GRM2 and Parkinson disease: Based on dysfunctional glutamatergic transmission observed in preclinical models and PD patients13, we measured the total protein amounts of the main NMDA and AMPA receptor subunits, and of the metabotropic glutamate receptors, mGluR2/3 and mGluR5, in the putamen and SN of MPTP-treated macaques with and without L-DOPA treatment, compared to naïve animals.