1974. Melatonin has been established as a reliable output of the SCN's timekeeping property, and melatonin research has been coupled with SCN research since 1974. Because melatonin is secreted according to signals to the pineal gland from the SCN, exogenous melatonin taken as a chronobiotic can affect feedback to the SCN and its subsequent circadian rhythms. Types Quiadon Quiadon (mepiprazole dihydrochloride) was one of the first chronobiotics used to affect circadian rhythms in humans. A 3-alkyl pyrazolyl piperazine, Quiadon is a serotonin-depleting tranquilizer. However, the original study performed by H.W. Simpson and colleagues in 1973 delivered inconclusive results, and Quiadon was never put on the market for human use. Melatonin Melatonin is a natural hormone produced by the body to encode nighttime. Endogenous melatonin is secreted daily in all mammals beginning after sunset and ending just before sunrise. Melatonin's chronobiotic property was initially suspected in the late 1980s when a high density of high-affinity melatonin receptors was discovered in the SCN. Little is known about the long-term effects of taking melatonin. Melatonin receptor agonists Chrononutrition The field of chrononutrition was established after dietary tryptophan was shown to synchronize the circadian rhythm with environmental time cues in 1968. Melatonin, which is also known for its chronobiotic properties, is synthesized from tryptophan. It is not only the nutrient that is relevant to chrononutrition, but the timing of nutrient consumption. By strategically planning meal times, the body can become resynchronized with exogenous time. References See also Circadian rhythm sleep disorder Chronobiology Sleep medicine Circadian rhythm Hypnotics