Operant models of self-administration can be extended to study the mechanisms thought to underlie craving and relapse by establishing a prolonged drug-free period after self-administration sessions (forced abstinence) or by initiating extinction training. During extinction, operant responding no longer delivers drug, thus responding significantly declines (Davis and Smith, 1976). After forced abstinence or extinction, an animal can be exposed to stimuli to precipitate drug-seeking behavior (“relapse”). Such stimuli include situations that approximate stressful events, cues predictive of drug reinforcement, or drug re-exposure. A number of studies have suggested that these models of drug relapse are useful for pharmacotherapeutic screening (Epstein et al., 2006).
