ROSSIGNOL, Serge; Universite de Montreal: Adaptive Mechanisms of Spinal Locomotion in Cats

My work has concentrated on various aspects of the neural control of locomotion in the cat, including descending, sensory and spinal controls. A long standing interest has been the recovery of treadmill locomotion with interactive training after complete lesions at T13 in adult cats. We have studied the roles of various neurotransmitters in triggering or modulating the characteristics of spinal locomotion. We have injected intrathecally the alpha-2 noradrenergic agonist, clonidine, to intensively train the cats every day and these could recover spinal locomotion within 7-9 days. Finally, we have shown that the receptors of most neurotransmitter systems are initially up-regulated within the first month post-spinalisation and later on some (not all) return to normal. Altogether, these results suggest that the spinal locomotor network is somewhat plastic, an issue we wanted to address more directly. We cut ankle flexor nerves (TA and EDL) on one side in otherwise intact cats. The kinematics of the recovered locomotion was very similar to control after only a few days and there were minor EMG changes in the hip and knee flexors. However, after spinalisation, stepping was asymmetrical and marked by large dysfunctional knee and hip hyperflexions during swing on the denervated side leading to a maladaptive withdrawal of the foot upwards while the other side performed almost normal locomotor movements. The abnormality of the spinal locomotor pattern in cats which has already been adapted to a neurectomy suggests that changes had occurred in the spinal cord itself. The experiments reported by Bouyer on ankle extensor neurectomies and hind paw cutaneous nerve lesions will extend this concept that the locomotor generating mechanisms in the spinal cord are adaptable which offers a solid background for rehabilitation strategies based on locomotor training.