Abstract
Dose-effect curves were determined in rats for the effects of drugs on punished and unpunished responding maintained by fixed-interval schedules of food presentation before, during and after the drinking of large daily doses of chlordiazepoxide and pentobarbital. An average intake of 50 mg/kg/day of chlordiazepoxide produced tolerance to the rate-decreasing effects of chlordiazepoxide on unpunished responding and cross-tolerance to the rate-decreasing effects of pentobarbital. During chlordiazepoxide drinking, rate-increasing effects of both chlordiazepoxide and pentobarbital on punished responding became apparent. There was no evidence for cross-tolerance between chlordiazepoxide and chlorpromazine. An average intake of 100 mg/kg/day of pentobarbital produced similar evidence of tolerance to the rate-decreasing effects of pentobarbital on unpunished responding and cross-tolerance to the rate-decreasing effects of chlordiazepoxide. Removal of chlordiazepoxide from the drinking water temporarily increased unpunished responding; however, 6 weeks after withdrawal of chlordiazepoxide or pentobarbital from the drinking water, the dose-effect curves for injections of these drugs appeared to be returning to their original positions.
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