Effects of chlordiazepoxide, ripazepam and d-amphetamine on conditioned acceleration of timing behaviour in rats.

The lever-pressing behaviour of three rats was maintained by a schedule in which food reinforcement was obtained by any response which was emitted at least 15 s after the previous response (DRL 15s). When performance on this schedule had stabilised, the animals were presented intermittently with 1-min periods of a white noise stimulus, the termination of which was accompanied by the delivery of a mild electric footshock. This procedure let to reliable increases in response rates furing the stimulus although responding at other times continued to be appropriate to the DRL 15-s schedule. Administration of the benzodiazepine chlordiazepoxide (1, 3, 10, 17 and 30 mg/kg) and of ripazepam (1, 3, 10, 30 and 56 mg/kg), a non-benzodiazepine reported to have anxiolytic properties, increased response rates on the DRL baseline while decreasing the acceleration of responding produced by the preshock stimulus. Baseline response rates were also increased by d-amphetamine (0.25, 0.5, 1.0 and 2.0 mg/kg) and at the higher doses this drug completely abolished the accelerated responding during the preshock stimulus. Although the effects of chlordiazepoxide and ripazepam are consistent with the suggestion that these drugs may attenuate the behavioural effects of aversive stimuli, in this experiment the behavioural effects of d-amphetamine were similar in many respects.