We used an 8-day protocol whereby mice were assessed for initial preference for the OXY-paired side on day 1 (D1, initial preference; Initial pref.), trained over four days with alternating injections of OXY (D2, D4) and SAL (D3, D5) in the respective contexts, and assessed for OXY-CPP on D8. Each day represents a 30 min session. Day = day of the protocol; Tx = treatment for that day; SAL = saline treatment; OXY = oxycodone treatment; - = mice were left undisturbed in their home cage in the vivarium on these days.