Effects of Clonidine and Yohimbine on Neuropathic Pain in a Rat Model

ABSTRACT

OBJECTIVE: In a rat model of peripheral neuropathy, to determine whether neuropathic pain is related to the alpha-2 adrenergic receptor. METHOD: The neuropathic pain was produced by unilateral transection of the superior caudal trunk between the S3 and S4 spinal nerves. These animals showed the behavioral signs of neuropathic pain in the tail. Two weeks after the neuropathic surgery, tail withdrawal responses to the mechanical stimuli with von Frey hair (2.0 g) were examined 1, 2 and 24 hrs following the administration of clonidine, alpha-2 receptor agonist. One week after the clonidine test, the same behavioral test was done after the administration of clonidine along with yohimbine, alpha-2 receptor antagonist. RESULTS: Clonidine significantly reduced the frequency of tail response and yohimbine reversed the clonidine-induced anti-allodynic effect. CONCLUSION: These results suggest that neuropathic pain is related to the sympathetic nervous system via alpha-2 adrenergic receptor.