The goal of the study is to determine whether there are alterations in synaptic vesicle glycoprotein 2A (SV2A), a protein expressed ubiquitously in synaptic vesicles, in depression and anxiety and whether ketamine, an N-Methyl-D-aspartate (NMDA) antagonist, normalizes SV2A density at time of its greatest anti-depressant response. This study will conduct an examination of SV2A and associated consequences using neuroreceptor imaging and behavioral techniques for the following aims.