While nicotine was not really used as a therapeutic drug, as a carbon-11 labeled PET tracer it successfully showed reduction of nAChR in AD patients reflecting the loss of the nicotinic receptors during disease progression, in comparison with control subjects (Nordberg et al., 1990; Nordberg et al., 1995; Kadir et al., 2006). The gene discussed is CHRNA4; the disease is Alzheimer disease.