Testing commenced when: (1) a rat completed the first fixed-ratio on the correct lever on at least 8 of 10 consecutive sessions; and (2) at least 80% of the total responses were made on the correct lever during those 8 sessions. Tests were conducted on Tuesdays and Fridays provided that the rat completed the first fixed ratio on the correct levers during the most recent THC- and vehicle-training sessions, otherwise, a training session was administered. During test sessions, responding on either lever was reinforced with food pellet delivery. Initially, vehicle and doses of THC (0.1–10 mg/kg) were tested followed by URB597 (3–56 mg/kg) and its vehicle. Subsequently, JZL184 (16 mg/kg) alone and in combination with URB597 (30 mg/kg) were tested. This dose of URB597 was chosen because it was the highest dose of URB597 that did not alter response rates when tested alone. JZL184 dose choice was based upon our prior work with this compound (Long et al., 2009a). After this set of tests was completed, the rats were retrained at 1 mg/kg THC until criteria as described above were
