A description of the nicotine stimulus and tests of its generalization to amphetamine

Abstract

The discriminative stimulus properties of nicotine were investigated under a variety of conditions in three separate experiments. In each of these experiments the subject's performance was assessed using a two-lever operant procedure with liquid food reinforcement. In the first study rats were trained to discriminate between various doses of nicotine (100, 200, or 400 μg/kg) and saline under a VI-15 s schedule of reinforcement. The second experiment investigated discrimination between 400 μg/kg of nicotine and saline under different schedules of reinforcement (VI-15 s, FR-10, or DRL-10 s). Generalization of the nicotine stimulus (400 μg/kg) to the stimulus effects of several doses of d-amphetamine (60, 120, 240, 480, and 720 μg/kg) was investigated in the third study. Dose-generalization and time-duration studies of the stimulus effects of nicotine indicate that the sensitivity of the rats to the nicotine cue was directly related to the training dose under the VI-15 s schedule. Although response rates differed across the schedules of reinforcement, the rats' sensitivity to the stimulus effects of nicotine was not affected. Lack of complete generalization of the nicotine stimulus to d-amphetamine supports our previous findings that these drugs were qualitatively different in relation to their discriminative control of behavior. This research has, in addition, suggested approaches necessary to the proper evaluation of the stimulus properties of test compounds.