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Search Results: 1 - 10 of 2680 matches for " Daisuke Sakai "
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In medium eta' mass and eta' N interaction based on chiral effective theory
Shuntaro Sakai,Daisuke Jido
Physics , 2013, DOI: 10.1103/PhysRevC.88.064906
Abstract: The in-medium eta' mass and the eta'N interaction are investigated in an effective theory based on the linear realization of the SU(3) chiral symmetry. We find that a large part of the eta' mass is generated by the spontaneous breaking of chiral symmetry through the U_A (1) anomaly. As a consequence of this observation, the eta' mass is reduced in nuclear matter where chiral symmetry is partially restored. In our model, the mass reduction is found to be 80MeV at the saturation density. Estimating the eta' N interaction based on the same effective theory, we find that the eta' N interaction in the scalar channel is attractive sufficiently to form a bound state in the eta' N system with a several MeV binding energy. We discuss the origin of attraction by emphasizing the special role of the sigma meson in the linear sigma model for the mass generation of eta' and N.
The $η'N$ interaction from a chiral effective model and $η'$-$N$ bound state
Shuntaro Sakai,Daisuke Jido
Physics , 2014, DOI: 10.1007/s10751-015-1162-8
Abstract: The $\eta'$ mass reduction in the nuclear medium is expected from the degeneracy of the pseudoscalar-singlet and octet mesons when chiral symmetry is manifest. In this study, we investigate the $\eta'N$ 2body interaction which is the foundation of the in-medium $\eta'$ properties using the linear sigma model as a chiral effective model. The $\eta'N$ interaction in the linear sigma model comes from the scalar meson exchange with U$_A$(1) symmetry effect and is found to be fairly strong attraction. Moreover, the $\eta N$ transition is included in our calculation, and is important for the imaginary part of the $\eta'$-optical potential. The transition amplitude of $\eta'N$ to the $\eta N$ channel is relatively small compared to that of elastic channel. From the analysis of the $\eta'N$ 2body system, we find a $\eta'N$ bound state with the binding energy $12.3-3.3i$MeV. We expect that this strongly attractive two body interaction leads to a deep and attractive optical potential.
In-medium η' mass and η'N interaction in vacuum in the linear sigma model
Shuntaro Sakai,Daisuke Jido
Physics , 2014,
Abstract: We investigate the \eta'N two-body interaction in the context of the \eta' meson mass modification in the nuclear medium. It has been argued in several articles that the masses of \eta' and the other pseudoscalar mesons (\pi, K, \eta) should degenerate in the chiral-symmetric phase. It is expected that the reduction of the mass difference between eta and eta' would take place in the nuclear matter if one assumes that the decrease of the quark condensate at the normal nuclear density occurs with partial restoration of chiral symmetry. At low density, the in-medium self-energy giving the mass modification by the medium effect can be obtained by the \eta'N two-body T matrix. Thus, we also estimate the \eta'N interaction strength in vacuum with the linear sigma model which involves the effect of partial restoration of chiral symmetry. In the view of the linear sigma model, we find that the \eta'N interaction is attractive and generated through the sigma meson exchange.We expect that the interaction is enough strong and for the existence of a bound state of the \eta'N system.
Efficacy of Modified Expansive Open-Door Laminoplasty for Cervical Myelopathy  [PDF]
Eiren Toh, Yukihiro Yamamoto, Daisuke Sakai, Masato Sato, Masahiko Watanabe, Joji Mochida
Surgical Science (SS) , 2012, DOI: 10.4236/ss.2012.312112
Abstract: Objectives: Expansive open-door laminoplasty is used widely for the treatment of cervical spondylosis and Ossification of the Posterior Longitudinal Ligament (OPLL). We have developed a unique modification of the surgical procedure to keep the lamina expanded, with the aim of preventing reclosure of the vertebral arch. To examine the effectiveness of and problems associated with the modified expansive open-door laminoplasty technique developed at our institution by evaluating the surgical outcomes. Methods and Materials: Fifty-six patients (46 men and 10 women) underwent the modified expansive open-door laminoplasty and were followed up for at least 1 year. Thirty-eight had Cervical Spondylotic Myelopathy (CSM) and 18 had OPLL. The patients were 34 to 89 years of age (mean: 60.9 years). The severity of myelopathy was evaluated according to the Japanese Orthopaedic Association’s scoring system. Surgical outcomes were evaluated using Hirabayashi’s system for determining recovery rate. In the radiographic analysis, the following angles were measured before and after surgery: lordosis angle and Range of Motion (ROM) at C2 - C7 on lateral radiographs, and opening angle on computerized tomography (CT). The presence and absence of axial pain and postoperative C5 palsy were also evaluated. Results: The rate of JOA score improvement was about 60%, the lordosis angle observed on lateral radiographs was maintained. ROM decreased after surgery in both the CSM and OPLL groups, and the extent of the decrease was similar to that in previous reports. The opening angle of the lamina was 62°- 65° on post-operative CT. Axial pain was reported by 34% of patients. Conclusions: Our modified procedure produced satisfactory postoperative outcomes based on the clinical data and imaging findings for both CSM and OPLL. The advantage of this procedure is that it avoids potential complications associated with bone grafts or implants.
