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Drug self-administration studies have recently employed progressive ratio (PR) schedules to examine psychostimulant and opiate reinforcement. This review addresses the technical, statistical, and theoretical issues related to the use of the PR schedule in self-administration studies in rats. Session parameters adopted for use in our laboratory and the(More)
Although it has been demonstrated that many of the behavioral responses to psychomotor stimulants are gender dependent and hormonally sensitive, few studies have examined the possibility that the estrous cycle interacts with drug reinforcement in laboratory animals. The present experiment assessed the effect of the estrous cycle on two aspects of cocaine(More)
The effect of the GABAB agonist baclofen on cocaine self-administration in the rat was investigated. In the first experiment, rats trained to self-administer i.v. cocaine (1.5 mg/kg/inj) on a progressive ratio (PR) schedule were pretreated with various doses of baclofen (1.25, 2.5, or 5.0 mg/kg). Baclofen produced a dose-dependent decrease in the break(More)
Heroin self-administration behavior under a progressive ratio (PR) schedule of reinforcement was evaluated in rats. The schedule was designed to restrict drug intake, minimize opiate dependency, and quantify the number of responses emitted (final response ratio) in order to receive a limited number of heroin infusions. Final ratios were found to be stable(More)
This paper is a critique of fixed and progressive ratio schedules used to examine the neural substrates of cocaine reinforcement. The discussion focuses on problems encountered while examining the effects of neurotoxic lesions and pharmacological pretreatments on cocaine reinforcement. We review the theoretical and interpretational problems associated with(More)
 We have previously reported that rats display a circadian pattern of cocaine self-administration if access to drug is limited to 10-min discrete trials that are separated by at least 20 min. In the present study, the pattern of cocaine intake (1.5 mg/kg per injection) was studied in two large groups of animals that were maintained on different 12-h(More)
The role of ascending noradrenergic (NA) and dopaminergic (DA) systems in intravenous self-administration of cocaine in rats was investigated by examining the effects of 6-hydroxydopamine-induced lesions of these systems on responding for the drug on a FR-1 schedule of reinforcement. Lesions of the dorsal and ventral NA bundles that reduced(More)
Intravenous cocaine self-administration behavior in rats was investigated using a progressive ratio (PR) schedule of reinforcement. The first response on the lever each day produced a drug infusion, whereupon the requirements of the schedule escalated with each reinforcement until the behavior extinguished. The final ratio completed each day was found to be(More)
The effect of microinjections of baclofen into the ventral tegmental area (VTA), nucleus accumbens, or striatum on cocaine self-administration reinforced on a progressive ratio schedule was investigated. Intra-VTA baclofen produced the most potent modulation of cocaine intake, causing a significant reduction in cocaine-reinforced break points at a dose (56(More)