Simulated Chronic Jet Lag Affects the Structural and Functional Complexity of Hippocampal Neurons in Mice

There has been a long history that chronic circadian disruption such as jet lag or shift work negatively affects brain and body physiology. Studies have shown that circadian misalignment act as a risk factor for developing anxiety and mood-related depression-like behavior. Till date, most studies focused on simulating jet lag in model animals under laboratory conditions by repeated phase advances or phase delay only, while the real-life conditions may differ. In the present study, adult male mice were subjected to simulated chronic jet lag (CJL) by alternately advancing and delaying the ambient light-dark (LD) cycle by 9 h every 2 days, thereby covering a total of 24 days. The effect of CJL was then examined for a range of stress and depression-related behavioral and physiological responses. The results showed that mice exposed to CJL exhibited depression-like behavior, such as anhedonia. In the open field and elevated plus maze test, CJL-exposed mice showed increased anxiety behavior compared to LD control. In addition, CJL-exposed mice showed an increased level of serum corticosterone and proinflammatory cytokine, TNF-α in both serum and hippocampus. Moreover, CJL-exposed mice exhibited a reduction in structural complexity of hippocampal CA1 neurons along with decreased expression of neurotrophic growth factors, BDNF and NGF in the hippocampus compared to LD control. Taken together, our findings suggest that simulated chronic jet lag adversely affects structural and functional complexity in hippocampal neurons along with interrelated endocrine and inflammatory responses, ultimately leading to stress, anxiety, and depression-like behavior in mice.

Addressing Circadian Disruptions in Visually Impaired Paralympic Athletes

PURPOSE

Transmeridian travel is common for elite athletes participating in competitions and training. However, this travel can lead to circadian misalignment wherein the internal biological clock becomes desynchronized with the light-dark cycle of the new environment, resulting in performance decrement and potential negative health consequences. Existing literature extensively discusses recommendations for managing jet lag, predominantly emphasizing light-based interventions to synchronize the internal clock with the anticipated time at the destination. Nevertheless, visually impaired (VI) athletes may lack photoreceptiveness, diminishing or nullifying the effectiveness of this therapy. Consequently, this invited commentary explores alternative strategies for addressing jet lag in VI athletes.

CONCLUSIONS

VI athletes with light perception but reduced visual acuity or visual fields may still benefit from light interventions in managing jet lag. However, VI athletes lacking a conscious perception of light should rely on gradual shifts in behavioral factors, such as meal timing and exercise, to facilitate the entrainment of circadian rhythms to the destination time. Furthermore, interventions like melatonin supplementation may prove useful during and after travel. In addition, it is recommended that athlete guides adopt phase-forward or phase-back approaches to synchronize with the athlete, aiding in jet-lag management and optimizing performance.

Jet Lag and COVID-19: Extra Challenges for Athletes during the Tokyo 2020 Olympic Games

Participating in the Tokyo 2020 Olympic Games demanded great efforts and had become extremely challenging compared with previous competitions. In addition to the physical performance of each modality, athletes had to deal with the coronavirus disease 2019 (COVID-19) pandemic and jet lag. The present manuscript pointed out negative factors that encompass the COVID-19 pandemic and the features brought out by the jet lag experienced by the athletes of this last Olympics. The influences of the pandemic and the procedures adopted to reduce transmission risk of the virus may have amplified the weight of jet lag for the athletes of Tokyo 2020 Olympic Games, even more considering the occurrence of this event in the far east of the globe.

Melatonin Does Not Affect the Stress-Induced Phase Shifts of Peripheral Clocks in Male Mice

Repeated or chronic stress can change the phase of peripheral circadian rhythms. Melatonin (Mel) is thought to be a circadian clock-controlled signal that might play a role in synchronizing peripheral rhythms, in addition to its direct suppressing effects on the stress axis. In this study we test whether Mel can reduce the social-defeat stress-induced phase shifts in peripheral rhythms, either by modulating circadian phase or by modulating the stress axis. Two experiments were performed with male Mel-deficient C57BL/6J mice carrying the circadian reporter gene construct (PER2::LUC). In the first experiment, mice received night-restricted (ZT11-21) Mel in their drinking water, resulting in physiological levels of plasma Mel peaking in the early dark phase. This treatment facilitated re-entrainment of the activity rhythm to a shifted light-dark cycle, but did not prevent the stress-induced (ZT21-22) reduction of activity during stress days. Also, this treatment did not attenuate the phase-delaying effects of stress in peripheral clocks in the pituitary, lung, and kidney. In a second experiment, pituitary, lung, and kidney collected from naive mice (ZT22-23), were treated with Mel, dexamethasone (Dex), or a combination of the two. Dex application affected PER2 rhythms in the pituitary, kidney, and lung by changing period, phase, or both. Administering Mel did not influence PER2 rhythms nor did it alleviate Dex-induced delays in PER2 rhythms in those tissues. We conclude that exogenous Mel is insufficient to affect peripheral PER2 rhythms and reduce stress effects on locomotor activity and phase changes in peripheral tissues.

