Drug addiction and abuse have now been extremely serious problems in our society.It has been reported that environmental conditions play a crucial role in susceptibility to drug addiction in animals.An important paradigm termed "enriched environment (EE)" has been employed to assess environment-induced behavior plasticity.However,few studies have examined if whether enriched environment affects subsequent responsivity to drugs of abuse.In this study,we investigated if an the enriched environment during postnatal development alters t morphine-induced reward in mice.Male C57BL/6 mice of 3 weeks were housed in a standard environment (SE) or enriched environment.Mice in the standard environment were housed in the regular animal facility cages receiving water and food ad libitum.