Chunk #19 — 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
However, in an effort to explore the possibility that differential access to intravenous cocaine self-administration in rats may produce different patterns of drug intake, rats were allowed access to intravenously self-administration cocaine for 1 or 6 h per day (Ahmed and Koob, 1998). One hour access (short access or ShA) to intravenous cocaine per session produced low and stable intake as observed previously. In contrast, 6 h access (long access or LgA) to cocaine produced drug intake that gradually escalated over days (Figure 4). Increased intake was observed in the extended access group during the first hour of the session, with sustained intake over the entire session and an upward shift in the dose-effect function, suggesting an increase in hedonic set point. When animals were allowed access to different doses of cocaine, both the LgA and ShA animals titrated their 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.,