Altered circadian behavior and light sensing in mouse models of Alzheimer's disease

Circadian symptoms have long been observed in Alzheimer's disease (AD) and often appear before cognitive symptoms, but the mechanisms underlying circadian alterations in AD are poorly understood. We studied circadian re-entrainment in AD model mice using a "jet lag" paradigm, observing their behavior on a running wheel after a 6 h advance in the light:dark cycle. Female 3xTg mice, which carry mutations producing progressive amyloid beta and tau pathology, re-entrained following jet lag more rapidly than age-matched wild type controls at both 8 and 13 months of age. This re-entrainment phenotype has not been previously reported in a murine AD model. Because microglia are activated in AD and in AD models, and inflammation can affect circadian rhythms, we hypothesized that microglia contribute to this re-entrainment phenotype. To test this, we used the colony stimulating factor 1 receptor (CSF1R) inhibitor PLX3397, which rapidly depletes microglia from the brain. Microglia depletion did not alter re-entrainment in either wild type or 3xTg mice, demonstrating that microglia activation is not acutely responsible for the re-entrainment phenotype. To test whether mutant tau pathology is necessary for this behavioral phenotype, we repeated the jet lag behavioral test with the 5xFAD mouse model, which develops amyloid plaques, but not neurofibrillary tangles. As with 3xTg mice, 7-month-old female 5xFAD mice re-entrained more rapidly than controls, demonstrating that mutant tau is not necessary for the re-entrainment phenotype. Because AD pathology affects the retina, we tested whether differences in light sensing may contribute to altered entrainment behavior. 3xTg mice demonstrated heightened negative masking, a circadian behavior measuring responses to different levels of light, and re-entrained dramatically faster than WT mice in a jet lag experiment performed in dim light. 3xTg mice show a heightened sensitivity to light as a circadian cue that may contribute to accelerated photic re-entrainment. Together, these experiments demonstrate novel circadian behavioral phenotypes with heightened responses to photic cues in AD model mice which are not dependent on tauopathy or microglia.

Modeling homeostatic and circadian modulation of human pain sensitivity

Introduction

Mathematical modeling has played a significant role in understanding how homeostatic sleep pressure and the circadian rhythm interact to influence sleep-wake behavior. Pain sensitivity is also affected by these processes, and recent experimental results have measured the circadian and homeostatic components of the 24 h rhythm of thermal pain sensitivity in humans. To analyze how rhythms in pain sensitivity are affected by disruptions in sleep behavior and shifts in circadian rhythms, we introduce a dynamic mathematical model for circadian and homeostatic regulation of sleep-wake states and pain intensity.

Methods

The model consists of a biophysically based, sleep-wake regulation network model coupled to data-driven functions for the circadian and homeostatic modulation of pain sensitivity. This coupled sleep-wake-pain sensitivity model is validated by comparison to thermal pain intensities in adult humans measured across a 34 h sleep deprivation protocol.

Results

We use the model to predict dysregulation of pain sensitivity rhythms across different scenarios of sleep deprivation and circadian rhythm shifts, including entrainment to new environmental light and activity timing as occurs with jet lag and chronic sleep restriction. Model results show that increases in pain sensitivity occur under conditions of increased homeostatic sleep drive with nonlinear modulation by the circadian rhythm, leading to unexpected decreased pain sensitivity in some scenarios.

Discussion

This model provides a useful tool for pain management by predicting alterations in pain sensitivity due to varying or disrupted sleep schedules.

Cholecystokinin neurons in mouse suprachiasmatic nucleus regulate the robustness of circadian clock

The suprachiasmatic nucleus (SCN) can generate robust circadian behaviors in mammals under different environments, but the underlying neural mechanisms remained unclear. Here, we showed that the activities of cholecystokinin (CCK) neurons in the mouse SCN preceded the onset of behavioral activities under different photoperiods. CCK-neuron-deficient mice displayed shortened free-running periods, failed to compress their activities under a long photoperiod, and developed rapid splitting or became arrhythmic under constant light. Furthermore, unlike vasoactive intestinal polypeptide (VIP) neurons, CCK neurons are not directly light sensitive, but their activation can elicit phase advance and counter light-induced phase delay mediated by VIP neurons. Under long photoperiods, the impact of CCK neurons on SCN dominates over that of VIP neurons. Finally, we found that the slow-responding CCK neurons control the rate of recovery during jet lag. Together, our results demonstrated that SCN CCK neurons are crucial for the robustness and plasticity of the mammalian circadian clock.

Travel Across More Time Zones Results in Worse Perceived Fatigue and Sleep in National-Team Footballers

PURPOSE

This study investigated the association between (1) time zone difference and (2) travel direction (east vs west) with posttravel changes in perceptual responses of national-team footballers.

METHODS

Travel schedules from 355 national-team trips (50 elite soccer players) were verified using an online flight database. All players provided perceptual ratings of fatigue, sleep quality, soreness, and stress to calculate changes in scores up to 2 days after travel. Trips were categorized as <3, 3 to 6, 6 to 9, or 9+ time zone changes, along with travel direction (eastward or westward). The pretravel to posttravel changes in perceptual ratings at days 1 and 2 postarrival were compared between time zone change and travel direction with linear mixed models.

RESULTS

For every time zone crossed, poorer ratings of perceptual fatigue (β = 0.068, P < .001), sleep (β = 0.095, P < .001), soreness (β = 0.0049, P < .001), and total wellness (β = 0.214, P < .001) were observed. However, the models explained only small proportions of the variation in postflight perceptual responses (7%-18%). Regardless, travel across 9+ time zones resulted in significantly worse perceived fatigue, sleep, and total wellness for days 1 and 2 postarrival compared with travel with <6 time zones (P < .05). Additionally, fatigue, sleep, and total scores were worse on day 2 following trips of 9+ time zones. Eastward travel resulted in poorer sleep ratings (β = 0.52, P < .001) than westward travel within time zone groupings.

