Abnormalities in the re-uptake of dopamine and serotonin have been described in various neuropsychiatric disorders and substance abuse. [I-123] Beta-CIT is a recently developed radioligand for SPECT imaging of dopamine and serotonin transporters. [I-123]Beta-CIT SPECT has been used at the SPECT-lab of the Clinical Brain Disorders Branch in over fifty subjects without adverse events. Due to the trace concentrations used, a pharmacological effect of Beta-CIT is unlikely and has not been observed. The purpose of this study is to use Beta-CIT and SPECT to study the expression of dopamine and serotonin transporters in vivo in normal controls and various patient populations to address hypothesized abnormalities of the transporters in different disorders and to understand the effects of genetic variations in the genes of these transporters on their in vivo expression.