Sciatic nerve transection in adult and young rats: abnormal EMG patterns during locomotion

Transections of peripheral nerves usually lead to serious handicaps. In order to enhance insights into the poor functional recovery, we studied the effects of a unilateral sciatic nerve lesion in adult and young rats. Electromyographic (EMG) patterns of the tibialis anterior (a hindlimb flexor) and the gastrocnemius muscle (a hindlimb extensor) during walking were recorded after transecting the sciatic nerve at adult age and at the 10th postnatal day. After recovery periods lasting up to 21 weeks, EMG patterns in the hindleg muscles during locomotion were highly abnormal, irrespective of the age at lesioning. Electromyographic bursts were markedly irregular and, generally, coactivation of these antagonists was observed during walking. Other evidence has shown that after peripheral nerve transection, nerves randomly reinnervate their target muscles and we conclude that the patterns of muscle activity may be associated with the properties of foreign, as well as genuine, motor nerves. Behaviourally, walking patterns after a transection at adult age are markedly abnormal but, after transection at the 10th day, locomotion is much less disturbed. The finding of a discrepancy between a near normal walking pattern in rats operated on at a young age and severely disturbed EMG activity may be due to subtle readjustments in the force recruitment in the respective muscles, despite a random reinnervation by the sciatic nerve branches. These compensatory readjustments are particularly prominent after transection at an early age.