Biomedical subjects

Naoki Masuda

Publications and source records attributed to Naoki Masuda.

At least 19 recordsLinked to original sources

PubMed2006

Dual coding hypotheses for neural information representation.

Information is represented and processed in neural systems in various ways. The rate coding, population coding, and temporal coding are typical examples of representation. It is a hot issue in neuroscience what kinds of coding is used in real neural systems. Different regions of the brain may resort to different coding strategies. Moreover, recent studies suggest the possibility of dual or multiple codes, in which different modes of information are embedded in one neural system. The present paper reviews various possibilities of neural codes focusing on dual codes.

Action Potentials↗

PubMed2006

Dynamic switching of neural codes in networks with gap junctions.

Population rate coding and temporal coding are common neural codes. Recent studies suggest that these two codes may be alternatively used in one neural system. Based on the fact that there are massive gap junctions in the brain, we explore how this switching behavior may be related to neural codes in networks of neurons connected by gap junctions. First, we show that under time-varying inputs, such neural networks show switching between synchronous and asynchronous states. Then, we quantify network dynamics by three mutual information measures to show that population rate coding carries more information in asynchronous states and temporal coding does so in synchronous states.

Action Potentials↗

PubMed2006

Multi-state epidemic processes on complex networks.

Infectious diseases are practically represented by models with multiple states and complex transition rules corresponding to, for example, birth, death, infection, recovery, disease progression, and quarantine. In addition, networks underlying infection events are often much more complex than described by meanfield equations or regular lattices. In models with simple transition rules such as the SIS and SIR models, heterogeneous contact rates are known to decrease epidemic thresholds. We analyse steady states of various multi-state disease propagation models with heterogeneous contact rates. In many models, heterogeneity simply decreases epidemic thresholds. However, in models with competing pathogens and mutation, coexistence of different pathogens for small infection rates requires network-independent conditions in addition to heterogeneity in contact rates. Furthermore, models without spontaneous neighbor-independent state transitions, such as cyclically competing species, do not show heterogeneity effects.

Communicable Diseases↗

PubMed2006

Simultaneous quantitative determination of cyclosporine A and its three main metabolites (AM1, AM4N and AM9) in human blood by liquid chromatography/mass spectrometry using a rapid sample processing method.

We have developed a sensitive and specific liquid chromatography/mass spectrometry (LC/MS) method for the simultaneous determination of cyclosporine A (CsA) and its three main metabolites (AM1, AM4N and AM9) in human blood. Following protein precipitation, supernatant was directly injected into the LC/MS system. Chromatographic separation was accomplished on a Symmetry C8 (4.6 x 75 mm, 3.5 microm) column with a linear gradient elution prior to detection by atmospheric pressure chemical ionization (APCI) MS using selected ion monitoring (SIM) in positive mode. This method can be applied to single mass equipment. The analytical range for each analyte was set at 1-2500 ng/mL using 100 microL of blood sample. The analytical method was fully validated according to FDA guidance. Intra-day mean accuracy and precision were 95.2-113.5% and 0.9-8.9%, respectively. Inter-day mean accuracy and precision were 95.8-107.0% and 1.5-10.7%, respectively. In blood all analytes were stable during three freeze/thaw cycles, for 24 h at room temperature and for 12 months at or below -15 degrees C. Stability was also confirmed in processed samples for 24 h at 10 degrees C and for 6 months at 4 degrees C in methanol. In addition, we confirmed the method could avoid matrix effects from transplant subjects' samples. This LC/MS technique provided an excellent method for simultaneous quantitative determination of CsA and its three metabolites for evaluation of their pharmacokinetic profiles.

Atmospheric Pressure↗

PubMed2006

Reperfusion strategy for acute myocardial infarction in elderly patients aged 75 to 80 years.

The increasing elderly population will influence the treatment policies adopted in cases of acute myocardial infarction. Considering reperfusion therapy in elderly patients with acute myocardial infarction, we compared three strategies, as follows: primary percutaneous coronary intervention (primary PCI: n = 26), facilitated PCI with half the standard dose of mutant tissue-type plasminogen activator (t-PA) (half + PCI: n = 24), and facilitated PCI with a standard dose of mutant t-PA (standard + PCI: n = 15) between patients 75 and 80 years of age. The rate of acquisition of thrombolysis in myocardial infarction (TIMI-3) flow on initial coronary arteriography was significantly lower in the primary PCI group than in the other two groups (7.7% in the primary PCI group vs 60% in the half + PCI and 66.7% in the standard + PCI group). The incidence of hemorrhagic complications including blood transfusion was not significantly different between primary PCI and facilitated PCI. Considering reperfusion therapy in elderly patients with acute myocardial infarction, we concluded that facilitated PCI may be effective in elderly patients aged 75-80 years.

