Sciatic cryoneurolysis in rats: a model of sympathetically independent pain. Part 1: Effects of sympathectomy.

The purpose of this study was to evaluate the effects of preemptive and postlesion sympathectomy in the sciatic cryoneurolysis (SCN) model of neuropathic pain in rats. SCN in rats produces a prolonged significant mechanical allodynia (hypersensitivity to previously non-noxious mechanical stimuli) with no thermal hyperalgesia. In at least two other models, sympathectomy is effective in attenuating existing mechanical allodynia and thermal hyperalgesia or deterring their development after nerve injury. These models appear to mimic the direct sympathetic involvement characteristic of the clinical syndrome termed sympathetically maintained pain (SMP). To investigate these concepts in the SCN model, sympathectomy was performed prior to SCN in animals with established SCN-induced allodynia. Sympathectomy did not alter the pattern of existing allodynia or its development in this model. The results suggest that SCN is a useful and easily reproducible model of sympathetically independent pain (SIP).