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 0W3.
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