Rationale and objectives Nicotine and D-amphetamine can strengthen reinforcing effects of unconditioned visual stimuli. We investigated whether these reinforcement-enhancing effects reflect a slowing of stimulus habituation and depend on food restriction. Methods Adult male rats pressed an active lever to illuminate a cue light during daily 60-min sessions. Depending on the experiment, rats were challenged with fixed or varying doses of D-amphetamine (0.25–2 mg/kg IP) and nicotine (0.025– 0.2 mg/kg SC) or with the tobacco constituent norharman (0.03–10 μg/kg IV). Experiment 1 tested for possible reinforcement-enhancing effects of D-amphetamine and norharman. Experiment 2 investigated whether nicotine and amphet- amine inhibited the spontaneous within-session decline in lever pressing. Experiment 3 assessed the effects of food restriction. Results Amphetamine (0.25–1 mg/kg) and nicotine (0.1 mg/kg) increased active lever pressing specifically (two- to threefold increase). The highest doses of nicotine and amphetamine also affected inactive lever responding (increase and decrease, respectively). With the visual reinforcer omitted, responding was largely extinguished. Neither drug appeared to slow habitua- tion, as assessed by the within-session decline in lever pressing, and reinforcement-enhancing effects still occurred if the drugs were given after this decline had occurred. Food restriction enhanced the reinforcement-enhancing effect of amphetamine but not that
Psychopharmacology – Springer Journals
Published: Dec 3, 2017
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