Effects of Progesterone on Morphine-induced Conditioned Place Preference and Levels of β-endorphin in Rat Brain

Objective:The aim of the study was to investigate the effects of progesterone on morphine rewarding effect and levels of β-endorphin(β-EP)in rat brain.Methods:40 male SD rats were designated to 4 groups randomly with 10 in each,including saline control group,morphine group,progesterone group and progesterone plus morphine group.In the morning,the group of saline and progesterone had hypodermic injection of cyclodextrin and progesterone of 15 mg/kg,10 min later,had intraperitoneal injection of saline of 5 mg/kg.The morphine and grogesterone plus morphine group had hypodermic injection of cyclodextrin and progesterone of 15 mg/kg,10 min later,had intraperitoneal injection of morphine 5 mg/kg.All rats were put into the white room for training.And in the afternoon,all rats had hypodermic injection of cyclodextrin and intraperitoneal injection of saline of the same dose,and all were put into the black room for the same training.Conditioned place preference(CPP)test was used to investigate the morphine rewarding effect,and radioimmunoassay(RIA)was established to determine the levels of β-EP in rat brain.Results:Compared with NS control group,5 mg/kg morphine successfully induced the formation of CPP(P0.01).15 mg/kg progesterone was not able to induce CPP effect itself,but was able to restrain the morphine CPP effect.Compared with NS control group,the levels of β-EP following morphine administration decreased significantly in hypothalamus,hippocampus and frontal cortex(P0.05,P0.01 and P0.05).Compared with morphine group,the levels of β-EP increased significantly by co-administration with 15 mg/kg dose of progesterone in hypothalamus(P0.01).Conclusion:It is estimated that progesterone can attenuate morphine induced CPP effectively.The effect of progesterone on morphine-induced CPP can be conduced through its action on β-EP.