a The schedule of the test. b On day 1–3, mice were subjected for pre-test. On day 4–9, mice were treated with SLL-1206 (2.0–7.0 mg/kg, i.p.) or saline (10 mL/kg, i.p.) 3 h prior morphine (4.0 mg/kg, i.p.) before each 50-min conditioning. On day 11, The residence time of the mice in both sides of the apparatus was recorded, and the CPP score was calculated. Morphine induces significant CPP. SLL-1206 had no antagonistic effect on morphine induced CPP (b). Data were analyzed by one-way ANOVA followed by Bonferroni post hoc test. Data were presented as the mean ± SEM from at least eight animals. **P < 0.01 vs control