EFFECTS OF TREADMILL EXERCISE AND HIGH-FAT FEEDING ON MUSCLE DEGENERATION IN MDX MICE AT THE TIME OF WEANING

1. Dystrophin-deficient hindlimb muscles of mdx mice undergo necrosis at the time of weaning when the motor activity of the mice greatly inc reases and muscle energy metabolism becomes more dependent on insulin and carbohydrates. 2. We have attempted to determine if the onset of n ecrosis in mdx mice at the time of is related to the development of mo tor activity and/or the change in diet. 3, Fourteen-day-old mdx mice w ere divided into two groups after weaning. One group was trained to ru n on a treadmill and the other group was kept on a high-fat diet. Musc le necrosis was assessed histologically in the soleus and extensor dig itorum longus muscles of mice in both experiments. 4. Keeping mice on a high-fat milk diet from the time of weaning up to 42 days of age did not influence the occurrence of necrosis in the soleus and extensor d igitorum longus muscles of the mdx pups. In contrast, treadmill exerci se greatly increased necrosis in both muscles. 5. We conclude that an increase in motor activity exacerbates the degeneration of hindlimb mu scles of mdx mice at the time of weaning.