Biomedical subjects

M Yamashita

Publications and source records attributed to M Yamashita.

At least 19 recordsLinked to original sources

PubMed2006

Simultaneous measurement of ionization and scintillation from nuclear recoils in liquid xenon for a dark matter experiment.

We report the first measurements of the absolute ionization yield of nuclear recoils in liquid xenon, as a function of energy and electric field. Independent experiments were carried out with two dual-phase time-projection chamber prototypes, developed for the XENON dark matter project. We find that the charge yield increases with decreasing recoil energy, and exhibits only a weak field dependence. These results are the first unambiguous demonstration of the capability of dual-phase xenon detectors to discriminate between electron and nuclear recoils down to 20 keV, a key requirement for a sensitive dark matter search.

Journal Article↗

PubMed2006

Dopamine profoundly suppresses excitatory transmission in neonatal rat hippocampus via phosphatidylinositol-linked D1-like receptor.

Dopamine modulates synaptic transmission in various brain regions. The disorder of dopamine system may be related to neurodevelopmental dysfunction. However, the action of dopamine on synaptic transmission during development is largely unknown. We studied the effect of dopamine on GABAergic and glutamatergic transmission in neonatal rat hippocampus from the early period of synapse formation by whole-cell patch-clamp recordings from CA1 pyramidal cells. Dopamine (100 muM) profoundly decreased the amplitude of GABA(A) receptor-mediated postsynaptic currents (GABA(A)-PSCs) to 32.2+/-5.4% (mean+/-S.E.M., EC(50): 2.9 muM) in the first postnatal week, when GABA provides excitatory drive. Dopamine also decreased the amplitude of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated excitatory postsynaptic currents (EPSCs) to 29.1+/-2.7% (EC(50): 18.7 muM) in the second postnatal week, when glutamate responses first appear. The dopamine-induced inhibition declined after these periods and became only partial after postnatal day 30. Further we identified the receptor subtype involved in the dopamine-induced inhibition as phosphatidylinositol-linked D1-like receptor, since 6-chloro-2,3,4,5-tetrahydro-3-methyl-1-(3-methylphenyl)-1H-3-benzazepine-7,8-diol hydrobromide (SKF 83959), a selective agonist for phosphatidylinositol-linked D1-like receptor, clearly mimicked the action of dopamine, and 1-[6-[((17beta)-3-methoxyestra-1,3,5[10]-trien-17-yl)amino]hexyl]-1H-pyrrole-2,5-dione (U-73122), an inhibitor of phospholipase C, significantly reduced the dopamine-induced inhibition. Dopamine did not change the response to puff-applied GABA or kainic acid, nor the amplitude of miniature GABA(A)-PSCs or miniature EPSCs. These results suggest that the activation of phosphatidylinositol-linked D1-like receptor profoundly suppresses the excitatory transmission during the early period of synapse formation in the developing hippocampus by presynaptic mechanisms. This study firstly demonstrates the effect of phosphatidylinositol-linked D1-like receptor on synaptic transmission.

Aging↗

PubMed2005

Pinning of texture and vortices of the rotating B-like phase of superfluid 3He confined in a 98% aerogel.

We have investigated pinning effects on texture and vortices of the B-like phase of superfluid (3)He in a rotating aerogel up to +/-2pi rad/s by cw-NMR. We observed deformation of the NMR spectra in rotation, due to counterflow between the superflow and the normal flow. The average intensity of the counterflow was calculated from the change of NMR spectra. The rotation dependence of the counterflow intensity is similar to the magnetization curve of hard type II superconductors or the counterflow response of (4)He-II in packed powders. This counterflow behavior is in qualitative agreement with a model that vortices are pinned unless the counterflow exceeds a critical velocity v(c). The temperature independence of v(c) suggests that v(c) is associated with the expansion of primordial vortices.

Journal Article↗

PubMed2005

Clinical diagnosis of MM2-type sporadic Creutzfeldt-Jakob disease.

