Effects of Smoking on Opioid Receptor Binding: A PET Study

Background: * Tobacco smoking is one of the most preventable causes of morbidity and mortality in the world, but the addictive property of nicotine is such that fewer than 10 percent of people who attempt to quit smoking remain tobacco-free after 1 year. Researchers are studying the addictive properties of nicotine in an attempt to develop more successful medication therapies for smoking cessation. * Nicotine acts on chemical receptors in the brain, including opioid receptors that affect the perception of pain. Repeated nicotine administration can cause adaptations in the brain s opioid receptors, which heightens the addictive properties of nicotine and increases the likelihood and severity of withdrawal symptoms associated with smoking cessation. Researchers are interested in using positron emission tomography (PET) scanning to study brain chemical responses to nicotine in current smokers and nonsmokers. Objectives: * To study brain chemical activity related to cigarette smoking and nicotine administration. * To compare the brain chemical activity of current daily smokers with that of nonsmokers. Eligibility: \- Individuals 21 to 50 years of age who are either current smokers (10 to 25 cigarettes daily for at least 2 years) or have had some exposure to tobacco but have never smoked regularly (may have had a maximum of 20 cigarettes in their lifetime and none in past year). Design: * Eligible participants will undergo initial medical and psychological screening and neuropsychological testing before beginning the main phase of the study. Participants will be required to abstain from alcohol and drugs (except caffeine, nicotine, and prescription drugs) for 24 hours before each session, and smokers will refrain from smoking after midnight on the night before each session. * Session 1: Participants will answer questions about nicotine craving and withdrawal symptoms, followed by a magnetic resonance imaging (MRI) scan to provide baseline information about brain a