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Biomedical subjects

K Yamada

Publications and source records attributed to K Yamada.

At least 37 records · Page 2Linked to original sources
PubMed2005

Thermodynamic properties in the approach to the quantum critical point of the spin-ladder material Na2Co2(C2O4)3(H2O)2.

Magnetic susceptibility and heat capacity measurements as a function of temperature on a single-crystal sample of a spin-ladder material, Na2Co2(C2O4)3(H2O)2, are reported. Principal susceptibilities, parallel and perpendicular to the ladder direction, respectively, show broad maxima around 22 and 17 K. Both susceptibilities decay exponentially down to about 5 K and thereafter they are essentially independent of temperature. These findings amount to a signature of a quantum phase transition from a spin-liquid to Néel ordered state previously predicted theoretically. No anomaly is found in the heat capacity around the transition temperature.

Journal Article↗
PubMed2005

Direct observation of a nonmonotonic dx2-y2- wave superconducting gap in the electron-doped high-Tc superconductor Pr0.89LaCe0.11CuO4.

We performed high-resolution angle-resolved photoemission spectroscopy on electron-doped high-Tc superconductor Pr0.89LaCe0.11CuO4 to study the anisotropy of the superconducting gap. The observed momentum dependence is basically consistent with the dx2-y2- wave symmetry, but obviously deviates from the monotonic dx2-y2- gap function. The maximum gap is observed not at the zone boundary, but at the hot spot where the antiferromagnetic spin fluctuation strongly couples to the electrons on the Fermi surface. The present experimental results suggest the spin-mediated pairing mechanism in electron-doped high-Tc superconductors.

Journal Article↗
PubMed2005

Momentum dependence of charge excitations in the electron-doped superconductor Nd1.85 Ce0.15 CuO4: a resonant inelastic x-ray scattering study.

We report a resonant inelastic x-ray scattering (RIXS) study of charge excitations in the electron-doped high-T(c) superconductor Nd1.85 Ce0.15 CuO4. The intraband and interband excitations across the Fermi energy are separated for the first time by tuning the experimental conditions properly to measure charge excitations at low energy. A dispersion relation with q-dependent width emerges clearly in the intraband excitation, while the intensity of the interband excitation is concentrated around 2 eV near the zone center. The experimental results are consistent with theoretical calculation of the RIXS spectra based on the Hubbard model.

Journal Article↗
PubMed2005

Expression levels of Rab2, a G protein, and Bag-1, a Bcl-2 binding protein are controlled by withdrawal of nicotine from cultured pheochromocytoma PC12 cells.

We previously reported that nicotine withdrawal up-regulates transcription of some immediately early genes (IEGs), c-fos (Ichino et al., 1999) and egr1, nur77 (Ichino et al., 2002) in cultures of pheochromocytoma PC12 cells, which are of neuronal lineage. In the present study we aimed at further elucidating the effects of nicotine withdrawal on the expression of the genes downstream of IEGs. We examined the changes in the protein levels of 2 GTP-binding proteins, Rab2 (Ras-related protein) and Rac1. PC12 cells were cultured in the presence of nicotine for 24 hours, and then the nicotine was removed from the medium. The protein level of Rab2 was low in the presence of nicotine, but was rapidly increased after nicotine withdrawal. In contrast, that of Rac1 did not change after the withdrawal. Considering the neuroprotective effect of nicotine, we also examined the level of Bag-1 protein, which is a binding protein for Bcl-2, an anti-apoptotic factor, and found a slight increase in the gene expression of Bag-1 following nicotine withdrawal. Among 56-kDa, 50-kDa, and 36-kDa protein components of the Bag-1 protein complex, the levels of 56-kDa and 50-kDa proteins were not changed by the addition or withdrawal of nicotine; but the level of the 36-kDa protein, which had been increased in the presence of nicotine, was markedly decreased after nicotine withdrawal. The present results suggest that such changes may also occur in individuals during abstaining from smoking and be related to the withdrawal symptoms experienced after smokers stop smoking.