CONCLUSIONS

Perceptual ratings of fatigue and sleep become progressively worse as travel increases in national-team soccer players, especially after travel across 9+ time zones and eastward travel.

Adult Neurogenesis Is Altered by Circadian Phase Shifts and the Duper Mutation in Female Syrian Hamsters

Cell birth and survival in the adult hippocampus are regulated by a circadian clock. Rotating shift work and jet lag disrupt circadian rhythms and aggravate disease. Internal misalignment, a state in which abnormal phase relationships prevail between and within organs, is proposed to account for adverse effects of circadian disruption. This hypothesis has been difficult to test because phase shifts of the entraining cycle inevitably lead to transient desynchrony. Thus, it remains possible that phase shifts, regardless of internal desynchrony, account for adverse effects of circadian disruption and alter neurogenesis and cell fate. To address this question, we examined cell birth and differentiation in the duper Syrian hamster (Mesocricetus auratus), a Cry1-null mutant in which re-entrainment of locomotor rhythms is greatly accelerated. Adult females were subjected to alternating 8 h advances and delays at eight 16 d intervals. BrdU, a cell birth marker, was given midway through the experiment. Repeated phase shifts decreased the number of newborn non-neuronal cells in WT, but not in duper hamsters. The duper mutation increased the number of BrdU-IR cells that stained for NeuN, which marks neuronal differentiation. Immunocytochemical staining for proliferating cell nuclear antigen indicated no overall effect of genotype or repeated shifts on cell division rates after 131 days. Cell differentiation, assessed by doublecortin, was higher in duper hamsters but was not significantly altered by repeated phase shifts. Our results support the internal misalignment hypothesis and indicate that Cry1 regulates cell differentiation. Phase shifts may determine neuronal stem cell survival and time course of differentiation after cell birth. Figure created with BioRender.

Circadian Rhythms Disrupted by Light at Night and Mistimed Food Intake Alter Hormonal Rhythms and Metabolism

Availability of artificial light and light-emitting devices have altered human temporal life, allowing 24-hour healthcare, commerce and production, and expanding social life around the clock. However, physiology and behavior that evolved in the context of 24 h solar days are frequently perturbed by exposure to artificial light at night. This is particularly salient in the context of circadian rhythms, the result of endogenous biological clocks with a rhythm of ~24 h. Circadian rhythms govern the temporal features of physiology and behavior, and are set to precisely 24 h primarily by exposure to light during the solar day, though other factors, such as the timing of meals, can also affect circadian rhythms. Circadian rhythms are significantly affected by night shift work because of exposure to nocturnal light, electronic devices, and shifts in the timing of meals. Night shift workers are at increased risk for metabolic disorder, as well as several types of cancer. Others who are exposed to artificial light at night or late mealtimes also show disrupted circadian rhythms and increased metabolic and cardiac disorders. It is imperative to understand how disrupted circadian rhythms alter metabolic function to develop strategies to mitigate their negative effects. In this review, we provide an introduction to circadian rhythms, physiological regulation of homeostasis by the suprachiasmatic nucleus (SCN), and SCN-mediated hormones that display circadian rhythms, including melatonin and glucocorticoids. Next, we discuss circadian-gated physiological processes including sleep and food intake, followed by types of disrupted circadian rhythms and how modern lighting disrupts molecular clock rhythms. Lastly, we identify how disruptions to hormones and metabolism can increase susceptibility to metabolic syndrome and risk for cardiovascular diseases, and discuss various strategies to mitigate the harmful consequences associated with disrupted circadian rhythms on human health.

Travel across time zones and the implications for human performance post pandemic: Insights from elite sport

Notwithstanding technological innovation, the COVID-19 pandemic, and new communication tools, the need for travel is growing again and, in some travel segments, it is stronger than ever. Interestingly, the public health implications of traveling across time zones are still poorly understood and this is especially true for organizations that send their workers across the globe. Using data from 173 Olympic teams over 15 Olympic Games, we show that crossing multiple time zones has negative implications for human (sports) performance. More importantly, the results indicate that performance impairment is especially visible after flying east, with peak performance particularly impaired, leading to a "gold demotion effect" of gold medals to silver medals as a result. Given that Olympic sporting teams typically have dedicated medical staff and active mitigation strategies, these findings have important public health implications. For example, organizations are demanding their workers to be on "top of their game" while traveling, without providing them with the support and tools to do so. The implications for public health management and human resource management are discussed.

Effects of long-haul transmeridian travel on physiological, sleep, perceptual and mood markers in Olympic team support staff

