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Biomedical subjects

Y Kuramoto

Publications and source records attributed to Y Kuramoto.

At least 19 recordsLinked to original sources
PubMed2001

High-temperature ferromagnetism in CaB2C2.

We report a high Curie-temperature ferromagnet, CaB2C2. Although the compound has neither transition metal nor rare earth ions, the ferromagnetic transition temperature Tc is about 770 Kelvin. Despite this high T(c), the magnitude of the ordered moment at room temperatures is on the order of 10(-4) Bohr magneton per formula unit. These properties are rather similar to those of doped divalent hexaborides, such as Ca(1-x)La(x)B6. The calculated electronic states also show similarity near the Fermi level between CaB2C2 and divalent hexaborides. However, there is an important difference: CaB2C2 crystallizes in a tetragonal structure, and there are no equivalent pockets in the energy bands for electrons and holes-in contrast with CaB6. Thus, the disputed threefold degeneracy, specific to the cubic structure, in the energy bands of divalent hexaborides turns out not to be essential for high-temperature ferromagnetism. It is the peculiar molecular orbitals near the Fermi level that appear to be crucial to the high-Tc ferromagnetism.

Journal Article↗
PubMed2001

Electron addition spectrum in the supersymmetric t-J model with inverse-square interaction.

The electron addition spectrum A+(k,omega) is obtained analytically for the one-dimensional (1D) supersymmetric t-J model with 1/r2 interaction. The result is obtained first for a small-sized system and its validity is checked against the numerical calculation. Then the general expression is found which is valid for arbitrary size of the system. The thermodynamic limit of A+(k,omega) has a simple analytic form with contributions from one spinon, one holon, and one antiholon-all of which obey fractional statistics. The upper edge of A+(k,omega) in the (k,omega) plane includes a delta-function peak which reduces to that of the single-electron band in the low-density limit.

Journal Article↗
PubMed2001

Slow switching in globally coupled oscillators: robustness and occurrence through delayed coupling.

The phenomenon of slow switching in populations of globally coupled oscillators is discussed. This characteristic collective dynamics, which was first discovered in a particular class of the phase oscillator model, is a result of the formation of a heteroclinic loop connecting a pair of clustered states of the population. We argue that the same behavior can arise in a wider class of oscillator models with the amplitude degree of freedom. We also argue how such heteroclinic loops arise inevitably and persist robustly in a homogeneous population of globally coupled oscillators. Although a heteroclinic loop might seem to arise only exceptionally, we find that it appears rather easily by introducing time delay into a population which would otherwise exhibit perfect phase synchrony. We argue that the appearance of the heteroclinic loop induced by the delayed coupling is then characterized by transcritical and saddle-node bifurcations. Slow switching arises when a system with a heteroclinic loop is weakly perturbed. This will be demonstrated with a vector model by applying weak noises. Other types of weak symmetry-breaking perturbations can also cause slow switching.

Journal Article↗
PubMed2001

Strong desynchronizing effects of weak noise in globally coupled systems.

In assemblies of globally coupled dynamical units, weak noise perturbing independently the individual units can cause anomalous dispersion in the synchronized cloud of the units in the phase space. When the noise-free dynamics of the synchronized assembly is nonperiodic, various moments of the linear dimension of the cloud as a function of the noise strength exhibit multiscaling properties with parameter-dependent scaling exponents. Some numerical evidence of this peculiar behavior as well as its interpretation in terms of a multiplicative stochastic process with small additive noise is provided. Universality of the phenomenon is also discussed.

Journal Article↗
PubMed2000

Identification and characterization of a novel follistatin-like protein as a binding protein for the TGF-beta family.

Follistatin is an activin-binding protein that prevents activin from binding to its receptors and neutralizes its activity. Follistatin also binds bone morphogenetic proteins (BMPs). In this study, we report the identification of a novel follistatin-like protein from mouse. The mouse cDNA encodes a 256-residue precursor and most likely a mouse homologue of human FLRG, which was found at the breakpoint of the chromosomal rearrangement in a B-cell line. Whereas follistatin has three follistatin domains, which are presumed to be growth factor binding motifs, FLRG possesses only two follistatin domains. Northern blotting revealed that mRNAs for FLRG were abundantly expressed in heart, lung, kidney, and testis in mouse. The recombinant mouse FLRG proteins were found to have binding activity for both activin and bone morphogenetic protein-2. Like follistatin, FLRG has higher affinity for activin than for BMP-2. The FLRG protein inhibited activin-induced and BMP-2-induced transcriptional responses in a dose-dependent manner. Glutathione S-transferase fusion proteins encoding various regions of FLRG were produced and studied. Ligand blotting using (125)I-activin revealed that the COOH-terminal region containing the second follistatin domain was able to bind activin. Our finding implies that cellular signaling by activin and BMPs is tightly regulated by multiple members of the follistatin family.

Activins↗
PubMed2000

Exact dynamical structure factor of the degenerate haldane-shastry model

The dynamical structure factor S(q,omega) of the K-component ( K = 2, 3, 4) spin chain with a 1/r(2) interaction is derived exactly at zero temperature for the arbitrary size of the system. The result is interpreted in terms of a free quasiparticle picture which is a generalization of the spinon picture in the SU(2) case. The excited states consist of K quasiparticles each of which is characterized by a set of K-1 quantum numbers. Divergent singularities of S(q,omega) at the spectral edges are derived analytically. The analytic result is checked numerically for finite systems.

