In Vivo imaging of nicotinic acetylcholine receptors in the central nervous system

Nicotinic acetylcholine receptors (nAChRs) in the central nervous system are involved in higher brain function, i.e., memory, cognition, learning, among others. These receptors also exert various pharmacological effects, such as neuroprotection and antinociception. Therefore, elucidating the localization and/or expression level of nAChRs in the brain is useful to clarify functions regulated by nAChRs, under physiological and pathological conditions. "Molecular imaging" is a powerful tool that enables one to noninvasively obtain information from living subjects. Many signal types, such as, radiation, nuclear magnetic resonance, fluorescence, bioluminescence, and ultrasound, are commonly used for molecular imaging. Among them, nuclear medical molecular imaging, which uses radioactive imaging probes, has a great advantage due to its high sensitivity and the fact that it is a quantitative approach. Many nuclear medical imaging probes targeting nAChRs have been developed and some of them have successfully visualized nAChRs in the animal and human brain. Moreover, changes in nAChR density under pathological conditions have been detected in patients. This chapter summarizes the history and recent advance of nAChR imaging.