Regulation of the size and distribution of ectopic neuromuscular junctionsin adult skeletal muscle by nerve-derived trophic factor and electrical muscle activity

Transplanted axons induced multiple, irregularly distributed acetylcholine receptor (AChR) aggregates on muscle fibers at early stages of ectopic neur omuscular junction formation in denervated adult rat soleus muscles. Subseq uently, most AChR aggregates disappeared (the losers). A few aggregates sur vived (the winners) and, as part of the surviving junctions, reached a cert ain size and spatial separation along the fibers. This elimination of loser s and development of winners occurred only in electrically active muscles w hether the activity was elicited by intact axons or by electrical muscle st imulation after the axons had been cut early. We conclude that electrical m uscle activity regulates the size and distribution of ectopic neuromuscular junctions by acting in conjunction with a nerve-derived priming influence that does not require the continued presence of nerve terminals.