Circadian rhythms: Seasonal affective disorder, Nocturnality, Circadian rhythm, Chronobiology, Free-running sleep, Jet lag, Melatonin, Delayed sleep phase syndrome, Roberto Refinetti, Shift work, Light therapy, Pineal gland, Photosensitive ganglion cell

Source: Wikipedia. Pages: 73. Chapters: Seasonal affective disorder, Nocturnality, Circadian rhythm, Chronobiology, Free-running sleep, Jet lag, Melatonin, Delayed sleep phase syndrome, Roberto Refinetti, Shift work, Light therapy, Pineal gland, Photosensitive ganglion cell, Bacterial circadian rhythms, Non-24-hour sleep-wake syndrome, Polyphasic sleep, Circadian oscillator, Suprachiasmatic nucleus, Chronotype, Phase response curve, Irregular sleep-wake rhythm, Circadian rhythm sleep disorder, Melanopsin, Shift work sleep disorder, Photoperiodism, N-Acetylserotonin, Advanced sleep phase syndrome, Dark therapy, Segmented sleep, Chronotherapy, Light effects on circadian rhythm, Actigraphy, Night owl, Circasemidian rhythm, Light in school buildings, Dawn simulation, David F. Dinges, Sara Mednick, Sundowning, Sleep diary, Sleep inertia, Jürgen Aschoff, Entrainment, Diurnality, Russell G. Foster, Photoreceptor protein, Spring Fever, Ultradian, Nathaniel Kleitman, Giant retinal ganglion cells, Lark, Circaseptan, Zeitgeber, Franz Halberg, Retinohypothalamic tract, Infradian rhythm. Excerpt: Melatonin (), also known chemically as N-acetyl-5-methoxytryptamine, is a naturally occurring compound found in animals, plants and microbes. In animals, circulating levels of the hormone melatonin vary in a daily 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. In mammals, melatonin is secreted into the blood by the pineal gland in the brain. Known as the "hormone of darkness" it is secreted in darkness in both day-active (diurnal) and night-active (nocturnal) animals. It may also be produced by a variety of peripheral cells such as bone marrow cells, lymphocytes and epithelial cells. Usually, the melatonin concentration in these cells is much higher than that found in the blood but it does not seem to be regulated by the photoperiod. Melatonin-rich plant feed, such as rice, ingested by chicks has been shown to reach and bind to melatonin receptors in their brains. No food has been found to elevate plasma melatonin levels in humans. Products containing melatonin have been available over-the-counter as a dietary supplement in the United States since the mid-1990s. In many other countries, the over-the-counter sale of this neurohormone is not permitted or requires a prescription, and the U.S. Postal Service lists unapproved melatonin preparations among items prohibited by Germany. Melatonin has been studied for the treatment of cancer, immune disorders, cardiovascular diseases, depression, seasonal affective disorder (SAD), circadian rhythm sleep disorders and sexual dysfunction. It may ameliorate circadian misalignment and SAD. Basic research indicates that melatonin may play a significant role in modulating the effects of drugs of abuse such as cocaine. Exogenous melatonin taken