Skeletal muscle regeneration during aging and after long-term denervation.

Data accumulated in recent years strongly suggest that the basis for at least part of the muscle atrophy seen in old age is related to the diminution of motor innervation in normal muscle and a decreased effectiveness of reinnervation of regenerating muscle fibers. Thus, attempts to stabilize reverse the decline of the skeletal musculature during aging must take into account both the effects of aging on the peripheral nervous system and the presence of populations of denervated muscle fibers in the aging muscles. Of considerable importance is the question of how long muscle fibers in old animals can remain denervated before they begin to lose their capacity for restoration if they ultimately become reinnervated. The experimental studies reviewed here have shown that normal muscles in old animals are capable of a high degree of restoration as long as their motor nerve supply remains undamaged. After a certain period of time, denervated muscle in young animals steadily loses the capacity to restore or repair itself. To date, so little information is available on the properties of denervated muscle in old animals that meaningful comparisons cannot be made. Ultimately, ensuring that normal or injured muscle in old individuals is supplied by an effective motor innervation may be a real key to the problems of muscle loss in old age, but if such could be provided, it will be important that the old musculature, whether normal or injured, is capable of adequately responding to the innervation.