A comparison of cryoprobe and crush lesions in the rat sciatic nerve

This study examines the behavioral, sensory, motor and structural recovery during the first 2 months following a freeze (cryoprobe) lesion compared to a nerve crush (forceps). There is a complete loss of sensory and motor function following either type of lesion during the first 2 weeks of recovery. The toe spreading reflex and the sciatic functional index of locomotion behavior returned to normal without significant group differences. Latency times for the pain withdrawal reflex were slightly shorter in the cryoprobe group, but both groups returned to baseline during the second month. An improved regenerative pattern was suggested for the motor recovery in the cryoprobe group as expressed by the amplitude of the digital twitch tension curves. However, the respective curve areas were not different. Morphometric analysis indicated a significant reduction in the distal nerve cross-sectional area, an increase in the mean myelinated fiber density and an increase in the estimated total number of myelinated nerve fibers in both experimental groups. Mean fiber diameter and myelin sheath thickness had not fully returned to normal in either experimental group. Both the fiber size and myelin sheath thickness were significantly reduced in the cryoprobe group. In conclusion, the two lesion types have remarkably similar patterns of recovery. Functional data suggest that motor recovery precedes sensory recovery following a cryoprobe lesion.