FLB-457 has been used in several PET centers and has recently been approved for use at the Yale University PET Center. We would like to determine whether there are sex differences in amphetamine induced DA release in healthy tobacco smokers and nonsmokers. Specifically, 40 healthy tobacco smokers and 40 healthy nonsmokers will have an magnetic resonance imaging (MRI) scan followed on another day by two FLB scans (ideally, the two PET scans will be carried out in the same day). Starting at 3 hours before the second PET scan, amphetamine (0.4mg/kg, PO) will be administered.