Recovery of locomotion in the cat following spinal cord lesions.

In most species, locomotor function beneath the level of a spinal cord lesion can be restored even if the cord is completely transected. This suggests that there is, within the spinal cord, an autonomous network of neurons capable of generating a locomotor pattern independently of supraspinal inputs. Recent studies suggest that several physiological and neurochemical changes have to occur in the neuronal networks located caudally to the lesion to allow the expression of spinal locomotion. Some evidence of this plasticity will be addressed in this review. In addition, original data on the functional organisation of the lumbar spinal cord will also be presented. Recent works in our lab show that segmental responsiveness of the spinal cord of the cat to locally micro-injected drugs in different lumbar segments, in combination with complete lesions at various level of the spinal cord, suggest a rostro-caudal organisation of spinal locomotor control. Moreover, the integrity of midlumbar segments seems to be crucial for the expression of spinal locomotion. These data suggest that the regions of critical importance for locomotion can be confined to a restricted portion of the spinal cord. Later, these midlumbar segments could be targeted by electrical stimulation or grafts to improve recovery of function. Understanding the changes in spinal cord neurophysiology and neurochemistry after a lesion is of critical importance to the improvement of treatments for locomotor rehabilitation in spinal-cord-injured patients.