effects of acute and chronic lithium on morphine-induced analgesia in mice by formalin test

in this study, the effects of acute and chronic lithium on nociception induced by formalin and its interactions with morphine-induced analgesia were studied in mice. formalin test was selected to study nociception. subcutaneous injection of different doses of morphine (1.5, 3 and 6 mg/kg) induced analgesia in a dose dependent manner in both phases of the formalin test. intraperitoneal administration of different doses of lithium (20, 40, 60 and 80 mg/kg) induced analgesia in late phase but didnot show any significant effect in early phase. acute administration of lithium (40, 80 mg/kg) increased analgesia induced by morphine (3 mg/kg) in both phases of formalin test. prctreatment of the animals with chronic lithium (1200 mg/l) for 15 days induced antinociception and increased .the analgesia induced by morphine in both phases of formalin test. it is concluded that administration of acute and chronic lithium can probably affect pain response in both phases of formalin test and interact with morphine-induced antinociception.