Patient description: The patient is a 63-year-old man presenting to the Emergency Department with a history of acute urinary retention in the past 2 days. Abdominopelvic CT scan revealed a large prostate and a bladder filled with urine. He is a candidate for urethral catheterization and TURP. Further evaluation revealed: Post-void residual: 71 mL Prostate volume (TRUS): 63 mL Prostate-specific antigen (PSA) level: 3.5 ng/mL His recent blood chemistry (3 days ago) was normal: Hgb: 13.6 g/dl WBC: 133000 /mm3 Plt: 370000 /ml PT: 12 second PTT: 34 second INR: 0.9 Creatinine: 0.5 mg/dl BUN: 10 mg/dl U/A: Color: yellow Appearance: cloudy PH: 5.3 Specific gravity: 1.010 Glc: 100 Nitrite: negative Ketone: none Leukocyte esterase: negative RBC: negative WBC: 2 WBCs/hpf U/C: negative

Clinical trial eligibility criteria: eligible ages (years): 20.0-65.0,  Healthy Adults Medically, psychiatrically and neurologically healthy individuals between the 20-30 or 50-65 years of age. Subjects must be able to give informed consent, have an estimated intelligence quotient of greater than 80, and be a fluent English speaker  Any condition which would interfere with or be a risk for MRI ( e.g. extreme obesity, claustrophobia, cochlear implant, metal fragments in eyes, cardiac pacemaker, neural stimulator, metallic body inclusions or other metal implanted in the body, facial tattoos with iron pigment). Difficulty lying on one's back and claustrophobia are also exclusions. 2. History of major psychiatric illness (including recurrent major depressive episodes or a depressive episode in the past 10 years, any anxiety disorders in the last 10 years, any history of bipolar disorder or psychotic disorder, a history of substance dependence (or substance abuse lasting more than 2 years), or any eating disorder in which symptoms persisted for more than two years 3. Current tobacco use, alcohol intake greater than 8 ounces of whiskey or equivalent per week, use of any psychotropic medication for the past 6 months (other than occasional use of benzodiazepines for sleep), psychostimulants taken more than 5 times in the subject's life, current marijuana use 4 Neurological illness (other than headache or strictly peripheral nerve disturbance), or head trauma (including more than 2 concussions) 5) Significant untreated or unregulated major medical condition deemed likely to influence cognitive functioning, dopaminergic functioning or neuroimaging measures. Diabetes is an even if well-controlled. 6) History of Syncope during blood draws 7) Anemia or hematocrit < 34. 8) Participation in any research studies in the past year that involved radiation, or exposure to radiation on a routine basis due to their occupation. 9) High blood pressure (Systolic B.P. > 150 in participants under the age of 61, or > 145 in subjects > 61 years of age). Diagnosis of labile hypertension. Abnormal EKG indicating potential cardiac risk under conditions of increased blood pressure. 10) Current pregnancy or lactation or plans to become pregnant during the study timeframe. As part of the screening process in protocol # 141812, participants are initially screened with a brief telephone interview to determine if they meet medical, psychiatric and neurological (all information screened is included in attached screening form). Participants are not consented until after completion of the brief health interview (a waiver of consent is in place in order to perform the initial telephone screening). After being consented participants complete a medical history and physical exam with one of the study MD's. They also complete a psychiatric interview (SCID-IV or V) with one of the trained psychology research assistants or Dr. Zald, and finally an EKG is completed. Participants are not enrolled in the present phase of the study until all are assessed and they are withdrawn from the study if new information arises that would alter the conclusion regarding any of the inclusion/ after enrollment