An experimental study of direct nerve implantation in denervated muscle--reinnervation by formation of new motor endplates

The author investigated the possibility and the mechanism of reinnervation of "endplate-free denervated muscle" by direct neurotization, using the anterior tibial muscles of rats. The proximal stump of the posterior tibial nerve, which was severed at the ankle level, was embedded into the transected distal 1/5 (5 mm) of the endplate-free segment of the muscle. M-waves by electromyogram appeared 6 weeks after neurotization. In the histological specimens with acetylcholine-esterase (Ach-E) stain, accumulations of Ach-E activity were detected from one week after neurotization. These increased gradually in both number and size. In the electron microscopy specimens, axons were seen in the synaptic fold-like indentations of the thickened sarcoplasm in 4 weeks. Eight weeks after neurotization, synaptic vesicles were observed in the axons. It was established by this study that direct neurotization resulted in the formation of new motor endplates and in the reinnervation of "endplate-free denervated muscle".