24-h Light-dark Research Articles

Brown adipose tissue thermogenesis rhythms are driven by the SCN independent of adipocyte clocks.

Circadian misalignment has been associated with obesity both in rodents and humans. Brown adipose tissue (BAT) thermogenesis contributes to energy expenditure and can be activated in adults to reduce body weight. Although previous studies suggest control of BAT thermogenesis by the circadian clock, the site and mechanisms of regulation remain unclear. We used mice with genetic disruption of the circadian clock in the suprachiasmatic nucleus (SCN) and peripheral tissues to delineate their role in BAT thermogenesis. Global post-natal deletion of Bmal1 in adult mice ( Bmal1 -/- ) abolishes the rhythms of interscapular BAT temperature, a measure of thermogenesis, while normal locomotor activity rhythms are maintained under a regular 12h light-12h dark schedule. Activation of thermogenesis either by exposure to cold or adrenergic stimulation of BAT displays a diurnal rhythm with higher activation during the active period. Both the rhythm and the magnitude of the thermogenic response is preserved in Bmal1 -/- mice. In contrast to mice with global deletion of Bmal1 , mice with brown adipocyte (Ucp1- Bmal1 -/- ) or brown and white adipocyte (Ad- Bmal1 -/- ) deletion of Bmal1 show intact rhythms of BAT thermogenic activity. The capacity of Ucp1- Bmal1 -/- mice to activate thermogenesis in response to exposure to cold is identical to WT mice, independent of time of stimulation. Circadian rhythmicity of interscapular BAT temperature is lost in mice with SCN deletion of Bmal1 (SCN- Bmal1 -/- ), indicating control of BAT thermogenesis rhythms by the SCN. Control mice exhibit rhythmic BAT glucose and fatty acid uptake - a rhythm that is not recapitulated in Bmal1 -/- and SCN- Bmal1 -/- mice but is present in Ucp1- Bmal1 -/- and Ad- Bmal1 -/- mice. BAT cAMP and phosphorylated hormone-sensitive lipase (pHSL) is reduced during the active period in Bmal1 -/- and SCN- Bmal1 -/- mice consistent with reduced sympathetic tone. Furthermore, sympathetic denervation of BAT ablates BAT temperature rhythms in WT mice. Taken together, our findings suggest that the SCN drives rhythms of BAT thermogenesis through adipocyte clock-independent, sympathetic signaling to the BAT.

Daylight exposure and circadian clocks in broilers: part I—photoperiod effect on broiler behavior, skeletal health, and fear response

The aim of this study was to examine effects of various daylight exposure during the 24-h light-dark (L-D) cycle on growth performance, skeletal health, and welfare state in broilers. Environmental photoperiod and related circadian clock, the 24-h L-D cycle, are important factors in maintaining productive performance, pathophysiological homeostasis, and psychological reaction in humans and animals. Currently, various lighting programs as management tools for providing a satisfactory environmental condition have been used in commercial broiler production. Four hundred thirty-two 1-day-old Rose 308 broiler chicks were assigned to 24 pens (18 birds/pen). The pens were randomly assigned to 1 of 4 thermal and lighting control rooms, then the birds were exposed to (n=6): 1) 12L, 2) 16L, 3) 18L, or 4) 20L at 15 d of age. Lighting program effects on bird body weight, behavioral patterns, bone health, and stress levels were evaluated from d 35 to d 45, respectively. The birds of 12L as well as 16L groups, reared under short photoperiods close to the natural 24-h L-D cycle, had improved production performance, leg bone health, and suppressed stress reaction compared to the birds of both 18L and 20L groups. Especially, 12L birds had heavier final body weight and averaged daily weight gain (P < 0.05), higher BMD and BMC with longer and wider femur (P < 0.05), lower H/L ratio (P < 0.05), and more birds reached the observer during the touch test (P < 0.05) but spent shorter latency during the tonic immobility test (P < 0.05). Taken together, the data suggest that supplying 12 h as well as 16L of daily light improves performance and health while decreasing stress levels in broilers, making it a potentially suitable approach for broiler production.

Alignment Between 24-h Light-Dark and Activity-Rest Rhythms Is Associated With Diabetes and Glucose Metabolism in a Nationally Representative Sample of American Adults.

