Imaging Cannabinoid CB1 Receptors in Schizophrenia

Background: \- The CB1 receptor is a protein in the brain that is targeted by the active ingredients in cannabis (marijuana). Brain systems that react to cannabis may be involved in the causes and symptoms of schizophrenia and schizoaffective disorder. For instance, research studies have shown that the number of CB1 receptors may be different in people with schizophrenia, and there may be differences in the receptors themselves. Researchers are interested in using positron emission tomography (PET) to study CB1 receptors in people with and without schizophrenia, using a chemical tracer that attaches specifically to CB1 receptors. Objectives: \- To determine whether the CB1 receptor brain protein is different in people with and without schizophrenia. Eligibility: \- Individuals between 18 and 55 years of age who either have been diagnosed with schizophrenia/schizoaffective disorder or are healthy volunteers. Design: * Participants in the study must have previously enrolled in the National Institute of Mental Health protocol A Neurobiological Investigation of Patients with Schizophrenia Spectrum Disorders and Their Siblings (95-M-0150). * Participants will provide blood samples to test for the gene that contains information on the specific type of CB1 receptor each participant has. * Participants will have a PET scan and/or a magnetic resonance imaging (MRI) scan. * The PET scan will last approximately 2 hours. Participants will receive an injection of a small amount of chemical tracer to improve the quality of the images taken during the scan. * The MRI scan will last approximately 1 hour.