Background and Objective: Isoniazid is a drug for the treatment of latent and active tuberculosis. This agent can easily enter the brain and affects the brain GABAergic systems. Because GABAergic agents have modulatory effects on morphine reward, the purpose of the present study was to evaluate the effects of isoniazid on the expression of conditioned place preference of morphine. Materials and Methods: For assessing the rewarding effects of morphine conditioned place preference (CPP) conducted on female mice. Standard maintenance conditions were provided for all the laboratory animals. Different groups of animals conditioned with saline, morphine (0.5, 1, 2.5, 5 and 10 mg/kg, s.c.) or isoniazid (25, 50 and 75 mg/kg, i.p.). For evaluation of isoniazid effects on the expression of morphine CPP, four groups of mice, in the conditioning phase of CPP received the effective dose of morphine (5 mg/kg, s.c); then on the test day, 40 minutes before the test session, four groups of animals received saline or isoniazid (25, 50 and 75 mg/kg, i.p.). Results: Morphine but not isoniazid induced a significant place preference compared to the saline. The most effective dose of morphine (5 mg/kg, s.c) was used for CPP induction in the next phase. Isoniazid administration on the test day reduced the CPP induced by the effective dose of morphine, significantly. Conclusion: Isoniazid may interfere in morphine rewarding effects.
