Increased motivation for self-administered cocaine after escalated cocaine intake

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Abstract
Escalation in cocaine self-administration is hypothesized to involve increased motivation to consume cocaine. The present study determined the effects of escalated cocaine self-administration in rats on the cocaine dose-response function under a progressive ratio schedule. Two groups of rats were allowed to self-administer cocaine under a fixed ratio schedule, for 1 h (ShA; n = 7) or 6 h (LgA; n = 6) per day. The subjects were then allowed to self-administer five doses of cocaine (0, 0.031, 0.063, 0.125 and 0.25 mg/infusion) under a progressive ratio schedule. The dose-response function was shifted upwards in the LgA compared to the ShA group. In conclusion, the present data suggest that escalation in cocaine self-administration is associated with a significant increase in the incentive motivational value of self-administered cocaine.