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Analysis of the Interaction Between the Dendritic Conductance Density and Activated Area in Modulating -Motoneuron EPSP: Statistical Computer Model

gidi.gradwohl{at}gmail.com Department of Physiology, Faculty of Health Sciences, and Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel, and Department of Software Engineering, Sami Shamoon College of Engineering, Beer-Sheva 84100, Israel

Yoram Grossman

ramig{at}bgu.ac.il Department of Physiology, Faculty of Health Sciences, and Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel

Five reconstructed -motoneurons (MNs) are simulated under physiological and morphological realistic parameters. We compare the resulting excitatory postsynaptic potential (EPSP) of models, containing voltage-dependent channels on the dendrites, with the EPSP of a passive MN and an active soma and axon model. In our simulations, we apply three different distribution functions of the voltage-dependent channels on the dendrites: a step function (ST) with uniform spatial dispersion; an exponential decay (ED) function, with proximal to the soma high-density location; and an exponential rise (ER) with distally located conductance density. In all cases, the synaptic inputs are located as a gaussian function on the dendrites. Our simulations lead to eight key observations. (1) The presence of the voltage-dependent channels conductance (g_Active) in the dendrites is vital for obtaining EPSP peak boosting. (2) The mean EPSP peaks of the ST, ER, and ED distributions are similar when the ranges of G (total conductance) are equal. (3) EPSP peak increases monotonically when the magnitude of g_{Na_step} (maximal g_Na at a particular run) is increased. (4) EPSP kinetics parameters were differentially affected; time integral was decreased monotonically with increased g_{Na_step}, but the rate of rise (the decay time was not analyzed) does not show clear relations. (5) The total G can be elevated by increasing the number of active dendrites; however, only a small active area of the dendritic tree is sufficient to get the maximal boosting. (6) The sometimes large variations in the parameters values for identical G depend on the g_{Na_step} and active dendritic area. (7) High g_{Na_step} in a few dendrites is more efficient in amplifying the EPSP peak than low g_{Na_step} in many dendrites. (8) The EPSP peak is approximately linear with respect to the MNs' R_N (input resistance).