Animals↗
PubMed2005

Large magnetic field-induced spectral weight enhancement of high-energy spin excitations in La1.88Sr0.12CuO4.

We report electronic Raman scattering experiments on a superconducting La(1.88)Sr(0.12)CuO(4) single crystal in a magnetic field. At low temperatures, the spectral weight of the high-energy two-magnon peak increases linearly with field and is amplified by a factor of more than two at 14 T. The effect disappears at elevated temperatures and is not present in undoped La(2)CuO(4). This observation is discussed in terms of an electronically inhomogeneous state in which the field enhances the volume fraction of a phase with local antiferromagnetic order at the expense of the superconducting phase.

Journal Article↗
PubMed2005

Angle-resolved photoemission spectroscopy of the antiferromagnetic superconductor Nd1.87Ce0.13CuO4: anisotropic spin-correlation gap, pseudogap, and the induced quasiparticle mass enhancement.

We performed high-resolution angle-resolved photoemission spectroscopy on Nd1.87Ce0.13CuO4, which is located at the boundary of the antiferromagnetic (AF) and the superconducting phase. We observed that the quasiparticle (QP) effective mass around (pi,0) is strongly enhanced due to the opening of the AF gap. The QP mass and the AF gap are found to be anisotropic, with the largest value near the intersecting point of the Fermi surface and the AF zone boundary. In addition, we observed that the QP peak disappears around the Néel temperature (TN) while the AF pseudogap is gradually filled up at much higher temperatures, possibly due to the short-range AF correlation.

Journal Article↗
PubMed2005

MR tractography for the evaluation of functional recovery from lenticulostriate infarcts.

OBJECTIVE: To evaluate the anatomic and clinical relationship between the lenticulostriate artery (LSA) territory and the corticospinal tract (CST) in patients with acute infarcts in this territory using MR tractography. METHODS: Thirteen consecutive patients who presented with acute infarcts in the LSA territory and who also had undergone an MRI study within 3 days after symptom onset were studied. Visualization of the CST was achieved by postprocessing the acquired diffusion tensor imaging data. To classify lesion location, the LSA territory was divided into four subsegments, the boundaries of which were drawn by axial and coronal planes crossing through the foramen of Monro. Infarct volume and extent of CST involvement were measured and compared with neurologic findings. RESULTS: All of the infarcts were located in the posterior segment. All of the depicted CSTs crossed the LSA territory only at the posterosuperior quadrant. The extent of CST involvement within the infarcts was correlated with the severity of the patient's motor deficit (p < 0.01) and with the clinical outcome (p < 0.05). CONCLUSIONS: The corticospinal tracts (CSTs) crossed the lenticulostriate artery territory exclusively at the posterosuperior quadrant, and the degree of CST involvement within the infarcts was directly related to stroke severity and functional recovery.

Adult↗
PubMed2005

Non-invasive measurement of intracranial compliance using cine MRI in normal pressure hydrocephalus.

The aim of this study is to clarify biophysics of normal pressure hydrocephalus (NPH) based on non-invasive intracranial compliance measurement using magnetic resonance imaging (MRI). Patients with NPH after subarachnoid hemorrhage (NPH group, n = 5), brain atrophy or asymptomatic ventricular dilation (VD group, n = 5), and healthy volunteers (control group, n = 12) were included in this study. Net blood flow (bilateral internal carotid and vertebral arteries, and jugular veins) and cerebrospinal fluid (CSF) flow in subarachnoid space at the C2 level of cervical vertebra were measured using phase-contrast cine MRI. CSF pressure gradient and intracranial volume changes during a cardiac cycle were calculated based on Alperin's method. Compliance index (Ci = delta V/delta P) was obtained from the maximum pressure gradient and volume changes. Pressure volume response (PVR) was measured in the NPH group during a shunt operation. Ci in the NPH group was the lowest among the three studies groups. No difference was found between the control and VD groups. There was a linear correlation between Ci and PVR. In conclusion, intracranial compliance can be determined by cine MRI non-invasively. It is well known that NPH has relatively low intracranial compliance, this non-invasive method can be used for the diagnosis of NPH.

