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Ksir CJ. 
“Rate-Dependent and Stimulus Control Effects of Drugs”. 
Psychopharmacol.Bull.. 1980;16(1):72.
Rate dependent and stimulus control effects of drugs were studied. Method Rats were trained to perform various tasks, such as brightness discrimination or key press for food under different schedules of response and reinforcement. The effects of different drugs (such as LSD, amphetamine, and scopolamine) on performance were compared. In some studies, the effects of drug removal and of the introduction of irrelevant stimuli are compared with the effects of representative psychoactive agents. A differential reinforcement of interresponse times procedure is used to examine whether the amount of drug-induced change in behavior is related to the difficulty of a behavioral test or to the degree of behavioral control generated by the test procedure. Results Rats showed a decrease in fixed-interval (FI) response rate at LSD doses of 0.32 mg/kg and above, but not at lower doses. This drug exerted little influence on the overall pattern of FI responding. Amphetamine produced a rate-dependent disruption of the FI response pattern without much change in overall rate over the range of test doses (0.5-2.0 mg/kg). These studies showed a lack of correspondence between the effects of the 2 drugs. Studies of the effect of changing from drug to nondrug state showed that switching from pretest injections of 1.0 mg/kg d-amphetamine to placebo could produce rate-dependent changes in FI responding. Rats trained to respond on a 2-key brightness discrimination showed greater drug effects on performance when the discrimination was difficult than when it was easy, when either scopolamine or d-amphetamine was used as the test compound. LSD produced no disruption of discrimination performance under either condition.
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