Analysis of dendritic distribution of voltage-dependent channels effects on EPSP and its reciprocal inhibition in α-motoneurons: computer model

摘要

Modeling of excitation and inhibition of morphologically and physiologically characterized triceps surea motoneuron (MN 42) was executed by a NEURON simulator. The voltage-dependent channels of MN 42 were allocated on six dendrites (the rest six dendrites remained passive) according to three types of distribution functions: a step function (SF), an exponential decay (ED, highest density proximally to the soma) and exponential rise (ER, highest density distally to the soma). Maximal densities of the sodium conductance varied between 0.01 and 0.06 S/cm~2. The peak of the EPSP became larger as the maximal density of the voltage-dependent channels is increased. In the SF distribution, with the highest total conductance (G, Siemens), the EPSP amplitudes were greater than these in the ER and ED models. The reciprocal EPSP inhibition in the model with the SF was most efficient in comparison to the ED and ER models. EPSP peak inhibition at ED and ER are similar, despite that the total active conductance in ED is about 10 times smaller than in ER distribution. The dependency of the inhibition on the density of the active conductance in the SF and ED models is not linear. We conclude that in an "ideal neuron" the presence of proximal voltage-dependent channels may boost distally located synaptic inputs thus "normalizing" the synaptic responses.