The objective of this study was to holistically examine the impact of long-haul transmeridian travel (LHTT) on perceptual, mood, sleep and physiological markers in Olympic team support staff travelling to Japan for the 2020 Summer Olympic Games. An observational descriptive study design was used. Nine support staff members of the Irish Olympic team (2 M/7 F; age 34.3 ± 8.3 y (mean ±SD)) embarked on a long-haul (LH) eastward flight across eight time-zones from Ireland to Japan (approx. 24 h total travel time), to work at the Irish Team's 2020 Summer pre-Olympic Games camp, postponed to July 2021 due to Covid-19 pandemic. Perceived jet lag and travel fatigue symptoms, mood states and salivary markers for circadian rhythm and stress were assessed in the morning and evening during the week prior to travel as baseline (BL) measures and on days 1 to 8 (C1-C8) and day 15 (C15) post-travel. Night-time sleep (duration and quality) was monitored via actigraphy monitors and self-report sleep diaries. Participants perceived themselves to be significantly jet lagged for six days post-travel (p < .05). Morning sCort decreased by 66% on C1 and remained significantly lower than BL until C6 (p ≤ .03). On arrival participants perceived sleep to be worse than BL on arrival (C1, C2, C4, C5; p ≤ .04), with significantly shorter sleep duration (C2, C3, C6; p ≤ .01) and lower sleep efficiency (C2, C6; p ≤ .04) recorded by actigraphy, all normalizing by C7. Negative changes in mood states were evident in the evening time following LHTT, with significant elevations in confusion (C2, C3, p ≤ .02), fatigue (C2, C3; p ≤ .03) and depression (C3, C7; p < .05) and reduction in vigour (C2, C6, C7; p < .05). Following LHTT in an eastward direction across eight time-zones, it took seven days for perceived jet lag, physiological markers for circadian rhythm and sleep to normalize in Olympic team support staff. Despite alleviation of jet lag and fatigue and return of sleep to normal by C15, vigor remained low, indicating a "submerged" mood profile in these Olympic team support staff. These findings highlight the need to put strategies in place before and after LHTT for the Olympic Games to assist Olympic team support staff to maximize sleep, minimize stress and assist with expediating recovery from jet lag and travel fatigue, allowing them to perform optimally in supporting Olympic athletes in their final preparations for the Games.

Circadian Rhythm Disruption as a Contributor to Racial Disparities in Prostate Cancer

In the United States, African American (AA) men have a 2.4 times higher mortality rate due to prostate cancer than White men. The multifactorial causes of the racial disparities in prostate cancer involve various social determinants of health, socioeconomic status, and access to healthcare. However, emerging evidence also suggests that circadian rhythm disruption (CRD) contributes to prostate cancer, and AA men may be more susceptible to developing CRDs. Circadian rhythms play a significant role in metabolism, hormone secretion, and sleep/wake cycles. Disruption in these circadian rhythms can be caused by airplane travel/jetlag, night shift work, exposure to light, and neighborhood noise levels, which can contribute to sleep disorders and chronic conditions such as obesity, diabetes, cardiovascular disease, and depression. The drivers of the racial disparities in CRD include night shift work, racial discrimination, elevated stress, and residing in poor neighborhoods characterized by high noise pollution. Given the increased vulnerability of AA men to CRDs, and the role that CRDs play in prostate cancer, elucidating the clock-related prostate cancer pathways and their behavior and environmental covariates may be critical to better understanding and reducing the racial disparities in prostate cancer.

Associations of circadian change, travel distance, and their interaction with basketball performance: a retrospective analysis of 2014-2018 National Basketball Association data

This investigation aimed to clarify the influence of circadian change and travel distance on National Basketball Association (NBA) team performance using a dataset from the 2014-2018 seasons. Data from 9,840 games were acquired from an open-access source. Game point differential and team free-throw percentage served as outcome variables. Time zone change (TZΔ) captured raw circadian delay/advance based on travel for a game and adjusted TZΔ (AdjTZΔ) evolved TZΔ by allowing acclimation to a novel TZ. We also further categorized AdjTZΔ into AdjTZΔ_A, which assumed travel the day before each game and AdjTZΔ_B, which assumed teams spent as many days in their home city as possible. Travel distance for each game was calculated. Linear mixed-effects modeling estimated associations, with games nested within team and year. Adjusted associations accounted for differences in team ability, whether the game was home or away, and whether the game occurred on the second half of a back-to-back game sequence. Greater circadian misalignment, regardless of delay or advance, and increasing travel distance negatively influenced NBA game performance. Yet, results suggest that performance outcomes may be more influenced by travel distance than circadian misalignment. Moreover, circadian misalignment and travel distance interacted to significantly influence game point differential. Furthermore, differences in results across analyses were observed between AdjTZΔ_A and AdjTZΔ_B, which suggests that subtle differences in constructed travel schedules can have notable impact on NBA performance outcomes. Lastly, playing on the second half of a back-to-back sequence emerged as a robust predictor of performance disadvantage, which corroborates the existing literature and provides further support for NBA schedule changes purposed to enhance competitive equity by reducing the number of back-to-back games across a season. These findings can help guide NBA teams on key strategies for reducing travel-related disadvantages and inform schedule makers on critical factors to prioritize across future schedules to attenuate competitive inequity from travel. Furthermore, they can help direct teams towards scenarios that are best to target for load management purposes due to the cumulative disadvantage arising from travel-related factors, opponent quality, game location, and game sequence.

The duper mutation reveals previously unsuspected functions of Cryptochrome 1 in circadian entrainment and heart disease

The Cryptochrome 1 (Cry1)-deficient duper mutant hamster has a short free-running period in constant darkness (τ_DD) and shows large phase shifts in response to brief light pulses. We tested whether this measure of the lability of the circadian phase is a general characteristic of Cry1-null animals and whether it indicates resistance to jet lag. Upon advance of the light:dark (LD) cycle, both duper hamsters and Cry1^-/- mice re-entrained locomotor rhythms three times as fast as wild types. However, accelerated re-entrainment was dissociated from the amplified phase-response curve (PRC): unlike duper hamsters, Cry1^-/- mice show no amplification of the phase response to 15' light pulses. Neither the amplified acute shifts nor the increased rate of re-entrainment in duper mutants is due to acceleration of the circadian clock: when mutants drank heavy water to lengthen the period, these aspects of the phenotype persisted. In light of the health consequences of circadian misalignment, we examined effects of duper and phase shifts on a hamster model of heart disease previously shown to be aggravated by repeated phase shifts. The mutation shortened the lifespan of cardiomyopathic hamsters relative to wild types, but this effect was eliminated when mutants experienced 8-h phase shifts every second week, to which they rapidly re-entrained. Our results reveal previously unsuspected roles of Cry1 in phase shifting and longevity in the face of heart disease. The duper mutant offers new opportunities to understand the basis of circadian disruption and jet lag.

