Reinnervation of sweat glands in the mouse: axonal regeneration versus collateral sprouting.

The capacity of sudomotor axons to reinnervate sweat glands by regeneration after freezing was compared with their capacity to reinnervate by the mechanism of collateral sprouting. Two groups of mice were prepared in the same manner, with a single exception. All nerves to the hind paw were cut and tied to prevent regrowth. The exception, the lateral plantar nerve, was left intact in one group and frozen at the ankle in the other group. Reinnervation of sweat glands in the paw was charted frequently for 10 weeks using a silastic mold method. We found that sudomotor axons regenerating from the frozen nerve functionally reinnervated sweat glands of the paw sooner, beginning at 15 days postoperation, and at a higher rate than reinnervation from the collateral branching intact nerve, that began at about 25 days. Full recovery occurred by 41 days in most animals of both groups. We also found that stimulation of sweating by pilocarpine activated more sweat glands during the reinnervation period than stimulation by heating the mice, suggesting that the newly regenerating sudomotor axons have a high threshold.