The alignment between environmental stimuli (e.g., dark, light) and behavior cycles (e.g., rest, activity) is an essential feature of the circadian timing system, a key contributor to metabolic health. However, no previous studies have investigated light-activity alignment in relation to glycemic control in human populations. The analysis included ∼7,000 adults (aged 20-80 years) from the National Health and Nutrition Examination Survey (NHANES) (2011-2014) with actigraphy-measured, multiday, 24-h activity and light data. We used phasor analysis to derive phasor magnitude and phasor angle, which measures coupling strength and phase difference between the activity-rest and light-dark cycles, respectively. We used multinomial logistic regression and multiple linear regression to study phasor magnitude and phasor angle in relation to diabetes (primary outcome) and multiple secondary biomarkers of glycemic control. Lower alignment strength (i.e., a shorter phasor magnitude) and more delayed activity relative to the light cycle (i.e., a larger phasor angle) were both associated with diabetes. Specifically, compared with individuals in the quintiles indicating the most proper alignment (Q5 for phasor magnitude and Q1 for phasor angle), those in the quintiles with the most impaired alignment had a >70% increase in the odds of diabetes for phasor magnitude (odds ratio 1.76 [95% CI 1.39, 2.24]) and for phasor angle (1.73 [1.34, 2.25]). Similar associations were observed for biomarkers for glucose metabolism. The results were generally consistent across diverse sociodemographic and obesity groups. The alignment pattern between 24-h activity-rest and light-dark cycles may be a critical factor in metabolic health.

Chronic jet lag reduces motivation and affects other mood-related behaviors in male mice.

Introduction: The circadian system regulates various physiological processes such as sleep-wake cycles, hormone secretion, metabolism, and the reaction to both natural and drug-based rewards. Chronic disruption of the circadian system caused by unsteady synchronization with light-dark (LD) schedules, such as advancing chronic jet lag (CJL), leads to adverse physiological effects and pathologies, and is linked with changes in mood and depressive behaviors in humans and rodent models. Methods: C57BL/6J male mice were subjected to circadian disruption through phase advances of 6h every 2days (CJL +6/2). Mice under 12:12-h LD cycle were used as controls. After 8weeks under these conditions, a battery of behavioral tests was performed to assess if mood-related behaviors were affected. Results: Compared to controls under 24h LD cycles, mice under CJL presented desynchronization of activity-rest rhythms that led to several behavioral impairments, including a decrease in motivation for food reward, and an increase in anxiety, anhedonia, and depressive-like behavior. Conclusion: Chronic circadian disruption, caused by an experimental CJL protocol, affects mood-related and reward-related behaviors in mice. Understanding the importance of the circadian system and its potential role for disruption due to CJL is important for maintaining good health and well-being.

Influence of light regulation on growth and enzyme production in rare endolichenic fungi.

The influence of light regulation on the growth and enzyme production of three endolichenic fungal isolates, i.e. Pseudopestalotiopsis theae (EF13), Fusarium solani (EF5), and Xylaria venustula (PH22), was determined. The isolates were exposed to blue, red, green, yellow, white fluorescent light (12h light-12h dark photoperiod) (test), and 24h dark (control) conditions. Results revealed that the alternating light-dark conditions resulted in the formation of dark rings in most fungal isolates but was absent in PH22. Red light induced sporulation while yellow light elicited higher biomass in all isolates (0.19 ± 0.01g, 0.07 ± 0.00g, and 0.11 ± 0.00g, for EF13, PH22, and EF5, respectively) as compared to incubation in the dark. Results also showed that blue light induced higher amylase activity in PH22 (15.31 ± 0.45 U/mL) and L-asparaginase activity in all isolates (0.45 ± 0.01 U/mL, 0.55 ± 0.39 U/mL, and 0.38 ± 0.01 U/mL, for EF13, PH22, and EF5, respectively) compared to both control conditions. Green light enhanced the production of xylanase (6.57 ± 0.42 U/mL, 10.64 ± 0.12 U/mL, and 7.55 ± 0.56 U/mL for EF13, PH22, and EF5, respectively) and cellulase (6.49 ± 0.48 U/mL, 9.57 ± 0.25 U/mL, and 7.28 ± 0.63 U/mL, for EF13, PH22, and EF5, respectively). In contrast, red light was the least effective light treatment as production of enzymes was the least, with lower levels of amylase, cellulase, xylanase, and L-asparaginase detected. To conclude, all three endolichenic fungi are light-responsive, with fungal growth regulated with the use of red light and yellow light, and manipulation of enzyme production via blue and green light.

