GRM5 and major depressive disorder: Widely expressed and mainly postsynaptic throughout the cerebral cortex, corpus striatum, hippocampus, olfactory bulb, caudate nucleus, nucleus accumbens but also in non-neuronal cells including astrocytes and microglia, mGluR5 have been implicated in the pathogenesis of numerous psychiatric, neurological, and neurodevelopmental disorders including schizophrenia, addiction, anxiety, depression, PD, fragile X syndrome (FXS), or autism spectrum disorders (ASD)2,13–17 Firstly, drug development programs targeting mGluR5 were interested in the orthosteric site of the receptor.