Regeneration of the rat sciatic nerve after different conditioning lesions: effects of the conditioning interval

Regeneration of the rat sciatic nerve was studied after a crush lesion (test lesion) on nerves previously subjected to a conditioning lesion. The test lesion was made approximately 30 mm proximal to the conditioning lesion. The period between the conditioning lesion and the test lesion was varied. Regeneration was measured by the pinch test. The conditioning procedure increased the rate of axonal elongation and decreased the initial delay. Conditioning intervals between 14 hours and 4 days were sufficient to increase the regeneration distance significantly, but only until day 4. If the conditioning interval was prolonged to 7 or 14 days, the conditioning effect persisted until day 6. A conditioning effect also was produced by transection of the sciatic nerve and by local compression produced with a silicone tube. The results of this study demonstrate that the type of injury and the conditioning intervals are important determinants in producing the conditioning effect in the rat.