[Functional reinnervation of skeletal muscle in the adult rat by means of a peripheral nerve graft introduced into the spinal cord by dorsal approach].

In the adult Mammal, different types of neurons, whose processes have been damaged in the CNS, may regrow lengthy axons along autologous PNS grafts. In the present study, PNS bridges were used to join the spinal cord (C5 level) to a nearby skeletal muscle (m. longissimus atlantis) which was denervated prior to direct graft insertion into an aneural region. From 3 to 5 months later, the following results were obtained: in situ and in vitro electrical stimulation of the graft determined partial or full contraction of the reconnected muscle. Intracellular recordings showed miniature endplate potentials (mepps). Endplate potentials (epps), evoked by stimulating the nerve graft, were recorded at the same points after partial blockade of the transmission with low doses of curare. They were suppressed with higher concentrations. The overall appearance of cross semithin and thin sections of the grafts was typical of regenerating nerves. EM observations of reinnervated muscles revealed typical neuromuscular junctions located either around the site of grafting or in the site of original endplates. In situ HRP application to the transected PNS bridges led to extensive labeling of neuronal somata located, close to the site of grafting, in the spinal grey matter and in adjacent spinal ganglia. When HRP was injected into the recommended muscle, neuronal labeling was almost restricted to typical motoneurons of the ventral horn. These results indicate that spinal neurons, and especially motoneurons, are probably involved in the formation, through PNS grafts, of new functional cholinergic connections with denervated skeletal muscles.