BACKGROUND: No method for the clinical diagnosis of MM2-type sporadic Creutzfeldt-Jakob disease (sCJD) has been established except for pathologic examination. OBJECTIVE: To identify a reliable marker for the clinical diagnosis of MM2-type sCJD. METHODS: CSF, EEG, and neuroimaging studies were performed in eight patients with MM2-type sCJD confirmed by neuropathologic, genetic, and western blot analyses. RESULTS: The eight cases were pathologically classified into the cortical (n = 2), thalamic (n = 5), and combined (corticothalamic) (n = 1) forms. The cortical form was characterized by late-onset, slowly progressive dementia, cortical hyperintensity signals on diffusion-weighted imaging (DWI) of brain, and elevated levels of CSF 14-3-3 protein. The thalamic form showed various neurologic manifestations including dementia, ataxia, and pyramidal and extrapyramidal signs with onset at various ages and relatively long disease duration. Characteristic EEG and MRI abnormalities were almost absent. However, all four patients examined with cerebral blood flow (CBF) study using SPECT showed reduction of the CBF in the thalamus as well as the cerebral cortex. The combined form had features of both the cortical and the thalamic forms, showing cortical hyperintensity signals on DWI and hypometabolism of the thalamus on [18F]2-fluoro-2-deoxy-d-glucose PET. CONCLUSION: For the clinical diagnosis of MM2-type sporadic Creutzfeldt-Jakob disease, cortical hyperintensity signals on diffusion-weighted MRI are useful for the cortical form and thalamic hypoperfusion or hypometabolism on cerebral blood flow SPECT or [18F]2-fluoro-2-deoxy-d-glucose PET for the thalamic form.

14-3-3 Proteins↗

PubMed2005

Autoantibodies against the amino terminal of alpha-enolase are a useful diagnostic marker of Hashimoto's encephalopathy.

We investigated autoantibodies and their epitope(s) in Hashimoto's encephalopathy associated with Hashimoto's thyroiditis. In a proteomic analysis, they proved to recognize alpha-enolase. We further searched the epitope region in alpha-enolase using different regions of recombinant proteins expressed in cultured human cells. The amino terminal region was recognized by autobodies from a much higher proportion of patients with Hashimoto's encephalopathy (83.3%; 5/6) than from patients with Hashimoto's thyroiditis (11.8%; 2/17), and not at all by sera from controls (25 healthy individuals and 25 controls with other neurological disorders) (0%; 0/50). Neither the carboxyl terminal nor the mid-region of alpha-enolase showed specificity for Hashimoto's encephalopathy. Autoantibodies against the amino terminal of alpha-enolase are a useful diagnostic marker for Hashimoto's encephalopathy.

Adult↗

PubMed2004

Vortex formation and annihilation in three textures of rotating superfluid 3He-A.

Textures, textural transformation, and formation and annihilation of a single vortex were investigated in narrow cylinders with 100 microm radius in A-phase under rotation up to 6.28 rad/sec. Three textures were found, depending on the cooling conditions of the sample through the superfluid transition temperature T(c). We found the gyromagnetic effect of textures; that is, two textures (A or B) could be selected either by applying a magnetic field in parallel or anti-parallel to the rotation axis. The critical angular speed of a single vortex formation Omega(f) and that of annihilation Omega(a) for each texture were measured. The textural transformation in type A texture was induced by rotation. Both type A and B textures held macroscopic angular momentum along the rotation axis. We identified the texture for type A, B, and C as Mermin-Ho, radial disgyration, and a soliton type of defect along the axis, respectively.

Journal Article↗

PubMed2004

Experimental concept for examination of biological effects of magnetic field concealed by gravity.

Space is not only a place to study biological effects of gravity, but also provides unique opportunities to examine other environmental factors, where the biological actions are masked by gravity on the ground. Even the earth's magnetic field is steadily acting on living systems, and is known to influence many biological processes. A systematic survey and assessment of its action are difficult to conduct in the presence of dominant factors, such as gravity. Investigation of responses of biological systems against the combined environment of zero-gravity and zero-magnetic field might establish the baseline for the analysis of biological effects of magnetic factors. We propose, in this paper, an experimental concept in this context, together with a practical approach of the experiments, both in orbit and on the ground, with a thin magnetic shielding film. Plant epicotyl growth was taken as an exemplar index to evaluate technical and scientific feasibility of the proposed system concept.

Cotyledon↗

PubMed2004

Transforming growth factor-beta signaling is enhanced following mitomycin-C treatment of islet xenograft.

