Serotonin (5-hydroxytryptamine, 5-HT) is a monoamine neurotransmitter that plays a crucial role in physiological functions, and of a total of 14 subtypes of 5-HT receptors, the 5-HT1A receptor is a prominent target for the treatment of various neuropsychiatric and neurological disorders, prominently depression [42]. Here, HTR1A is linked to major depressive disorder.