Electrophysiological, morphological, and morphometric effects of aging on nerve regeneration in rats.

To investigate the influence of age on the process of nerve regeneration, the right common peroneal nerves of 14 2 month old and 14 10 month old rats were transected and resutured. At four and eight weeks after the nerve repair, the motor nerve conduction velocity (MNCV), latency, and amplitude of the evoked potential from the peroneus longus muscle were measured. The number of regenerated myelinated fibres, axon diameter, axon area, axon circumference, and myelin thickness were also measured. Compared with the control side (left common peroneal nerve and muscle), MNCV, latency, and amplitude showed higher recovery rates (recovery rate (%) = operated/control x 100) in 2 month old rats than in 10 month old rats, particularly at four weeks after the operation. In the morphometric study, axon diameter, axon area, and myelin thickness also recovered more quickly (recovery rate (%) = operated/control x 100) in 2 month old rats, particularly four weeks after the operation. Morphologically, myelin remnants were not found in 2 month old rats eight weeks after the operation, though they remained in 10 month old rats. These studies show that the recovery rate was significantly greater in 2 month old rats than in 10 month old rats. The explanation seems to be the difference in the speed of Wallerian degeneration, axonal regeneration, and myelin regeneration.