Relationship between ethylene and leaf-yellowing induced by darkness in cut small-flowered chrysanthemum

Chrysanthemums (Chrysanthemum × morifolium) are the most widely produced cut flowers in Japan. During transportation, the leaves of cut small-flowered chrysanthemums grown in the summer season sometimes turn yellow. The previous study used detached chrysanthemum leaves to clarify the acceleration of leaf yellowing due to warm temperatures and dark conditions. In this study, to clarify the relationship between ethylene and leaf-yellowing senescence induced in cut small-flowered ‘Kosuzu’ chrysanthemums, ethylene production and sensitivity to ethylene were investigated. Under 24 h of continuous darkness (DD conditions), leaves turned yellow during the experimental period (days 0 to 9), with lightness (L*) and chroma (C*) values of leaves increasing from 35.8 to 53.6 and from 19.1 to 42.8, respectively, and hue values decreasing from 128.0 to 112.9. The concentrations of chlorophyll a and b decreased more under DD conditions than under storage under 12 h light/12 h dark (LD) conditions. Ethylene production by leaves decreased under both light regimes. At days 3 and 4, the leaves of LD flowers produced more ethylene than those of DD flowers. Under both light regimes, treatment with ethylene (10 µL/L for 24 h) did not accelerate leaf-yellowing compared to the control (no ethylene treatment). Hue values of leaves decreased immediately in DD flowers, regardless of ethylene treatment, but there was almost no change in LD flowers during the experimental period. The results suggest that dark conditions induce chlorophyll degradation and leaf-yellowing senescence, chlorophyll degradation under dark conditions is not associated with an increase in endogenous ethylene, and dark conditions may accelerate leaf yellowing markedly compared to exogenous ethylene application in cut small-flowered chrysanthemums.

Chronic circadian disruption on a high-fat diet impairs glucose tolerance

BackgroundNearly 14% of Americans experience chronic circadian disruption due to shift work, increasing their risk of obesity, diabetes, and other cardiometabolic disorders. These disorders are also exacerbated by modern eating habits such as frequent snacking and consumption of high-fat foods. MethodsWe investigated the effects of recurrent circadian disruption (RCD) on glucose metabolism in C57BL/6 mice and in human participants exposed to non-24-h light-dark (LD) schedules vs. those on standard 24-h LD schedules. These LD schedules were designed to induce circadian misalignment between behaviors including rest/activity and fasting/eating with the output of the near-24-h central circadian pacemaker, while minimizing sleep loss, and were maintained for 12 weeks in mice and 3 weeks in humans. We examined interactions of these circadian-disrupted schedules compared to control 24-h schedules with a lower-fat diet (LFD, 13% in mouse and 25–27% in humans) and high-fat diet (HFD, 45% in mouse and 45–50% in humans). We also used young vs. older mice to determine whether they would respond differently to RCD. ResultsWhen combined with a HFD, we found that RCD caused significant weight gain in mice and increased body fat in humans, and significantly impaired glucose tolerance and insulin sensitivity in both mice and humans, but this did not occur when RCD was combined with a LFD. This effect was similar in both young and older mice. ConclusionThese results in both humans and a model organism indicate that circadian disruption has an adverse effect on metabolism among individuals eating a high-fat Western-style diet, even in the absence of significant sleep loss, and suggest that reducing dietary fat may protect against the metabolic consequences of a lifestyle (such as shift work) that involves chronic circadian disruption.

