Experimental study of spinal nerve repair after plexus brachialis injury in newborn rats: A horseradish peroxidase study

Abstract

As an animal model of nerve injury at delivery, traction injury was made to the plexus brachialis nerves of newborn rats. By traction, spinal root avulsion or plexus brachialis injury was produced. Horseradish peroxidase (HRP) was injected into the denervated biceps or triceps brachii muscle at various intervals after the experimental nerve injury. Four weeks after the injury, HRP-labeled neurons were identified in the ventral horn of the injected side. In the experimental animals the labeled neurons were found in the ipsilateral ventral horn of the C 4 through T 1 levels regardless of whether the injection was into the denervated biceps or triceps brachii muscle. In the control animals the distribution of the labeled neurons differed depending on the site of injection; labeled neurons were found in the ipsilateral ventral horn of C 4 through C 8 after the injection of HRP into the biceps and in that of C 5 through C 8 after injection into the triceps. Within the same level of the cord, the labeled neurons in the experimental animal showed more widespread distribution in the vental horn than those in the control animal. Regeneration of the injured nerves by axonal sprouts from the proximal stumps with subsequent confusion of growth was supported by the present study. In a small number of experimental animals, the labeled neurons were identified not only in the ipsilateral but also in the contralateral ventral horns, suggesting the persistence of an immature mode of innervation of the forelimb muscle by bilateral ventral horn neurons. We also correlated the results of the study and the peculiar clinical findings that follow recovery of the nerve injury during delivery.