GRM5 and major depressive disorder: The highly potent mGluR5-speciific negative allosteric modulator CTEP (2-chloro-4-[2[2,5-dimethyl-1-[4-(trifluoromethoxy) phenyl] imidazol-4-yl] ethynyl] pyridine) was chosen for this study because it is orally bioavailable, crosses the blood brain barrier, has a half-life of 18 h and its analogue, Basimglurant, was proven to be well- tolerated in phase II trials for major depressive disorder [16, 17].