The radioligand that will be used is the2- F-A-85380 labelled with fluorin-18, a fluoro derivative of the A85380 (Abbott compound). The 2-F-A-85380 present a high affinity and high selectivity for the alpha4beta2 nicotinic receptor subtype, which is the major nicotinic receptor subtype in the brain. Radiolabelling, with fluorin-18 (half-life=110 min) performed in our laboratory, allow produciton of a high specific activity.