GRM1 and Parkinson disease: CNITM is a derivative of a PET probe for metabotropic glutamate receptor type 1 (mGlu1),28 a type-C G protein-coupled receptor (GPCR) expressed in the cerebellum and thalamus regions, whose expression level may be related to Parkinson’s disease.29,30 CNITM bearing the affinity with mGlu1 (Ki = 27 nM), was modified with a primary amine and a fluorescent Alexa Fluor 647 (Ax647) dye to produce the CNITM probe 1 (mGlu1) (Figure 1D).