Effects of drugs on avoidance behavior

Summary Thirty-five rats were observed on two occasions in a novel environment, and then trained in a Sidman avoidance response. Each was tested in the avoidance situation following injection of a single dose of chlorpromazine, d-amphetamine, atropine, and scopolamine.Effects of the drugs on avoidance behavior were similar to those reported in earlier studies. Changes from baseline values in response rate and shock rate under drug were found to be the best measures of individual rats' susceptibilities to the drugs.Susceptibilities to the response-stimulating effects of amphetamine, atropine and scopolamine were highly interrelated, but susceptibility to chlorpromazine was distinct. Susceptibility to chlorpromazine was greatest in rats with high baseline rates of responding and shock avoidance. Change in shock rates after administration of stimulant drugs was greatest in rats with high baseline rates of shocks (poor avoiders). Increase in response rate under the stimulants was greatest in animals that tended to groom and freeze in the novel environment, rather than boldly exploring.The effects of the stimulants are discussed in terms of a model relating to the balance of excitation versus inhibition in response to aversive stimulation. Differences in baseline avoidance rates and in susceptibilityThis experiment was supported by grant MH-04139 from The National Institute of Mental Health and by The California Department of Mental Hygiene.