Early behavioral and histological outcomes following a novel traumatic partial nerve lesion

A new partial nerve lesion (PNL) model is needed to better simulate traumatic lesions seen clinically that result in both dysfunction and neuropathic pain. We assessed surgical variability and several outcome measures including histology during the acute postoperative period. A surgical lesion was created in the rat tibial nerve by removing a segment, later confirmed by myelinated axon counts. Variability in the model was assessed with four different outcome measures during the first postoperative week (n=24), with additional histological outcomes at 7 days (n=13) and pain testing at 21 days (n=9). At 7 days postoperative, the PNL resulted in a tibial functional index (TFI) of -41.3% distinct from a percent motor deficit (PMD) of -76.3%. However, the respective deficits from 2 to 7 days were similar. Either test could detect outliers, but PMD measurements had a lower coefficient of variation and were easier to perform and analyze. The deleted segment contained 26% of the myelinated axons and resulted in distal degeneration that was either 46% based on axon counts or 54% based on area. Replicated experiments confirmed the PMD, muscle atrophy, and formation of neuropathic pain. In conclusion, our partial lesion histologically progresses twofold during the first postoperative week with profound behavioral deficits involving both motor and sensory loss. These results based on sensitive and correlative outcome measures support the application of this novel model in experimental nerve lesion studies.