| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 Département d'éducation physique, Université Pau, Pau, France
2
Département de kinésiologie, Université de Montréal, Montréal, Canada
3
Spinal Cord Research Center, University of Manitoba, Winnipeg, Manitoba, Canada
We sought to determine whether decreased neuromuscular use in the form of hindlimb unweighting (HU) would affect the properties of innervating motoneurones. Hindlimb weight-bearing was removed in rats for a period of 2 weeks via hindlimb suspension by the tail. Following this the electrophysiological properties of tibial motoneurones were recorded under anaesthesia in situ. After HU, motoneurones had significantly (P < 0.05) elevated rheobase currents, lower antidromic spike amplitudes, lower afterhyperpolarization (AHP) amplitudes, faster membrane time constants, lower cell capacitances, and depolarized spike thresholds. Frequency–current (f–I) relationships were shifted significantly to the right (i.e. more current required to obtain a given firing frequency), although there was no change in f–I slopes. ‘Slow’ motoneurones (AHP half-decay times, > 20 ms) were unchanged in proportions in HU compared to weight-bearing rats. Slow motoneurones had significantly lower minimum firing frequencies and minimum currents necessary for rhythmic firing than ‘fast’ motoneurones in weight-bearing rats; these differences were lost in HU rats, where slow motoneurones resembled fast motoneurones in these properties. In a five-compartment motoneurone model with ion conductances incorporated to resemble firing behaviour in vivo, most of the changes in passive and rhythmic firing properties could be reproduced by reducing sodium conductance by 25% and 15% in the initial segment and soma, respectively, or by increasing potassium conductance by 55% and 42%, respectively. This supports previous conclusions that changes in chronic neuromuscular activity, either an increase or decrease, may result in physiological adaptations in motoneurones due to chronic changes in ion conductances.
(Received 1 June 2005;
accepted after revision 22 August 2005;
first published online 25 August 2005)
Corresponding author P. Gardiner: Spinal Cord Research Center, Department of Physiology, University of Manitoba, 730 William Avenue, 436 Basic Medical Sciences Building, Winnipeg, Manitoba, Canada R3E 3J7. Email: gardine2{at}c.umanitoba.ca
This article has been cited by other articles:
|
|
 |
|
  J. S. Carp, A. M. Tennissen, D. L. Mongeluzi, C. J. Dudek, X. Y. Chen, and J. R. Wolpaw An In Vitro Protocol for Recording From Spinal Motoneurons of Adult Rats J Neurophysiol, July 1, 2008; 100(1): 474 - 481. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. C. Button, J. M. Kalmar, K. Gardiner, T. Marqueste, H. Zhong, R. R. Roy, V. R. Edgerton, and P. F. Gardiner Does elimination of afferent input modify the changes in rat motoneurone properties that occur following chronic spinal cord transection? J. Physiol., January 15, 2008; 586(2): 529 - 544. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. C. Button, J. M. Kalmar, K. Gardiner, F. Cahill, and P. F. Gardiner Spike frequency adaptation of rat hindlimb motoneurons J Appl Physiol, March 1, 2007; 102(3): 1041 - 1050. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. Gardiner, Y. Dai, and C. J. Heckman Effects of exercise training on {alpha}-motoneurons J Appl Physiol, October 1, 2006; 101(4): 1228 - 1236. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. C. Button, K. Gardiner, T. Marqueste, and P. F. Gardiner Frequency-current relationships of rat hindlimb {alpha}-motoneurones J. Physiol., June 15, 2006; 573(3): 663 - 677. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
