Increased NGF Levels in a Rat Partial Nerve Injury Model

Methods: In 4 Sprague Dawley rats, the left sciatic nerve was exposed and constricted with four 4/0 chromic gut sutures. Behavioural testing was undertaken 10, 8, 6, 3 and 1 day pre-operatively and 1, 4, 6, 8, 11, 13 and 14 days post-operatively. The uninjured contralateral side served as a control. The mean latencies of foot withdrawal to cold (acetone) and hot (radiant heat) stimuli were determined (n=5 per session). Fifty percent withdrawal thresholds to graded mechanical stimuli (0.2 – 26g) were also determined using von Frey hairs. Fourteen days post-injury, glabrous hindpaw skin was harvested under terminal anaesthesia. An ELISA was used to assay the NGF content of skin that was snap frozen in liquid nitrogen.

Results: Following partial nerve injury, there were behavioural changes in paw withdrawal consistent with thermal and mechanical hyperalgesia that occurred within 14 days of the injury. Preliminary results show higher NGF levels in ipsilateral footpads compared to contralateral.

Conclusion: Preliminary data suggest that a constriction injury to the rat sciatic nerve results in thermal and mechanical hypersensitivity and that there are increased levels of NGF in ipsilateral footpad skin compared to contralateral. These results suggest a possible role for NGF in the aetiology of neuropathic pain after a partial nerve injury.