A 24-hour lighting scheme to promote alertness and circadian entrainment in railroad dispatchers on rotating shifts: A field study

Shift-working railway personnel are highly susceptible to fatigue stemming from poor-quality sleep that can impair the performance of safety-critical functions. Disruption of the 24-h light–dark pattern incident on the retinae appears to play a central role in exacerbating these problems, especially with respect to exposure to light at night and circadian rhythms disruption. This field study tested and demonstrated the effectiveness and acceptability of an intervention (red and blue light combined with white light) to (1) promote circadian alignment, (2) advance the timing of dim light melatonin onset, (3) improve objective and subjective sleep quality, and (4) reduce subjective sleepiness in an operational context compared to a baseline (conventional lighting) condition. The lighting intervention promoted significantly greater synchrony between day-shift participants’ light–dark exposures and rest–activity patterns, but did not significantly advance the timing of dim light melatonin onset. The intervention was also associated with reduced objective sleep disturbances and improved (albeit less robustly) subjective sleep quality, but it only reduced participants’ subjective sleepiness while they were off duty during the day shift. This research demonstrates that lighting interventions can promote circadian alignment and improve sleep quality among railway shift workers and may be translatable to other 24-h industries.

Desynchrony and synchronisation underpinning sleep–wake cycles

This paper studies mechanisms of synchronisation and loss of synchrony among the three key oscillatory processes controlling sleep–wake cycles in the human brain: the 24-h circadian oscillator, the homeostatic sleep drive, and the environmental light–dark cycle. Synchronisation of these three rhythms promotes sleep and brain clearance and is critical for human health. Their desynchrony, on the other hand, is associated with impaired performance and disease development, including cancer, cardiovascular disease, and mental disorders. A biophysical model of arousal dynamics simulating sleep–wake cycles and circadian rhythms is used as the study system. It is based on established neurobiological mechanisms controlling sleep–wake transitions and incorporates the three oscillatory processes. Nonlinear dynamics methods and synchronisation theory are used to numerically investigate model dynamics under conditions that are not easily achievable in experiments. The role of homeostatic brain clearance rate in synchronisation is investigated, and selective turning on and off of coupling strengths between the oscillators allows us to determine their role in oscillators’ dynamics. We find that, in the absence of coupling between the circadian and homeostatic oscillators, the default state of the model corresponds to the endogenous homeostatic period that is far from $$\sim $$ 24-h rhythm of the circadian and light–dark cycles. Combined action of light and circadian oscillator on the homeostatic rhythm is required to achieve the typical sleep–wake pattern that is observed in young healthy people. Under 12-/12-h light–dark conditions with light at 80 lux, change of homeostatic clearance rate is found to induce two types of desynchronisation: (i) fast clearance rates $$\tau _H<58.1$$ h desynchronise the homeostatic oscillator from the circadian, while the circadian rhythm remains entrained to the light–dark cycle, and (ii) slow clearance rates $$\tau _H>69$$ h maintain synchronisation between the homeostatic and circadian oscillators, but the period of both is different from that of the light–dark cycle. Between these regimes, all three rhythms are synchronised under the studied conditions. The model predicts that the system is highly sensitive to external inputs to the neuronal populations of the sleep–wake switch, which affect the endogenous period of the homeostatic oscillator and can lead to complete loss of sleep. Model dynamics show that loss of synchronisation, which is traditionally ascribed solely to impairment of the circadian oscillator, can be caused by changes in the homeostatic clearance rate of the brain or external input to the neuronal populations of the sleep–wake switch. Thus, changes in circadian, homeostatic, and external factors (combined or specific) may be responsible for conditions of desynchronisation. This has significant implications for understanding individual variability in sleep–wake patterns and in mechanisms of sleep and circadian disorders, indicating that both the homeostatic and circadian mechanisms can be responsible for the same clinical or behavioural presentation of a disease.