Synergistic role of c-Myc and ERK1/2 in the mitogenic response to TGFβ-1 in cultured rat nucleus pulposus cells
Tomoko Nakai, Joji Mochida, Daisuke Sakai
Arthritis Research & Therapy , 2008, DOI: 10.1186/ar2567
Abstract: We tested cultured rat nucleus pulposus cells for proliferation and cell cycle distribution under exogenous TGFβ1 stimulation with and without putative pharmaceutical inhibitors. To understand the molecular mechanism, we evaluated the expression levels of key regulatory G1 phase proteins, c-Myc and the cyclin-dependent kinase inhibitors.We found that TGFβ1 promoted proliferation and cell cycle progression while reducing expression of the cyclin-dependent kinase inhibitors p21 and p27, which are downregulators of the cell cycle. Robust c-Myc expression for 2 h and immediate phosphorylation of extra cellular signal regulated kinase (ERK1/2) were detected in cultures when TGFβ1 was added. However, pretreatment with 10058-F4 (an inhibitor of c-Myc transcriptional activity) or PD98059 (an inhibitor of ERK1/2) suppressed c-Myc expression and ERK1/2 phosphorylation, and inhibited cell cycle promotion by TGFβ1.Our experimental results indicate that TGFβ1 promotes cell proliferation and cell cycle progression in rat nucleus pulposus cells and that c-Myc and phosphorylated ERK1/2 play important roles in this mechanism. While the difference between rat and human disc tissues requires future studies using different species, investigation of distinct response in the rat model provides fundamental information to elucidate a specific regulatory pathway of TGFβ1.Transforming growth factor β1 (TGFβ1) is known to be a potent inhibitor of proliferation in most cell types, including keratinocytes [1], endothelial cells [2-4] lymphoid cells [5-7] and mesangial cells [8]. Conversely, TGFβ1 stimulates proliferation in certain mesenchymal cells such as bone marrow derived mesenchymal stem cells (BM-MSCs) [9], chondrocytes [10-12] and cells with osteoblastic phenotypes [13]. However, the exact mechanism of stimulation of cell proliferation by TGFβ1 has not been elucidated.Previous studies suggested that endogenous c-Myc mRNA and protein decrease rapidly when TGFβ1 inhibits cell growth [14-1
Mammalian Neurogenesis Requires Treacle-Plk1 for Precise Control of Spindle Orientation, Mitotic Progression, and Maintenance of Neural Progenitor Cells
Daisuke Sakai,Jill Dixon,Michael J. Dixon,Paul A. Trainor
PLOS Genetics , 2012, DOI: 10.1371/journal.pgen.1002566
Abstract: The cerebral cortex is a specialized region of the brain that processes cognitive, motor, somatosensory, auditory, and visual functions. Its characteristic architecture and size is dependent upon the number of neurons generated during embryogenesis and has been postulated to be governed by symmetric versus asymmetric cell divisions, which mediate the balance between progenitor cell maintenance and neuron differentiation, respectively. The mechanistic importance of spindle orientation remains controversial, hence there is considerable interest in understanding how neural progenitor cell mitosis is controlled during neurogenesis. We discovered that Treacle, which is encoded by the Tcof1 gene, is a novel centrosome- and kinetochore-associated protein that is critical for spindle fidelity and mitotic progression. Tcof1/Treacle loss-of-function disrupts spindle orientation and cell cycle progression, which perturbs the maintenance, proliferation, and localization of neural progenitors during cortical neurogenesis. Consistent with this, Tcof1+/? mice exhibit reduced brain size as a consequence of defects in neural progenitor maintenance. We determined that Treacle elicits its effect via a direct interaction with Polo-like kinase1 (Plk1), and furthermore we discovered novel in vivo roles for Plk1 in governing mitotic progression and spindle orientation in the developing mammalian cortex. Increased asymmetric cell division, however, did not promote increased neuronal differentiation. Collectively our research has therefore identified Treacle and Plk1 as novel in vivo regulators of spindle fidelity, mitotic progression, and proliferation in the maintenance and localization of neural progenitor cells. Together, Treacle and Plk1 are critically required for proper cortical neurogenesis, which has important implications in the regulation of mammalian brain size and the pathogenesis of congenital neurodevelopmental disorders such as microcephaly.
