[Reinnervation after direct neurotization in cross innervated rats--a study of spinal anterior horn cells by horseradish peroxidase method].

This experiment was performed to clarify the progress of the reinnervation of the denervated muscle after direct neurotization using cross innervation. In this study 79 rats were used. The common peroneal nerve was cut and neurotized into the previously denervated gastrocnemius muscle. At different stages after neurotization, evoked M-waves of the neurotized muscle, and muscle weights were analyzed. Histological findings of the neurotized and denervated gastrocnemius muscles, and the number of spinal anterior horn cells labeled by the horseradish peroxidase method, were also studied. The labeled cells of the neurotized gastrocnemius muscle were located in the spinal level between L3 and L5, which was almost the same site as that of the anterior tibial muscle in normal rats. This finding showed that the denervated gastrocnemius muscle was reinnervated by the implanted common peroneal nerve. The labeled cells of the neurotized gastrocnemius muscle started to appear 2 weeks after neurotization, and the number of cells were almost the same as in the control side from 3 weeks to the end of the experiment. The fixed formed M-wave was observed in some cases 3 weeks after neurotization and in all cases at 6 weeks and thereafter. Four weeks after neurotization and denervation, the weight of neurotized muscle was significantly heavier than that of denervated muscle. The histological findings of the gastrocnemius muscle 3 months after neurotization were almost normal. These results showed that the reinnervation of denervated muscle after direct neurotization using cross innervation began after 2 weeks and the neurotized muscle started to regain its function 3 weeks after the neurotization. The present study also suggested that the muscle power of the neurotized muscle recovered fully resulting from increasing number of labeled spinal anterior horn cells.