In the present study we report a negative correlation between baseline craving scores, e.g., prior to quitting smoking, and β2*-nAChR availability at 1 day of abstinence in the thalamus and parietal cortices. Because receptor availability is defined as receptors that are available to be bound by the radiotracer, at 1 day of abstinence subjects with lower receptor availability have more nicotine present in the brain occupying receptors and blocking the radiotracer from binding to the receptor. Thus, we believe that subjects who reported high baseline craving, likely smoked more cigarettes immediately prior to their quit day and had lower receptor availability at 1 day of abstinence. However, the experience of craving in the presence of nicotine occupancy of the β2*-nAChR is not unusual. Smokers experience craving within 2 h of their last cigarette despite continued occupancy of the receptor by nicotine13. Dopamine release has been associated with the feeling of craving58, and both nicotine59 and cotinine60 have been shown to facilitate dopamine release, thus the prolonged partial occupancy of the receptor by nicotine or cotinine, may contribute to the feelings of craving that are reported 2 h after the last cigarette and throughout the first week of abstinence.
