Prevention of myonecrosis in mdx mice: effect of immobilization by the local tetanus method.

Sixteen mdx mice of three-week-old were injected with tetanus toxin into the right gastrocnemius muscle and then subjected to sustained dorsiflexion of the right ankle joint (local tetanus) for 2 to 56 days. Another 16 mdx mice of the same age were not injected with tetanus toxin, serving as controls. The incidence of centronucleated muscle fibers, which indicate preceding myodegeneration, was significantly reduced in the tetanus toxin injected soleus muscle (SOL) and extensor digitorum longus muscle (EDL), compared with that in the untreated control mdx mice. It seems that myonecrosis in the mdx mouse is facilitated by muscle movement itself and that immobilization of muscle prevents myonecrosis. This concept is helpful for understanding the mechanism underlying myonecrosis in patients with Duchenne muscular dystrophy, and for instruction concerning rehabilitation programs and activities in daily life.