The daily gene transcription cycle in mouse retina

Many physiological retinal processes, such as outer segment disk shedding and visual sensitivity, exhibit a daily rhythm. However, the detailed transcriptome dynamics and related biological processes of the retina are not fully understood. Retinal tissues were collected from C57BL/6J male mice housed in a 12h light/12h dark (LD) cycle for 4 weeks, at Zeitgeber time (ZT) 0, 4, 8, 12, 16, and 20. Total RNA was extracted from the tissues and used for unique identifier RNA sequencing experiments. The rhythmicity of gene expression was determined using the MetaCycle R package. We found that 1741 genes (10.26%) were rhythmically expressed in the retina. According to the expression patterns, the rhythmically expressed genes were assigned to four clusters, each with about 361–492 genes, using the Mfuzz R package. The Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) analyses were conducted to identify pathways and biological processes of the profiled genes. Genes in Clusters 1 and 4 were associated with glycolysis and energy production, showed higher activity at night (from ZT16 to ZT20), and were enriched in the Hif-1α signaling pathway and low-oxygen-related terms. Genes in Cluster 2 were predominantly involved in cilium assembly and organization and were relatively upregulated during the day. Genes in Cluster 3 were associated with ribosome biosynthesis and were highly expressed during the day-night transition period. Taken together, these results demonstrate that a large proportion of retinal genes are expressed rhythmically. Genes involved in energy production and glycolysis are highly expressed at night, leading to relative hypoxia and activation of the Hif-1α signaling pathway. Genes associated with the formation of photoreceptor cilia are expressed during the day.

Light cycle phase advance as a model for jet lag reprograms the circadian rhythms of murine extraorbital lacrimal glands

PurposeJet lag causes a disruption in physiological rhythms in humans. This study aims to explore the extent to which jet lag affects the circadian rhythmicity in the lacrimal glands. MethodsC57BL/6J mice were subjected to a 12-h light/12-h dark (LD) cycle and an 8-h advanced LD schedule as a model for jet lag. On day 5 after the LD advance, the extraorbital lacrimal glands (ELGs) were collected at 3-h intervals during a 24-h cycle. Total mRNA was extracted from normal and advanced LD-treated ELGs and assayed using high-throughput RNA sequencing. The rhythmic transcripts were identified, analyzed, and visualized by bioinformatics techniques. Finally, (i) animal behavior; (ii) the mass, cell size, and secretion response of ELGs; and (iii) circadian migration of immune cells to ELGs were also assayed. ResultsJet lag treatment drastically altered the phase and composition of the rhythmic transcripts compared to that of normal ELGs. The key biological processes, signaling pathways, and protein–protein association networks were also dramatically altered in a spatiotemporal pattern. Furthermore, the circadian migration of neutrophils, T cells, B cells, and macrophages to the ELGs increased and shifted later by 6-h. Finally, the circadian rhythms of the ELGs with respect to mass, cell size, and secretion response were also impaired in jet lag-treated animals. ConclusionsJet lag impairs the circadian rhythm of the transcriptomic profile, structure, and secretion function of the lacrimal glands. This information provides novel insight into the negative effects of jet lag on ELGs.

Circadian clock components Bmal1 and Clock1 regulate tlr9 gene expression in the Japanese medaka (Oryzias latipes)

Currently, circadian regulation of immune molecules in lower vertebrates, particularly, diurnal oscillation in the immune status of a fish, is not well understood. In this study, the diurnal oscillation of toll-like receptor (Tlr) 9, which plays a role in pathogen recognition, was investigated in the Japanese medaka fish (Oryzias latipes). We confirmed the expression of tlr9 and clock genes (bmal1 and clock1) in the central and peripheral tissues of medaka. These genes were expressed in a diurnal manner in medaka acclimated to a 12-h:12-h light-dark (12:12 LD) cycle. In addition, increased tlr9 expression was detected in medaka embryo cells (OLHdrR-e3) overexpressing both bmal1 and clock1 genes; however, this result was not obtained when only one or neither of the genes was overexpressed. This suggests that the increase in expression was mediated by the Bmal1 and Clock1 proteins together. In vitro stimulation of the head kidney with CpG-oligodeoxynucleotides (CpG-ODNs) at different zeitgeber times (ZTs; ZT0 = light on, ZT12 = light off) affected the degree of tlr9 gene expression, showing high and low responsiveness to CpG-ODN stimulation at ZT6/10 and ZT18/22, respectively. Similarly, bacterial infection at different ZT points induced a difference in the expression of Tlr9 signaling pathway-related genes (tlr9 and myd88). These results suggested that fish tlr9 exhibits diurnal oscillation, which is regulated by clock proteins, and its responsiveness to immune-stimulation/pathogen infection depends on the time of the day.

