Chunk #20 — 1. Definitions and conceptual framework for compulsivity in addiction — 1.3. Animal models of compulsivity in addiction as defined by increased drug taking: Escalation in drug self-administration with prolonged access
cocaine intake, but the LgA rats consistently self-administered almost twice as much cocaine at any dose tested, further suggesting an upward shift in the set point for cocaine reward in the escalated animals (Ahmed and Koob, 1999; Deroche-Gamonet et al., 2004; Mantsch et al., 2004). Escalation also is associated with an increase in break point for cocaine in a progressive-ratio schedule of reinforcement, suggesting an enhanced motivation to seek cocaine or an enhanced efficacy of cocaine reward (Paterson and Markou, 2003; Wee et al., 2008). Such increased self-administration in dependent animals has now been observed with cocaine, methamphetamine, nicotine, heroin, and alcohol (Ahmed et al., 2000; Ahmed and Koob, 1998; Kitamura et al., 2006; O’Dell et al., 2004; George et al., 2007) (Figure 4). This model is a key element for evaluating the motivational significance of opponent process changes in the brain reward and stress systems in addiction that lead to compulsivity in addiction. Similar changes in the reinforcing and incentive effects of cocaine as drug intake have been observed following extended access and include increased cocaine-induced reinstatement after extinction and a decreased latency to goal time in a runway model for cocaine reward (Deroche et al., 1999). Altogether, these
