Acetylcholinesterase and nerve axon formation during muscle regeneration in rats

Histochemical activity of acetylcholinesterase (AChE) in the regenerating elements and infiltration of axons into the muscle regenerate was followed during 5 weeks after partial excision of the rat gastrocnemius muscle. AChE was first noticed in the newly formed myotubes 10 days after injury. Thereafter an increase in its activity was observed and 3 weeks after muscle excision regenerating elements were highly labelled with AChE end product activity which was diffusely distributed along them. In the fourth week after muscle excision, AChE staining was found to be organized in several clusters in the periphery of each new myofiber. Nerve axons were first observed in the regenerate at l6 days after injury and in the 4-week regenerate they were closely apposed to the new myofibers. Finally, mature endplates with a single nerve axon leading to them were seen in a 5-week muscle regenerate. It is concluded that the pattern of changes in AChE content and its distribution in the regenerating elements and their reinnervation process is similar in many respects to those occurring during embryonic myogenesis.