Seed germination response of a potential rangeland weed Psilocaulon granulicaule to selected environmental conditions

Studies show that just over 620 non-native naturalised plant species have been recorded within the Australian rangelands, some of which have a capacity to cause significant impacts on rangeland flora and grazing activity. Although Psilocaulon granulicaule (Haw.), Schwantes is listed as a highly invasive environmental weed species, there has been no previous research into its seed ecology. Therefore, this study was conducted to investigate the effects of temperature, light, pH, water stress, heat-shock, and salinity on the germination of P. granulicaule. In this study, four temperature regimes covering four different day and night temperature variations (17–7°C, 25–15°C, 30–25°C and 40–30°C) and two light regimes (12-h light–12-h dark, 24-h dark) were investigated. The effects of pH, water stress, heat-shock and salinity were investigated, using pH buffers, polyethylene glycol solutions, three heat shock events under four temperatures and a range of NaCl solutions. These tests were conducted under the identified optimum temperature range (25/15°C) and light regime for seed germination. The results showed that both temperature and photoperiod significantly influenced the germination rate, with 94.2% germination in the 25–15°C range under a 12-h light-12-h dark regime. Higher temperatures (30–40°C) reduced seed germination to &amp;lt;58% germination in both light regimes (57.5%, 12-h light-12-h dark; 54.17%, 24-h dark). The highest germination rates were observed in low pH solutions, high moisture levels, low heat-shocks and low salinity. The study showed that this species is sensitive to environmental factors such as temperature, light, pH, moisture, heat shock and salinity, suggesting that these factors can be used as critical indicators to guide effective management practices to address this weed problem. Given that seeds are sensitive to radiant heat, burning could be used as a tool to effectively manage this species.

Circadian learning and memory changes in Aβ1-42 induced Alzheimer's mice.

Alzheimer disease (AD) is a growing health problem globally, which causes a progressive decline in learning and memory and multiple disturbances of circadian rhythms. Six Alzheimer's mice and six wild type (WT) mice were involved in this study. Morris Water Maze (MWM) tasks were conducted hourly to evaluate their circadian learning and memory performance. We used a single cosinor-based method to evaluate the circadian learning and memory of Alzheimer's mice and WT mice, respectively. An area sensor was used to record locomotor activity for 2weeks continuously, including 7days of 12h light/12h dark (LD) conditions and 7days of 12h dark/12h dark (DD) conditions. All WT mice showed circadian rhythm presence in learning and memory, and the peak of escape latency appeared at circadian time (CT) 12. Only one in six Alzheimer's mice showed a circadian rhythm, but the peak of escape latency was postponed to CT20. Alzheimer's mice showed rhythm absence under LD or DD conditions. Under LD conditions, the WT mice activity was higher than that in the Alzheimer's mice during ZT0-5 (p = 0.007) and ZT18-23 (p = 0.353) but lower during ZT6-11 (p < 0.001) and ZT12-17 (p < 0.001). Learning and memory of wild type mice is proved to have a circadian variation throughout a day. In Alzheimer's mice, rhythmic locomotor activity and circadian learning and memory performance were disrupted. Understanding the role of rhythmic disturbances in the process of AD may assist to identify therapeutic targets.

Transcriptional Profiling of Daily Patterns of mRNA Expression in the C57BL/6J Mouse Cornea

ABSTRACTPurpose: The purpose of this study was to determine how the transcriptome of the murine cornea adapts to diurnal changes in physiology.Methods: C57BL/6J mice were maintained under a 12-h light/12-h dark (LD) cycle for two weeks. Corneas were collected from euthanized mice at Zeitgeber time (ZT) 0, 3, 6, 9, 12, 15, 18, and 21. Total RNA was extracted and subjected to RNA sequencing (RNA-Seq). A JTK_CYCLE algoithm and other software tools were used to analyze the transcriptional data to determine the periodicity, rhythmicity, and amplitude of the transcripts. Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) were used to analyze the enrichment of cycling transcripts.Results: Approximately 24% of the total transcripts from the murine corneal genome were rhythmically expressed over an LD cycle. GO analysis showed that these cycling genes are primarily involved in cellular and metabolic processes. A KEGG pathway analysis identified 6 branches and 44 pathways that encode the gene outputs necessary for basic cellular functions and processes. More importantly, most of the rhythmic genes between the day and night are enriched in their own unique pathways in addition to some common pathways. Furthermore, most of the rhythmic gene expression was concentrated in the 12-h and 24-h periods. A comparative analysis of GO and KEGG showed large differences in metabolic processes, but not cellular processes. Finally, the murine cornea also rhythmically expressed 11 canonical components of circadian clock genes over an LD cycle at the transcriptional level.Conclusions: One fourth of the corneal transcriptome follows a rhythmic expression pattern involved in basic molecular and cellular mechanisms. This implies that the time of day contributes significantly to the overall temporal organization of the corneal transcriptome.

