Cerecor Inc. acquired rights to an NMDA (N-methyl-d-aspartate) antagonist for development in the area of depression from Merck and Co. Inc. The drug, MK-0657, was initially in development at Merck for Parkinson's disease. Increasing evidence in the literature points to NMDA receptors as promising targets in treating depression, including well-known studies with ketamine, an NMDA antagonist.