All subjects will have up to four study-related visits to the Clinical Center in Bethesda over a one-year period, including an overnight stay. Participants will also be asked to complete an initial comprehensive telephone questionnaire to elicit whether they meet criteria for study participation, followed by on-site visits to NIH to complete a modified battery of neuropsychiatric screening tests related to symptom presence and severity. Questions relating to medical, family, psychiatric and developmental histories and lifestyle will be asked. In addition, visits will include a physical exam as well as blood and urine collection, and structural magnetic resonance imaging (MRI) of the head. Subject participation will culminate with sequential subcutaneous administration of a single dose of control vehicle solution (control) followed by the dopamine agonist apomorphine (after appropriate pre-medication with the anti-emetic, trimethobenzamide) or two sequential injections of vehicle for PET scans with attendant radiolabeled compounds.