Brain↗
PubMed2005

Radical resection for intrinsic midbrain pilocytic astrocytoma: report of two cases.

BACKGROUND: Intrinsic midbrain glioma has been one of the most challenging therapeutic tasks in neurosurgery due to its prognosis and risks associated with surgical procedures. It is known that the prognosis of pilocytic astrocytoma is relatively good if radical resection can be achieved without severe complications. In order to remove pilocytic astrocytoma within the midbrain radically, we used microsurgical techniques. METHOD: Two patients with intrinsic pilocytic astrocytomas located at the midbrain were operated on. The subtemporal approach was used with a point of entry on the lateral surface of the midbrain just behind the cerebral peduncle. Major vessels were preserved, followed by resection of the intrinsic tumor making the cleavage between tumour and midbrain. FINDINGS: In both patients, intrinsic pilocytic astrocytoma was grossly totally removed with minimal permanent morbidity. They have been able to maintain independent activities in their daily lives without tumor recurrance. CONCLUSIONS: Surgical cure can be accomplished in some cases of midbrain pilocytic astrocytoma, even if the lesions are intrinsic to the midbrain. To remove the tumor totally without further neurological deficits, it is necessary to select a safe access or entrance point to the tumor, and to demarcate the gliotic plane between tumour and midbrain. A long-term follow up with a larger number of patients is needed to establish the significance of radical resection for intrinsic midbrain pilocytic astrocytoma.

Astrocytoma↗
PubMed2005

Possible involvement of urokinase-type plasminogen activator release from human peripheral blood lymphocytes in the pathophysiology of chronic allograft nephropathy.

BACKGROUND: Little is known of the fibrinolytic host immune mechanisms responsible for induction of chronic allograft nephropathy (CAN), defined as a loss in glomerular filtration rate (GFR) caused by tubular atrophy and interstitial fibrosis, often with fibrous intimal thickening in the small arteries. However, chronic rejection has been reported to be associated with decreased activity of the fibrinolytic system. In our previous study, [Deamino-Cys1, D-Arg8]-vasopressin (dDAVP) induced urokinase-type plasminogen activator (uPA) release from human peripheral T lymphocytes via arginine vasopressin (AVP) V2-receptor-mediated reaction enhanced by an AVP V1-receptor antagonist. Therefore, we examined the level of uPA released from peripheral T lymphocytes by AVP in transplant patients with CAN in comparison with control groups. PATIENTS AND METHODS: In this study, we evaluated in vitro uPA releasing activity of lymphocytes obtained from renal allograft patients with well-functioning grafts (n = 9), CAN (n = 5), or acute rejection episodes (n = 5) compared with lymphocytes from healthy volunteers with normal renal function (n = 12) or patients with renal insufficiency (n = 5). RESULTS: Lymphocytes prepared from patients with chronic allograft nephropathy showed a significantly lower increase in uPA release induced by the combination of the V1-receptor antagonist and dDAVP compared with those from the other groups. CONCLUSION: This finding suggested that a decrease in uPA release from human peripheral blood lymphocytes by AVP-related peptides may be potentially involved in the pathophysiology of CAN.

Adult↗
PubMed2005

Electroporation-mediated HGF gene transfection protected the kidney against graft injury.

The annual rate of kidney graft loss caused by chronic allograft nephropathy (CAN) has not improved over the past decade. Recent reports suggest that acute renal ischemia results in development of CAN. The goal of the present study was to assess the renoprotective potential and safety of hepatocyte growth factor (HGF) gene transfer using a porcine kidney transplant warm ischemia injury model. Following left porcine kidney removal, 10 min of warm ischemic injury was intentionally induced. Next, the HGF expression vector or vehicle was infused into the renal artery with the renal vein clamped ex vivo, and electric pulses were discharged using bathtub-type electrodes. Kidney grafts were then transplanted after removing the right kidney. Histopathological examination of vehicle-transfected kidney transplant revealed initial tubular injury followed by tubulointerstitial fibrosis. In contrast, HGF-transfected kidneys showed no initial tubular damage and no interstitial fibrosis at 6 months post-transplant. We conclude that electroporation-mediated ex vivo HGF gene transfection protects the kidney against graft injury in a porcine model.

