Most (> 90%) of the activity was extracellular. The extracellular activity was 2-fold greater in NO4. These findings indicate that the introduced xynA was expressed constitutively and the xylanase protein was exported into the culture supernatant. Growth of NO4 on glucose was similar to that of OB156C, which suggests little extra load for plasmid maintenance and foreign xylanase production in the transformant. The plasmid pYK4XT was maintained stably in the transformant for more than 100 generations.

Animals↗
PubMed1998

Increase in odontoclast nuclei number by cell fusion: a three-dimensional reconstruction of cell fusion of human odontoclasts.

Osteoclasts and odontoclasts are known to increase their nuclear number by fusion of mononuclear precursors. However, the pattern of fusion remains morphologically unclear. One lower right deciduous canine of an 8-year-old male was investigated. Tartrate-resistant acid phosphatase activity (TRAP) positive cells on the resorbing surface of the tooth were serially sectioned into 0.5 microm-thick semithin sections. The sections were photographed, and cells possessing a light microscopic brush border facing a resorptive lacuna were identified as odontoclasts. Fourteen odontoclasts appearing as a continuous figure of cellular membrane between cells on one section were three-dimensionally reconstructed using NIKON COSMOZONE 2SA. A criterion for fusion was established in this study, requiring that there must be two or more nucleated cells which contacted each other at one site only in the three-dimensional reconstruction. Among 14 reconstructed cells, 10 odontoclasts satisfied the criterion for fusion. The observations of the three-dimensional structures of these odontoclasts showed that mononuclear and multinucleated odontoclasts participated in fusion. Cell fusion occurred between resorbing odontoclasts and cells not forming lacunae, and between resorbing odontoclasts. A case of odontoclastic fusion among three cells was also observed. The results establish that fusion resulting in multinucleation occurred among various odontoclasts with different numbers of nuclei including mononuclear odontoclasts.

Cell Fusion↗
PubMed1998

The structure and function of periodontal ligament cells in acellular cementum in rat molars.

To elucidate the structure and function of periodontal ligament cells at the periodontal ligament-cementum interface in advanced acellular cementogenesis, the cervical regions of molars in rats aged 6 weeks were observed by light and electron microscopy. The light and transmission electron microscopy showed the periodontal ligament cells to be elongated between dense, well-developed principal fibers. The transmission and scanning electron microscopy showed that these cells extended wing-like projections from the lateral surface, forming cylindrical compartments surrounding the principal fibers. In addition, finger-like projections extended toward the cementum from the cementum-facing ends. The main results suggest the following: at the periodontal ligament-cementum interface, the periodontal ligament cells maintain the architecture of the principal fibers by means of extracellular compartments. The arrangement of finger-like projections results in the formation of acellular cementum containing only Sharpey's fibers as a fibrous component.

Animals↗