Abstract

The effects of phenobarbital sodium (10-60 mg/kg s.c.), chlordiazepoxide hydrochloride (10-60 mg/kg s.c.) and diazepam (1-10 mg/kg i.p.) were studied in rats performing a continuous lever pressing avoidance task with light as warning signal. The conditions of this discriminated Sidman avoidance test were the following: shock-shock interval = 30 seconds; response-warning signal 20 seconds; warning signal-shock = 10 seconds; shock of 2 mA for 2 seconds. Interindividual differences in control shock base lines after an extended period of training influenced the direction of the drug effects, whereas differences between drugs were mostly of a quantitative nature. In fact, all agents provoked a decrease in shock rate in animals with high shock base lines and an increase in shock rate in animals with low shock base lines. The latter effect was more marked after diazepam than after phenobarbital or chlordiazepoxide. Response rates were generally increased, particularly in animals with low or intermediate shock rates after treatment with phenobarbital or chlordiazepoxide. Dosedependent increases in the relative frequency of responses emitted in the absence of the warning signal were observed after all drugs, also in cases in which overall response rate was little affected.