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J Appl Physiol 103: 1824-1836, 2007. First published August 16, 2007; doi:10.1152/japplphysiol.00362.2007
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Suppressing the excitability of spinal motoneurons by extracellularly applied electrical fields: insights from computer simulations

Sherif M. ElBasiouny1 and Vivian K. Mushahwar2,3

Departments of 1Biomedical Engineering and 2Cell Biology and 3Centre for Neuroscience, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada

Submitted 4 April 2007 ; accepted in final form 10 August 2007

The effect of extracellularly applied electrical fields on neuronal excitability and firing behavior is attributed to the interaction between neuronal morphology and the spatial distribution and level of differential polarization induced by the applied field in different elements of the neuron. The presence of voltage-gated ion channels that mediate persistent inward currents (PICs) on the dendrites of spinal motoneurons enhances the influence of electrical fields on the motoneuronal firing behavior. The goal of the present study was to investigate, with a realistic motoneuron computer model, the effects of extracellularly applied electrical fields on the excitability of spinal motoneurons with the aim of reducing the increased motoneuronal excitability after spinal cord injury (SCI). Our results suggest that electrical fields could suppress the excitability of motoneurons and reduce their firing rate significantly by modulating the magnitude of their dendritic PIC. This effect was achieved at different field directions, intensities, and polarities. The reduction in motoneuronal firing rate resulted from the reduction in the magnitude of the dendritic PIC reaching the soma by the effect of the applied electrical field. This reduction in PIC was attributed to the dendritic field-induced differential polarization and the nonlinear current-voltage relationship of the dendritic PIC-mediating channels. Because of the location of the motoneuronal somata and initial segment with respect to the dendrites, these structures were minimally polarized by the applied field compared with the extended dendrites. In conclusion, electrical fields could be used for suppressing the hyperexcitability of spinal motoneurons after SCI and reducing the level of spasticity.

spasticity; persistent inward current; polarization


Address for reprint requests and other correspondence: V. K. Mushahwar, 513 Heritage Medical Research Ctr., Dept. of Cell Biology, Centre for Neuroscience, Univ. of Alberta, Edmonton, AB, Canada T6G 2S2 (e-mail: vivian.mushahwar{at}ualberta.ca)






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