Abstract
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 α2-adrenergic agonist, is proved to enhance postoperative analgesia. It has also been shown that morphine-dependent rats experience more chronic pain than naïve rats.
In this study we have explored the effect of certain doses of i.t. and i.p. clonidine on postoperative pain in morphine-dependent and naïve rats. Rats were addicted by oral morphine. For one group, an intrathecal catheter was inserted 48 hours before surgery. A 1-cm longitudinal incision was made through skin, fascia and muscle of the plantar aspect of the right hind paw. Both morphine-dependent and naïve rats received i.t. (17µg.kg-1) or i.p. (0.7 mg.kg-1) clonidine immediately and 15 minutes befor formalin test, respectively. Then, formalin-induced behaviors were recorded. In both phases of formalin test in morphine-depondent rats, i.p clonidine produced more analgesic effect, compared to i.t. injection (P<0.01). On the other hand i.p. clonidine caused more analgesic effect in phase II of formalin test in morphine-dependent than naïve rats (P<0.05).
Clonidine may potentiate the analgesic effect of chronically administered morphine. Also it seems that clonidine acts better in supraspinal level, compared to the spinal level.
Keywords
Formalin test Clonidine Post-operative pain Opioid-related disorders Rat
Copyright
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