Spaglumic Acid is a neuropeptide found in millimolar concentrations in brain. In Vitro: Spaglumic Acid (N-Acetylaspartylglutamate; NAAG) is released upon depolarization by a Ca²⁺-dependent process and is an agonist at mGluR3 receptors and an antagonist at NMDA receptors. Spaglumic Acid is catabolized to N-acetylaspartate and glutamate primarily by glutamate carboxypeptidase II, which is expressed on the extracellular surface of astrocytes. The levels of Spaglumic Acid and the activity of carboxypeptidase II are altered in a regionally specific fashion in several neuropsychiatric disorders^[1].