Radiotracers for the nAChR have been developed in recent years, with labeled A-85380 (3-(2(S)-azetidinylmethoxy pyridine) (Koren et al. 1998) compounds having the most widespread use. Radiolabeling of A-85380 was a major advance in imaging nAChRs, because administration of radiolabeled nicotine (used for previous imaging studies) resulted in high nonspecific binding and short drug–receptor interaction times (Sihver et al. 2000). 2-[18F]F-A-85380 or simply 2-FA and related compounds (Chefer et al. 1999; Horti et al. 1998; Koren et al. 1998) are being used for PET imaging, and 5-[123/125I]iodo-A85380 is being used for SPECT imaging (Chefer et al. 1998; Horti et al. 1999; Mukhin et al. 2000) of α4β2 nAChRs.
