Fine structure of neuromuscular junctions after nerve section and implantation of nerve in denervated muscle

Abstract The first evidence of spontaneous reinnervation of neuromuscular junctions occurred 4 weeks after nerve section. In these experiments, the regenerating axons returned to old subneural apparatuses. There was little tendency to form new junctions as judged by light and electron microscopic studies. When the peroneal nerve was cut and reimplanted in the m. tibialis anterior at a new site distant from the original innervation band, a new innervation band developed near the point of entry of the transplanted nerve 6–8 weeks after operation. Electron microscopic study revealed atrophic subneural apparatuses with characteristic features of previous denervation and other junctions with fine structure resembling that observed in the embryonic morphogenesis of neuromuscular junctions. Similar patterns of neuromuscular junction reinnervation were observed in experiments in which after denervation, a foreign nerve was implanted into the muscle. Under these circumstances, an additional observation was the formation of abnormal tubular structures probably related to the regeneration of the transverse tubular system in atrophic muscle.