There have been numeral animal studies on drug addiction that explored individual propensities to develop addictive behavior, including locomotor responses to novelty, to initial drug challenges or development of behavioral sensitization [e.g., 1, 2]. While these factors could contribute to the initiation and maintenance of drug self-administration, there is limited data exploring the core feature of addiction: individual vulnerability to relapse during abstinence from chronic drug self-administration. In animal studies of drug self-administration, vulnerability for relapse can be assessed using reinstatement procedures [3, 4]. These procedures may represent valid models of drug craving because similar environmental and pharmacological stimuli trigger both drug-seeking behavior in animals and drug craving in humans [4, 5], and may have predictive validity in evaluating anti-craving compounds for use in the treatment of addiction [e.g., 6].
