HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 583/2/611    most recent jphysiol.2007.134999v2 jphysiol.2007.134999v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Grande, G. Articles by Rose, P. K. Search for Related Content PubMed PubMed Citation Articles by Grande, G. Articles by Rose, P. K. Related Collections Neuroscience

¹ Canadian Institute for Health Research Group in Sensory-Motor Systems, Department of Physiology, Centre for Neuroscience Studies, Queen's University, Kingston, Ontario, Canada

Previous studies show that the activation of voltage-dependent channels is dependent on the local density of synapses in the dendritic region containing voltage-dependent channels. We hypothesized that the selective innervation of excitatory vestibulospinal (VST) neurons on the medial dendrites of contralateral splenius motoneurons is designed to enhance the activation of persistent inward currents (PICs) mediated by dendritic L-type Ca²⁺ channels. Using compartmental models of splenius motoneurons we compared the synaptic current reaching the soma in response to excitatory input generated by synapses with two different distribution patterns. The MEDIAL distribution was based on the arrangement of VST synapses on the dendrites of contralateral splenius motoneurons and the UNIFORM distribution was based on an arrangement of synapses with no particular bias to any region of the dendritic tree. The number of synapses in each distribution was designed to match estimates of the number of VST synapses activated by head movements. In the absence of PICs, the current delivered by the synapses in the UNIFORM distribution was slightly greater. However, the maximal currents were small, 4.1 nA, regardless of the distribution of synapses. In models equipped with L-type Ca²⁺ channels, PIC activation was largely determined by the local density of synapses in proximity to the L-type Ca²⁺ channels. In 3 of 5 cells, this led to a 2- to 4-fold increase in the current generated by synapses in the MEDIAL distribution compared to the UNIFORM distribution. In the other two cells, the amplification bias was in favour of the MEDIAL distribution but was either small or restricted to a narrow range of frequencies. These simulations suggest that the innervation pattern of VST axons on contralateral splenius motoneurons is arranged to strengthen an otherwise weak synaptic input by increasing the likelihood of activating PICs. Additional simulations suggest that this prediction can be tested using common experimental protocols.

(Received 19 April 2007; accepted after revision 3 July 2007; first published online 5 July 2007)
Corresponding author G. Grande: Department of Physiology, 4th Floor Botterell Hall, Queen's University, Kingston, Ontario, Canada K7L 3N6. Email: john{at}biomed.queensu.ca

This article has been cited by other articles:

				A. S. Hyngstrom, M. D. Johnson, and C. J. Heckman Summation of Excitatory and Inhibitory Synaptic Inputs by Motoneurons With Highly Active Dendrites J Neurophysiol, April 1, 2008; 99(4): 1643 - 1652. [Abstract] [Full Text] [PDF]

				A. Hyngstrom, M. Johnson, J. Schuster, and C. J. Heckman Movement-related receptive fields of spinal motoneurones with active dendrites J. Physiol., March 15, 2008; 586(6): 1581 - 1593. [Abstract] [Full Text] [PDF]