Nicotine and bupropion share a similar discriminative stimulus effect

Bupropion is a weakly potent central nervous system (CNS) stimulant that is marketed both as an antidepressant and as an anti-smoking aid. The mechanism(s) by which it produces its effects is not well understood. In the present study, the effect of bupropion was examined in rats trained to discriminate the stimulus effect of 0.60 mg/kg of (-)-nicotine from saline in a two-lever drug discrimination task. In tests of stimulus generalization (substitution), the nicotine (ED(50)=0.17 mg/kg) stimulus completely generalized to bupropion (ED(50)=5.50 mg/kg). In addition, interaction studies were conducted that evaluated the effect of 3.0 mg/kg of bupropion, a dose that when given alone produced saline-appropriate responding, in combination with various doses of nicotine. This application resulted in an enhancement of the potency of nicotine (ED(50)=0.05 mg/kg), as indicated by a leftward shift of the nicotine dose-effect function. In tests of stimulus antagonism, various doses of bupropion were administered prior to the training dose of nicotine and were found to be ineffective as antagonists of the nicotine stimulus. In contrast, the nicotinic acetylcholine receptor (nicotine receptor) antagonist mecamylamine (AD(50)=0.40 mg/kg) completely blocked the stimulus effect of nicotine. Mecamylamine did not attenuate the stimulus generalization of bupropion. The results demonstrated that bupropion can produce a nicotine-like response in nicotine-trained animals, but it does so via a mechanism of action that is unlike that of nicotine. It is speculated that bupropion may be somewhat effective as an anti-smoking treatment in people who are motivated to quit smoking because low doses of bupropion produce a nicotine-like effect(s) that serve as a suitable substitute for nicotine.