GRM8 and Parkinson disease: As with mGluR7, the lack of selective agonists for mGluR8 limits our ability to study its potential benefits in PD (Broadstock et al., 2012).Recent studies have demonstrated that the orthosteric agonist (S)-3, 4-dicarboxyphenylglycine (DCPG) exerts no influence in rodent models of PD (Broadstock et al., 2012).