Effect of granisetron on morphine-induced analgesia in mice by formalin test

1. In this investigation, the influence of a selective 5HT3 antagonist, granisetron, on morphine-induced antinociception in the formalin test has been studied. There is evidence that the 5HT3 receptor system takes part in analgesic response. 2. Male albino mice weighing 22-27 g were used in the experiments. All drugs were administered 30 min before formalin injection. Comparison between groups was made by analysis of variance and then Newman-Keuls test. 3. Different doses of morphine (1.5-9.0 mg/kg) subcutaneously induced antinociception in both phases of the formalin test. 4. Coadministration of granisetron (0.1-10.0 mg/kg) intraperitoneally had no effect on morphine analgesia, but granisetron injection alone induced dose-dependent analgesia in both phases of the formalin test. 5. Results of this study suggest a role for a new selective 5HT3 antagonist in analgesia.