Aged↗

PubMed2006

Simultaneous rate-synchrony codes in populations of spiking neurons.

Firing rates and synchronous firing are often simultaneously relevant signals, and they independently or cooperatively represent external sensory inputs, cognitive events, and environmental situations such as body position. However, how rates and synchrony comodulate and which aspects of inputs are effectively encoded, particularly in the presence of dynamical inputs, are unanswered questions. We examine theoretically how mixed information in dynamic mean input and noise input is represented by dynamic population firing rates and synchrony. In a subthreshold regime, amplitudes of spatially uncorrelated noise are encoded up to a fairly high input frequency, but this requires both rate and synchrony output channels. In a suprathreshold regime, means and common noise amplitudes can be simultaneously and separately encoded by rates and synchrony, respectively, but the input frequency for which this is possible has a lower limit.

Action Potentials↗

PubMed2006

Predictive factors of TIMI-3 flow before percutaneous coronary intervention in facilitated percutaneous coronary intervention for acute myocardial infarction.

The outcome for facilitated percutaneous coronary intervention (PCI) for acute myocardial infarction (AMI) is known to be more favorable in cases in which TIMI-3 flow is obtained before PCI. We investigated factors that affect the acquisition of TIMI-3 flow before PCI. Facilitated PCI was performed on 178 patients divided into two groups, a group in which TIMI-3 flow was acquired before conducting PCI and another in which it was not, and their background factors and short-term outcomes were investigated. The hemoglobin concentrations, white blood cell (WBC) counts, and HbA1c values were significantly lower in the group in which TIMI-3 flow was acquired before PCI and significantly more had a history of past smoking. According to the results of logistic analysis, WBC count (odds ratio [OR], 0.865, P = 0.0077), hemoglobin concentration (OR, 0.77, P = 0.0257), and smoking history (OR, 0.266, P = 0.0021) were independent factors that predicted acquisition of TIMI-3 flow. The WBC count and hemoglobin value on arrival at the emergency room and history of smoking were shown to be independent factors for acquisition of TIMI-3 flow before PCI in facilitated PCI.

Aged↗

PubMed2005

Geographical threshold graphs with small-world and scale-free properties.

Many real networks are equipped with short diameters, high clustering, and power-law degree distributions. With preferential attachment and network growth, the model by Barabási and Albert simultaneously reproduces these properties, and geographical versions of growing networks have also been analyzed. However, nongrowing networks with intrinsic vertex weights often explain these features more plausibly, since not all networks are really growing. We propose a geographical nongrowing network model with vertex weights. Edges are assumed to form when a pair of vertices are spatially close and/or have large summed weights. Our model generalizes a variety of models as well as the original nongeographical counterpart, such as the unit disk graph, the Boolean model, and the gravity model, which appear in the contexts of percolation, wire communication, mechanical and solid physics, sociology, economy, and marketing. In appropriate configurations, our model produces small-world networks with power-law degree distributions. We also discuss the relation between geography, power laws in networks, and power laws in general quantities serving as vertex weights.

Journal Article↗

PubMed2005

Development and validation for high selective quantitative determination of metformin in human plasma by cation exchanging with normal-phase LC/MS/MS.

An assay based on cation exchange solid-phase extraction and liquid chromatography-tandem mass spectrometry (LC/MS/MS) has been developed for the quantitative determination of metformin in human plasma. The analytical method consists of cation exchange solid-phase extraction (VersaPlate CBA) without any further evaporation/dissolution steps and cation exchange-based HPLC separation (Capcell Pak SCX column) with a normal-phase gradient system followed by semi-micro LC/MS/MS in positive ion selected reaction monitoring mode using electrospray ionization. The method exhibited excellent performance in terms of selectivity, robustness, short run time (7 min/sample) and simplicity of sample preparation. The calibration range was 10-1000 ng/ml with 0.2 ml of plasma. Intra- and inter-day mean accuracies were within the ranges of 100.3-105.0% and 101.2-105.3%, respectively. Intra- and inter-day precisions were within the ranges of 0.8-1.9% and 1.5-8.6%, respectively. Mean absolute recovery was 67.0% for metformin. No apparent loss of metformin after extraction was observed in an autosampler at 10 degrees C for 24 h. Dilution of metformin by blank human plasma up to 20-fold was tested and revealed no impact on the results of determination. Furthermore, the method exhibited high selectivity, since no effect on metformin analysis was observed on comparison of samples with or without nateglinide and other agents in plasma. Results obtained with the method were also comparable to a published LC-UV method on cross-validation. This method can be applied to various clinical pharmacokinetic studies of metformin.