Impact of Long-Haul Travel to International Competition on Sleep and Recovery in Elite Male and Female Soccer Athletes

PURPOSE

To investigate the impact of eastward travel across 7 time zones on sleep, jet lag, and recovery in elite soccer athletes.

METHODS

Twenty-one male and 20 female athletes (21.5 [1.7] y) traveled from Ireland to Taiwan to represent their national team at the World University Games 2017. Daily monitoring via actigraphy and subjective sleep and well-being measures were obtained for 1 week in Ireland (baseline), and for the duration of an international soccer tournament (days 1-5 [precompetition] and days 6-18 [competition]).

RESULTS

Sleep duration (P = .028) and time in bed (P = .006) were significantly lower at precompetition compared with baseline. Sleep quality (P < .001) was significantly decreased in precompetition compared with baseline and competition. Subjective jet lag symptoms continued for up to 13 days posttravel. Athletes reported significantly greater fatigue during precompetition compared with competition (P = .005); however, there were no significant differences for recovery (P = .35) and readiness to train (P = .35). Sleep hygiene changed significantly during precompetition and competition compared with baseline in relation to reduced electronic device use (P = .005) and reduced caffeine intake (P < .001). Females reported significantly greater presleep tension-anxiety compared with males at all timepoints (P = .02).

CONCLUSION

Long-haul eastward travel across 7 time zones has a significant impact on sleep duration and quality, likely related to changes in sleep patterns and jet lag. Athletes report changes in sleep hygiene posttravel; however, sleep remained negatively impacted for up to 5 days. Despite significant sleep disturbance and jet lag symptoms, young healthy athletes appear to recover well from long-haul travel; however, it is unknown if this interferes with training and competition performance.

Effect of regular and irregular stimulation cycles of dexamethasone on circadian clock in NIH3T3 cells

Animal studies have shown that irregular light-dark cycles cause circadian desynchronization, while few studies have addressed the effect of regular/irregular stimulation cycles of signaling hormones on the cellular clock in vitro. Here, we examined how cellular clocks respond to regular and irregular stimulation cycles of dexamethasone, using NIH3T3 cells transfected with the Bmal1 promoter-driven luciferase (Bmal1-Luc) reporter gene. Cyclic stimulation with dexamethasone at different time intervals (18-28 h, 3 times regularly) revealed that Bmal1-Luc bioluminescence rhythms can be entrained to 22 and 24 h cycles during the stimulation period, but not to other cycles. The rhythm entrained for 24 h cycles persisted for at least one day after the last stimulation. Irregular dexamethasone treatment (16, 24, and 16 h, sequentially; short-term jet lag protocol) resulted in an overall upregulation and phase shifts of the temporal expression of several clock genes and cell cycle genes, including c-Myc and p53. Regular dexamethasone stimulation three times with 24 h cycles also caused upregulation of Per1 and Per2 expression, but not c-Myc and p53 expression. In conclusion, our study identified the entrainable range of the circadian clock in NIH3T3 cells to the dexamethasone stimulation cycle and demonstrated that irregular dexamethasone treatment could disturb the expression of cell cycle genes.

Chronic Jet Lag Exacerbates Jejunal and Colonic Microenvironment in Mice

Background

Evidence suggests that circadian rhythm disorder is associated with a variety of gastrointestinal diseases, and the circadian rhythm plays a key role in maintaining the homeostasis of intestinal flora. The underlying mechanisms are still not completely identified. This study was aimed to explore whether jet lag-caused circadian disruption influences gut microbiome and its metabolites.

Methods

Mice were synchronized with 12-h light/dark cycles (control group) or subjected to daily 8-h advance of the light/dark cycle for every 3 days (jet-lagged group). Four months later, fecal samples and jejunal contents were collected and analyzed by 16S rRNA gene sequencing. In addition, fecal samples were subjected to metabolome analysis with ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS).

Results

The results of 16s rRNA sequencing showed that chronic jet lag led to decreased microbial abundance, richness, and diversity in both feces and jejunal contents. ANOSIM analysis revealed significant difference between control and jet-lagged groups. As the colonic microbiome, the abundance of Bacteroidetes phylum was significantly decreased and that of Actinobacteria phylum was increased in jet-lagged mice. Jet lag increased the ratio of Firmicutes to Bacteroidetes, an indicator for the imbalance of gut microbiota. Metabolome analysis of fecal samples showed that the levels of tryptophan and its derivatives were decreased in jet-lagged mice. In addition, fecal levels of secondary bile acids changed under jet lag conditions. Correlation analysis identified associations between tryptophan (and its derivatives) levels and colonic microbiota.

Conclusions

This study presents a comprehensive landscape of gut microbiota and its metabolites in mice subjected to chronic jet lag. The results suggest that circadian disruption may lead to changes in fecal and jejunal microbiota and fecal metabolites. Moreover, our results demonstrate a novel interplay between the gut microbiome and metabolome.

