FIGURE 5

Effects of various treatments during extinction on reinstatement of morphine-induced place preference. Morphine-conditioned groups were treated with 0.5 mg/kg of LSD-25, 10 mg/kg of chlordiazepoxide, or 1 mg/kg of morphine, 20 min before the extinction conditionings. Another morphine-conditioned group was treated with 7.5 mg/kg of memantine immediately after the extinction conditionings. Vehicle-conditioned control group was treated with saline before the extinction phase. Before test 3, all morphine-conditioned groups were challenged with 1 mg/kg of morphine. Two-way ANOVA demonstrated significant effect of the interaction between treatment and test number: F(8,92)=3.319, P<0.01. Separate between-subject ANOVAs for tests 1, 2, and 3 revealed the following effects of treatment: F(4,46)=3.515, 3.17, and 5.836 (P<0.05, P<0.05, and P<0.001), respectively. Post hoc tests demonstrated significant effects of conditioning with morphine on test 1 (^## P<0.01), extinction with LSD-25 on test 2 (^§§ P<0.01), and extinction with LSD, chlordiazepoxide and morphine on test 3 (^* P<0.05; ^** P<0.01) (all significant effects toward the group 'vehicle-conditioned/saline-extinguished/saline-challenged'). Two-way ANOVA on locomotor activity data (that ranged from 20.212.29 entrances on test 3 in morphine-conditioned/memantine-(given after conditionings)-extinguished/morphine-challenged to 29.02.24 entrances on test 3 in morphine-conditioned/morphine-extinguished/morphine-challenged) revealed no significant effect of the interaction between the test number and treatment F(8,92)=1.771, NS.