Positron emission tomography (PET) is a noninvasive in vivo imaging technique that enablesthe visualization and quantification of neuroreceptor binding.28−30 Given the growing interest in mGluR2-targeted therapeuticsfor neurological and psychiatric disorders, the availability of a suitable mGluR2PET ligand would substantially facilitate the clinical development of potential drugcandidates.31,32 Todate, several mGluR2 PET ligands have been reported, including both PAM- andNAM-based probes (Figure 1). Here, GRM2 is linked to psychiatric disorder.