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Biomedical subjects

Y Okabe

Publications and source records attributed to Y Okabe.

At least 19 recordsLinked to original sources
PubMed2001

Theoretical analysis of array-enhanced stochastic resonance in the diffusively coupled FitzHugh-Nagumo equation.

The array-enhanced stochastic resonance (AESR) in the diffusively coupled FitzHugh-Nagumo equation is investigated. The two properties of AESR, namely, the scaling of the optimal noise intensity and the enhancement of the maximum value of the correlation coefficient as a function of the coupling strength, are analyzed theoretically. By transforming the dynamics of N elements into that of the mean and the deviation from it, it is found that AESR is caused by the correlation between them. A low-dimensional model that reproduces the above properties is constructed.

Animals↗
PubMed2001

Fluctuation-induced memory retrieval in a pulsed neural network storing sparse patterns with hierarchical correlations.

An associative memory in a pulsed neural network composed of the FitzHugh-Nagumo models storing sparse patterns with hierarchical correlations is investigated. The memory patterns composed of 0/1 digits are represented by the synchronous periodic firings of the neurons. It is found that the target pattern and the OR pattern are retrieved individually by controlling the intensity of fluctuations in the system.

Animals↗
PubMed2001

Universal relations in the finite-size correction terms of two-dimensional Ising models.

Quite recently, Izmailian and Hu [Phys. Rev. Lett. 86, 5160 (2001)] studied the finite-size correction terms for the free energy per spin and the inverse correlation length of the critical two-dimensional Ising model. They obtained the universal amplitude ratio for the coefficients of two series. In this study we give a simple derivation of this universal relation; we do not use an explicit form of series expansion. Moreover, we show that the Izmailian and Hu's relation is reduced to a simple and exact relation between the free energy and the correlation length. This equation holds at any temperature and has the same form as the finite-size scaling.

Journal Article↗
PubMed2001

Crossover and self-averaging in the two-dimensional site-diluted Ising model: application of probability-changing cluster algorithm.

Using the newly proposed probability-changing cluster (PCC) Monte Carlo algorithm, we simulate the two-dimensional (2D) site-diluted Ising model. Since we can tune the critical point of each random sample automatically with the PCC algorithm, we succeed in studying the sample-dependent T(c)(L) and the sample average of physical quantities at each T(c)(L) systematically. Using the finite-size scaling (FSS) analysis for T(c)(L), we discuss the importance of corrections to FSS both in the strong-dilution and weak-dilution regions. The critical phenomena of the 2D site-diluted Ising model are shown to be controlled by the pure fixed point. The crossover from the percolation fixed point to the pure Ising fixed point with the system size is explicitly demonstrated by the study of the Binder parameter. We also study the distribution of critical temperature T(c)(L). Its variance shows the power-law L dependence, L(-n), and the estimate of the exponent n is consistent with the prediction of Aharony and Harris [Phys. Rev. Lett. 77, 3700 (1996)]. Calculating the relative variance of critical magnetization at the sample-dependent T(c)(L), we show that the 2D site-diluted Ising model exhibits weak self-averaging.

Journal Article↗
PubMed2001

PACT, a double-stranded RNA binding protein acts as a positive regulator for type I interferon gene induced by Newcastle disease virus.

Virus infection triggers innate responses to host cells including production of type I interferon (IFN). Since IFN production is also induced by treatment with poly(I:C), viral double-stranded (ds) RNA has been postulated to play a direct role in the process. In the present study, we investigated the effect of dsRNA binding proteins on virus-induced activation of the IFN-beta gene. We found that PACT, originally identified as protein activator for dsRNA-dependent protein kinase (PKR) and implicated in the regulation of translation, augmented IFN-beta gene activation induced by Newcastle disease virus. Concomitantly with the augmented activity of IFN-beta enhancer, increased activity of NF-kappaB and IRF-3 and IRF-7 was observed. For the observed effect, the dsRNA-binding activity of PACT was essential. We identified residues of PACT that interact with a presumptive target molecule to exert its function. Furthermore, PACT colocalized with viral replication complex in the infected cells. Thus the observed effect of PACT is novel and PACT is involved in the regulation of viral replication and results in a marked increase of cellular IFN-beta gene expression.

