This study is designed to look at that involvement of a process in the brain called the
glutamate system in depression. Participants will undergo a screening session, up to two
functional Magnetic Resonance Imaging (fMRI) scans, and up to three Positron Emission
Tomography (PET) scans, as well as cognitive testing at each scan session. For one of the PET
scans, a drug (either ketamine or n-acetyl cysteine) will be administered.
Hypothesis 1: The investigators hypothesize administration of ketamine or n-acetylcysteine
(NAC) will lead to a decrease in mGluR5.
Hypothesis 2: The investigators hypothesize an improvement in memory and attentional skills
after drug challenge.
Hypothesis 3: The investigators hypothesize an increase in mGluR5 availability and change in
MRI measures post drug challenge as compared to baseline, signifying synaptogenesis.
Hypothesis 4: We expect there should not be a significant difference in reduction in mGluR5
availability due to differences in ABP688 radiotracer infusion.