Studies of nonhuman primates and humans have examined distributions of nAChRs with these new radiotracers, and found regional densities of these receptors similar to those in the animal work cited above (Chefer et al. 2003, 1999; Fujita et al. 2002, 2003; Kimes et al. 2003; Valette et al. 1999). Two recent studies on baboons examined effects of nicotine or tobacco smoke on nAChR availability. In a 2-FA PET study (Valette et al. 2003), IV nicotine (0.6 mg), inhalation of tobacco smoke from one cigarette (0.9 mg nicotine), and IV nornicotine were all found to reduce the volume of distribution of the tracer by roughly 30–60% in the thalamus and putamen at 80 min, and this reduction of 2-FA binding was relatively long lived (up to 6 h). Similarly, a 50% reduction in nAChR availability was found with IV nicotine administration to baboons using an epibatidine analog and PET scanning (Ding et al. 2000). Taken together, these studies demonstrate that radiotracers for nAChRs can be administered safely to measure nAChR densities, and that nicotine and smoking substantially decrease α4β2 nAChR availability.