Amino Acid Sequence↗
PubMed2001

Finite-size scaling for the ising model on the Möbius strip and the klein bottle.

We study the finite-size scaling properties of the Ising model on the Möbius strip and the Klein bottle. The results are compared with those of the Ising model under different boundary conditions, that is, the free, cylindrical, and toroidal boundary conditions. The difference in the magnetization distribution function p(m) for various boundary conditions is discussed in terms of the number of the percolating clusters and the cluster size. We also find interesting aspect-ratio dependence of the value of the Binder parameter at T = T(c) for various boundary conditions. We discuss the relation to the finite-size correction calculations for the dimer statistics.

Journal Article↗
PubMed2001

Probability-changing cluster algorithm for Potts models.

We propose a new effective cluster algorithm of tuning the critical point automatically, which is an extended version of the Swendsen-Wang algorithm. We change the probability of connecting spins of the same type, p = 1-e(-J/k(B)T), in the process of the Monte Carlo spin update. Since we approach the canonical ensemble asymptotically, we can use the finite-size scaling analysis for physical quantities near the critical point. Simulating the two-dimensional Potts models to demonstrate the validity of the algorithm, we have obtained the critical temperatures and critical exponents which are consistent with the exact values; the comparison has been made with the invaded cluster algorithm.

Journal Article↗
PubMed2001

Chemical force microscopy of self-assembled monolayers on sputtered gold films patterned by phase separation.

Patterned self-assembled monolayers (SAMs) were formed on gold films and observed by friction force microscopy (FFM) and adhesive force mapping with pulsed-force mode atomic force microscopy (PFM-AFM). The substrate gold films were prepared by sputtering gold on flat surfaces of osmium-coated cover glass with surface roughness, Ra, of 0.3 nm. The patterned samples with the CH3 and COOH terminated regions were prepared using the Langmuir-Blodgett (LB) method, partial removal of the LB film by ultrasonication, and SAM formation. The CH3 and COOH terminated regions of the patterned SAMs in air and in water were observed by mapping friction and adhesive forces with FFM and PFM-AFM, respectively, using gold-coated AFM tips chemically modified with a thiol compound terminating in CH3 or COOH. The adhesive forces measured in air increased in the order of CH3/CH3, CH3/COOH (or COOH/CH3) and COOH/COOH, while those in water increased in reverse order. The enormous high adhesive force observed in water for CH3/CH3 was attributed to hydrophobic interaction between the CH3 tip and the CH3 terminated sample surface. With CH3 tip, the lower friction force was observed, however, in water on the CH3 terminated region than on the COOH terminated region. This experimental finding raises a question as to what is the effective normal load in friction measurements in water.

Journal Article↗
PubMed2001

Increased lymphoid MxA expression in acute asthma exacerbation in children.

BACKGROUND: Although the association between acute asthma exacerbation and viral infection has been well documented, virus identification rates vary. It has recently been reported that the expression of MxA protein in lymphocytes, inducible by type I interferons, can serve as a sensitive marker for viral infection in the host. The objective was to determine the contribution of viral infection to precipitation of asthma attacks in children. METHODS: We studied 186 asthmatic children, aged 0-12 years, over a 1-year period to evaluate MxA protein levels in peripheral blood lymphocytes by using a flow cytometric analysis in whole blood. RESULTS: Of all the subjects, 80 (47%) exhibited significantly elevated levels of MxA expression in lymphocytes, presumably indicating the states of viral infection. The association of viral infections with acute asthma exacerbation seemed to be marked in younger children: enhanced MxA expression was seen in 73.3% of infants (aged 0-1 year), 49.5% of toddlers (aged 2-5 years), and 26% of schoolchildren (aged 6-12 years). Seasonal changes in the frequency of viral infection associated with deterioration were also observed. CONCLUSIONS: Flow cytometric assay of MxA protein expression in whole blood appears to be an easy and useful method to evaluate viral infections in acute asthma exacerbation.

