EFFECTS OF SYMPATHECTOMY ON A RAT MODEL OF PERIPHERAL NEUROPATHY

The aim of this study was to determine the effects of sympathectomy on our previously developed animal model for neuropathic pain. The neuro pathy was produced by a unilateral tight ligation of the L5 and L6 spi nal nerves in 81 rats, all of which showed a marked increase in freque ncy of paw lifting in response to innocuous mechanical stimuli and a s hortened latency of paw withdrawal in response to noxious radiant heat stimuli on the affected limb. We interpreted these as behavioral sign s of mechanical allodynia and heat hyperalgesia. Surgical sympathectom y was performed by removing the sympathetic chain bilaterally from the L2 to L6 levels at 1 week prior to and 1, 3 and 5 weeks after nerve i njury. In addition, the effect of sympathetic block was tested by syst emically injecting guanethidine or phentolamine. Surgical sympathectom y relieved the signs of both mechanical allodynia and heat hyperalgesi a. The effect of sympathectomy for mechanical allodynia is estimated t o be almost fully expressed within 30 min after the operation. Sympath etic block by chemical agents reversibly relieved the mechanical allod ynia. These data suggest that the rats in our model exhibit behavioral signs of neuropathic pain that are sympathetically maintained.