Mitomycin-C (MMC) is categorized as an agent that causes genotoxic stress by triggering various intracellular signaling pathways. We have previously shown that MMC pretreatment of highly immunogenic crude islets leads to significant prolongation of graft survival in a rat-to-mouse model. In the present study, we examined whether TH1/TH2 cytokine, including the inflammatory cytokines interferon-gamma and interleukin (IL)-2, or the Th2 group, IL-4, IL-10, TNF-alpha, IL-1 beta, IL-6, GM-CSF, and transforming growth factor (TGF)-beta were up-regulated or down-regulated following MMC treatment of islets. We found changes in TGF-beta messenger RNA (mRNA) transcription as the only events among the measured cytokines. TGF-beta concentration was elevated in blebs formed under the kidney capsule, but not in the serum or ascites among animals given MMC-treated islets than in animals given untreated islets, suggesting local processes induced by MMC might inhibit xenograft rejection.

Animals↗

PubMed2004

Variation in pollen dispersal between years with different pollination conditions in a tropical emergent tree.

We examined differences in pollen dispersal efficiency between 2 years in terms of both spatial dispersal range and genetic relatedness of pollen in a tropical emergent tree, Dipterocarpus tempehes. The species was pollinated by the giant honeybee (Apis dorsata) in a year of intensive community-level mass-flowering or general flowering (1996), but by several species of moths in a year of less-intensive general flowering (1998). We carried out paternity analysis based on six DNA microsatellite markers on a total of 277 mature trees forming four spatially distinct subpopulations in a 70 ha area, and 147 and 188 2-year-old seedlings originating from seeds produced in 1996 and 1998 (cohorts 96 and 98, respectively). Outcrossing rates (0.93 and 0.96 for cohorts 96 and 98, respectively) did not differ between years. Mean dispersal distances (222 and 192 m) were not significantly different between the 2 years but marginally more biased to long distance in 1996. The mean relatedness among cross-pollinated seedlings sharing the same mothers in cohort 96 was lower than that in cohort 98. This can be attributed to the two facts that the proportion of intersubpopulations pollen flow among cross-pollination events was marginally higher in cohort 96 (44%) than in cohort 98 (33%), and that mature trees within the same subpopulations are genetically more related to each other than those between different subpopulations. We conclude that D. tempehes maintained effective pollen dispersal in terms of outcrossing rate and pollen dispersal distance in spite of the large difference in foraging characteristics between two types of pollinators. In terms of pollen relatedness, however, a slight difference was suggested between years in the level of biparental inbreeding.

DNA, Plant↗

PubMed2004

Abdominal aortic aneurysm with left-sided inferior vena cava. Report of a case.

The combination of abdominal aortic aneurysms and congenital anomalies of the inferior vena cava and its tributaries, such as double inferior vena cava, left-sided inferior vena cava, circumaortic renal collar, and retroaortic renal vein, are very rare but of clinical importance to vascular surgeons since these conditions can increase the difficulty of aneurysm resection as well as the risk of venous injury and subsequent excessive bleeding. This report describes a case of an abdominal aortic aneurysm with a left-sided inferior vena cava, and reviews of the incidence, diagnosis, and treatment of these conditions.

Aged↗

PubMed2003

Novel optical and magnetic bistability and photoinduced transition in a one-dimensional halogen-bridged binuclear pt complex.

In iodine-bridged binuclear Pt compounds, R(4)[Pt(2)(pop)(4)I]nH(2)O and R(')(2)[Pt(2)(pop)(4)I]nH(2)O (pop=P(2)O5H2-2), electronic structures on the PtPtI chains have been controlled between a diamagnetic charge-density-wave (CDW) state and a paramagnetic charge-polarization (CP) state by modification of the counterions (R, R') located between chains. In the R=(C2H5)2NH+2 compound, a pressure-induced CP to CDW transition with a drastic color change is identified. This transition is accompanied by a large hysteresis loop within which photoinduced transition between CDW and CP can be driven by selecting the excitation photon energy.

Journal Article↗

PubMed2003

Involvement of arginine vasotocin in reproductive events in the male newt Cynops pyrrhogaster.

