The photoperiod, circadian regulation and chronodisruption: the requisite interplay between the suprachiasmatic nuclei and the pineal and gut melatonin.

Sep 7, 2011Journal of physiology and pharmacology : an official journal of the Polish Physiological Society

How Day Length and Body Clocks Work Together Through Brain and Gut Melatonin

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Abstract

Disruptions in the melatonin cycle may be linked to various pathologies, including those affecting the gastrointestinal tract.

Circadian rhythms influence nearly every function in an organism over a 24-hour cycle.
The suprachiasmatic nucleus (SCN) regulates these rhythms through neural and hormonal signals.
Light exposure at night can disrupt the SCN's function and alter the body’s timing signals.
Melatonin levels are typically low during the day and high at night, signaling time of day.
Alterations in melatonin production can occur due to nighttime light exposure and dietary factors.
Changes in the gastrointestinal tract's melatonin production may be associated with various health issues.

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The current scientific literature is replete with investigations providing information on the molecular mechanisms governing the regulation of circadian rhythms by neurons in the suprachiasmatic nucleus (SCN), the master circadian generator. Virtually every function in an organism changes in a highly regular manner during every 24-hour period. These rhythms are believed to be a consequence of the SCN, via neural and humoral means, regulating the intrinsic clocks that perhaps all cells in organisms possess. These rhythms optimize the functions of cells and thereby prevent or lower the incidence of pathologies. Since these cyclic events are essential for improved cellular physiology, it is imperative that the SCN provide the peripheral cellular oscillators with the appropriate time cues. Inasmuch as the 24-hour light:dark cycle is a primary input to the central circadian clock, it is obvious that disturbances in the photoperiodic environment, e.g., light exposure at night, would cause disruption in the function of the SCN which would then pass this inappropriate information to cells in the periphery. One circadian rhythm that transfers time of day information to the organism is the melatonin cycle which is always at low levels in the blood during the day and at high levels during darkness. With light exposure at night the amount of melatonin produced is compromised and this important rhythm is disturbed. Another important source of melatonin is the gastrointestinal tract (GIT) that also influences the circulating melatonin is the generation of this hormone by the entero-endocrine (EE) cells in the gut following ingestion of tryptophan-containing meal. The consequences of the altered melatonin cycle with the chronodisruption as well as the alterations of GIT melatonin that have been linked to a variety of pathologies, including those of the gastrointestinal tract.

The photoperiod, circadian regulation and chronodisruption: the requisite interplay between the suprachiasmatic nuclei and the pineal and gut melatonin.

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