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First published online on September 15, 2005.
Copyright © 2005 by The Physiological Society
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jphysiol.2005.091744v1
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Received May 30, 2005
Revised June 20, 2005
Accepted after revision September 8, 2005

Organization of common synaptic drive to motoneurones during fictive locomotion in the spinal cat

Jens Bo Nielsen1*, Bernard A Conway2, David Halliday3, Marie-Claude Perreault4, and Hans R Hultborn1

1 University of Copenhagen
2 University of Strathclyde
3 University of York
4 University of Oslo

* To whom correspondence should be addressed. E-mail: j.b.nielsen{at}mfi.ku.dk.

The basic locomotor rhythm in the cat is generated by a neuronal network in the spinal cord. The exact organization of this network its drive to the spinal motoneurones is unknown. The purpose of the present study was to use time- (cumulant density) and frequency domain (coherence) analysis to examine the organization of the last order drive to motoneurones during fictive locomotion (evoked by application of Nialamide and DOPA) in the spinal cat. In all cats, narrow central synchronization peaks (half-width <3 ms) were observed in cumulants estimated between electroneurograms (ENGs) of close synergists, but not between nerves belonging to muscles acting on different joints or to antagonistic muscles. Coherence was not observed at frequencies above 100 Hz and was mainly observed between synergists. Intracellular recording was obtained from a population of 70 lumbar motoneurones. Significant short-term synchronisation was observed between the individual intracellular recordings and the ENGs recorded from nerves of the same pool and of close synergists. Recordings from 34 pairs of motoneurones (10 pairs belonged to the same motor pool, 11 pairs to close synergists and 13 pairs to antagonistic pools) failed to reveal any short lasting synchronisation. These data demonstrate that short-term synchronisation during fictive locomotion is relatively weak and is restricted to close synergists. In addition, coherence analysis failed to identify any specific rhythmic component in the locomotor drive that could be associated with this synchronisation. These results resemble findings obtained during human treadmill walking and imply that the spinal interneurones participating in the generation of the locomotor rhythm are themselves weakly synchronised. The restricted synchronisation within the locomotor drive to motoneuronal pools may be a feature of the locomotor generating networks that is related to the ability of these networks to produce highly adaptive patterns of muscle activity during locomotion.


Key words: Locomotion • Motoneurones • Neural network







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