<qa>  What is the primary target of the widely prescribed specific serotonin reuptake inhibitorThe serotonin transporter SERT modulates the activity of the central serotonergic system and SERT is also the primary target of the widely prescribed specific serotonin reuptake inhibitors. Until recently, suitable radioligands for in vivo imaging of SERT have not been available. However, a recently developed PET radioligand, 11CDASB, appears suitable for quantifying SERT in humans. In the two protocols that have been approved by the CSRP for submission to the IRB, we planned to use 11CDASB PET to study the pathophysiology of SERT in Parkinsons disease and OCD. This protocol was created to address criticisms raised by the NIH RDRC committee and the external scientific review. 