Does Collateral Sprouting from Corticospinal Fibers Participate in Motor Recovery After Spinal Hemisection in Monkeys?

Abstract

Hemisection of the spinal cord at the lower thoracic level produces an ipsilateral flaccid paralysis of the hindlimb in the monkey. In the course of several weeks after the operation, the animal shows gradual recovery of some useful motor functions such as standing and locomotion, in parallel with exaggeration of tendon reflexes (Aoki et al. 1976; Aoki and Mori 1978). In the following recovery period several months after the hemisection, the animal appears to have no motor deficits on casual observation. These findings suggest the possibility that the supraspinal descending fibers through the remaining pathways make new functional connections with lumbosacral motoneurons on the hemisected side in the recovery period (Nathan and Smith 1973). We previously demonstrated parallel recovery from the effects of motor cortical stimulation on the hindlimb muscles and the capability of voluntary movement of the affected limb (Aoki and Mori 1978, 1979, 1980). Recent histological study has suggested the possibility that collateral sprouting (McCouch et al. 1958) from the descending fibers in the remaining cord could be correlated with motor recovery in the affected limb (Aoki et al. 1985, 1986).