Differential-reinforcement-of-low-rate-schedule performance and nicotine administration: a systematic investigation of dose, dose-regimen, and schedule requirement.

Differential-reinforcement-of-low-rate (DRL) schedules have been used to evaluate the effects of a wide variety of drugs, including amphetamines, cannabinoids, and antidepressant medication. To earn a reinforcer, organisms operating under a DRL schedule are required to withhold a response for a predetermined amount of time before responding, and therefore this schedule maintains a low rate of responding and can be viewed as a response-inhibition task. In experiment 1, three different DRL schedules (4.5, 9.5, and 29.5 s) were used to evaluate systematically a range of nicotine doses (0.0, 0.1, 0.3, and 0.5 mg/kg). The dose-response effect of nicotine then was compared with the effects of increased reinforcer magnitude on responding. Both the administration of nicotine and increased reinforcer magnitude engendered less accurate DRL-schedule performance compared with baseline conditions, and the dose and magnitude-dependent shifts were most evident on the DRL 29.5-s schedule. Experiment 2 compared the differences between acute and chronic dosing regimens (0.3 mg/kg nicotine) on DRL 29.5-s schedule responding. After 20 consecutive sessions of nicotine dosing, accuracy deteriorated significantly, demonstrating that chronic nicotine dosing leads to a behavioral sensitization apparent on the DRL 29.5-s schedule. The results from both experiments suggest that responding on the DRL 29.5-s schedule is sensitive to both dose-response and regimen-dependent effects of nicotine.