Nicotine-induced attentional enhancement in rats: effects of chronic exposure to nicotine.

Consistent with human literature, previous studies identified attention-enhancing effects of nicotine in rats, using a 5-choice task. The present study addressed the influence of repeated exposure to nicotine on these effects. Over six weeks, the effects of nicotine (0.0, 0.05 and 0.2 mg/kg) given ten min before sessions were tested each week. In addition, rats were injected daily two hours after sessions. In the first week, when these post-session injections were of saline for all rats, pre-session nicotine had profound rate-disruptive effects at the larger dose. In weeks 2-6, when half the rats received post-session injections of saline and the other half of nicotine (0.4 mg/kg), the disruptive effects of pre-session nicotine had disappeared and it enhanced attentional performance on all response indices. These effects did not differ significantly between post-session treatment groups or weeks, although they appeared less pronounced in the last two weeks. When tested under modified task parameters in weeks 9 and 10, nicotine (0.1 mg/kg) robustly enhanced performance in both groups despite continuing daily post-session administration of nicotine or saline. These studies provide evidence that, following tolerance to initial disruptive effects, the nicotine-induced attentional enhancement is stable across lengthy periods of chronic exposure. This is important for potential therapeutic applications of the drug and indicates that these effects can be a continuous motive for smoking behavior.