Animals↗
PubMed2005

Gene expression and association analyses of LIM (PDLIM5) in bipolar disorder and schizophrenia.

We previously reported that expression level of LIM (ENH, PDLIM5) was significantly and commonly increased in the brains of patients with bipolar disorder, schizophrenia, and major depression. Expression of LIM was decreased in the lymphoblastoid cells derived from patients with bipolar disorders and schizophrenia. LIM protein reportedly plays an important role in linking protein kinase C with calcium channel. These findings suggested the role of LIM in the pathophysiology of bipolar disorder and schizophrenia. To further investigate the role of LIM in these mental disorders, we performed a replication study of gene expression analysis and performed genetic association studies. Upregulation of LIM was confirmed in the independent sample set obtained from Stanley Array Collection. No effect of sample pH or medication was observed. Genetic association study revealed the association of single nucleotide polymorphism (SNP)1 (rs10008257) with bipolar disorder. In an independent sample set, SNP2 (rs2433320) close to SNP1 was associated with bipolar disorder. In total samples, haplotype of these two SNPs was associated with bipolar disorder. No association was observed in case-control analysis and family-based association analysis in schizophrenia. These results suggest that SNPs in the upstream region of LIM may confer the genetic risk for bipolar disorder.

Adaptor Proteins, Signal Transducing↗
PubMed2005

Accumulation of plasma cells expressing CXCR3 in the synovial sublining regions of early rheumatoid arthritis in association with production of Mig/CXCL9 by synovial fibroblasts.

Accumulation of plasma cells in the synovium is one of the diagnostic hallmarks in the histopathological manifestations of rheumatoid arthritis (RA). This seems to be prominent even prior to significant B cell infiltration and/or formation of lymphoid follicles in the synovium. To clarify the mechanism of early plasma cell accumulation, we examined in situ expression of chemokines and their receptors using synovial targeting biopsy specimens, which were obtained under arthroscopy from early RA patients. By immunohistochemical staining, plasma cells were found to express a chemokine receptor CXCR3, while synovial fibroblasts in the synovial sublining regions expressed its ligand, Mig/CXCL9. By reverse transcription-polymerase chain reaction (RT-PCR), using targeted lesions of synovial tissues obtained by laser capture microdissection, expression levels of Mig/CXCL9 in the synovial sublining regions were remarkably high and were likely to be associated with interferon (IFN)-gamma expression. Furthermore, cultured synovial fibroblasts were confirmed to produce Mig/CXCL9 upon stimulation with IFN-gamma. Our results indicate that in the early stage of RA, plasma cells expressing CXCR3 may be recruited directly from the circulation into the synovial sublining regions by its ligand, Mig/CXCL9, produced by synovial fibroblasts.

Adult↗
PubMed2005

Mandibular antegonial and ramus notch depths and condylar bone change.

The present study sought to clarify the relationship between antegonial and ramus notch depths and condylar bone change, and analyse the effects of such change on craniofacial structure. The study sample was of 28 pre-orthodontic patients with signs and symptoms of temporomandibular joint (TMJ) disorders, who underwent helical computed tomography to diagnose their TMJ pathology. Craniofacial structures were compared between 14 subjects with bilateral condylar bone change (BBC group: two male and 12 female) and 14 subjects with no bone change (NBC group: two male and 12 female). Sella-nasion-point B (SNB) and point A-nasion-point B (ANB) angles were significantly smaller in BBC than in NBC, with ramus height and mandibular body lengths significantly shorter in BBC than in NBC. The BBC lower facial height and SN-Go-Ar angle, as well as antegonial and ramus notch depths, were significantly greater than in NBC, and the mandible was significantly more retruded in BBC than in NBC. These results showed that condylar bone change might be related not only to mandibular size (e.g. retrusion) but also to mandibular outline (including antegonial and ramus notch depth).

