Dopamine Receptor Imaging in Mood Disorders

This study seeks to increase the understanding of dopamine receptor function in the brain during major depressive disorder and bipolar depression, as well as genetic changes that may be behind changes in those receptors' actions. Dopamine is a natural messenger in the brain, involved in reward, motivation, and mood. Volunteers aged 18 to 55 who have primary major depressive disorder and those who have bipolar depression (20 in each group), who are not HIV positive and do not have AIDS, and who are not pregnant or breastfeeding may be eligible for this study. A telephone interview will be held, for patients to answer standardized questions about psychiatric or medical symptoms they may have experienced during their lifetime. Those eligible for the study will undergo interviews and laboratory tests. A psychiatric interview and clinical assessment will collect various data. Patients will undergo the following procedures and tests: * A brief neurological examination * A one-minute electrocardiogram to measure electrical activity of the heart. * Laboratory tests measuring several substances in the blood and urine. * Pregnancy test. A magnetic resonance imaging (MRI) scan will be done to create an image of the volunteer's brain structure. The technique of MRI uses a strong magnetic field and radio waves to obtain images of body organs and tissues. During the MRI scan, volunteers will lie still on a table that will slide into the scanner for 30 minutes and in some cases up to but no more than 90 minutes. Volunteers will be asked to lie as still as possible during the procedure. Then a PET system will create two images of brain blood flow-one of brain dopamine 1 receptor and one of dopamine 2/3 receptor binding. Volunteers will be given a radiotracer, a tiny amount of a drug that can be detected by a special camera in the PET scanner. A tiny flexible tube will be placed in the vein of one arm during each PET scan but during the MRI scan. Volunteers will be asked to lie