ACTH/MSH 4-10 improves motor unit reorganization during peripheral nerve regeneration in the rat.

ACTH/MSH 4-10 administration (10 micrograms/48 hr IP for 7 days) enhances neuromuscular activity following crush denervation of rat extensor digitorum longus muscle. The number of regenerated functional motor units is greater in peptide treated rats than in saline treated denervated controls. Selective activation of responding motor units indicates that ACTH/MSH 4-10 preferentially accelerates the reformation and stabilization of small size motor units. These observed effects may be beneficial since they contribute to the early reestablishment of more organized motor units, thereby restoring fine control of motor functions, in contrast to the disorderly reorganization of untreated regenerating systems. Possible mechanisms of peptide action (neurotransmitter synthesis and release, excitability changes, etc.) are discussed.