In addition, 5-HT1A heteroreceptors are abundantly expressed post-synaptically in the PFC, amygdala, and hippocampus to mediate serotonin actions on fear, anxiety, stress, and cognition, indicating a primary role of the 5-HT-PFC circuitry in effective treatment of depression [22-24]. The gene discussed is HTR1A; the disease is depressive disorder.