Biomedical subjects

Shigeru Tanaka

Publications and source records attributed to Shigeru Tanaka.

46 records · Page 3Linked to original sources

PubMed2002

Intrinsic optical signals from rat primary auditory cortex in response to sound stimuli presented to contralateral, ipsilateral and bilateral ears.

In the auditory cortex, primitive features of acoustic stimuli are represented for auditory scene analysis. A typical example of a feature representation is the tonotopic map, in which sound frequencies are spatially arranged in an orderly manner. Some neurons in the auditory cortex are sensitive to sound source location, which is another important feature for auditory scene analysis. In the present study, using the intrinsic optical imaging technique, we attempted to visualize the two-dimensional pattern of neuronal population responses in the primary auditory cortex of rats to pure tones presented at various frequencies and sound intensities. The observed arrangements of sound frequencies were consistent with those obtained by electrophysiological mapping, which indicates that our intrinsic optical recording can visualize populational responses of neurons. We also found different temporal patterns of intrinsic signals elicited in response to contralateral, ipsilateral, and bilateral ear stimulations. Finally we try to explain the observed differential time courses of intrinsic signal responses from the theoretical point of view on the conduction of neural activities, based on the so far anatomically identified neural pathways in the rodent auditory system.

Acoustic Stimulation↗

PubMed2002

Kinetic analysis of multisite phosphorylation using analytic solutions to Michaelis-Menten equations.

Phosphorylation-induced expression or modulation of a functional protein is a common signal in living cells. Many functional proteins are phosphorylated at multiple sites and it is frequently observed that phosphorylation at one site enhances or suppresses phosphorylation at another site. Therefore, characterizing such cooperative phosphorylation is important. In this study, we determine a temporal progress curve of multisite phosphorylation by analytically integrating the Michaelis-Menten equations in time. Using this theoretical progress curve, we derive the useful criterion that an intersection of two progress curves implies the presence of cooperativity. Experiments generally yield noisy progress curves. We fit the theoretical progress curves to noisy progress curves containing 4% Gaussian noise in order to determine the kinetics of the phosphorylation. This fitting correctly identifies the sites involved in cooperative phosphorylation.

Animals↗

PubMed2002

Protective effect of apolipoprotein E against ischemic neuronal injury is mediated through antioxidant action.

Recent studies have demonstrated that apolipoprotein E (APOE) deficiency worsened neuronal injuries after transient focal and global cerebral ischemia. However, the molecular mechanism underlying the protective effect of APOE remains uncertain, even though several mechanisms, including excitotoxicty, free radicals, and apoptosis, have been cited as causes of selective neuronal vulnerability in cerebral ischemia. In the present study, we first compared the vulnerability of cultured neurons prepared from APOE-knockout mice upon exposure to glutamate, hydrogen peroxide, and staurosporine. No significant difference in cell viability was observed after exposure to glutamate or staurosporine between APOE-deficient and wild-type mice. However, exposure to hydrogen peroxide significantly increased the level of cell death in APOE-deficient mice compared with that in wild-type mice. After transient forebrain ischemia for 12 min, APOE-deficient mice showed more neuronal death than wild-type mice. Pretreatment of APOE-deficient mice with vitamin E for 2 months markedly reduced neuronal death caused by ischemia. The results suggest that APOE exerted its neuroprotective effect against ischemia through its antioxidant action but not through mitigation of glutamate toxicity or blocking of apoptosis.

Animals↗

PubMed2002

Synergistic induction of HSP40 and HSC70 in the mouse hippocampal neurons after cerebral ischemia and ischemic tolerance in gerbil hippocampus.

An ischemia-induced gene was screened using a differential display technique in mouse transient forebrain ischemia. One of the ischemia-responsive clones was found to encode mouse hsp40. HSP40 has a critical regulatory function in the HSC70 ATPase activity. Expression of hsp40 mRNA was low in the nonischemic mouse hippocampus, but it was significantly upregulated 4 hr after ischemia by Northern blot analysis. In situ hybridization analysis revealed hsp40 mRNA induction in the neuron. HSP40 protein expression was also enhanced in the pyramidal and dentate granular neurons from 2 to 4 days after ischemia. The temporal expression and distribution profile of HSC70 protein was similar to that of HSP40, and both proteins were colocalized in ischemic hippocampal neurons. In the gerbil transient forebrain ischemia model, both HSP40 and HSC70 proteins were expressed strongly in ischemia-resistant CA3 neurons and dentate granule cells 1 day after 5 min ischemia, but were not expressed in vulnerable CA1 neurons. However, both proteins were in parallel expressed in the tolerance-acquired CA1 neurons. Based on the current observation that both HSP40 and HSC70 proteins were synergistically expressed in the ischemia-resistant and tolerance-acquired neurons, cochaperone HSP40 may play a significant role against postischemic neuronal response and lead to cell survival through interaction with simultaneously induced HSC70.