Effect of jet lag on brain white matter functional connectivity

Background

A long-haul flight across more than five time zones may produce a circadian rhythm sleep disorder known as jet lag. Little is known about the effect of jet lag on white matter (WM) functional connectivity (FC).

Objective

The present study is to investigate changes in WM FC in subjects due to recovery from jet lag after flying across six time zones.

Methods

Here, resting-state functional magnetic resonance imaging was performed in 23 participants within 24 hours of flying and again 50 days later. Gray matter (GM) and WM networks were identified by k-means clustering. WM FC and functional covariance connectivity (FCC) were analyzed. Next, a sliding window method was used to establish dynamic WM FC. WM static and dynamic FC and FCC were compared between when participants had initially completed their journey and 50 days later. Emotion was assessed using the Positive and Negative Affect Schedule and the State Anxiety Inventory.

Results

All participants were confirmed to have jet lag symptoms by the Columbian Jet Lag Scale. The static FC strengthes of cingulate network (WM7)- sensorimotor network and ventral frontal network- visual network were lower after the long-haul flight compared with recovery. Corresponding results were obtained for the dynamic FC analysis. The analysis of FCC revealed weakened connections between the WM7 and several other brain networks, especially the precentral/postcentral network. Moreover, a negative correlation was found between emotion scores and the FC between the WM7 and sensorimotor related regions.

Conclusions

The results of this study provide further evidence for the existence of WM networks and show that jet lag is associated with alterations in static and dynamic WM FC and FCC, especially in sensorimotor networks. Jet lag is a complex problem that not only is related to sleep rhythm but also influences emotion.

Changes in 24 h Rhythmicity of Spontaneous Locomotor Activity in the Triple Transgenic Mouse for Alzheimer's Disease (3xTg-AD) in a Jet Lag Protocol: Correlations with Retinal Sensitivity

The progression of amyloid plaques and neurofibrillary tangles in different brain areas is associated with the effects of Alzheimer’s disease (AD). In addition to cognitive impairment, circadian alterations in locomotor activity have also been detected, but they have not been characterized in a jet lag protocol. Therefore, the present study aimed to compare 3xTg-AD and non-transgenic mice in changes of 24 h cycles of spontaneous locomotor activity in a jet lag protocol, in an environment without a running wheel, at 3 different states of neuronal damage: early, intermediate and advanced (3, 8 and 13 months, respectively). The 3xTg-AD mice at 3 months presented differences in phase angle and acrophase, and differentially increased activity after advances more than after delays. At 13 months, a shortening of the free-running period in constant darkness was also noted. 3xTg-AD mice showed a significant increase (123%) in global activity at 8 to 13 months and in nighttime activity (153%) at 13 months. In the advance protocol (ADV), 3xTg-AD mice displayed a significant increase in global activity (171%) at 8 and 13 months. The differences in masking effect were evident at 8 months. To assess a possible retinal dysfunction that could interfere with photic entrainment as part of the neurodegenerative process, we compared electroretinogram recordings. The results showed early deterioration in the retinal response to light flashes in mesopic conditions, observed in the B-wave latency and amplitude. Thus, our study presents new behavioral and pathological characteristics of 3xTg-AD mice and reveals the usefulness of non-invasive tools in early diagnosis.

Obstructive sleep apnea in airline pilots during daytime sleep following overnight flights

To identify the vulnerability of recovery sleep, this study investigated the occurrence of obstructive sleep apnea during daytime sleep following overnight flights in healthy airline pilots. We conducted daytime polysomnography following a long-haul night-time flight in 103 pilots. The following variables were assessed: apnea-hypopnea index, respiratory disturbance index and oxygen desaturation index. Moderate-to-severe obstructive sleep apnea was defined as an apnea-hypopnea index ≥15. Seventy-three pilots (70.9%) with no known history of obstructive sleep apnea presented with moderate-to-severe obstructive sleep apnea. Pilots showed high mean apnea-hypopnea, respiratory disturbance and oxygen desaturation indices. The body mass index, Berlin questionnaire score and cumulative flight time contributed to these indices, with both body mass index and cumulative flight time remaining significant at an apnea-hypopnea index ≥15. We found that pilots are vulnerable to obstructive sleep apnea during daytime sleep after night-time flights, which may deteriorate their health, increase fatigue and impair overall flight safety. Further research is needed to ensure flight safety, as daytime recovery sleep is unavoidable for night-time flight pilots. The pilots' normal and recovery sleep patterns should both be studied to develop an effective sleep management protocol.

Impact of Time-Restricted Feeding to Late Night on Adaptation to a 6 h Phase Advance of the Light-Dark Cycle in Mice

In modern society, more and more people suffer from circadian disruption, which in turn affects health. But until now, there are no widely accepted therapies for circadian disorders. Rhythmic feeding behavior is one of the most potent non-photic zeitgebers, thus it has been suggested that it was important to eat during specific periods of time (time-restricted feeding, TRF) so that feeding is aligned with environmental cues under normal light/dark conditions. Here, we challenged mice with a 6 h advanced shift, combined with various approaches to TRF, and found that food restricted to the second half of the nights after the shift facilitated adaptation. This coincided with improved resilience to sepsis. These results raise the possibility of reducing the adverse responses to jet lag by subsequent timing of food intake.

The Travel Demands of an Elite Rugby Sevens Team: Effects on Objective and Subjective Sleep Parameters

PURPOSE

To explore the effects of travel related to international rugby sevens competition on sleep patterns.

