Rats learned to self-administer nicotine (30 μg/kg/injection i.v.) as described above, and then were placed under extinction, during which responding had no programmed consequence. When there were <10 active responses per session for three consecutive sessions, reinstatement tests were conducted with a pretreatment injection (vehicle, 20 or 40 mg/kg WY14643, i.p., 20 min before the session) and a priming injection (vehicle or 0.2 mg/kg nicotine, s.c., 10 min before the session). Rats were required to meet the response-cessation requirement prior to each test. Nine rats were tested at both doses of WY14643, and some (2 rats at 20 mg/kg and 6 rats at 40 mg/kg WY14643) were only tested with one dose of WY14643. During the reinstatement test session, responding in the active hole pulsed the houselight for 20 seconds; to increase sensitivity of the reinstatement test, only a single response was required to produce this cue. This reinstatement procedure combines nicotine- and cue-induced reinstatement, has been used in several previous studies (20-23), and has several advantages. First, when the cues are removed during extinction, the response-cessation criterion is met
