Effect of Spinal and Systemic Clonidine Administration on the Postoperative Analgesia in Morphine-dependent and Naive Rats

Post operative pain and its control remains one of the most important issues in the field ofsurgery and health care system. formalin test has been used as a method for assessing painand analgesia in rats. systemic and spinally administered clonidine, an a2-adrenergic agonist,is proved to enhance postoperative analgesia. it has also been shown that morphine-dependentrats experience more chronic pain than naive rats.in this study we have explored the effect of certain doses of i.t. and i.p. cionidine onpostoperative pain in morphine-dependent and naive rats. rats were addicted by oralmorphine. for one group, an intrathecal catheter was inserted 48 hours before surgery. a 1cmlongitudinal incision was made through skin , fascia and muscle of the plantar aspect ofthe right hind paw. both morphine-dependent and naive rats received i.t. (l7!1g.kg l) or i.p.(0.7 mg.kg') clonidine immediately and 15 minutes befor formalin test, respectively. then,formalin -induced behaviors were recorded. in both phases of formalin test in morphinedepondentrats, i.p clonidine produced more analgesic effect, compared to i.t. injection(p