GRM5 and Parkinson disease: Then, the combined use of A2A and mGluR5 agonist, targeting A2A-D2-mGluR5 heteroreceptor complexes in the ventral striatal–pallidal GABA pathway, is a new strategy for a pharmacological treatment of schizophrenia, while the use of A2A and mGluR5 antagonists may be an alternative therapeutic approach to PD [132,133].