THE NMDA RECEPTOR ANTAGONIST DIZOCILPINE (MK-801) STEREOSELECTIVELY INHIBITS MORPHINE-INDUCED PLACE PREFERENCE CONDITIONING IN MICE

The effect of the non-competitive NMDA receptor antagonist dizocilpine (MK-801) on conditioned place preference induced by morphine was stud ied in mice. As expected, morphine (1-8 mg/kg, IP) elicited a signific ant preference for the drug-paired compartment. Pretreatment of mice w ith (+)-dizocilpine (0.1 and 0.2 mg/kg, IP), the more active dizocilpi ne enantiomer, dose-dependently reversed the conditioned place prefere nce produced by morphine (4 mg/kg, IP), whereas (-)-dizocilpine (0.2 m g/kg, IP) did not modify morphine-induced effects. In contrast, both e nantiomers of dizocilpine (at a dose of 0.2 mg/kg, IP) elicited a cond itioned place preference. These data suggest that (1) NMDA receptors p lay a role in morphine-induced place preference, and (2) dizocilpine-r einforcing properties in the place preference paradigm do not seem to be dependent on NMDA receptor blockade.