Effect of aging on recovery of cutaneous nociception after end-to-side nerve repair in the rat.

Age-related differences in the recovery of cutaneous mechanonociception after end-to-side nerve repair were examined in rats. Recovery of the dorsal foot skin nociception, determined by pinch test 19 weeks after the end-to-side coaptation between the recipient peroneal and the donor sural nerves, was about 20% larger in young adult rats. It was found in 66% and 16% of young and aged rats, respectively. The presence of nociceptive axons in the recipient nerve was determined by pinch test in 75% and 25% of young and aged rats, respectively (P = 0.039). The number of myelinated (but not of unmyelinated) axons was significantly larger in young than in aged rats, and the majority of them in both age groups were thin fibers. Functional recovery of cutaneous mechanonociception after end-to-side nerve repair is less extensive in aged rats because of severely reduced sprouting into the end-to-side coapted nerve compared with young adult rats.