Adolescent↗
PubMed2005

The influence of Goldbonder and pre-heat treatment on the adhesion of titanium alloy and porcelain.

The present study examines the influence of a goldbonder and pre-heat treatment of the titanium on the adhesion of porcelain. Three groups of titanium substrates were given various heat treatments, namely; none, 200 degrees and 600 degrees C, respectively before applying goldbonder. The surfaces of the titanium specimens following heat treatment were examined with an electron spectroscopy for chemical analysis (ESCA). The adhesion strength was measured by the strain energy release rate (G), which was proposed by Suansuwan N and Swain MV (Int J Prosthodont. 1999;12:547). After bonding porcelain onto titanium substrates with the aid of the goldbonder, the porcelain side of specimens was notched to the interface with a thin diamond saw. Then the samples were subject to a four-point bending test. Following fracture testing, specimens were examined with a scanning electron microscope (SEM) and SEM with energy-dispersive spectroscopic analysis (EDS). The mean G-values were 38.87, 28.64 and 16.33 J m(-2), respectively. ESCA analysis showed the composition of aluminium of the surface of 600 degrees C pre-heat treatment became richer than that of the others. SEM images of the fracture surfaces showed that for the 600 degrees C pre-heat treatment fracture occurred within the oxidation layer on the titanium. High temperature pre-heat treatment prior to bonding significantly reduces porcelain bonded to titanium with the goldbonder. The Influence of Goldbonder and Pre-heat Treatment on the Adhesion of Titanium Alloy and Porcelain.

Adhesiveness↗
PubMed2005

Synthesis, crystal structure and molecular conformation of Nalpha-Boc-L-leucyl-(Z)-beta-(3-pyridyl)-alpha,beta- dehydroalanyl-L-leucine methyl ester.

A protected tridehydropeptide containing (Z)-beta-(3-pyridyl)-alpha,beta-dehydroalanine (Delta(Z)3Pal) residue, Boc-Leu-Delta(Z)3Pal-Leu-OMe (1), was synthesized via Erlenmeyer azlactone method. X-ray crystallographic analysis revealed that the peptide 1 adopts an extended conformation, which is similar to that of a Delta(Z)Phe analog, Boc-Leu-Delta(Z)Phe-Leu-OMe (2).

Crystallography, X-Ray↗
PubMed2005

Dose-response study of recombinant human soluble thrombomodulin (ART-123) in the prevention of venous thromboembolism after total hip replacement.

BACKGROUND: Recombinant human soluble thrombomodulin (ART-123) is composed of the active, extracellular, domain of thrombomodulin. ART-123 binds to thrombin and this complex converts protein C into the natural anticoagulant activated protein C. This study was performed to identify an effective and safe dose of ART-123 for prevention of venous thromboembolism after elective, unilateral total hip replacement. METHODS AND RESULTS: An open-label, sequential, dose-ranging study was performed in which 312 patients received either 0.3 mg kg(-1) or 0.45 mg kg(-1) of ART-123, subcutaneously, 2-4 h after surgery (day 1). Those who received 0.3 mg kg(-1) were given a second dose of 0.3 mg kg(-1) on day 6, and the first 29 of these patients also used intermittent pneumatic compression devices. Those who received 0.45 mg kg(-1) were not given a second dose. Primary efficacy outcome was all deep vein thrombosis on mandatory bilateral venography performed on day 9 +/- 2 and symptomatic venous thromboembolism up to day 11. Primary safety outcome was major bleeding up to day 11. Among patients who did not use intermittent pneumatic compression, venous thromboembolism occurred in 3.4% of 116 evaluable patients in the 0.3 mg kg(-1) group and 0.9% of 111 patients in the 0.45 mg kg(-1) group. Major bleeding occurred in 1.4% of 139 patients in the 0.3 mg kg(-1) group and 6.3% of 144 patients in the 0.45 mg kg(-1) group. CONCLUSION: ART-123 is a highly effective antithrombotic agent that should be directly compared with current methods of prophylaxis in patients who have major orthopedic surgery.

Aged↗