GRM5 and Parkinson disease: Considerable interest in mGluR5 [20] has developed in the last few years due to: 1) its potential involvement in AD [21] and PD [22,23], 2) the role of this receptor in learning and memory [24,25], 3) mGluR5 is abundantly expressed in the neocortex, limbic system and caudoputamen [26]—brain regions selectively affected in AD and PD, and 4) selective inhibitors of mGluR5, 2-methyl-6-(phenylethynyl)pyridine (MPEP) and 3-((2-Methyl-4-thiazolyl)ethynyl)pyridine (MTEP), are currently being considered as potential therapies for neurodegenerative disorders [23].