Locomotor Rhythm Evoked by Ventrolateral Funiculus Stimulation in the
Neonatal Rat Spinal Cord, In Vitro.
Magnuson, David S. K. and Tammy C. Trinder.
Department of Physiology, University of Manitoba, Winnipeg, Manitoba. R3E
APStracts 3:0194N, 1996.
The rhythmicity of the responses, leaving only long-duration simultaneous
activation of the ipsilateral roots following VLF stimulus trains. The minimum
lesion that effectively abolished the rhythmicity was one that divided only
the L2 and L3 segments. In preparations rendered arrhythmic to VLF stimulation
by an L2/3 midsagittal lesion, rhythmicity could still be induced by N-methyl-
D-aspartate (NMDA; 2-5_M) and serotonin (5-HT; 20-50_M), a drug combination
commonly used to induce locomotor-like rhythmicity and air-stepping in vitro.
Field potentials recorded following single stimuli delivered to the VLF
revealed short latency, large amplitude responses in the ventral horn and
intermediate grey both ipsilateral and contralateral to the stimulus site at
T12 and L2. These observations suggest that: 1) the discrete pathway under
study may be an important descending locomotor command pathway and 2) this
pathway has a strong bilateral projection in the lower thoracic and upper
lumbar segments that is crucial for the initiation of VLF-induced rhythmic
motor output. The induction of rhythmicity by NMDA/5-HT in an L2/3 lesioned
preparation suggests that these two rhythmogenic mechanisms may represent
different levels within the circuitry that comprises the central pattern
generator for locomotion. The rhythmic activity resulting from VLF stimulation
being dependent on a bilateral projection that can be bypassed by the
generalized excitation and subsequent rhythmicity that results from bath
application of the NMDA/5-HT combination.
Received 3 July 1996; accepted in final form 28 August 1996.
APS Manuscript Number J422-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 7 October 1996