It also downregulated mGluR5 and modulated the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunits: GluA1 was downregulated, inhibiting long-term potentiation, while GluA2 and GluA3 were upregulated in the nigrostriatal pathway in PD animal models. Here, GRM5 is linked to Parkinson disease.