The effects of ketamine, a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, on morphine-induced place preference were examined in mice. Morphine (1-5 mg/kg, s.c.)produced a dose-related place preference in mice. Ketamine alone (3, 10 mg/kg, i.p.), like dizocilpine alone (0.2 mg/kg, i.p.), also produced a preference for the drug-associated place. Pretreatment with ketamine (10 mg/kg, i.p.) or dizocilpine (0.1 and 0.2 mg/kg, i.p) suppressed the place preference produced by morphine in a dose-dependent manner. These findings provide the first demonstration that ketamine alone produces a place preference using the conditioned-place preference (CPP) paradigm, but that mice treated with ketamine combined with morphine show neither a morphine-nor a ketamine-induced place preference. (C) 2000 Elsevier Science Inc.
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