How is melatonin synthesized during sleep?

Updated: Sep 11, 2018
  • Author: Jasvinder Chawla, MD, MBA; Chief Editor: Selim R Benbadis, MD  more...
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Answer

The suprachiasmatic nucleus (SCN) is entrained to the external environment by the cycle of light and darkness. The retinal ganglion cells transmit light signals via the retinohypothalamic tract to stimulate the SCN. A multisynaptic pathway from the SCN projects to the pineal gland, which produces melatonin.

Melatonin synthesis is inhibited by light and stimulated by darkness. The nocturnal rise in melatonin begins between 8 and 10 pm and peaks between 2 and 4 am, then declines gradually over the morning. [18] Melatonin acts via 2 specific melatonin receptors: MT1 attenuates the alerting signal, and MT2 phase shifts the SCN clock. The novel sleep-promoting drug ramelteon acts specifically at the MT1 and MT2 receptors to promote sleep but is structurally unrelated to melatonin. It has a relatively a short half- life (2.6 hours)


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