The rate of intravenous cocaine or amphetamine delivery does not influence drug-taking and drug-seeking behavior in rats

We studied the influence of rate of intravenous infusion of cocaine or amphetamine on drug-taking and seeking behavior. First. drug-naive rats were tested for acquisition of self-administration of increasing doses of amphetamine or cocaine infused over 5 or 100 s. Second, self-administration of cocaine or amphetamine infused over 5-100 s was assessed on fixed or progressive-ratio (PR) reinforcement schedules. Finally, the ability of a single 5 or 100 s amphetamine or cocaine infusion to reinstate extinguished drug seeking was assessed. Although slower infusion rates produced a small effect on drug taking under continuous-reinforcement conditions, infusion rate did not alter drug taking on intermittent or PR reinforcement schedules, or the ability of cocaine or amphetamine to reinstate drug seeking. Taken together, our results suggest that variation in drug delivery rate over a range that we previously found alters the induction of behavioral sensitization, gene-expression and striatal dopamine activity, does not markedly alter drug-taking or seeking behavior. (C) 2008 Elsevier Inc. All rights reserved.