PET Whole Body Distribution Studies Using [11C]CUMI

Background: * Researchers studying new treatments for major depressive disorder are looking at how medications to treat depression act on the brain chemical serotonin, which interacts with specific serotonin receptors on brain cells. New methods of studying serotonin receptors in the brain may help provide a better understanding of depression and treatment options. * A new radioactive chemical called \[11C\]CUMI may be useful for studying serotonin receptors in the brain. By using positron emission tomography (PET) scanning to see how \[11C\]CUMI bonds with serotonin receptors, researchers will investigate whether \[11C\]CUMI can be used to study depression and how antidepressant medications work. Objectives: \- To determine the usefulness of \[11C\]CUMI as a method of studying serotonin receptors in the brain. Eligibility: \- Healthy individuals between 18 and 65 who have no history of psychiatric illness. Design: * This study requires 8 outpatient visits to the NIH clinic. * Visit 1: Participants will have a full physical examination and medical history, as well as a psychiatric evaluation and questions about alcohol and drug use. Other tests will include blood and urine samples and an electrocardiogram (EKG). Testing will take approximately 3 hours. * Visit 2: Participants will have a magnetic resonance imaging (MRI) scan to evaluate brain function and activity. * Visit 3: Participants will have a PET scan, in which a small amount of the radioactive chemical \[11C\]CUMI will be injected through an intravenous (IV) catheter, and will have another IV line put in place to draw regular blood samples during the scan. The scan will last approximately 4 hours. * Visits 4-8: Participants will have regular blood tests after the scan between days 1-3 and at about weeks 1, 2, 3, and 4. The blood tests will check muscle, heart, and liver function.