Background : Tricyclic antidepressants have been widely used in the treatment of chronic and acute pain conditions. The antinociceptive effect of tricyclic antidepressants results from the activation of noradrenergic and serotonergic pathways. But the effect of clomipramine on inflammatory hyperalgesia is not well blown. So we investigated the analgesic effect of acute and chronic clomipramine treatment on the formalin test.
Methods : Thirty rats were divided into six groups. Normal saline and clomipramine were administered subcutaneously once (Group 1 & 2), daily 4 times (Group 3 & 4) & daily 8 times (Group 5 & 6). Thirty minute after the last administration of clomipramine, 10% formalin 50 μl was injected on the dorsum of right paw. Pain
behaviors of rats were investigated by scoring 1; (clinching, 2; sustained elevation, 3; licking, biting, shaking.
Results : Acute clomipramine treatment produced not significantly different pain behavior from saline in phase Ⅰ and Ⅱ. Chronic clomipramine treatment showed time dependent depression of pain behavior in phase Ⅱ, but not in phase Ⅰ.
Conclusions : Clomipramine produced weak effect on acute pain but inflammatory hyperalgesia evoked by central sensitization might be modulated by chronic
administration of clomipramine.