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

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Post operative pain and its control remains one of the most important issues in the field of surgery and health care system. Formalin test has been used as a method for assessing pain and 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-dependent rats 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 on postoperative pain in morphine-dependent and naive rats. Rats were addicted by oral morphine. For one group, an intrathecal catheter was inserted 48 hours before surgery. A 1cm longitudinal incision was made through skin , fascia and muscle of the plantar aspect of the right hind paw. Both morphine-dependent and naive rats received i.t. (l7!1g.kg l) or i.p. (0.7 mg.kgי) clonidine immediately and 15 minutes befor formalin test, respectively. Then, formalin -induced behaviors were recorded. In both phases of formalin test in morphinedepondent rats, i.p clonidine produced more analgesic effect, compared to i.t. injection (P

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