Altered electromyographic activity pattern of rat soleus muscle transposed into the bed of antagonist muscle.

Human patients suffering from motor paralysis of the leg can learn, to some extent, how to use the transposed antagonistic muscle in place of the damaged or ineffective muscle. Experiments on animals showed opposite results, although in a few experiments the functional reorganization of the activity of the transposed muscle was not excluded. In our experiments, we performed transposition of the soleus (Sol) with a preserved innervation into the bed of the removed extensor digitorum longus (EDL) in 6-d-old pups and 3-month-old rats. The locomotor and reflex EMG activity of the transposed Sol (trSol) was recorded in chronic experiments 3-4 months later. Our results showed that the EMG activity of the Sol might be modified when the muscle is transposed into the bed of the antagonistic muscle EDL. The modification consisted of an additional burst of activity during the swing phase and of reflex response of the muscle to the plantar flexion. This modification was present in all animals operated on at 6 d of age and in two of six adults. After chronic experiments, we excluded the possibility that the flexor-like activity was induced by additional innervation of the trSol by the cut end of the EDL nerve. We suggest that the observed modifications of activity of trSol might be caused by readjustment of the spinal network organization to the new functional demands. Two factors might be responsible for this readjustment: the immaturity of the nervous system at the moment of surgery and preserved afferent innervation of the transposed muscle.