N-METHYL-D-ASPARTIC ACID-RECEPTOR ANTAGONISTS BLOCK MORPHINE-INDUCED CONDITIONED PLACE PREFERENCE IN RATS

We addressed the question of whether 0,11-dihydro-5H-dibenzo[a,d]cyclo hepten-5,10-imine (MK-801) and DL-(E)-2-amino-4-methyl-5-phosphono-3-p entenoic acid (CGP37849), a non-competitive and a competitive N-methyl -D-aspartate (NMDA) receptor antagonist, respectively, are able to blo ck morphine-induced conditioned place preference (CPP). MK-801 alone ( 0.1 mg/kg) produced neither a place preference nor a place aversion, b ut was able to completely block morphine-induced CPP. CGP37849 alone ( 10 mg/kg) produced a small but significant CPP, and was able to signif icantly attenuate morphine-induced CPP. These results cannot be due to simple additive effects of drug actions, but suggest that NMDA recept ors play a complex role in the development of morphine CPP.