GRM5 and major depressive disorder: A recent post-mortem study showed reduced GRM5 (which encodes mGluR5) in depressed subjects (in males only).51 However, in preclinical studies, mGluR5 knockout mice exhibit reduced depression-like behaviors and blockade of mGluR5 produces an antidepressant effect52 (which has also been shown in humans with mGluR5-negative allosteric modulators53).