Background and Aim: Previous studies have shown that the hydroalcoholic extract of Echinophora platyloba inhibits the acquisition of morphine dependence and the rewarding effects of the drug. Therefore, the purpose of the present study was to evaluate the impact of the plant's hydroethanolic extract on tolerance to morphine-induced hyperactivity. Materials and methods: Male mice (24-28 g) were randomly assigned into groups of 8. To evaluate the effects of drugs on locomotor activity, mice received morphine (0.5, 5, 10, 20, 40 mg/kg, s.c.) and the plant extract (25,50, 75 mg/kg, i.p.). Respective control groups received saline. In the next phase, the plant extract (25,50, 75 mg/kg) or saline was administered one hour before the dose of morphine (40 mg/kg), which induced hyperactivity. Finally, during the induction of tolerance to hyperactivity by morphine, four groups of mice received saline or plant extract (25,50, 75 mg/kg) one hour before receiving morphine doses. Results: Morphine, depending on its dose, had dual inhibitory or stimulatory effects on locomotor activity, but all doses of the plant extract inhibited the spontaneous locomotor activity of the animals. In addition, when the plant extract was administered before morphine (40 mg/kg), it completely abolished the morphine-induced hyperactivity. Lastly, administration of the plant extract before morphine, in days of tolerance induction, attenuated the development of tolerance to morphine hyperactivity in mice. Conclusion: The hydroethanolic extract of E. platyloba may have preventive effects on the induction of morphine tolerance. Therefore, E. platyloba may have therapeutic potential in morphine addiction treatment.