Perinatal Stress Programs Sex Differences in the Behavioral and Molecular Chronobiological Profile of Rats Maintained Under a 12-h Light-Dark Cycle.

Stress and the circadian systems play a major role in an organism’s adaptation to environmental changes. The adaptive value of the stress system is reactive while that of the circadian system is predictive. Dysfunctions in these two systems may account for many clinically relevant disorders. Despite the evidence that interindividual differences in stress sensitivity and in the functioning of the circadian system are related, there is limited integrated research on these topics. Moreover, sex differences in these systems are poorly investigated. We used the perinatal stress (PRS) rat model, a well-characterized model of maladaptive programming of reactive and predictive adaptation, to monitor the running wheel behavior in male and female adult PRS rats, under a normal light/dark cycle as well as in response to a chronobiological stressor (6-h phase advance/shift). We then analyzed across different time points the expression of genes involved in circadian clocks, stress response, signaling, and glucose metabolism regulation in the suprachiasmatic nucleus (SCN). In the unstressed control group, we found a sex-specific profile that was either enhanced or inverted by PRS. Also, PRS disrupted circadian wheel-running behavior by inducing a phase advance in the activity of males and hypoactivity in females and increased vulnerability to chronobiological stress in both sexes. We also observed oscillations of several genes in the SCN of the unstressed group in both sexes. PRS affected males to greater extent than females, with PRS males displaying a pattern similar to unstressed females. Altogether, our findings provide evidence for a specific profile of dysmasculinization induced by PRS at the behavioral and molecular level, thus advocating the necessity to include sex as a biological variable to study the set-up of circadian system in animal models.

Circadian Disruption Changes Gut Microbiome Taxa and Functional Gene Composition.

Disrupted circadian rhythms and alterations of the gut microbiome composition were proposed to affect host health. Therefore, the aim of this research was to identify whether these events are connected and if circadian rhythm disruption by abnormal light–dark (LD) cycles affects microbial community gene expression and host vulnerability to intestinal dysfunction. Mice were subjected to either a 4-week period of constant 24-h light or of normal 12-h LD cycles. Stool samples were collected at the beginning and after the circadian rhythm disruption. A metatranscriptomic analysis revealed an increase in Ruminococcus torques, a bacterial species known to decrease gut barrier integrity, and a decrease in Lactobacillus johnsonii, a bacterium that helps maintain the intestinal epithelial cell layer, after circadian rhythm disruption. In addition, genes involved in pathways promoting host beneficial immune responses were downregulated, while genes involved in the synthesis and transportation of the endotoxin lipopolysaccharide were upregulated in mice with disrupted circadian cycles. Importantly, these mice were also more prone to dysfunction of the intestinal barrier. These results further elucidate the impact of light-cycle disruption on the gut microbiome and its connection with increased incidence of disease in response to circadian rhythm disturbances.

