After 4-5 sessions of vehicle pretreatment in which responding was stable (<15% variability), drug pretreatments were given for 5 consecutive sessions. Data from the 5 drug pretreatment sessions were compared to the 3 preceding vehicle pretreatment sessions. The drug pretreatments were WY14643 (10, 20 and 40 mg/kg i.m., 20 min before the session), MK886 (1 mg/kg i.m., 45 min before the session), MK886 (1 mg/kg) plus WY14643 (20 mg/kg), and methOEA (10 mg/kg i.m., 40 min before the session). WY14643 pretreatments (20 and 40 mg/kg i.m., 20 min before the session) were also tested in two additional groups of monkeys self-administering cocaine (30 μg/kg/injection) or food pellets under the same fixed-ratio schedule.
