Rationale: Nicotine is a tobacco alkaloid known to be important in the acquisition and maintenance of tobacco smoking. However, other constituents in tobacco may contribute to the dependence liability.
Objective: The present report sought to determine whether nornicotine, a tobacco alkaloid and metabolite of nicotine, has a reinforcing effect.
Methods: Rats were prepared with a jugular catheter, then were allowed to self-administer intravenously either S(-)-nicotine (0.03 mg/kg/infusion), RS(+/-)-nornicotine (0.3 mg/kg/infusion) or saline using a two-lever operant procedure. The response requirement for each infusion was incremented gradually from a fixed ratio 1 (FR1) to FR5. When responding stabilized on the FR5, other doses of nicotine (0.01 mg/kg/infusion and 0.06 mg/kg/infusion) and nornicotine (0.075, 0.15, and 0.6 mg/kg/infusion) were tested for their ability to control responding.
Results: Similar to nicotine, rats self-administered nornicotine significantly above saline control levels. Within the dose ranges tested, both nicotine and nornicotine yielded relatively flat dose-response functions. Extinction of responding was evident when saline was substituted for nornicotine, and responding was reinstated when nornicotine again was available. The rate of nornicotine self-administration was similar between rats tested with either 24-h or 48-h inter-session intervals.
Conclusion: These results indicate that nornicotine contributes to the dependence liability associated with tobacco use.