Muscle regeneration after imposed injury is better in younger than older mdx dystrophic mice.

The ability of a fast-twitch dystrophic muscle to regenerate was compared at two ages to control muscle regeneration. Myofiber growth, and the distribution of nuclei in fibers were used to characterize the muscle regeneration 3 and 6 weeks after injury. In control and mdx muscles, myosatellite cell proliferation was completed by 3 weeks after injury. Mdx muscle regenerated as well as controls, based on similar distribution of myofiber cross sectional area, and the percent of centronucleation, typical of regenerated fibers. In addition, muscle from the younger dystrophic mdx mice grew to unoperated levels with no net change in fiber area distribution, while older muscles did not regenerate as well. There were also more peripheral (satellite cell) nuclei observed in younger mdx muscle than in older muscles, after the most active phase of dystrophy.