FIGURE 3

Specificity of reinstatement of extinguished morphine-induced place preference. During the extinction phase, morphine-conditioned mice were treated with saline (the control group represented by dotted bars was treated with morphine) and exposed to the previously morphine- and vehicle-associated arms of the apparatus. Test 2 revealed that all groups extinguished conditioned place preference. Before test 3, mice were challenged with saline or morphine. Two-way ANOVA demonstrated significant interaction between treatment and test number: F(10,96)=4.92, P<0.001. Separate between-subject ANOVAs for tests 1, 2, and 3 revealed the following effects of treatment: F(5,48)=5.44, 0.99 and 9.572 (P<0.001, NS and P<0.001), respectively. Post hoc Duncan's tests demonstrated significant effects of conditioning with morphine on test 1 (significance toward group 'vehicle-conditioned/saline-extinguished/saline-challenged', ^## P<0.01), and the effects of a challenge with morphine before test 3 (significance toward group 'morphine-conditioned/saline-extinguished/saline-challenged' ^** P<0.01, ^*** P<0.001). Two-way ANOVA on locomotor activity data (that ranged from 21.252.79 entrances on test 1 in vehicle-conditioned/saline-extinguished/morphine (1 mg/kg)-challenged to 35.373.13 entrances on test 1 in vehicle-conditioned/saline-extinguished/saline-challenged) revealed no significant effect of the interaction between the test number and treatment F(10,96)=0.998, NS.