Effect of drugs on the cardiac conditioned response of dogs

Dogs were conditioned to an anxiety response characterized by an increase in heart rate upon presentation of a musical tone. Meprobamate, chlordiazepoxide and diazepam effectively prevented the cardiac conditioned response. Phenobarbital and chlorpromazine were less effective. Amphetamine, 1.5 orally, also blocked the cardiac conditioned response. Atropine, meperidine, caffeine, imipramine and -methyl-dopa had no effect on the cardiac conditioned response. Morphine and methyl phenidate were clearly active only in doses producing marked side effects. Ethanol in relatively small doses was mildly effective.