Chunk #23 — 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
before the onset of each subsequent self-administration session, thereby deviating more and more from control levels. The progressive elevation in reward thresholds was associated with the dramatic escalation in cocaine consumption that was observed previously. After escalation had occurred, an acute cocaine challenge facilitated brain reward responsiveness to the same degree as before but resulted in higher absolute brain reward thresholds in LgA compared with ShA rats (Ahmed et al., 2002). Similar results have been observed with extended access to heroin (Kenny et al., 2006). Rats allowed 23 h access to heroin also showed a time-dependent increase in reward thresholds that paralleled the increases in heroin intake (Figure 5).
