Regional Distribution of the Locomotor Pattern Generating Network in the
Neonatal Rat Spinal Cord
Cowley, K. C. and B.J. Schmidt.
Department of Physiology, Faculty of Medicine, University of Manitoba,
Winnipeg, Manitoba, CANADA R3E 0W3.
APStracts 3:0235N, 1996.
The regional distribution of spinal cord networks producing locomotor-like, as
well as non-locomotor-like, activity was studied using an in vitro neonatal
rat preparation. Rhythmic activity was induced by bath application of either
5-HT, acetylcholine (ACh), N-methyl-D,L-aspartate (NMA), or combined 5-HT/NMA,
and was monitored via hindlimb flexor (peroneal) and extensor (tibial)
electroneurograms (ENGs) or ventral root recordings. In some experiments,
synchronous patterns were produced by the addition of inhibitory amino acid
(IAA) receptor antagonists. Selective application of 5-HT to cervical and
thoracic cord regions induced rhythmic activity in these segments but failed
to evoke hindlimb ENG discharge. Exposure of the isolated lumbar region to 5-
HT produced tonic activity only. Application of 5-HT to the whole cord
produced locomotor-like activity in hindlimb ENGs which persisted after
midsagittal section of the spinal cord from the conus to the thoraco-lumbar
junction. In other experiments, transverse hemisection of the rostral lumbar
cord during whole cord exposure to 5-HT abolished rhythmic activity in
ipsilateral hindlimb ENGs, suggesting that under these conditions rhythmic
activity on one side of the lumbar cord was insufficient to maintain rhythmic
activity on the contralateral side. Selective application of NMA or ACh to
cervical and/or thoracic cord regions evoked rhythmic activity in these
supralumbar segments, as well as rhythmic, but non-locomotor-like, activity in
the lumbar region. In contrast to the effect of 5-HT, both NMA and ACh evoked
rhythmic activity when applied solely to the lumbar region, and the side-to-
side alternation produced by whole cord ACh application was uncoupled by
midsagittal lesions of the lumbar region. In the presence of IAA antagonists,
the side-to-side coupling of bilaterally synchronous rhythms was maintained
despite extensive midsagittal lesions leaving all but one or two segments of
either cervical, thoracic, or lumbar cord bilaterally intact, and rhythmic
activity could be maintained even in single isolated hemisegments. The effects
of 5-HT/NMA were similar to those observed using 5-HT alone, although 5-HT/NMA
induced rhythmic activity in hindlimb ENGs when applied selectively to
supralumbar regions. The results suggest that 1) a 5-HT-sensitive oscillatory
network, capable of producing a locomotor-like pattern of activity, is
distributed throughout the supralumbar region of the spinal cord and mediates
descending rhythmic drive to lumbar motor centers, 2) NMA- and ACh-sensitive
rhythmogenic elements are distributed throughout the spinal cord, including
the lumbar region, and 3) the spinal cord contains an extensive propriospinal
network of reciprocal inhibitory and excitatory connections characterized by
redundantly organized side-to-side projections.
Received 23 April 1996; accepted in final form 24 September 1996.
APS Manuscript Number J343-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996