DLG4 and major depressive disorder: The administration of DOI, a 5-HT2A/5-HT2C agonist, in the orbitofrontal cortex (OFC), induces the following responses: (1) Depression-like behaviors; (2) reduced expression of Kalirin-7 (Kal7), an essential component of excitatory synapses; and (3) reduced expression of PSD-95, a protein capable of modulating 5-HT2A receptor expression.