[123 I]5-IA or simply 5-I-A is a SPECT radioligand that binds to β2nAChRs. In a recent study, Staley et al. (2006) hypothesized that an abnormally high number of β2nAChRs in early abstinence may be responsible for continued tobacco usage. In this study, 16 smokers and 16 nonsmokers underwent 5-I-A SPECT scanning. Smokers were imaged in the abstinent phase, 7 days after their last cigarette. Each group consisted of seven men and nine women who were matched for age. Women smokers and nonsmokers were also matched by phase of menstrual cycle. Smokers quit cigarettes with brief behavioral counseling, and no medication was used for smoking cessation. In this study, recently abstinent smokers were found to have significantly higher 5-I-A uptake in the striatum, parietal cortex, frontal cortex, anterior cingulate, temporal cortex, occipital cortex, and cerebellum, which suggests that smoking upregulates the number of β2nAChRs.
