Man Sleeping with Visible Brain : The sleep-wake cycle is an important circadian rhythm. When it is dark, the suprachiasmatic nucleus directs the pineal gland (located in another part of the brain) to secrete melatonin. This hormone peaks at night and ebbs during the day, and plays a key role in the sleep-wake cycle. Light disrupts melatonin production, and individuals who are exposed to too much light in the evenings, or who work the night shift, may experience problems sleeping as well as disruption in the menstrual cycle and other systems.
Melatonin /ˌmɛləˈtoʊnɪn/, chemically N-acetyl-5-methoxytryptamine, is a hormone found in animals, plants, fungi and bacteria. It is synthesized in animal cells directly from the amino acid tryptophan, but in other organisms through the Shikimic acid pathway, in response to dark-light periods (photoperiod). The penultimate enzyme, aralkylamine N-acetyltransferase (AANAT), is the key regulator of melatonin synthesis from tryptophan, as its gene AANAT is directly influenced by photoperiod.
In animals, melatonin controls the daily night-day cycle, thereby allowing the entrainment of the circadian rhythms of several biological functions. Many biological effects of melatonin are produced through activation of melatonin receptors, while others are due to its role as a pervasive and powerful antioxidant, with a particular role in the protection of nuclear and mitochondrial DNA.
The hormone can be used as a sleep aid and in the treatment of sleep disorders. It can be taken orally as capsules, tablets, or liquid. It is also available in a form to be used sublingually, and there are transdermal patches. There have been few clinical trials, particularly long-term ones, in the use of melatonin in humans.
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