Specificity of effects of chronically administered diazepam on the responding of rats under two different...

Lever pressing of rats was maintained in different chambers during two different sessions each day. At 0900 h, responding was maintained under a two-component multiple schedule in which responses initiated an interval that had to elapse before delivery of food (time delay of 20 s and 40 s). In this schedule, a 'response-pause' sequence preceded reinforcers, and acutely administered diazepam only decreased responding. At 1400 h, responding by the same subjects was maintained under a different two-component multiple schedule, in which individual responses initiated an interval that had to be terminated by another response before delivery of food (DRL 20 s and 40 s). In this second schedule, a 'response-pause-response' sequence preceded reinforcers, and acutely administered diazepam increased responding. After studying the acute behavioral effects of diazepam during each separate 'timing' schedule, animals systematically received 1.7 mg/kg per day diazepam 2-5 min prior to their different schedule components, in order to study the influence of reinforcement contingency on the chronic effects of this drug. Diminution of the initial effects of diazepam during daily drug administration prior to DRL 20 s responding did not extend to DRL 40 s responding or to time-delay responding, and tolerance did not develop at all for time-delay responding. When diazepam was again administered after all the daily schedules for approximately 1 month, and then given before the individual DRL schedules, DRL responding was increased again as it had been prior to chronic drug administration. These results suggest that the behavioral effects of acutely administered diazepam are influenced by different 'timing' requirements, and that the behavioral effects of chronically administered diazepam are influenced by 'timing' requirements and by drug- and chamber-related stimuli.