Consistent with our previous study8 we report significantly higher β2*-nAChR availability in smokers at one week of abstinence in the cortex, striatum and cerebellum, but not thalamus compared to nonsmokers. The difference between recently abstinent smokers and never smokers in the previous study8 was of a greater magnitude, e.g., 26-36% in the cerebral cortex and 27% in the striatum, than in the current study, e.g., 21-29% in the cerebral cortex and 22% in the striatum. This may be due to the older average age (approximately 5 years) of subjects in the current study, since β2*-nAChR availability has been shown to decrease with age in nonsmokers77. This study and previous in vivo PET78 and SPECT8, 18 studies report no upregulation of thalamic β2*-nAChR availability during acute abstinence, which conflicts with postmortem2 and animal8, 79 studies. In general, this may be due to differences in methodology or the higher relative dose of nicotine in the postmortem and animal studies. However, two smokers in the current study exhibited increased β2*-nAChR availability in the thalamus compared to nonsmokers, highlighting the role of individual differences in receptor regulation.