The effects of oxygen tension and antiaging factor Klotho on Wnt signaling in nucleus pulposus cells
Akihiko Hiyama, Fumiyuki Arai, Daisuke Sakai, Katsuya Yokoyama, Joji Mochida
Arthritis Research & Therapy , 2012, DOI: 10.1186/ar3830
Abstract: Rat nucleus pulposus cells were cultured under normoxic (21% O2) or hypoxic (2% O2) conditions, and the expression and promoter activity of Wnt signaling and Klotho were evaluated. The effect of Klotho protein was examined with transfection experiments, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, senescence-associated β-galactosidase staining, and cell-cycle analysis. To determine the methylation status of the Klotho promoter region, bisulfite genomic sequencing analysis was performed. Its relation with the activation of Wnt signaling was assessed. We also examined whether the expression of Klotho could block the effects of pathological Wnt expression in nucleus pulposus cells.Nucleus pulposus cells exhibited increased β-catenin mRNA and protein under the hypoxic condition. Klotho protein was expressed in vivo, and protein and messenger RNA expression decreased under the hypoxic condition. Klotho treatment decreased cell proliferation and induced the quiescence of nucleus pulposus cells. In addition, Klotho treatment inhibited expression of β-catenin gene and protein compared with untreated control cells.These data indicate that Wnt signaling and Klotho form a negative-feedback loop in nucleus pulposus cells. These results suggest that the expression of Klotho is regulated by the balance between upregulation and downregulation of Wnt signaling.Regenerative therapy for intervertebral disc degeneration has been recently reported [1-3]. Cell-based therapies for tissue regeneration offer an attractive alternative to current conservative, surgical, pharmaceutical, or gene-therapy interventions. However, to clarify the mechanism underlying low-back pain, the molecular mechanisms involved in intervertebral disc degeneration must be identified.Wnt/β-catenin (hereafter called Wnt) signaling is thought to be involved in the maintenance and destruction of bone and cartilage. Dysregulation of members of this signaling family has been described in osteoar
η' meson under partial restoration of chiral symmetry in nuclear medium*
Jido Daisuke,Nagahiro Hideko,Hirenzaki Satoru,Sakai Shuntaro
EPJ Web of Conferences , 2012, DOI: 10.1051/epjconf/20123709019
Abstract: We shed light upon the η' mass in nuclear matter in the context of partial restoration of chiral symmetry, pointing out that the UA(1) anomaly effects causes the η'-η mass difference necessarily through the chiral symmetry breaking. As a consequence, it is expected that the η' mass is reduced by order of 100 MeV in nuclear matter where partial restoration of chiral symmetry takes place. The discussion given here is based on Ref. [1]
$η^\prime$ meson under partial restoration of chiral symmetry in nuclear medium
Daisuke Jido,Shuntaro Sakai,Hideko Nagahiro,Satoru Hirenzaki,Natsumi Ikeno
Physics , 2012, DOI: 10.1016/j.nuclphysa.2012.12.097
Abstract: In-medium modification of the eta' mass is discussed in the context of partial restoration of chiral symmetry in nuclear medium. We emphasize that the U_A(1) anomaly effects causes the eta'-eta mass difference necessarily through the chiral symmetry breaking. As a consequence, the eta' mass is expected to be reduced by order of 100 MeV in nuclear matter where about 30% reduction of chiral symmetry takes place. The strong attraction relating to the eta' mass generation eventually implies that there should be also a strong attractive interaction in the scalar channel of the eta'-N two-body system. We find that the attraction can be strong enough to form a bound state.
Head Position of Patients with Right Hemisphere Damage during a Visual Search Task in a Large Field  [PDF]
Ken Nakatani, Shusuke Takahashi, Daisuke Kimura, Masako Notoya, Nobuyuki Sunahara, Takashi Fujita, Minoru Toyama, Shinya Fukunaga, Naoe Mori, Kiyoe Sakai, Shinya Fuwa
World Journal of Neuroscience (WJNS) , 2018, DOI: 10.4236/wjns.2018.82018
Abstract: Spatial neglect syndrome with cerebral lesions is characterized by the ina-bility to orient, report, or respond to relevant visual stimuli contralateral to the lesions. In this study, we investigated the pattern of horizontal visual search in a large space; this search was performed by patients with right hemisphere damage caused by cerebrovascular disease. The neck rotation angle and search time in each increment were continuously recorded during the task, and quantitative data of the measurements were collected. Head position during the visual search task in a large space (%) was then calculated. We set angular bands in increments of 5 degrees from the midline on the left and right sides, and calculated the total search time in each angular band. In patients with unilateral spatial neglect (USN), the search time in the angular band of 5 - 9 on the right side was significantly longer (with USN 16.7%, without USN 4.5%, t = 2.52, df = 16, p < 0.05). Furthermore, in patients with neglect in the leftmost end area in a large space, the search time was significantly shorter in the angular band of 1 - 4 degrees to the left (with neglect 13.1%, without neglect 23.7%, t = 2.13, df = 16, p < 0.05), and tended to be long in the angular band of 5 - 9 to the right. The neck rotation angle and pattern during the search task in a large field deviated slightly to the right, and the search time slightly to the left was short. We believe that these results support the rightward deviation of the search pattern and frame of USN patients.
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