Acute Disease↗
PubMed2001

Induction of IRF-3/-7 kinase and NF-kappaB in response to double-stranded RNA and virus infection: common and unique pathways.

BACKGROUND: Infection by virus or treatment with double-stranded RNA (dsRNA) results in the activation of transcription factors including IRF-3, IRF-7 and a pleiotropic regulator NF-kappaB by specific phosphorylation. These factors are important in triggering a cascade of antiviral responses. A protein kinase that is yet to be identified is responsible for the activation of these factors and plays a key role in the responses. RESULTS: The signal cascade was analysed using sensitive assays for the activation of IRF-3 and NF-kappaB, and various inhibitors. We found that the activation of IRF-3 and NF-kappaB by dsRNA or virus involves a process that is sensitive to Geldanamycin. Although the induction of NF-kappaB by dsRNA/virus and TNF-alpha involves common downstream pathways including IKK activation, the upstream, Geldanamycin-sensitive process was unique to the dsRNA/virus-induced signal. By an in vitro assay using cell extract, we found an inducible protein kinase activity with physiological specificity of IRF-3 phosphorylation. Furthermore, the same extract specifically phosphorylated IRF-7 in a similar manner. CONCLUSIONS: Double-stranded RNA or virus triggers a specific signal cascade that results in the activation of the IRF-3/-7 kinase we detected, which corresponds to the long-sought signalling machinery that is responsible for triggering the early phase of innate response. The signal branches to a common NF-kappaB activation cascade, thus resulting in the activation of a set of critical transcription factors for the response.

Benzoquinones↗
PubMed2001

Preventive effects of Bifidobacterium- and Lactobacillus-fermented milk on the development of inflammatory bowel disease in senescence-accelerated mouse P1/Yit strain mice.

BACKGROUND/AIMS: We recently discovered inflammatory bowel disease (IBD) in the ileum and cecum of SAMP1/Yit strain mice under specific pathogen-free (SPF) conditions. To determine the effect of lactic acid bacteria (LAB - Bifidobacterium breve, Bifidobacterium bifidum and Lactobacillus acidophilus)-fermented milk on the prevention of IBD in SAMP1/Yit strain mice, we compared the disease severity on the intestinal inflammation among the group of mice fed saline, unfermented milk or LAB-fermented milk. METHODS: Three-week-old SAMP1/Yit strain mice (n = 72) were subdivided into three groups, that were fed saline, unfermented milk and LAB-fermented milk, respectively. The diets were orally administered daily via a gastric tube. When the mice reached 20 weeks of age, they were sacrificed and the IBD scores were compared among the three groups. RESULTS: Administration of the LAB-fermented milk to SAMP1/Yit strain mice reduced histological injury score, compared with those in saline-treated or unfermented milk-treated SAMP1/Yit strain mice. Ileal tissue weight and myeloperoxidase activity also reduced by treatment of LAB-fermented milk. Moreover, the tissue contents of immunoglobulins such as IgG1 and IgG2a were lower in the inflammatory regions in the SAMP1/Yit strain group fed LAB-fermented milk than that fed saline and unfermented milk. Cytokine-specific ELISA assays indicated the production of T-helper 1 cytokines such as interferon-gamma and tumor necrosis factor-alpha in the culture supernatants of MLN cells in the SAMP1/Yit strain group fed LAB-fermented milk was lower than those fed saline and unfermented milk. On the contrary, the production of interleukin-10 in MLN cells increased by prevention with LAB-fermented milk. CONCLUSION: LAB-fermented milk is beneficial for the treatment of murine IBD and this effect may be modulated through stabilization of the mucosal immunity by LAB.

Aging↗
PubMed2001

Intrahepatic spontaneous retrograde portal flow in patients with cirrhosis of the liver: reversal by food intake.

