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 more rapidly (mean ± SEM. = 5.2 ±0.8 sessions in the present study without the stimulus, versus 11.3 ± 1.5 in a pilot group with the stimulus). Second, reinstatement by the combination of nicotine and cues is more robust than when only nicotine or only the cues are presented. This was important because, consistent with the findings of others (20), we have found that a substantial number of rats fail to show reinstatement when given nicotine alone. Finally, the combination of nicotine and cues may be a more relevant and stringent model of the human relapse situation than cues alone or nicotine alone.
