PET Imaging of Brain Peripheral Benzodiazepine Receptors

This study will use positron emission tomography (PET) and magnetic resonance imaging (MRI) to measure peripheral benzodiazepine receptors (PBRs) in the brain. PBRs were initially found in peripheral organs such as kidneys, endocrine glands and lungs, but later studies identified PBRs in the CNS. PBRs can be a marker to detect nervous system inflammation. Development of a test to image PBRs may improve the management of brain disorders such as multiple sclerosis, Alzheimer's disease, Parkinson's disease, and others in which inflammation is involved in progression of the disease. Healthy volunteers from 18 to 40 years old may be eligible for this study. Candidates are screened with tests that may include some or all of the following: diagnostic interview; ratings of mood, anxiety, functioning, and other parameters; neuropsychological testing; physical examination; electrocardiogram; blood and urine tests; and personal, social and family histories. Participants undergo the following procedures: * Evaluation: Subjects provide a medical history, including detailed questions about their psychological health, and have a physical examination and blood and urine tests. * PET scanning: PET uses small amounts of a radioactive chemical called a tracer that "labels" active areas of the brain. The tracer used in this study is \[11C\]PBR28. For the procedure, the subject lies on the scanner bed. A special mask is fitted to the head and attached to the bed to help keep the head still during the scan so the images will be clear. A brief scan is done just before the radioactive tracer is injected to provide measures of the brain that will help to precisely calculate information from subsequent scans. After the tracer is injected through a catheter (plastic tube) placed in the arm, pictures are taken for 2 to 3 hours, during which the subject lies still on the scanner bed. Subjects return to the clinic the following day for more blood and urine sample collections. * MRI: The MRI s