GRM1 and schizophrenia: In support of this hypothesis, mutations in mGluR1 and mGluR555–59, and changes in mGluR1 expression60–62 are associated with schizophrenia in human patients, and genetic and pharmacological inhibition of group 1 mGluR signaling results in schizophrenia-related impairments in rodents both alone and in combination with NMDAR antagonist administration (reviewed in63,64).