Journal Article↗
PubMed1999

A case of neuroleptic-induced unilateral akathisia with periodic limb movements in the opposite side during sleep.

We report on a patient with schizoaffective disorder who developed unilateral akathisia. This is the first case report of a patient with neuroleptic-induced unilateral akathisia on whom an all-night polysomnogram was recorded. On the polysomnogram we observed right side periodic limb movements (PLM) with left side unilateral akathisia, and after her akathisia disappeared, the PLM also disappeared. Brain MRI findings and neurological findings were within normal limits. The pathogenetic lesion causing akathisia could not be elucidated.

Acute Disease↗
PubMed1999

Nocturnal eating/drinking syndrome and neuroleptic-induced restless legs syndrome.

Nocturnal eating/drinking syndrome secondary to neuroleptic-induced restless legs syndrome (RLS) occurred under treatment with low-dose haloperidol in a 51-year-old female schizophrenic patient. Polysomnographic investigation showed a low level of sleep efficacy, periodic leg movements, and a strict relationship between nocturnal eating episodes and non-rapid eye movement sleep. Her nocturnal eating and RLS were completely inhibited by clonazepam treatment. To our knowledge, this is the first published case of nocturnal eating/drinking syndrome secondary to neuroleptic-induced RLS.

Antipsychotic Agents↗
PubMed1999

[Recent progress in akathisia].

Neuroleptic-induced akathisia should be definitely diagnosed as acute, tardive, withdrawal, and chronic. The diagnostic assessment must be identified from the subjective report and objective features. Various assessments of measuring akathisia can be clinically used by instrumental methods and rating scales. The pharmacological basis of neuroleptic-induced akathisia is the inhibition of the dopamine receptors in the brain. The pathogenesis of neuroleptic-induced akathisia may involve GABAergic hypoactivity, noradrenergic hyperactivity, and serotonergic dysfunction in CNS. Iron deficiency and hyperglycemia may be risk factors of neuroleptic induced akathisia in relation to the dopamine function in the brain. Neurological disorders may be associated with the development of a syndrome resembling drug-induced akathisia. The lesion of the thalamic nuclei would originally produce the syndrome. The difference between acute and tardive akathisia on the strategy of the drug treatment should be sufficiently comprehended. In particular, the long-term use of anticholinergic drugs and benzodiazepines should not be prevailed.

Akathisia, Drug-Induced↗
PubMed1997

Dietary fibers modulate indices of intestinal immune function in rats.

To explore the immunological roles of dietary fiber, male 4-wk-old Sprague-Dawley rats were fed for 2 wk cellulose (water-insoluble), konjak mannan (water-soluble), pectin (water-soluble) or chitosan (acid-soluble) at 5 g/100 g diet. Serum IgE concentrations in rats fed konjak mannan, pectin and chitosan were significantly lower than in those fed cellulose (mean +/- SEM: 5.0 +/- 1.1, 3.6 +/- 1.3, 3.0 +/- 1.2 and 9.6 +/- 1.9 microg/L, respectively). Rats fed pectin had significantly higher serum IgA and IgG concentrations (358 +/- 38 and 424 +/- 36 mg/L for IgA and IgG, respectively) than those fed cellulose (240 +/- 31 and 337 +/- 25 mg/L) or chitosan (176 +/- 22 and 379 +/- 23 mg/L), while the IgM concentration did not differ among the groups. Concentrations of IgA, IgG and IgM in mesenteric lymph node (MLN) lymphocytes generally were greater, while IgE concentration was lower, in rats fed pectin and chitosan than in those fed cellulose. The proportion of CD4+ T-cells in MLN lymphocytes was also dietary fiber-dependent, and the CD4+/CD8+ ratio was significantly higher in the pectin fed group than in all other groups. Under certain experimental conditions, MLN lymphocytes from rats fed pectin had markedly greater interferon-gamma concentration than cells from other groups, while the effect on tumor necrosis factor-alpha concentration was less marked. Thus, dietary fiber may have an immunoregulatory effect on the intestinal immune system of rats.

Animals↗
PubMed1997

Stimulating effect of xanthene dyes on immunoglobulin produced in vitro by rat spleen lymphocytes.

The effects of food additives on immunoglobulin produced in rat splenic lymphocytes were examined. The xanthene dye, Rose Bengal, enhanced IgE production, while inhibiting the production of IgG and IgM, at 50 microM. Among the xanthene dyes, Rose Bengal having 4 iodine and 4 chlorine atoms exerted the highest Ig production-regulating activity in splenocytes, and dihalogenated fluorescein, a diiodo compound, exerted similar activity, while the dichloro and dibromo compounds did not. These results suggest that halogen atoms, especially the iodine atom, in xanthene dyes play an important role in regulation of Ig production.

Animals↗
PubMed1996

Effect of natural food colorings on immunoglobulin production in vitro by rat spleen lymphocytes.

Water-soluble (cacao pigment, cochineal pigment, corn pigment, betanin, carthamus yellow, and monascus pigment) and water-insoluble (gardenia yellow, laccaic acid, bixin, and curcumin) natural colorings inhibited IgE production by rat spleen lymphocytes at 10 and microM, respectively. Although many of these colorings only inhibited the production of IgG and IgM at high concentrations, the water-insoluble colorings enhanced IgM production even at 1 microM. These results suggest that natural colorings have immunoglobulin production-regulating activity.

Animals↗