Abstract: The biological clock expresses circadian rhythms, whose endogenous period (tau) is close to 24 h. Daily resetting of the circadian clock to the 24 h natural photoperiod might induce marginal costs that would accumulate over time and forward affect fitness. It was proposed as the circadian resonance theory. For the first time, we aimed to evaluate these physiological and cognitive costs that would partially explain the mechanisms of the circadian resonance hypothesis. We evaluated the potential costs of imposing a 26 h photoperiodic regimen compared to the classical 24 h entrainment measuring several physiological and cognitive parameters (body temperature, energetic expenditure, oxidative stress, cognitive performances) in males of a non-human primate (Microcebus murinus), a nocturnal species whose endogenous period is about 23.5 h. We found significant higher resting body temperature and energy expenditure and lower cognitive performances when the photoperiodic cycle length was 26 h. Together these results suggest that a great deviation of external cycles from tau leads to daily greater energetic expenditure, and lower cognitive capacities. To our knowledge, this study is the first to highlight potential mechanisms of circadian resonance theory.
Abstract: The disruption of circadian rhythms by environmental conditions can induce alterations in body homeostasis, from behavior to metabolism. The light:dark cycle is the most reliable environmental agent, which entrains circadian rhythms, although its credibility has decreased because of the extensive use of artificial light at night. Light pollution can compromise performance and health, but underlying mechanisms are not fully understood. The present review assesses the consequences induced by constant light (LL) in comparison with dim light at night (dLAN) on the circadian control of metabolism and behavior in rodents, since such an approach can identify the key mechanisms of chronodisruption. Data suggest that the effects of LL are more pronounced compared to dLAN and are directly related to the light level and duration of exposure. Dim LAN reduces nocturnal melatonin levels, similarly to LL, but the consequences on the rhythms of corticosterone and behavioral traits are not uniform and an improved quantification of the disrupted rhythms is needed. Metabolism is under strong circadian control and its disruption can lead to various pathologies. Moreover, metabolism is not only an output, but some metabolites and peripheral signal molecules can feedback on the circadian clockwork and either stabilize or amplify its desynchronization.
Abstract: Altered circadian rhythms have negative consequences on health and behavior. Emerging evidence suggests genetics influences the physiological and behavioral responses to circadian disruption. We investigated the effects of a 21 h day (T = 21 cycle), with high-fat diet consumption, on locomotor activity, explorative behaviors, and health in male C57BL/6J and C57BL/6N mice. Mice were exposed to either a T = 24 or T = 21 cycle and given standard rodent chow (RC) or a 60% high-fat diet (HFD) followed by behavioral assays and physiological measures. We uncovered numerous strain differences within the behavioral and physiological assays, mainly that C57BL/6J mice exhibit reduced susceptibility to the obesogenic effects of (HFD) and anxiety-like behavior as well as increased circadian and novelty-induced locomotor activity compared to C57BL/6N mice. There were also substrain-specific differences in behavioral responses to the T = 21 cycle, including exploratory behaviors and circadian locomotor activity. Under the 21-h day, mice consuming RC displayed entrainment, while mice exposed to HFD exhibited a lengthening of activity rhythms. In the open-field and light-dark box, mice exposed to the T = 21 cycle had increased novelty-induced locomotor activity with no further effects of diet, suggesting daylength may affect mood-related behaviors. These results indicate that different circadian cycles impact metabolic and behavioral responses depending on genetic background, and despite circadian entrainment.
Keywords: Animals; Mouse; circadian; high-fat diet; locomotor activity; photoperiod; strain differences
Abstract: Adverse effects of light at night are associated with human health problems and with changes in seasonal reproduction in several species. Owing to its role in the circadian timing system, melatonin production is suspected to mediate excess nocturnal light. To test this hypothesis, we examined the effect of light pollution on the timing of seasonal reproduction on a strict Malagasy long-day breeder, the nocturnal mouse lemur (Microcebus murinus). We randomly exposed 12 males in wintering sexual rest to moonlight or to a light-mimicking nocturnal streetlight for 5 weeks. We monitored urinary 6-sulfatoxymelatonin concentrations (aMT6s), plasma testosterone concentrations, and testis size, and we recorded daily rhythms of core temperature and locomotor activity. In males exposed to light pollution, we observed a significant decrease in urinary aMT6s concentrations associated with changes in daily rhythm profiles and with activation of reproductive function. These results showed that males entered spontaneous sexual recrudescence leading to a summer acclimatization state, which suggests that light at night disrupts perception of day length cues, leading to an inappropriate photoentrainment of seasonal rhythms.
Abstract: The circadian clock regulates many aspects of physiology, energy metabolism, and sleep. Restricted feeding (RF), a regimen that restricts the duration of food availability entrains the circadian clock. Caffeine has been shown to affect both metabolism and sleep. However, its effect on clock gene and clock-controlled gene expression has not been studied. Here, we tested the effect of caffeine on circadian rhythms and the expression of disease and metabolic markers in the serum, liver, and jejunum of mice supplemented with caffeine under ad libitum (AL) feeding or RF for 16 weeks. Caffeine significantly affected circadian oscillation and the daily levels of disease and metabolic markers. Under AL, caffeine reduced the average daily mRNA levels of certain disease and inflammatory markers, such as liver alpha fetoprotein (Afp), C-reactive protein (Crp), jejunum alanine aminotransferase (Alt), growth arrest and DNA damage 45beta (Gadd45beta), Interleukin 1alpha (Il-1alpha), Il-1beta mRNA and serum plasminogen activator inhibitor 1 (PAI-1). Under RF, caffeine reduced the average daily levels of Alt, Gadd45beta, Il-1alpha and Il-1beta mRNA in the jejunum, but not in the liver. In addition, caffeine supplementation led to decreased expression of catabolic factors under RF. In conclusion, caffeine affects circadian gene expression and metabolism possibly leading to beneficial effects mainly under AL feeding.
Keywords: Human Health; Animals; Biological Markers/blood/metabolism; Body Weight/drug effects/physiology; Caffeine/*pharmacology; Caloric Restriction; Circadian Rhythm/*drug effects/genetics/physiology; *Disease/genetics; Eating/drug effects/physiology; Gene Expression Regulation/*drug effects/genetics; HEK293 Cells; Humans; Inflammation/metabolism; Male; Mice; Mice, Inbred C57BL; Motor Activity/drug effects/physiology