Biomaterial Database

Melatonin and seasonal rhythms. 1997

T A Wehr

Clinical Psychobiology Branch, National Institute of Mental Health, Bethesda, MD 20892-1390, USA.

The pineal hormone melatonin plays a ubiquitous role in biology as a chemical mediator of the effects of season on animal physiology and behavior. Seasonal changes in night length (scotoperiod) induce parallel changes in the duration of melatonin secretion (which occurs exclusively at night), so that it is longer in winter and shorter in summer. These changes in duration of nocturnal melatonin secretion, in turn, trigger seasonal changes in behavior. The retinohypothalamic-pineal (RHP) axis's responses to light are highly conserved in humans. Like other animals, humans secrete melatonin exclusively at night, and they interrupt its secretion when they are exposed to light during the nocturnal period of its secretion. In many individuals, the RHP axis also is capable of detecting changes in the length of the night and making proportional adjustments in the duration of nocturnal melatonin secretion, producing the type of melatonin message that animals use to trigger seasonal changes in their behavior. This has been shown both in naturalistic studies in which melatonin profiles were compared in summer and winter and in experimental studies in which melatonin profiles were compared after chronic exposure to long and short artificial "nights." Individuals who live in modern urban environments differ in the degree to which, or even whether, the intrinsic duration of melatonin secretion (the duration measured in constant dim light) responds to seasonal changes in the length of the solar night. Changes in the intrinsic duration of melatonin secretion that are induced by changes in the scotoperiod are highly correlated with changes in the intrinsic timing of the morning offset of secretion and are only weakly correlated with changes in the intrinsic timing of evening onset of secretion. This finding suggests that differences in the way in which individuals are exposed to, or process, morning light may explain differences in their responsiveness to changes in duration of natural and experimental scotoperiods. Although the human RHP axis clearly is capable of detecting changes in the length of the night and in producing the melatonin message that other animals use to trigger seasonal changes in their behavior, it is not yet known whether or how the human reproductive system or other systems respond to this message.

UI	MeSH Term	Description	Entries
D008550	Melatonin	A biogenic amine that is found in animals and plants. In mammals, melatonin is produced by the PINEAL GLAND. Its secretion increases in darkness and decreases during exposure to light. Melatonin is implicated in the regulation of SLEEP, mood, and REPRODUCTION. Melatonin is also an effective antioxidant.
D010507	Periodicity	The tendency of a phenomenon to recur at regular intervals; in biological systems, the recurrence of certain activities (including hormonal, cellular, neural) may be annual, seasonal, monthly, daily, or more frequently (ultradian).	Cyclicity,Rhythmicity,Biological Rhythms,Bioperiodicity,Biorhythms,Biological Rhythm,Bioperiodicities,Biorhythm,Cyclicities,Periodicities,Rhythm, Biological,Rhythmicities,Rhythms, Biological
D006801	Humans	Members of the species Homo sapiens.	Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D012621	Seasons	Divisions of the year according to some regularly recurrent phenomena usually astronomical or climatic. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)	Seasonal Variation,Season,Seasonal Variations,Variation, Seasonal,Variations, Seasonal
D017440	Photoperiod	The time period of daily exposure that an organism receives from daylight or artificial light. It is believed that photoperiodic responses may affect the control of energy balance and thermoregulation.	Dark-Light Cycle,Daylight Cycle,Light Cycle,Light-Dark Cycle,Cycle, Dark-Light,Cycle, Daylight,Cycle, Light,Cycle, Light-Dark,Cycles, Dark-Light,Cycles, Daylight,Cycles, Light,Cycles, Light-Dark,Dark Light Cycle,Dark-Light Cycles,Daylight Cycles,Light Cycles,Light Dark Cycle,Light-Dark Cycles,Photoperiods