Effect of age on collateral reinnervation of sweat glands in the mouse.

This study demonstrates that the number of sweat glands (SGs) innervated by individual peripheral nerves in the mouse hind paw decreases with aging but the ability for reinnervation by collateral sprouting is maintained throughout life. In one experiment, the saphenous, peroneal and tibial nerves were cut and tied, denervating all SGs of the hind paw except those receiving axons from the intact sural nerve. In another, the saphenous was the only nerve left intact. The initial number of SGs supplied only by the single intact nerve was significantly higher in young adult than older mice. The capacity of the sural and saphenous nerves to collaterally reinnervate the denervated SGs was followed by serial testing for the return of sensitivity to pilocarpine stimulation. Collaterally reinnervated SGs appeared during the second and third weeks postoperation adjacent to already active SGs, thereby increasing the total sweat area of the intact nerve, and its SG number about 3, 2 and 5 times for the sural, and 8, 2 and 2 times for saphenous nerve, in young, adult and old animals respectively. Reinnervation was slightly faster and the degree of extension greater in young than adult mice, and the degree of extension was decreased in older mice. These observations suggest that the number of sudomotor axons in the peripheral nerve, as well as their capacity for collateral reinnervation, is reduced with aging.