| PART I Effects of acute and repeated injection of corticosterone and footshock on morphine conditioned place preference in ratsObjectives To explore the formation of morphine(M) dependence followed footshock exposure and the role of corticosterone(CORT) in the interaction of stress and addiction.Methods Seventy-eight male Sprague-Dawley rats were randomly assigned to footshock + M group, CORT + M group, CORT group and control group. Rats of the footshock + M group were shocked once a day for 1 day in acute footshock exposure (AFS) and for 7 days in chronic footshock exposure (CFS), and then were injected i.p. with morphine (3mg/kg) 30 minutes after footshock exposure for 4 days. Rats of the CORT + M group were injected i.p. with CORT once a day in acute CORT exposure (ACORT) and for 7 days in chronic CORT exposure (CCORT), and then were injected M (identical to the footshock +M group). Rats of the CORT group were injected with CORT (identical to the CORT +M group). Rats of control group were treated by saline and morphine according to control principle. The natural non-preferred compartment of rats was the drug compartment. The time for rats in drug compartment was observed at before and 2 hours after treatment. Data were analyzed using one-way ANOVA followed by LSD.Results (1) The time for rats spent in drug-paired chamber were no significantly longer in AFS + M group, ACORT+M group, ACORT group than in control group (P>0.05). (2) The time were significantly longer in rats of CFS+M group, CCORT+M group, CCORT group than in control group(P=0.001, P=0.023, P=0.000, respectively). (3) The time were significantly longer in rats of CFS+M group, CCORT+M group, CCORT group than in AFS+M group, ACORT+M group, ACORT group respectively(P=0.004, P=0.014, P=0.000, respectively). (4) There was no statistically significant difference not only between ACORT+M group and AFS+M group(P=0.345), but also between CCORT+M group and...
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