Recovery of motor-unit function after peripheral nerve injury in aged rats.
The potential capacity of aged motoneurons for the reconstruction of motor-units after nerve crush injury was studied in the medial gastrocnemius (MG) muscle of male Fischer rats. The MG nerve in middle-aged (8 months old) and aged (24 months) rats was aseptically crushed under pentobarbital anesthesia. After a 3-month recovery period, the animal was reanesthetized and physiological properties of individual motor-units were recorded. The three different types (fast twitch, fatigable: FF; fast twitch, fatigue resistant: FR and slow twitch: S) of normal motor-unit organization were restored in both middle-aged and aged reinnervated muscles as measured by their relative distributions, mean twitch contraction times and mean tetanic tensions. Some reinnervated units in both aged and middle-aged rats produced a large tetanic tension which exceeded the range for intact units. These findings indicate that aged motoneurons maintain their ability for axonal regenerating and muscle fiber innervation to reestablish normal function of motor-units.
Kanda
K
K
Laboratory of Central Nervous System, Tokyo Metropolitan Institute of Gerontology, Japan.
Hashizume
K
K
D000375:Aging / Q000502:physiology*; D000818:Animals; D001369:Axons / Q000502:physiology; D004594:Electrophysiology; D009046:Motor Neurons / Q000502:physiology*; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D059348:Peripheral Nerve Injuries; D011817:Rabbits; D051381:Rats; D011916:Rats, Inbred F344; D013116:Spinal Cord / Q000166:cytology