Cation Exchange Resins↗

PubMed2005

Coding of temporally varying signals in networks of spiking neurons with global delayed feedback.

Oscillatory and synchronized neural activities are commonly found in the brain, and evidence suggests that many of them are caused by global feedback. Their mechanisms and roles in information processing have been discussed often using purely feedforward networks or recurrent networks with constant inputs. On the other hand, real recurrent neural networks are abundant and continually receive information-rich inputs from the outside environment or other parts of the brain. We examine how feedforward networks of spiking neurons with delayed global feedback process information about temporally changing inputs. We show that the network behavior is more synchronous as well as more correlated with and phase-locked to the stimulus when the stimulus frequency is resonant with the inherent frequency of the neuron or that of the network oscillation generated by the feedback architecture. The two eigenmodes have distinct dynamical characteristics, which are supported by numerical simulations and by analytical arguments based on frequency response and bifurcation theory. This distinction is similar to the class I versus class II classification of single neurons according to the bifurcation from quiescence to periodic firing, and the two modes depend differently on system parameters. These two mechanisms may be associated with different types of information processing.

Action Potentials↗

PubMed2004

Analysis of scale-free networks based on a threshold graph with intrinsic vertex weights.

Many real networks are complex and have power-law vertex degree distribution, short diameter, and high clustering. We analyze the network model based on thresholding of the summed vertex weights, which belongs to the class of networks proposed by Phys. Rev. Lett. 89, 258702 (2002)]. Power-law degree distributions, particularly with the dynamically stable scaling exponent 2, realistic clustering, and short path lengths are produced for many types of weight distributions. Thresholding mechanisms can underlie a family of real complex networks that is characterized by cooperativeness and the baseline scaling exponent 2. It contrasts with the class of growth models with preferential attachment, which is marked by competitiveness and baseline scaling exponent 3.

Journal Article↗

PubMed2004

Return times of random walk on generalized random graphs.

Random walks are used for modeling various dynamics in, for example, physical, biological, and social contexts. Furthermore, their characteristics provide us with useful information on the phase transition and critical phenomena of even broader classes of related stochastic models. Abundant results are obtained for random walk on simple graphs such as the regular lattices and the Cayley trees. However, random walks and related processes on more complex networks, which are often more relevant in the real world, are still open issues, possibly yielding different characteristics. In this paper, we investigate the return times of random walks on random graphs with arbitrary vertex degree distributions. We analytically derive the distributions of the return times. The results are applied to some types of networks and compared with numerical data.

Journal Article↗

PubMed2004

Global and local synchrony of coupled neurons in small-world networks.

Synchronous firing of neurons is thought to play important functional roles such as feature binding and switching of cognitive states. Although synchronization has mainly been investigated so far using model neurons with simple connection topology, real neural networks have more complex structures. Here we examine the behavior of pulse-coupled leaky integrate-and-fire neurons with various network structures. We first show that the dispersion of the number of connections for neurons influences dynamical behavior even if other major topological statistics are kept fixed. The rewiring probability parameter representing the randomness of networks bridges two spatially opposite frameworks: precise local synchrony and rough global synchrony. Finally, cooperation of the global connections and the local clustering property, which is prominent in small-world networks, forces synchrony of distant neuronal groups receiving coherent inputs.

Action Potentials↗

PubMed2004

Simultaneous determination of levodopa and 3-O-methyldopa in human plasma by liquid chromatography with electrochemical detection.

A simple and rapid assay is described for the simultaneous analysis of levodopa (l-DOPA) and 3-O-methyldopa (3-OMD) in human plasma samples, applying an ion-pair reversed-phase liquid chromatographic method with electrochemical detection, designed for clinical trials performed to study the effect of peripheral catechol-O-methyltransferase inhibitors on the metabolism of l-DOPA. After protein precipitation of 100 microl plasma sample aliquots with perchloric acid, the analytes are directly injected, separated within 10 min and simultaneously quantified down to 20 ng/ml by an electrochemical detector equipped with a dual-electrode system operating in redox mode eliminating effectively potential endogenous and exogenous interferences. The intra-assay precision for l-DOPA and 3-OMD was 1.34-6.54 and 3.90-5.50%, whereas the inter-assay precision was 2.09-7.69 and 4.16-9.90%, respectively. The recoveries were close to 90% for l-DOPA and almost 100% for 3-OMD. Satisfactory storage stability was achieved for up to 16 weeks at -70 degrees C by stabilizing plasma samples with antioxidants.

Calibration↗

PubMed2004

Transmission of severe acute respiratory syndrome in dynamical small-world networks.

