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Simulation of Dendritic Ca_V1.3 Channels in Cat Lumbar Motoneurons: Spatial Distribution

¹Department of Biomedical Engineering, and ²Centre for Neuroscience, Faculty of Medicine and Dentistry; and ³Faculty of Rehabilitation Medicine, University of Alberta, Edmonton, Alberta, Canada

Submitted 18 April 2005; accepted in final form 19 August 2005

We used computer simulations to study the dendritic spatial distribution of low voltage-activated L-type calcium (Ca_V1.3 type) channels, which mediate hysteretic persistent inward current (PIC) in spinal motoneurons. This study was prompted by the growing experimental evidence of the functional interactions between synaptic inputs and active conductances over the motoneuron dendritic tree. A compartmental cable model of an adult cat -motoneuron was developed in NEURON simulation environment constituting the detailed morphology of type-identified triceps surae -motoneuron and realistic distribution of group Ia afferent-to-motoneuron contacts. Simulations of different distributions of Ca_V1.3 channels were conducted and the resultant behavior was compared to experimental data. Our results suggest that Ca_V1.3 channels do not uniformly cover the whole motoneuron dendritic tree. Instead, their distribution is similar to that of synaptic contacts. We found that Ca_V1.3 channels are primarily localized to a wide intermediate band overlapping with the dendritic Ia-synaptic territory at dendritic distances of 300 to 850 µm (0.62 ± 0.21) from the soma in triceps surae -motoneurons. These findings explain the functional interaction between synaptic inputs and the Ca_V1.3 channels over the motoneuron dendritic tree.

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