Innervation of the caudal denervated ventral roots and their target muscles by the rostral spinal motoneurons after implanting a nerve autograft in spinal cord-injured adult marmosets

Object. The authors conducted a study to determine the effects of using a n erve autograft (NAG) to promote and guide axonal regrowth from the rostral spinal cord to the caudal lumbar ventral nerve roots to restore hindlimb mo tor function in adult marmosets after lower thoracic cord injury. Methods. Nine animals underwent a left-sided hemisection of the spinal cord at T-12 via left-sided T9-L3 hemilaminectomy, with section of all ipsilate ral lumbrosacral ventral nerve roots. In the experimental group (five anima ls), an NAG obtained from the right peroneal nerve was anastomosed with the sectioned and electrophysiologically selected lumbar ventral roots (left L -3 and L-4) controlling the left quadriceps muscle and then implanted into the left ventrolateral T-10 cord. In the control group (four animals), the sectioned/selected lumbar ventral roots were only ligated. After surgery, all marmosets immediately suffered from complete paralysis o f their left hindlimb. Five months later, some clinical signs of reinnervat ion such as tension and resistance began to appear in the paralyzed quadric eps of all experimental animals that received autografts. Nine months posto peratively, three of the five experimental marmosets could maintain their l esioned hindlimb in hip flexion. Muscle action potentials and motor evoked potentials were recorded from the target quadriceps in all experimental mar mosets, but these potentials were absent in the control animals; Horseradis h peroxidase retrograde labeling from the distal sectioned/reconnected lumb ar ventral roots traced 234 +/- 178 labeled neurons in the ipsilateral T8-1 0 ventral horn, mainly close to the NAG tip. Histological analysis showed n umerous regenerating axons in this denervated/reconnected nerve root pathwa y, as well as newly formed motor endplates in the denervated/reinnervated q uadriceps. No axonal regeneration was detected in the control animals. Conclusions. These data indicate that the rostral spinal neurons can regrow into the caudal ventral roots through an NAG, thereby innervating the targ et muscle in adult marmosets after spinal cord injury.