Disrupted Circadian Control of Hormonal Rhythms and Anticipatory Thirst by Dim Light at Night

Mar 22, 2022Neuroendocrinology

Dim Nighttime Light May Disrupt Daily Hormone Cycles and Thirst Signals

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Abstract

Low-intensity artificial light at night (ALAN) suppressed circadian clock genes in rats after 2 weeks of exposure.

ALAN significantly disrupted the rhythmic expression of clock genes in the suprachiasmatic nuclei, the brain's master clock.
The expression of Per1 in the paraventricular and dorsomedial hypothalamic nuclei was disturbed, impacting hormonal and behavioral rhythms.
Corticosterone rhythms were phase-advanced and suppressed, with daily variations in melatonin, testosterone, and vasopressin lost.
ALAN altered daily patterns of food and water intake, removing the typical increase in drinking behavior before sleep.

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AIMS: Our study addresses underlying mechanisms of disruption of the circadian timing system by low-intensity artificial light at night (ALAN), which is a growing global problem, associated with serious health consequences.

METHODS: Rats were exposed to low-intensity (∼2 lx) ALAN for 2 weeks. Using in situ hybridization, we assessed 24-h profiles of clock and clock-controlled genes in the suprachiasmatic nuclei (SCN) and other hypothalamic regions, which receive input from the master clock. Moreover, we measured the daily rhythms of hormones within the main neuroendocrine axes as well as the detailed daily pattern of feeding and drinking behavior in metabolic cages.

RESULTS: ALAN strongly suppressed the molecular clockwork in the SCN, as indicated by the suppressed rhythmicity in the clock (Per1, Per2, and Nr1d1) and clock output (arginine vasopressin) genes. ALAN disturbed rhythmic Per1 expression in the paraventricular and dorsomedial hypothalamic nuclei, which convey the circadian signals from the master clock to endocrine and behavioral rhythms. Disruption of hormonal output pathways was manifested by the suppressed and phase-advanced corticosterone rhythm and lost daily variations in plasma melatonin, testosterone, and vasopressin. Importantly, ALAN altered the daily profile in food and water intake and eliminated the clock-controlled surge of drinking 2 h prior to the onset of the rest period, indicating disturbed circadian control of anticipatory thirst and fluid balance during sleep.

CONCLUSION: Our findings highlight compromised time-keeping function of the central clock and multiple circadian outputs, through which ALAN disturbs the temporal organization of physiology and behavior.

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Disrupted Circadian Control of Hormonal Rhythms and Anticipatory Thirst by Dim Light at Night

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