CNR1 and major depressive disorder: We also showed that ACC glutamate levels were associated with greater symptom severity on the positive factor (R = 0.613, p = 0.007) and the depression and anxiety factor (R = 0.514, p = 0.029) using a five-factor model [63].This is the first study, as far as we’re aware, to investigate the association between cannabinoid 1 receptor levels and glutamate levels in humans or patients with schizophrenia.