Animals↗

PubMed2002

Increased proliferation of neural progenitor cells but reduced survival of newborn cells in the contralateral hippocampus after focal cerebral ischemia in rats.

Recent studies demonstrated that neurogenesis in the adult hippocampus increased after transient global ischemia; however, the molecular mechanism underlying increased neurogenesis after ischemia remains unclear. The finding that proliferation of progenitor cells occurred at least a week after ischemic insult suggests that the stimulus was not an ischemic insult to progenitor cells. To clarify whether focal ischemia increases the rate of neurogenesis in the remote area, the authors examined the contralateral hemisphere in rats subjected to permanent occlusion of the middle cerebral artery. In the subgranular zone of the hippocampal dentate gyrus, the numbers of bromodeoxyuridine (BrdU)-positive cells increased approximately sixfold 7 days after ischemia. In double immunofluorescence staining, more than 80% of newborn cells expressed Musashi1, a marker of neural stem/progenitor cells, but only approximately 10% of BrdU-positive cells expressed glial fibrillary acidic protein (GFAP), a marker of astrocytes. The number of BrdU-positive cells markedly decreased 28 days after BrdU administration after ischemia, but it was still elevated compared with that of sham-operated rats. In double immunofluorescence staining, 80% of newborn cells expressed NeuN, a marker of differentiated neurons, and 10% of BrdU-positive cells expressed GFAP. However, in the other areas of the contralateral hemisphere including the rostral subventricular zone, the number of BrdU-positive cells remained unchanged. These results showed that focal ischemia stimulated the proliferation of neuronal progenitor cells, but did not support survival of newborn cells in the contralateral hippocampus.

Animals↗

PubMed2002

Keeping the catheter exit site clean by sealing with a dressing film in patients under continuous ambulatory peritoneal dialysis.

In patients on continuous ambulatory peritoneal dialysis (CAPD), exit-site care is troublesome. We developed a new method for exit-site care, using a dressing film. We investigated the possibility of keeping the exit site clean for up to 6 weeks, using seven protocols: Control group (n = 24)--the exit site was cleaned with a povidone iodine solution daily and a gauze dressing was applied. Group A (n = 120)--the exit site was cleaned with a povidone iodine solution once weekly, was covered with a small piece of gauze, and was completely sealed using a dressing film. Group B (n = 181)--as with Group A, except once every 2 weeks. Group C (n = 64)--as with Group A, except once every 3 weeks. And so on: Group D (n = 45)--once every 4 weeks. Group E (n = 8)--once every 5 weeks. Group F (n = 2)--once every 6 weeks. At each session, we examined the small gauze bacteriologically. In groups A-F, the patients were asked to bathe every day and not to do anything about the exit site for 1-6 weeks, as applicable. In the control group, the rate of positive bacterial culture was 87.5%. In the other groups, the rates were group A, 15%; group B, 6.6%; group C, 6.3%; group D, 2.2%; and groups E and F, 0%. In the film-method groups, the rates of positive bacterial culture were significantly low. We thought that the film method kept the exit site clean.

Aged↗

PubMedDate not supplied

Firing properties of a stochastic PDE model of a rat sensory cortex layer 2/3 pyramidal cell.

