Sciatic nerve transection in the adult rat: Abnormal EMG patterns during locomotion by aberrant innervation of hindleg muscles

The effects of lesions in the sciatic nerve were studied in adult rats, In the left hindleg, a segment 12 mm long was resected from the proximal part of the nerve, before the bifurcation into the peroneal and tibial nerves, T his segment in a reversed orientation was used as a nerve graft. EMG patter ns in the tibialis anterior and the gastrocnemius muscles at both sides wer e recorded during locomotion in six rats after recovery periods varying fro m 15 to 21 weeks. The specificity of axonal outgrowth was studied in nine r ats by retrogradely labeling the motoneurons with unconjugated Cholera Toxi n subunit B (CTB) after injections into the gastrocnemius, the soleus, and the tibialis anterior muscles at both sides. EMG patterns at the operated s ide were irregular and we often observed coactivation of the gastrocnemius and tibialis anterior muscle. Moreover, burst activity was badly adjusted t o the phases of the stepcycle, Retrogradely labeling indicated that the poo ls of motoneurons innervating the respective muscles at the left side had i ncreased in volume. Neuronal diameters were slightly decreased but a consid erable decrease was observed in dendritic branching and dendrite bundles in the pools of the SOL and in the GC were absent. No consistent trends in ne uronal numbers at the affected side in comparison to the right side were de tected. We conclude that axons, sprouting from the proximal stump of the sc iatic nerve, innervate the muscles aselectively and that the motoneurons of origin maintain their original activation pattern. (C) 2000 academic Press .