Quisqualic acid is an agonist of (AMPA)-subtype glutamate receptor, GRIA2, and group I metabotropic glutamate receptors. Quisqualic acid has been shown to inhibit human glutamate carboxypeptidase II (GCPII), an enzyme occurs in the central nervous system as well as in human prostate (where it is called prostate-specific membrane antigen; PSMA). Inhibitors of this enzyme as was discovered can provide neuroprotection, but can also be useful for the detection, imaging, and treatment of prostate cancer.