No abstract

The primary goal of this study is to ascertain whether relapse to drug dependence, in terms of continuous abstinence assessment, exhibits a typical pattern that can be characterized by a common quantitative function. If the relapse curve is indeed ubiquitous, then some underlying mechanism must be operating to shape the curve that transcends variables such as drug class, population or treatment type. Survival analyses are performed on 20 alcohol and tobaccotreatment studies using the proportions of individuals remaining abstinent following a period of initial abstinence. Several parametric models of relapse are compared and the results demonstrate that a log-logistic distribution is the most accurate reflection of the available data and the basic shape of the relapse curve is uniform. In the vast majority of reports examined, the rate of relapse decelerates after initial abstinence has been achieved, and therefore the amount of accumulated time abstinent may be the transcending variable that operates to shape the relapse curve.

Differential-reinforcement-of-low-rate (DRL) schedules have been used to evaluate the effects of a wide variety of drugs, including amphetamines, cannabanoids, 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.