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Recovery of motor-unit function after peripheral nerve injury in aged rats
1Laboratory of Central Nervous System, Tokyo Metropolitan Institute of Gerontology, Japan.
Abstract:
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.
Insights
Aging does not prevent aged motoneurons from regenerating axons and reinnervating muscle fibers. This study shows aged motor units can be restored to normal function after nerve injury.
Area of Science:
- Neuroscience
- Gerontology
- Muscle Physiology
Background:
- Aging is associated with a decline in motor function.
- The regenerative capacity of aged motoneurons after injury is not fully understood.
- Motor-unit reconstruction is crucial for restoring muscle function.
Purpose of the Study:
- To investigate the potential of aged motoneurons to regenerate and reinnervate muscle fibers after nerve crush injury.
- To compare the functional recovery of motor units in middle-aged versus aged rats.
Main Methods:
- Nerve crush injury was induced in the medial gastrocnemius (MG) muscle of middle-aged (8 months) and aged (24 months) male Fischer rats.
- A 3-month recovery period was allowed for axonal regeneration and reinnervation.
- Physiological properties of individual motor units were recorded and analyzed.
Main Results:
- Normal motor-unit organization (fast twitch, fatigable; fast twitch, fatigue resistant; slow twitch) was restored in both middle-aged and aged rats.
- Restored motor units exhibited distributions, contraction times, and tetanic tensions comparable to intact units.
- Some reinnervated motor units in aged rats produced tetanic tensions exceeding those of intact units.
Conclusions:
- Aged motoneurons retain significant capacity for axonal regeneration and functional reinnervation after nerve injury.
- Motor-unit reconstruction and restoration of normal physiological properties are achievable even in aged animals.
- These findings suggest that interventions aimed at enhancing neuroregeneration may be beneficial for improving motor function in aging populations.