Motoneurons of the adult marmoset can grow axons and reform motor endplates through a peripheral nerve bridge joining the locally injured cervical spinal cord to the denervated biceps brachii muscle

Reconnection of the injured spinal cord (SC) of the marmoset with the dener vated biceps brachii muscle (BB) was obtained by using a peripheral nerve ( PN) bridge. in 13 adult males, a 45 mm segment of the peroneal nerve was re moved: one end was implanted unilaterally into the cervical SC of the same animal (autograft), determining a local injury, although the other end was either directly inserted into the BE (Group A) or, alternatively, sutured t o its transected motor nerve, the musculocutaneous nerve (Group B). From 2- 4 months post-surgery, eight out of the 10 surviving animals responded by a contraction of the BE to electrical stimulations of the PN bridge. All ten were then processed for a morphological study. As documented by retrograde axonal tracing studies using horse radish peroxidase or Fast Blue (FB), a mean number of 314 (Group A) or 45 Group B) spinal neurons, mainly located close to the site of injury and grafting, re-expressed a capacity to grow a nd extend axons into the PN bridge. Most of these regenerated axons were ab le to grow up to the BE and form or reform functional motor endplates. Many of the spinal neurons that were retrogradely labeled with FB simultaneousl y displayed immunoreactivity for choline acetyl-transferase and consequentl y were assumed to be motoneurons. Reinnervation and regeneration of the BE were documented by methods revealing axon terminals, endplates and myofibri llary ATPase activity. Our results indicate that motoneurons of the focally injured SC of a small-sized primate can, following the example of the adul t vat, re-establish a lost motor function by extending new axons all the wa y through a PN bridge connected to a denervated skeletal muscle. (C) 2000 W iley-Liss, Inc.