The effect of a conditioning lesion on sudomotor axon regeneration.

The effects of a conditioning lesion on the rate of sudomotor axon regeneration were judged by the recovery of sweat gland (SG) secretion after cholinergic stimulation. Three groups of mice were given a conditioning lesion by crushing the sciatic nerve at mid-thigh 4, 7, and 14 days before a test lesion. A 4th group received a conditioning crush of the tibial nerve at the ankle 7 days before the test lesion. Control mice had a single test lesion. SG reinnervation in control mice began 19 days after the test lesion, and was functionally complete by 41 days. In groups with the conditioning lesion 4, 7, and 14 days before the test operation, the first reactive SGs reappeared at 16, 15, and 16 days respectively after the test lesion, and maximal recovery occurred by 33, 32, and 39 days. In mice with the distal conditioning lesion, reinnervation began at 19 days and was maximal by 36 days. In summary, a nerve conditioning lesion placed from 4 to 14 days prior to and at the same site as a test lesion significantly accelerated the growth rate of the fastest regenerating unmyelinated sudomotor axons and reduced the time until most SGs were reinnervated. A more distally placed test lesion reduced the interval for recovery.