Biomarker Assessment of Glutamatergic Target Engagement

This is a pilot study of healthy subject to assess the feasibility of Glx MRS and BOLD fMRI to measure ketamine induced changes in glutamatergic indices. The investigators will randomize 18 subjects at each site. Subjects will be randomized to ketamine or placebo in a 2:1 ratio and receive two drug challenges separated by at least two weeks. Ketamine challenge is used to induce a "glutamate surge" within prefrontal brain regions that can be detected using neurochemical and functional imaging techniques. Each subject will receive MRS and BOLD fMRI during each challenge day. The goal of the pilot study is to assess the feasibility of both the proposed ketamine challenge paradigm and of the proposed imaging-based biomarkers. Specific indices to be used in assessing feasibility will include effect size, cross-site and cross-subject reliability, safety, and subject tolerability as similar studies will be performed independently at Yale and UC Davis. Second this information will be used to select and refine final study parameters for a subsequent full proof-of-clinical mechanism (POCM) study investigating the effect of Pomaglumetad on ketamine-induced MRS and fMRI effects.