Normal behavioral responses to light and darkness and the pupillary light reflex are dependent upon the olivary pretectal nucleus in the diurnal Nile grass rat

The olivary pretectal nucleus (OPT) is a midbrain structure that receives reciprocal bilateral retinal projections, is involved in the pupillary light reflex, and connects reciprocally with the intergeniculate leaflet (IGL), a retinorecipient brain region that mediates behavioral responses to light pulses (i.e., masking) in diurnal Nile grass rats. Here, we lesioned the OPT and evaluated behavioral responses in grass rats to various lighting conditions, as well as their anxiety-like responses to light exposure. While control grass rats remained diurnal, grass rats with OPT lesions exhibited a more night-active pattern under 12h:12h light–dark (LD) conditions. However, when placed in constant darkness, OPT-lesioned grass rats became more active during their subjective day, suggesting that an exaggerated masking response to light may be responsible for the effect of OPT lesions on locomotor activity in LD. To test this hypothesis, we presented dark and light pulses to controls and grass rats with OPT lesions; controls increased their activity in response to light, whereas those with OPT lesions significantly increased activity in response to darkness. Further, when placed in a 7-h ultradian LD cycle, animals with OPT lesions were more active during darkness than controls. OPT lesions also abolished the pupillary light reflex, but did not affect anxiety-like behaviors. Finally, in animals with OPT lesions, light did not induce Fos expression in the ventrolateral geniculate nucleus, as it did in controls. Altogether, these results suggest that masking responses to light and darkness are dependent upon nuclei within the subcortical visual shell in grass rats.

The Role of Beta-Adrenergic Receptors in the Regulation of Circadian Intraocular Pressure Rhythm in Mice

ABSTRACTPurpose: To investigate whether the elimination of β1- and β2-adrenergic receptors alters the diurnal intraocular pressure (IOP) rhythm in mice.Materials and Methods: β1-/β2-adrenergic receptor double-knockout and C57BL/6J mice were anesthetized intraperitoneally, with their IOPs measured via microneedle method. After entrainment to a 12-h light–dark (LD) cycle (light phase 6:00–18:00), IOPs were measured every 3 h from 9:00 to 24:00 (group 1, β1-/β2-adrenergic receptor double-knockout mice, n = 11; C57BL/6J, n = 15). The IOP measurements at 15:00 and 24:00 under a 12-h LD cycle and in the constant darkness (1 day and 8 days after exposure to darkness, respectively) were performed in another group of β1-/β2-adrenergic receptor double-knockout mice (group 2, n = 12). IOP variance throughout the day and mean IOP differences among time points were evaluated using a linear mixed model.Results: β1-/β2-adrenergic receptor double-knockout and C57BL/6J mice showed biphasic IOP curves, low during the light phase and high during the dark phase; the fluctuation was significant (P < 0.001). The peak IOP (18.7 ± 1.4 mmHg) occurred at 24:00 and the trough IOP (13.5 ± 1.5 mmHg) occurred at 15:00 in β1-/β2-adrenergic receptor double-knockout mice group. IOP curves of β1-/β2-adrenergic receptor double-knockout and C57BL/6J were nearly parallel, and the IOPs of β1-/β2-adrenergic receptor double-knockout mice were significantly higher than those of C57BL/6J mice (P < 0.001). Under constant dark (DD) conditions, IOP at 24:00 (18.1 ± 1.5 mmHg) was significantly higher than that at 15:00 (13.3 ± 1.2 mmHg) (P < 0.001). The transition from the LD cycle to DD environment produced no significant change in IOP (P = 0.728).Conclusions: Elimination of both β1- and β2-adrenergic receptors did not disturb the biphasic diurnal IOP rhythm in mice.

Glucose tolerance in mice exposed to light\u2013dark stimulus patterns mirroring dayshift and rotating shift schedules

Glucose tolerance was measured in (nocturnal) mice exposed to light–dark stimulus patterns simulating those that (diurnal) humans would experience while working dayshift (DSS) and 2 rotating night shift patterns (1 rotating night shift per week [RSS1] and 3 rotating night shifts per week [RSS3]). Oral glucose tolerance tests were administered at the same time and light phase during the third week of each experimental session. In contrast to the RSS1 and RSS3 conditions, glucose levels reduced more quickly for the DSS condition. Glucose area-under-the-curve measured for the DSS condition was also significantly less than that for the RSS1 and RSS3 conditions. Circadian disruption for the 3 light–dark patterns was quantified using phasor magnitude based on the 24-h light–dark patterns and their associated activity–rest patterns. Circadian disruption for mice in the DSS condition was significantly less than that for the RSS1 and RSS3 conditions. This study extends previous studies showing that even 1 night of shift work decreases glucose tolerance and that circadian disruption is linked to glucose tolerance in mice.