N-Acetylserotonin (NAS), also known as normelatonin, is a naturally occurring chemical intermediate in the endogenous production of melatonin from serotonin. It is produced from serotonin by the enzyme aralkylamine N-acetyltransferase (AANAT) and is converted to melatonin by acetylserotonin O-methyltransferase (ASMT). Like melatonin, NAS is an agonist at the melatonin receptors MT₁, MT₂, and MT₃, and may be considered to be a neurotransmitter. In addition, NAS is distributed in some areas of the brain where serotonin and melatonin are not, suggesting that it may have unique central duties of its own instead of merely functioning as a precursor in the synthesis of melatonin. NAS is able to penetrate the blood–brain barrier, unlike serotonin. NAS is known to have anti-depressant, neurotrophic and cognition-enhancing effects and has been proposed to be a target for the treatment of aging-associated cognitive decline and depression