Task-specific effects of nicotine in rats. Intracranial self-stimulation and locomotor activity

The acute effects of nicotine (0.03-1.0 mg/kg) were studied in a locomotor activity procedure and in a series of intracranial self-stimulation (ICSS) paradigms. Nicotine produced a dose-dependent decrease in locomotor activity. When animals were trained to lever-press for intracranial self-stimulation on a continuous reinforcement schedule (CRF), the drug was ineffective except at the 1.0 mg/kg dose, which produced a moderate decrease in the rate of responding. However, when animals were tested in a fixed-ratio:15 (FR:15) paradigm, nicotine produced a steep, biphasic dose-response curve. At the 0.1 mg/kg dose, the response rates were increased to approx. 60% above baseline, while at the 1.0 mg/kg dose, response rates were decreased to approx. 90% below baseline values. The effects of nicotine were also studied in an auto-titration procedure which measured the rewarding value of the stimulus. There was a decrease in performance at larger doses similar to that observed in the continuous reinforcement procedure, but there were no significant changes in the threshold for reinforcement. Nicotine did not produce any change in the detection threshold for stimulation of the brain. In acute studies, therefore, nicotine produced both stimulation and disruption of behavior, effects that were brought to light by the fixed-ratio schedule of reinforcement, and this may relate to the rewarding effects of nicotine.