Formation of ectopic neuromuscular junctions in adult rats

The formation of ectopic neuromuscular junctions between a transplanted foreign nerve (the superficial fibular nerve) and the denervated soleus muscle was examined in adult rats. Formation of new junctions was induced by denervating the soleus muscle by cutting the tibial nerve. Junctional transmission began 3 days after denervation when denervation was done 3 weeks after transplantation of the foreign nerve, and progressively later when denervation was done 8, 16 and 24 weeks after transplantation. The rate at which the transmission, once started, acquired mature characteristics was approximately the same in each case. Initially, spontaneous m.e.p.p.s were infrequent, long lasting with a skewed amplitude distribution. The e.p.p.s evoked by stimulation of the foreign nerve were then commonly below threshold for eliciting action potentials and were occasionally no larger than the size of the spontaneous m.e.p.p.s. M.e.p.p. characteristics became normal in the 2nd week after transmission had started. Fully effective evoked transmission with every innervated fibre responding with overshooting action potential occurred 1-3 months after onset of transmission.