Escalation of cocaine intake with extended access in rats: dysregulated addiction or regulated acquisition?
Beckmann, J. S., Gipson, C. D., Marusich, J., & Bardo, M. T. (2012). Escalation of cocaine intake with extended access in rats: dysregulated addiction or regulated acquisition? Psychopharmacology, 222(2), 257-267. DOI: 10.1007/s00213-012-2641-0
Understanding the neurobehavioral mechanisms underlying dysregulated cocaine intake is important for the development of new cocaine abuse therapies. The current study determined if cocaine escalation under extended access conditions (6-h access) is regulated by discrimination learning processes. Rats were initially trained on cocaine self-administration (0.1 or 0.25 mg/kg/infusion) using a fixed ratio 1 (FR 1) schedule under 1-h access for 12 sessions. Some rats were then trained to self-administer cocaine under 1-h or 6-h access conditions exclusively for 14 additional sessions, while other rats were trained under both 1- and 6-h access conditions that were cued or noncued for 28 additional sessions (14 sessions for each 1- and 6-h access). Two additional groups of rats were initially trained to self-administer cocaine using an FR 1 schedule under 10-min access for 12 sessions; half of the animals were then switched to 60-min access conditions for 14 additional sessions. When access conditions were differentially cued, escalation of cocaine intake was evident in animals with both 1- and 6-h access conditions during the escalation phase. Escalation also was evident in animals initially trained with 10-min access and then switched to 60-min access. The results demonstrate that dysregulated and regulated intakes can be expressed within the same animal, indicating that escalation is context-dependent. Furthermore, escalated cocaine intake can be expressed under 1-h access conditions. Overall, these results suggest that escalated cocaine intake may be representative of discrimination-dependent regulated intake rather than addiction-like, compulsive intake