HTR4 and Anxiety: Dysfunctionsof the serotonin (5-hydroxytryptamine, 5-HT) systemin the mammalian brain are related to the pathogenesis of depression.1 The serotonin 4 receptors (5-HT4Rs)in the medial prefrontal cortex (mPFC) may serve to reduce depressive-and anxiety-like behaviors.2,3 The locations of 5-HT4Rsin different structures of the brain are conserved in humans.