METHODS

A total of 17 international male rugby sevens players participated in this study. Actigraphic and subjective sleep assessments were performed daily during 2 separate Sevens World Series competition legs (Oceania and America). The duration of each competition leg was subdivided into key periods (pretour, precompetition, tournament 1, relocation, tournament 2, and posttour) lasting 2 to 7 nights. Linear mixed models in combination with magnitude-based decisions were used to assess (1) the difference between preseason and key periods and (2) the effect of travel direction (eastward or westward).

RESULTS

Shorter total sleep time (hours:minutes) was observed during tournament 2 (mean [SD], 06:16 [01:08]), relocation (06:09 [01:09]), and the pretour week (06:34 [01:24]) compared with the preseason (06:52 [01:00]). Worse sleep quality (arbitrary units) was observed during tournament 1 (6.1 [2.0]) and 2 (5.7 [1.2]), as well as during the relocation week (6.3 [1.5]) than during the preseason (6.5 [1.8]). When traveling eastward compared with westward, earlier fall-asleep time was observed during tournament 1 (ES - 0.57; 90% CI, -1.12 to -0.01), the relocation week (-0.70 [-1.11 to -0.28]), and the posttour (-0.57 [-0.95 to -0.18]). However, possibly trivial and unclear differences were observed during the precompetition week (0.15 [-0.15 to 0.45]) and tournament 2 (0.81 [-0.29 to 1.91]).

CONCLUSION

The sleep patterns of elite rugby sevens players are robust to the effects of long-haul travel and jet lag. However, the staff should consider promoting sleep during the tournament and relocation week.

Transgenic rats expressing dominant negative BMAL1 showed circadian clock amplitude reduction and rapid recovery from jet lag

The circadian rhythms are endogenous rhythms of about 24 h, and are driven by the circadian clock. The clock centre locates in the suprachiasmatic nucleus. Light signals from the retina shift the circadian rhythm in the suprachiasmatic nucleus, but there is a robust part of the suprachiasmatic nucleus that causes jet lag after an abrupt shift of the environmental lighting condition. To examine the effect of attenuated circadian rhythm on the duration of jet lag, we established a transgenic rat expressing BMAL1 dominant negative form under control by mouse Prnp-based transcriptional regulation cassette [BMAL1 DN (+)]. The transgenic rats became active earlier than controls, just after light offset. Compared to control rats, BMAL1 DN (+) rats showed smaller circadian rhythm amplitudes in both behavioural and Per2 promoter driven luciferase activity rhythms. A light pulse during the night resulted in a larger phase shift of behavioural rhythm. Furthermore, at an abrupt shift of the light-dark cycle, BMAL1 DN (+) rat showed faster entrainment to the new light-dark cycle compared to controls. The circadian rhythm has been regarded as a limit cycle phenomenon, and our results support the hypothesis that modification of the amplitude of the circadian limit cycle leads to alteration in the length of the phase shift.

Sleep Hygiene and Light Exposure Can Improve Performance Following Long-Haul Air Travel

PURPOSE

To assess the efficacy of a combined light exposure and sleep hygiene intervention to improve team-sport performance following eastward long-haul transmeridian travel.

METHODS

Twenty physically trained males underwent testing at 09:00 and 17:00 hours local time on 4 consecutive days at home (baseline) and the first 4 days following 21 hours of air travel east across 8 time zones. In a randomized, matched-pairs design, participants traveled with (INT; n = 10) or without (CON; n = 10) a light exposure and sleep hygiene intervention. Performance was assessed via countermovement jump, 20-m sprint, T test, and Yo-Yo Intermittent Recovery Level 1 tests, together with perceptual measures of jet lag, fatigue, mood, and motivation. Sleep was measured using wrist activity monitors in conjunction with self-report diaries.

RESULTS

Magnitude-based inference and standardized effect-size analysis indicated there was a very likely improvement in the mean change in countermovement jump peak power (effect size 1.10, ±0.55), and likely improvement in 5-m (0.54, ±0.67) and 20-m (0.74, ±0.71) sprint time in INT compared with CON across the 4 days posttravel. Sleep duration was most likely greater in INT both during travel (1.61, ±0.82) and across the 4 nights following travel (1.28, ±0.58) compared with CON. Finally, perceived mood and motivation were likely worse (0.73, ±0.88 and 0.63, ±0.87) across the 4 days posttravel in CON compared with INT.

CONCLUSIONS

Combined light exposure and sleep hygiene improved speed and power but not intermittent-sprint performance up to 96 hours following long-haul transmeridian travel. The reduction of sleep disruption during and following travel is a likely contributor to improved performance.

Jet Lag Recovery and Memory Functions Are Correlated with Direct Light Effects on Locomotion

Jet lag is a circadian disruption that affects millions of people, resulting, among other things, in extreme sleepiness and memory loss. The hazardous implications of such effects are evident in situations in which focus and attention are required. Remarkably, there is a limited understanding of how jet lag recovery and associated memory loss vary year round under different photoperiods. Here we show, using different cycles representing winter, summer, and equinox in male mice, that jet lag recovery and memory vary significantly with photoperiod changes. We uncover a positive correlation of acute light effects on circadian-driven locomotion (known as negative masking) with photoentrainment speed and memory enhancement during jet lag. Specifically, we show that enhancing or reducing negative masking is correlated with better or worse memory performance, respectively. This study indicates that in addition to timed-light exposure for phase shifting, the negative masking response could also be biologically relevant when designing effective treatments of jet lag.

