Locomotor Capacity Attributable to Step Training Versus Spontaneous
Recovery following Spinalization in Adult Cats.
R. D. de Leon, J. A. Hodgson, R. R. Roy and V. R. Edgerton.
Department of Physiological Science and 2Brain Research Institute
UCLA, LA, CA 90095..
APStracts 4:309N, 1997.
ABSTRACT
Locomotor performance, hindlimb muscle activity and gait patterns during
stepping were studied in step-trained and non-trained female, adult spinal
cats. Changes in locomotor characteristics relative to pre-spinalization
bipedal and quadrupedal stepping patterns were used to evaluate the effects of
step training on the capacity to execute full weight-bearing stepping
following spinalization. Step training consisted of full weight-bearing
stepping of the hindlimbs at the greatest range of treadmill speeds possible
at any given stage of locomotor recovery. In the initial stages of training
the limbs were assisted as needed to execute successful steps. Based on two
behavioral criteria, the maximum speed of treadmill stepping and the number of
successful steps per unit time, the ability to step was at least 3 times
greater in animals trained to step versus those allowed to recover
spontaneously, i.e. non-trained. The greater success in stepping was reflected
in several physiological and kinematic properties. For example, the amplitude
of EMG bursts in the tibialis anterior (an ankle dorsiflexor), the amount of
extension at the end of both the stance (E3) and swing (E1) phases of the step
cycle, and the amount lift of the hindlimb during swing were greater in step-
trained than in non-trained spinal cats. The changes that occurred in response
to training reflected functional adaptations at specific phases of the step
cycle, e.g., enhanced flexor and extensor function. The improved stepping
capacity attributable to step training is interpreted as a change in the
probability of the appropriate neurons being activated in a temporally
appropriate manner. This interpretation, in turn, suggests that step training
facilitated or reinforced the function of extant sensorimotor pathways rather
than promoting the generation of additional pathways. These results show that
the capacity of the adult lumbar spinal cord to generate full weight-bearing
stepping over a range of speeds is defined, in large part, by the functional
experience of the spinal cord after supraspinal connectivity has been
eliminated. These results have obvious implications with regards to 1) the
possibility of motor learning occurring in the spinal cord; 2) the importance
of considering "motor experience" in assessing the effect of any post-
spinalization intervention; and 3) the utilization of use-dependent
interventions in facilitating and enhancing motor recovery.
Received 14 August 1997; accepted in final form 4 November 1997.
APS Manuscript Number J676-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 14 November 1997