Bupropion and varenicline are widely prescribed pharmacological treatments for smoking cessation. These treatments are only marginally effective in clinical populations but most preclinical studies show that they are effective in decreasing self-administration in rats on a group level. The present study investigated individual differences in responding to bupropion or varenicline in a preclinical model of long-access to nicotine (0.03 mg/kg/inf; 12 h/day) in female rats. Rats were first assessed for their individual economic demand for nicotine and for their individual performance in open field and elevated plus maze prior to nicotine access and during withdrawal. Rats were then tested for the acute effects of bupropion, varenicline, and yohimbine. We found that neither bupropion nor varenicline decreased responding for nicotine on test days. On the contrary, a moderate dose of bupropion (30 mg/kg) significantly increased responding for nicotine. We also found that rats with higher demand for nicotine were more sensitive to pretreatment with yohimbine which resulted in increased responding for nicotine during the dose-effect tests. Finally, we show that rats that had a higher demand for nicotine also were more persistent in seeking nicotine during extinction and reinstatement tests with nicotine or yohimbine as triggers. Our findings suggest that the length of access to daily nicotine may be an important factor underlying the response to pharmacological treatments like bupropion or varenicline. Future studies modeling chronic treatment approaches that include both sexes will be needed to further extend our findings.
