State-dependent effect of carbamazepine on analgesia in stressed and nonstressed rats

The effects of carbamazepine for analgesia (in tail flick method) and core temperature were studied in two dittetent states, i.e., stressed and nonstressed states in rats. Carbamazepine (10-50mg/kg i.p.) or immobilization stress alone did not induce significant analgesia for rats, but when carbamazepine was given in a combination with stress, it could produce a long-lasting analgesia which ecerted dual peal somponents (after 30 minutes and after 4 hours of prescripition). Carbamazepine produced initialy slight hypothrmia which was potentiated by immobilization stress. The effects of carbamazepine on analgesia induced by N^6-cyclohecyl adenosine (CHA : 0.2mg/kg i.p.), an adenosine A_1-receptor afonist, were an inhibition in nonstressed rats and stimulation in stressed rats. Initial cabazepine (25mg/kg i.p.)-induced analgesia in stressed rats was antagonized bu caffeine (5mg/kg i.p.), an adenosine antafonisr, and subsequent continuous analgesia was anatagonized by carbamazepine and morphine. These results suggest that the effect of carbamazepine on analgesia and core temperature are alterd depending upon the state of animals. Carbamazepine-induced hyperanalgesia in stressed rats is characterized in dual compoents. The initial hyperanalgesia may be due to an activation of adenosine receptors, whereas the subsequent long-lasting analgetic and antiulcerative action may be mediated by central opioid system.