(A) Schematic of morphine CPP (3 mg/kg) acquisition, extinction, and reinstatement experiment. (B) Acquisition was examined on D8 of the mCPP paradigm. (C-D) Extinction testing of mCPP was performed weekly for 7 weeks. (C) Weekly and (D) averaged extinction tests are shown. *P<0.05, Student t-test. (E) Reinstatement to saline (D60) and morphine (D61, 3 mg/kg, s.c.) was performed. **P<0.01, *P<0.05 two-way ANOVA, Mean±SEM. SAL, saline; MOR, morphine.