GRM1 and central nervous system cancer: Metabotropic glutamate receptor 1 (GRM1), 5-Hydroxytryptamine (serotonin) receptor 7 (HTR7), and 5-Hydroxytryptamine (5-HT) receptor 2A (HTR2A) may play a role in glioma by participating in the interaction pathway of neuroactive ligand receptor interaction pathway [47,48].