The outbreak of severe acute respiratory syndrome (SARS) is still threatening the world because of a possible resurgence. In the current situation that effective medical treatments such as antiviral drugs are not discovered yet, dynamical features of the epidemics should be clarified for establishing strategies for tracing, quarantine, isolation, and regulating social behavior of the public at appropriate costs. Here we propose a network model for SARS epidemics and discuss why superspreaders emerged and why SARS spread especially in hospitals, which were key factors of the recent outbreak. We suggest that superspreaders are biologically contagious patients, and they may amplify the spreads by going to potentially contagious places such as hospitals. To avoid mass transmission in hospitals, it may be a good measure to treat suspected cases without hospitalizing them. Finally, we indicate that SARS probably propagates in small-world networks associated with human contacts and that the biological nature of individuals and social group properties are factors more important than the heterogeneous rates of social contacts among individuals. This is in marked contrast with epidemics of sexually transmitted diseases or computer viruses to which scale-free network models often apply.

Communicable Disease Control↗

PubMed2004

Simultaneous analytical method for the determination of TCH346 and its four metabolites in human plasma by liquid chromatography/tandem mass spectrometry.

TCH346 (dibenzo[b,f]oxepin-10-ylmethyl-prop-2-ynylamine) is a novel propargylamine compound under investigation as a putative agent in the treatment of chronic neurodegenerative illnesses. To support clinical studies an analytical method was developed for TCH346 plus its three amine metabolites and a carboxylic acid metabolite in human plasma. Using a two-step liquid-liquid extraction, one under acidic and one under basic conditions, by pH-switching both the basic and acidic analytes were extracted from 0.5 mL of plasma. All these basic and acidic compounds could be analyzed simultaneously using gradient high-performance liquid chromatographic (HPLC) separation with positive/negative selected reaction monitoring mass spectrometry. As a result of the validation study, the analytical method was shown to be appropriate for the determination of TCH346 and its metabolites CGP70861, GP42120, CGP71090, and GP54840 in plasma for forthcoming clinical studies. The LLOQs were set to 2, 200, 20, 20, and 200 pg/mL for TCH346, CGP70861, GP42120, CGP71090, and GP54840, respectively, and the ULOQ for all analytes was 20 000 pg/mL. All analytes were stable in 50% MeOH at 4 degrees C for at least one year, in human plasma stored below -70 degrees C for at least 7 months, in human plasma below -18 degrees C for at least 6 months, in human plasma at room temperature for at least 1 day, and in the final extract solution at 4 degrees C for at least 3 days.

Amines↗

PubMed2004

Self-organizing dual coding based on spike-time-dependent plasticity.

It has been a matter of debate how firing rates or spatiotemporal spike patterns carry information in the brain. Recent experimental and theoretical work in part showed that these codes, especially a population rate code and a synchronous code, can be dually used in a single architecture. However, we are not yet able to relate the role of firing rates and synchrony to the spatiotemporal structure of inputs and the architecture of neural networks. In this article, we examine how feedforward neural networks encode multiple input sources in the firing patterns. We apply spike-time-dependent plasticity as a fundamental mechanism to yield synaptic competition and the associated input filtering. We use the Fokker-Planck formalism to analyze the mechanism for synaptic competition in the case of multiple inputs, which underlies the formation of functional clusters in downstream layers in a self-organizing manner. Depending on the types of feedback coupling and shared connectivity, clusters are independently engaged in population rate coding or synchronous coding, or they interact to serve as input filters. Classes of dual codings and functional roles of spike-time-dependent plasticity are also discussed.

Action Potentials↗

PubMed2004

Relationship between the generation and the facilitated percutaneous coronary intervention in patients with acute myocardial infarction--analysis based on the fibrinolysis and subsequent transluminal trial--.

BACKGROUND: The purpose of the present study was to evaluate the efficacy and safety of facilitated percutaneous coronary intervention (PCI) in comparing young and elderly patients with acute myocardial infarction. METHODS AND RESULTS: The present study enrolled 168 initial myocardial infarction patients within 12 h of the symptom onset between 40 and 80 years of age who were indicated on the fibrinolysis and subsequent transluminal (FAST-3) trial. The patients were divided into 4 groups according to their age, peak creatine kinase (CK), peak CK-MB and peak troponin T (Tn-T) levels, and cardiac function were compared between the 4 groups. There were no differences between the 4 groups in terms of the time from arrival at the emergency room (ER) to the achievement of TIMI-3 patency. There were also no significant differences between the 4 groups in terms of the peak CK, peak CK-MB or peak Tn-T levels. Furthermore, there were no significant differences between the 4 groups in terms of the mortality rate or the incidence of hemorrhagic complications at 30 days. CONCLUSIONS: Facilitated PCI is considered to have an important potential role in the treatment of myocardial infarction in Japan, in which the age of the population is steadily increasing.

Adult↗