BEHAVIOR OF RATS UNDER FIXED CONSECUTIVE NUMBER SCHEDULES - EFFECTS OF DRUGS OF ABUSE

Four rats responded under a simple fixed consecutive number schedule i n which eight or more consecutive responses on the run lever, followed by a single response on the reinforcement lever, produced the food re inforcer. Under this simple schedule, dose-response curves were determ ined for diazepam, morphine, pentobarbital, and phencyclidine. The rat s were then trained to respond under a multiple fixed consecutive numb er schedule in which a discriminative stimulus signaled when the respo nse requirement on the run lever had been completed in one of the two fixed consecutive number component schedules. Under control conditions , the percentage of reinforced runs under the multiple-schedule compon ent with the discriminative stimulus added was much higher than the pe rcentage of reinforced runs under the multiple-schedule component with out the discriminative stimulus. All of the drugs decreased the percen tage of reinforced runs under each of the fixed consecutive number sch edules by increasing the conditional probability of short run lengths. This effect was most consistently produced by morphine. The drugs pro duced few differences in responding between the multiple fixed consecu tive number components. Responding under the simple fixed consecutive number schedule, however, was affected at lower doses of the drugs tha n was responding under the same fixed consecutive number schedule when it was a component of the multiple schedule. This result may be due t o the difference in schedule context or, perhaps, to the order of the experiments.