Muscle coordination in hindlimbs of mice after bilateral nerve regeneration

The common peroneal nerve was transected bilaterally in 25 adult mice. Nerve stumps were immediately readapted without nerve suture. Before transection and after nerve regeneration the muscle coordination of tibialis anterior (TA) and medial gastrocnemius (MG) muscle was examined by electromyographic recordings from both muscles (EMG) during free running. Using a personal computer, the degree of muscle coordination between TA and MG was determined by calculating a coordination index. In normal mice an antagonistic innervation pattern was observed. After nerve transection and regeneration the degree of muscle coordination of TA and MG substantially decreased with great interindividual but also great intraindividual variation. In 16 mice there was no correlation between the coordination index of the left and right hindlimbs. In nine out of 25 mice reinnervation was absent on one side. These results suggest that nerve regeneration by axonal sprouting to appropriate or foreign muscles occurs at random and that there are no intraindividual factors which might promote the finding of the proper target muscle.