The effects of tranquillizing drugs on timing behaviour in rats

Timing behaviour was generated in rats by a schedule which required responses to be spaced at least 15 sec apart in order for them to produce food reinforcement (DRL 15 sec). The behaviour maintained by this schedule was then studied after administration of chlordiazepoxide, phenobarbitone and chlorpromazine. Several doses of both chlordiazepoxide and phenobarbitone were found to disrupt timing behaviour by increasing overall response rates although the highest dose of each of these two drugs produced sedative effects. Chlorpromazine produced mainly a decrease in overall response rates. Analysis of performance in terms of interresponse times (IRTs) showed that both chlordiazepoxide and phenobarbitone markedly increased the percentage of IRTs less than 1.5 sec in duration (response bursts). Chlorpromazine had no consistent effect on response bursts. Reduction of the animals' body weights from 85% to 75% of their preexperimental levels had no effect on operant performance, suggesting that the effects of the drugs were probably not due to actions on motivational processes.