Neuroscience 2003 Abstract
| Presentation Number: | 496.8 |
|---|---|
| Abstract Title: | Influence of L-type calcium channels on the input-output properties of spinal motoneurons: insights from compartmental models. |
| Authors: |
Rose, K.*1
; Ter-Mikaelian, M.1
; Bui, T.1
; Cushing, S.1
; Bedrossian, D.1
1CIHR Group in Sensory-Motor Syst., Queen's Univ, Kingston, Canada |
| Primary Theme and Topics |
Motor Systems - Spinal Cord -- Motoneurons |
| Session: |
496. Motoneuron Physiology Poster |
| Presentation Time: | Monday, November 10, 2003 4:00 PM-5:00 PM |
| Location: | Morial Convention Center - Hall F-I, Board # H57 |
| Keywords: | DENDRITE, MODELING, MOTONEURON, CALCIUM CHANNEL |
Activation of L-type Ca channels on the dendrites of spinal motoneurons provides a powerful means of amplifying synaptic currents that would otherwise cause marginal changes in motoneuron activity. Simulations using compartmental models constrained by anatomical and physiological data (i.e. changes in the threshold for plateau potentials, as recorded in the soma, due to tonic excitatory or inhibitory synaptic activity; Bennett et al., 1998), predict that L-type Ca channels are located in hot-spots, 150-400 µm, from the soma (Rose et al., SFN 2002). The goal of this study was to determine the impact of these hot spots on the current delivered to the soma in response to tonic activation of uniformly distributed excitatory and inhibitory synapses. In the absence of L-type Ca channels, the relationship between the current reaching the soma and the number of active synapses is non-linear. The current/synapse falls more than 2 fold at higher levels of synaptic activity due to non-linear summation. In contrast, with the addition of L-type Ca channels, the current/synapse reaching the soma is independent of the level of synaptic activity and reaches maximum values more than two times that observed in the absence of L-type Ca channels. This result is a consequence of an orderly recruitment of hot-spots as the number of active synapses increased. Moving the hot spots 100 µm proximally suppressed activation of the L-type Ca channels. On the other hand, shifting their location 100 µm distally resulted in an abrupt increase in somatic current at low levels of synaptic activity. Further increases in synaptic activity caused very small increases in somatic current (i.e. saturation). Thus, by strategically placing L-type Ca channels 150 to 400 µm from the soma, the gain of the input-output relationship governing motoneuron activity is increased and is independent of the level of synaptic activity.
Supported by CIHR
Sample Citation:
[Authors]. [Abstract Title]. Program No. XXX.XX. 2003 Neuroscience Meeting Planner. New Orleans, LA: Society for Neuroscience, 2003. Online.
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