OBJECTIVE: The purpose of our study was to assess whether intrahepatic spontaneous retrograde portal flow in patients with cirrhosis of the liver can be reversed to a normal portal venous flow by food intake. CONCLUSION: Of the 18 cirrhotic patients with intrahepatic spontaneous retrograde portal flow, 16 (89%) showed a marked change in portal flow direction after food intake. This evidence strongly suggests that intrahepatic spontaneous retrograde portal flow may be reversible. Furthermore, this finding implies that regular food intake may be important in the maintenance of effective hepatic blood flow in cirrhotic patients.

Adult↗
PubMed2000

Support for an association between HLA-DR1 and schizophrenia in the Japanese population.

An increase of HLA-DR1 has been observed in schizophrenia patients from the Japanese population. A decrease of DR4, which was reported in Caucasian patients, has also been found in some of the Japanese studies. This small study further investigated frequencies of HLA-DR1 and DR4 in unrelated Japanese patients with schizophrenia (n = 45) and healthy comparison subjects (n = 117). The number of patients possessing DR1 was higher (10 of 45, 22%) compared with the comparison group (11 of 117, 9.4%, P = 0.03). This may support the previous observation of an increased DR1 frequency in the Japanese patients. When the present data is combined with three previous studies, proportions of the Japanese subjects with DR1 were 98 of 588 schizophrenia patients (16.7%) vs. 93 of 942 comparison subjects (9.9%). However, no difference was observed in DR4 frequencies between the patients (51%) and comparison subjects (44%). Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:725-727, 2000.

Adult↗
PubMed2000

Chemical force microscopy of microcontact-printed self-assembled monolayers by pulsed-force-mode atomic force microscopy

A novel chemically sensitive imaging mode based on adhesive force detection by previously developed pulsed-force-mode atomic force microscopy (PFM-AFM) is presented. PFM-AFM enables simultaneous imaging of surface topography and adhesive force between tip and sample surfaces. Since the adhesive forces are directly related to interaction between chemical functional groups on tip and sample surfaces, we combined the adhesive force mapping by PFM-AFM with chemically modified tips to accomplish imaging of a sample surface with chemical sensitivity. The adhesive force mapping by PFM-AFM both in air and pure water with CH3- and COOH-modified tips clearly discriminated the chemical functional groups on the patterned self-assembled monolayers (SAMs) consisting of COOH- and CH3-terminated regions prepared by microcontact printing (microCP). These results indicate that the adhesive force mapping by PFM-AFM can be used to image distribution of different chemical functional groups on a sample surface. The discrimination mechanism based upon adhesive forces measured by PFM-AFM was compared with that based upon friction forces measured by friction force microscopy. The former is related to observed difference in interactions between tip and sample surfaces when the different interfaces are detached, while the latter depends on difference in periodic corrugated interfacial potentials due to Pauli repulsive forces between the outermost functional groups facing each other and also difference in shear moduli of elasticities between different SAMs.

Journal Article↗
PubMed2000

A novel cleaning method of gold-coated atomic force microscope tips for their chemical modification

For chemical modification of gold-coated AFM tips with thiol or sulfide compounds, a new two-step precleaning procedure was studied. The two-step cleaning procedure involves (i) oxidation of organic contaminants on the AFM tips with ozone treatment and (ii) reduction of the oxidized gold surface by immersing the oxidized tip into pure hot ethanol at ca. 65 degrees C. The chemically modified tips prepared from gold-coated AFM tips precleaned by the two-step procedure gave almost the same tip characteristics as those chemically modified immediately after gold vapor deposition in a factory. The present two-step cleaning procedure can be used widely for chemical modification of commercially available gold-coated AFM tips with thiol or disulfide compounds for chemical force microscopy.

Journal Article↗
PubMed2000

Associative memory retrieval induced by fluctuations in a pulsed neural network.

An associative memory retrieval in a pulsed neural network composed of the FitzHugh-Nagumo neurons is investigated. The memory is represented in the spatio-temporal firing pattern of the neurons, and the memory retrieval is accomplished using the fluctuations in the system. The storage capacity of the network is investigated numerically. It is demonstrated that this pulsed neural network is capable of an alternate retrieval of two patterns.

Action Potentials↗