GRM1 and neoplasm: Different from the report that the activation of mGluR1 and mGluR5 is associated with an increase in tumor cell proliferation and migration as well as a poor outcome in glioma (59, 75), the activation of mGluR4 is associated with a decrease in cell proliferation and the reduction of cell viability in glioblastoma multiforme (GBM) in a time and dose-dependent manner after 24, 48, and 72-hours treatment with 30 and 50 μM of mGluR4 specific agonist VU0155041 (84).