Effects of arginine vasotocin (AVT) on reproductive events such as courtship behavior, pheromone release, and spermatophore discharge were investigated in the male newt Cynops pyrrhogaster. AVT enhanced the incidence and frequency of androgen-induced courtship behavior. In this case, AVT was likely to act centrally because the behavior was evoked with a much smaller amount of AVT when the hormone was administered intracerebroventricularly than when given intraperitoneally. Involvement of endogenous AVT in spontaneously occurring courtship behavior was also evidenced by the fact that administration of a V1 (vasopressor) receptor antagonist, [d(CH2)5(1), Tyr(Me)2, Arg8-vasopressin] suppressed the expression of the courtship behavior. The water in which AVT-treated males had been kept showed considerable female-attracting activity as compared with the water in which saline-injected males had been kept. Moreover, the content of sodefrin, a female-attracting pheromone in the abdominal gland, was decreased by the intraperitoneal injection of AVT, suggesting that the neurohypophyseal hormone stimulated the release of sodefrin from the abdominal gland into the water. AVT induced contraction of the excised abdominal gland concentration-dependently, and, again, the V1 receptor antagonist suppressed the AVT-induced contraction. Thus, we concluded that AVT induces the pheromone discharge, acting peripherally on a contractile structure of the abdominal gland. AVT was also found to induce spermatophore deposition in the male kept in the absence of the female. Administration of the V1 receptor blocker to the sexually developed males suppressed the spermatophore deposition. All these results indicate the involvement of AVT in reproductive events acting centrally and peripherally.

Animals↗

PubMed2003

Studying the visceral physiology of tadpoles through their naturally transparent abdominal walls.

We propose using anuran tadpoles with naturally transparent abdominal skin to study the visceral physiology of amphibian larvae under microgravity. The transparency of the abdominal wall in certain tadpoles enables one to evaluate the basal physiological state and temporal changes in viscera from their movements without any invasive treatment. In order to validate our experimental design, the intestinal motility and heart rate of Rhacophorus tadpoles were examined as indices of physiological responses to stepwise changes in temperature.

Adaptation, Physiological↗

PubMed2003

Detectable dioxins in human saliva and their effects on gingival epithelial cells.

Dioxin, a powerful hormone-disrupting chemical, exhibits serious health effects when it reaches body fat. Here we analyzed coplanar polychlorinated biphenyls (PCBs) and polychlorinated-dibenzo-p-dioxins (PCDDs) in human saliva as compared with blood specimens, and examined their effects on human gingival epithelial cells (HGEC). High levels of tri- and tetrachlorinated PCBs were found in saliva, whereas we detected predominantly hexa- and heptachlorinated PCBs in blood. Among PCDDs, the saliva and blood specimens contained mainly 1,2,3,4,6,7,8,9-octachlorodibenzo-p-dioxin (OCDD). Among the toxic dioxins proposed by the World Health Organization (WHO) in 1998, 2,3',4,4',5-pentachlorobiphenyl (PCB 118) and OCDD, which were mainly found in saliva, significantly induced IL-8 production in HGEC. Furthermore, these two dioxins markedly augmented IL-8 production stimulated with fimbriae from Porphyromonas gingivalis, which is well-known as a pathogenic factor in periodontal diseases. These results suggest that dioxins in saliva may be a risk factor for periodontal diseases.

Analysis of Variance↗

PubMed2002

Escherichia coli cells penetrated by chrysotile fibers are transformed to antibiotic resistance by incorporation of exogenous plasmid DNA.

A suspension of recipient Escherichia coli cells in stationary phase, chrysotile asbestos, and pUC18 donor DNA spread over the surface of a Luria-Bertani agar plate using a streak bar several times, resulted in intracellular uptake of the plasmid DNA by the E. coli cells. The transformation efficiency was highest with a duration of cell exposure to chrysotile of more than 60 s and an agar concentration of 2%. To improve chrysotile-mediated transformation efficiency, we systematically optimized various conditions and parameters. In comparison to chrysotile exposure without cations, exposure with cations produced up to 100-fold more transformants. Optimized conditions resulted in 10(6) transformants/ micro g pUC18 DNA. The drastic physical change due to 'quick drying on the surface of the agar plate' when cells were exposed to chrysotile, was essential for chrysotile-mediated transformation. We suggest that DNA uptake mediated by chrysotile asbestos is the result of a mechanical physical transformation of E. coli, since the E. coli cells are not chemically competent. Electron microscopy of cells exposed to chrysotile suggested penetration of the E. coli membrane by chrysotile fibers. It is suggested that E. coli transformation by the plasmid DNA was the result of penetration by chrysotile fibers to which plasmid DNA is bound or adsorbed.

Agar↗

PubMed2002

Tuning of electronic structures of quasi-one-dimensional bromo-bridged Ni(III) complexes with strong electron-correlation by doping of Co(III) ions, [Ni(1-x)Co(x)(Chxn)(2)Br]Br(2).

