Tatsuo Kitajima

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In this paper our previous model of activity-dependent synaptic modification is extended and applied to a model neuron with active dendrites and is used in computer simulations to examine in detail the dependence of synaptic modifications on the interval between the onset of excitatory postsynaptic potentials (EPSPs) and postsynaptic action potentials(More)
As a step toward the fabrication of small tendon grafts, fibroblast–collagen gels were constructed with orientated fibrils induced by static or dynamic loading. Three groups of gel samples, each consisting of 1.0 × 106 fibroblasts and 2 mg type I collagen, were fabricated: freely contracted gels formed the control group; contraction-directed gels made up(More)
Long-Term Potentiation (LTP) in the hippocampus has been considered to be a phenomenon closely related to learning and memory in the brain. In this paper, an integrated model of LTP is constructed based on hypotheses about both the mechanism of LTP induction and that of LTP maintenance, that is, the NMDA-receptor channel, protein phosphorylation and protein(More)
Activation of NMDA receptors (NMDARs) is highly involved in the potentiation and depression of synaptic transmission. NMDARs comprise NR1 and NR2B subunits in the neonatal forebrain, while the expression of NR2A subunit is increased over time, leading to shortening of NMDAR-mediated synaptic currents. It has been suggested that the developmental switch in(More)
The phenomenon whereby the relative timing between presynaptic and postsynaptic spiking determines the direction and extent of synaptic changes in a critical temporal window is known as spike timing-dependent synaptic plasticity (STDP). We have previously reported that STDP profiles can be classified into two types depending on their layer-specific location(More)
The maturation of cortical circuits is strongly influenced by sensory experience during a restricted critical period. The developmental alteration in the subunit composition of NMDA receptors (NMDARs) has been suggested to be involved in regulating the timing of such plasticity. However, this hypothesis does not explain the evidence that enhancing GABA(More)
Spike-timing-dependent plasticity (STDP) has been suggested to play a role in developing functional cortical circuits. However, for STDP to contribute to the organization of synapses, the STDP learning curve should satisfy a requirement that the magnitude of long-term potentiation (LTP) is slightly smaller than that of long-term depression (LTD). In the(More)
Spike-timing-dependent plasticity (STDP) has been suggested to play a role in the development of functional neuronal connections. However, for STDP to contribute to the synaptic organization, its learning curve should satisfy a requirement that the magnitude of long-term potentiation (LTP) is approximately the same as that of long-term depression (LTD).(More)
The viscoelastic characteristics of contracted collagen gels populated with rat fibroblasts or cardiomyocytes were investigated by uniaxial tensile testing. Rat type I collagen–Dulbecco’s modified Eagle’s medium solution (each 2 ml in volume, 0.5 mg/ml collagen concentration) containing 2.0 million rat fibroblasts or cardiomyocytes were cast in a circular(More)