the nonsmoker group at 1 day of abstinence. This is interesting and likely due to high levels of residual nicotine or metabolites present in the brain at 4 hr of abstinence (versus ∼24 hours in the current study) resulting in lower β2*-nAChR availability. Also, while the current study did not find a significant decrease, on average, in β2*-nAChR availability by 4 weeks of abstinence compared to 1 week of abstinence, in some subjects normalization did occur by this point. The high heterogeneity of the subject population in the current study compared to the previous study in men only18 likely accounts for the high individual variability with regard to receptor changes during prolonged abstinence. Thus, the present study contributes to the literature with a larger, more heterogeneous subject group, a more prolonged period of abstinence, and additional assessments of behavioral features of tobacco smoking.