We have succeeded in synthesizing the Ni(III) complexes doped by Co(III) ions, [Ni(1-x)Co(x)(chxn)(2)Br]Br(2) (x = 0, 0.043, 0.093, and 0.118) by using an electrochemical oxidation method. The single-crystal reflectance spectrum of x = 0.118 shows an intense CT band about 0.5 eV, which is lower than that of [Ni(chxn)(2)Br]Br(2) (1.3 eV). The single-crystal electrical conductivities at room temperature of these compounds increase with increase of the amounts of doping of Co(III) ions. In the ESR spectra, peak-to-peak line widths DeltaH(pp) at room temperature change about 600 G in [Ni(chxn)(2)Br]Br(2) to 200 G in x = 0.118. Such a large x dependence of DeltaH(pp) seems to be ascribed to the increasing contribution from the increasing Curie spins which have smaller line width. Therefore, we have tuned the electronic structures of quasi-one-dimensional bromo-bridged Ni(III) complexes with strong electron correlations by doping of Co(III) ions.

Journal Article↗

PubMed2002

The magnocellular neuronal phenotype: cell-specific gene expression in the hypothalamo-neurohypophysial system.

The magnocellular oxytocin (OT) and vasopressin (VP) neurons of the hypothalamo-neurohypophysial system are exceptional cell biological models to study mechanisms of cell-specific gene expression and neurosecretion of neuropeptides in the central nervous system. Single cell differential gene expression experiments have further defined these phenotypes by identifying novel and distinct regulatory molecules in these neurons. Transgenic mouse studies have led to the intergenic region (IGR) hypothesis, which states that the DNA sequences between the OT- and VP-genes contain critical enhancer sites for their cell-specific expression. The recent cloning and sequencing of the human IGR, and its comparison with the mouse IGR sequence has identified conserved sequences as putative, cell-specific enhancer sites which are now being evaluated by biolistic transfections of organotypic hypothalamic cultures. With these data, it is possible to target the gene expression of specific molecules to magnocellular neurons both in vivo and in vitro, in order to perturb and/or visualize neurosecretory and other processes.

Animals↗

PubMed2002

Virtual endoscopic view of salivary gland ducts using MR sialography data from three dimension fast asymmetric spin-echo (3D-FASE) sequences: a preliminary study.

OBJECTIVES: We performed magnetic resonance (MR) sialography of parotid gland and/or submandibular gland ducts using three-dimensional fast asymmetric spin-echo (3D-FASE) sequencing. The objective was to make three-dimensional (3D) reconstruction images and virtual endoscopic views of the parotid gland ducts using MR sialography data sets of 3D-FASE sequences. METHODS: We reviewed the MR sialography data sets with 3D-FASE sequencing of 10 control volunteers and six patients. Three-dimensional reconstruction images and virtual endoscopic views of the parotid gland and/or submandibular gland ducts were generated with maximum intensity projection (MIP), shaded surface display (SSD), and volume rendering techniques (VRT). RESULTS: The main parotid gland and/or submandibular gland ducts, large branches within the glands, and small branches were fairly well defined in a very short acquisition time on MR sialographic images with 3D-FASE sequencing in nine of the 10 healthy volunteers. The 3D-reconstruction images of the parotid gland ducts and/or submandibular gland ducts showed the entire length of the branch paths and complete images from all angles, and the virtual endoscopic views showed the endoluminal tracts of the main ducts and the large branches in nine. In the patient with Sjogren's syndrome, chronic sialoadenitis, and salivary calculi in the Wharton ducts, the MR sialographic images showed diffuse areas of punctate high signal intensity, dilatation of Stensen's duct, or stones of Wharton's duct, respectively. Furthermore, the 3D-reconstruction images of the salivary gland ducts showed the stenoses and stones in the branch paths and complete images from all angles, and the virtual endoscopic views showed the stenoses and stones in the endoluminal tracts of the main and large branches. CONCLUSIONS: Our initial experience showed that virtual MR endoscopy could be performed to observe the endoluminal tracts of parotid and submandibular glands. The clinical use of the virtual MR endoscopy for salivary gland ducts has not been established yet. Future applications of the 3D-reconstruction images and virtual endoscopic views using MR sialography data sets of 3D-FASE sequences are very attractive and further expansion of this field is expected.

Adolescent↗