Benefits to participants and/or society: This protocol will provide no direct benefits to the research participants other than routine medical screening and attention from the research staff. The knowledge gained in this study may lead to the availability of an agent for external monitoring of nAChRs using PET. This agent would be a valuable tool for determining the role of nAChRs in the pathogenesis of neuropsychiatric diseases, including nicotine dependence and for developing medications for diseases that respond to nicotinic agonists.