Melatonin
Melatonin (N-acetyl-5-methoxytryptamine) is a neurohormone produced in and secreted by the pineal gland of humans. This hormone is only produced during the hours of darkness and thus, as day length decreases when nights become longer in the winter, melatonin is produced for a longer time. Conversely, as day length increases and nights shorten in the summer, melatonin is produced for a shorter time. The highest levels of secreted melatonin occur during the dark period of a circadian light-dark cycle. This hormone is also found in the retina and the gut. Melatonin production has been shown to change across the lifespan, peaking in childhood and gradually decreasing after puberty. The pineal hormone melatonin (N-acetyl-5-c) has several putative functions, including regulation of circadian rhythms, regulation of the reproductive axis and antioxidant activity. Autoradiographic studies and receptor assays have demonstrated the presence of melatonin receptors in various regions of the central nervous system and in other tissues in humans. The physiological effects of melatonin appear to be the regulation of the circadian biological timing system and modulation of sleep, acting on sleep propensity and core body temperature. Melatonin elicits potent neurobiological effects. Melatonin influences circadian rhythm and mediates the effects of photoperiod on reproductive function in seasonally breeding mammals. In humans, melatonin administration has been shown to alleviate the symptoms of jet lag after air travel across several time zones. The hormone also has potent sedative effects in humans and may be a useful hypnotic agent. In humans, melatonin administration has been shown to alleviate the symptoms of jet lag after air travel across several time zones. The hormone also has potent sedative effects in humans and may be a useful hypnotic agent. Many of the biological effects of melatonin result from its action on serotonergic neurons indicating that the neurotransmitter serotonin is an important mediator of melatonin's biological actions and that deficient serotonin neurotransmission may disrupt melatonin's biological functions. Melatonin is produced and secreted into the plasma in a circadian rhythm which parallels the sleep-wake cycle. A derangement of the normal, diurnal melatonin production often results in sleep disorders. Melatonin binding sites have been characterized in membrane preparations from mammalian brains. Autoradiographic studies have revealed the existence of melatonin binding sites in the human biological clock. Melatonin is involved in the transduction of photoperiodic information and appears to modulate a variety of neural and endocrine functions in vertebrates, including the regulation of reproduction, body weight and metabolism in photoperiodic mammals, control of circadian rhythms, and modulation of retinal physiology. Impaired pineal melatonin function has been implicated in the pathophysiology of numerous systemic, neurological and mental disorders including cancer, diabetes mellitus, autoimmune disorders, AIDS, hyper-cholesterolemia, mental depression including seasonal affective disorder (SAD), schizophrenia, autism, panic disorder, obsessive compulsive disorder, trichotillomania, impulsive and aggressive behavior, chronic insomnia, sleep paralysis, substance abuse including alcoholism, posttraumatic stress disorder, bulimia, Parkinson's disease, juvenile Parkinsonism, Shy-Drager syndrome, progressive supranuclear palsy (PSP), Huntington's chorea, AIDS dementia, Alzheimer's disease, Korsakoffs dementia, tardive dyskinesia, diabetic neuropathy, epilepsy, narcolepsy, migraine, multiple sclerosis, chronic pain syndromes, ischemic stroke, motor neuron disease, traumatic spinal cord injuries and macular degeneration.
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