We have developed a non-linear stochastic PDE (partial differential equation) model of a rat layer 2/3 somatosensory pyramidal neuron which approximates several of the dynamical properties of these cells. The model distinguishes telodendrites, a myelinated axon, initial segment, hillock, soma and a simplified dendritic tree. Distributions and properties of excitatory and inhibitory synapses were included, in accordance with recent anatomical and physiological findings. Using simulation methods, we aim to show that the spatial separation between regions of spatially distributed randomly activated excitatory and inhibitory synaptic inputs may be an important parameter which can influence neuronal firing properties. Due to the complexity of the problem, with respect to configurations of spatially and temporally activated excitatory and inhibitory synaptic inputs, we consider two simple configurations in which the spatial region of activated excitatory and inhibitory synaptic inputs overlap and when they are far from each. In the first, denoted configuration A, activated excitatory and inhibitory synapses were located close to the soma. In the second, denoted configuration B, active inhibitory synapses were close the soma, while active excitatory synapses were located on distal regions of the dendrite. For the first configuration, we find that increases in the mean rate of inhibition results in an increase in the width of the firing rate tuning curves, and that for particular mean input frequencies of excitation, increasing the mean input rate of inhibition does not always imply that the neuron fires at a slower rate. Furthermore, we observed for mean input frequencies of excitation between 15 and 60 (Hz), that increasing the mean rate of inhibition resulted in the linearization of the firing rate over this interval. For configuration B, no increase in width nor a linearization effect via inhibition was observed. These differences indicate that the distance between regions of active excitatory and inhibitory synapses may be an important factor to consider in determining how the interaction between excitation and inhibition contributes to neuronal firing.

Animals↗

PubMedDate not supplied

Roles of visual experience and intrinsic mechanism in the activity-dependent self-organization of orientation maps: theory and experiment.

It is widely accepted that functional maps in the mammalian visual cortex such as ocular dominance columns and orientation columns are formed depending on neural activity. There is still, however, controversy on how much visual experience contributes to the map formation during development. In the present study, we address this issue from mathematical modeling and experimental investigation. Using a model of activity-dependent self-organization of geniculo-cortical afferent inputs, we showed that spontaneous activity in the LGN can produce orientation maps, while the exposure to drifting gratings results in sharply segregated orientation maps as observed in cat visual cortex. The restricted exposure to a single orientation of the grating led to the over-representation of the exposed orientation, which was moderated by the contribution of learning based on the spontaneous activity. These theoretical results were confirmed by intrinsic optical recordings from area 18 of kittens reared under various visual conditions.

Animals↗

PubMedDate not supplied

Monitoring for N,N-dimethylformamide and N,N-dimethylacetamide with a diffusive sampler using distilled water as an absorbent.

To obtain an appropriate sampling method for evaluating individual workers' exposure concentrations to chemicals highly soluble in water, the suitability of LiPS (liquid passive sampler) as diffusive sampler was examined. Although adsorbed chemical substances with activated carbon felt being used as the adsorbent must be desorbed in such samplers, this process can be omitted by using liquid as the absorbent. This kind of simplification can be utilized for water-soluble solvents such as N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAC). In laboratory experiments DMF and DMAC levels determined by this method were sufficiently correlated with exposure concentrations, exposure duration, and cumulative exposure levels. The sampling rates for DMF and DMAC obtained from these results were 0.50 and 0.43 mL/min, respectively, and the theoretical sampling rate for DMF obtained using Fick's diffusion formula was consistent with the experimental value. The effects of relative humidity, wind velocity, and temperature on the measured values were negligible within the range expected in a practical industrial environment. In a field survey the exposure concentrations for 38 workers handling DMF in the process of manufacturing spandex fiber and polyurethane gloves were determined both by this method and by the National Institute of Occupational Safety and Health (NIOSH) method, in which silica gel tubes are used. The DMF concentrations detected by the two methods were comparable (Y = 0.912X, correlation coefficient: 0.932). This LiPS method proved to be useful in determining the concentrations of DMF and DMAC to which workers were exposed.

Absorption↗

PubMedDate not supplied

A neural network model for trace conditioning.

We studied the dynamics of a neural network that has both recurrent excitatory and random inhibitory connections. Neurons started to become active when a relatively weak transient excitatory signal was presented and the activity was sustained due to the recurrent excitatory connections. The sustained activity stopped when a strong transient signal was presented or when neurons were disinhibited. The random inhibitory connections modulated the activity patterns of neurons so that the patterns evolved without recurrence with time. Hence, a time passage between the onsets of the two transient signals was represented by the sequence of activity patterns. We then applied this model to represent the trace eye blink conditioning, which is mediated by the hippocampus. We assumed this model as CA3 of the hippocampus and considered an output neuron corresponding to a neuron in CA1. The activity pattern of the output neuron was similar to that of CA1 neurons during trace eye blink conditioning, which was experimentally observed.

Animals↗