Efficacy of Tasimelteon (HETLIOZ®) in the Treatment of Jet Lag Disorder Evaluated in an 8-h Phase Advance Model; a Multicenter, Randomized, Double-Blind, Placebo-Controlled Trial

Background: Most travelers experience Jet Lag Disorder (JLD) symptoms due to misalignment of their circadian rhythms with respect to the new time zone. We assessed the efficacy and safety of tasimelteon (HETLIOZ®) in healthy participants using a laboratory model of JLD induced by an 8-h phase advance of the sleep-wake cycle (JET8 Study). We hypothesized that tasimelteon treatment in participants experiencing JLD would cause increased sleep time, increased next-day alertness, and reduced next-day sleepiness.

Methods: We undertook a randomized, double-blind, placebo-controlled trial in 12 US clinical research sleep centers. We screened healthy adults ages 18–73 years, who were eligible for the randomization phase of JET8 if they typically went to bed between 21:00 and 01:00, slept between 7 and 9 h each night, and slept at a consistent bedtime. We used block randomization stratified by site to assign participants (1:1) to receive a single oral dose of tasimelteon (20 mg) or placebo 30 min before their 8-h phase-advanced bedtime. The primary endpoint was Total Sleep Time in the first 2/3 of the night (TST_2/3), which was measured by polysomnography during the 8-h sleep episode, and assessed in the intent-to-treat population. The trial is completed and registered with ClinicalTrials.gov, NCT03373201.

Results: Between October 16, 2017 and January 17, 2018, we screened 607 healthy participants for JET8, of whom 320 (53%) were assigned to receive tasimelteon (n = 160) or placebo (n = 160). Tasimelteon treatment increased TST_2/3 (primary endpoint) by 60.3 min (95%CI 44.0 to 76.7, P < 0.0001) and whole night TST by 85.5 min (95% CI 64.3 to 106.6, P < 0.0001), improved next day alertness, next day sleepiness, and shortened latency to persistent sleep by −15.1 min (95% CI −26.2 to −4.0, P = 0.0081).

Conclusion: A single dose of tasimelteon improves the primary symptoms of JLD, including nighttime insomnia and next day functioning among participants in a laboratory model of JLD simulating eastward trans-meridian travel by inducing an 8-h phase advance of the sleep-wake cycle.

Environmental Circadian Disruption Increases Stroke Severity and Dysregulates Immune Response

Understanding the health consequences of chronic disruption of circadian rhythms can contribute to improving prevention strategies for shift workers. Chronic circadian disruption in shift work has been linked to a higher risk of stroke. Dysregulated immune responses are also linked to circadian disruption and may be a factor in stroke outcomes in shift workers. In this study, we test the hypotheses that specific schedules of circadian disruption exacerbate inflammatory responses in the brain, causing an increase in infarct size after experimentally induced ischemic stroke. Mice were exposed to 1 of 5 different lighting schedules followed by a 30-min middle cerebral artery occlusion, then reperfusion and 3-day recovery. A history of weekly phase advances resulted in an increased infarct volume versus the control lighting schedule. These effects were shift-direction specific, nonpermanent, and required multiple shifts to occur. In a separate cohort, stereotaxic injections of lipopolysaccharide were given bilaterally after exposure to 1 of 3 different lighting schedules. Ratios of pro- to anti-inflammatory cytokine expression show dysregulated responses after a history of phase advances. We conclude that chronic circadian disruption leads to worsened stroke outcome in a direction- and schedule-specific manner likely because of priming of the inflammatory response in the brain. These pieces of evidence suggest that the health impacts of shift work may be improved by targeting shift work scheduling, inflammatory mediators, or both.

The effect of jet lag on the human brain: A neuroimaging study

Jet lag is commonly experienced when travelers cross multiple time zones, leaving the wake-sleep cycle and intrinsic biological "clocks" out of synchrony with the current environment. The effect of jet lag on intrinsic cortical function remains unclear. Twenty-two healthy individuals experiencing west-to-east jet lag flight were recruited. Brain structural and functional magnetic resonance studies, as well as psychological and neurohormonal tests, were carried out when participants returned from travel over six time zones and 50 days later when their jet lag symptoms had resolved. During jet lag, the functional brain network exhibited a small-world topology that was shifted toward regularity. Alterations during jet lag relative to recovery included decreased basal ganglia-thalamocortical network connections and increased functional connectivity between the medial temporal lobe subsystem and medial visual cortex. The lower melatonin and higher thyroid hormone levels during jet lag showed the same trend as brain activity in the right lingual gyrus. Although there was no significant difference between cortisol measurements during and after jet lag, cortisol levels were associated with temporal lobe activity in the jet lag condition. Brain and neuroendocrine changes during jet lag were related to jet lag symptoms. Further prospective studies are needed to explore the time course over which jet lag acts on the human brain.

Environmental Circadian Disruption Increases Stroke Severity and Dysregulates Immune Response

Understanding the health consequences of chronic disruption of circadian rhythms can contribute to improving prevention strategies for shift workers. Chronic circadian disruption in shift work has been linked to a higher risk of stroke. Dysregulated immune responses are also linked to circadian disruption and may be a factor in stroke outcomes in shift workers. In this study, we test the hypotheses that specific schedules of circadian disruption exacerbate inflammatory responses in the brain, causing an increase in infarct size after experimentally induced ischemic stroke. Mice were exposed to 1 of 5 different lighting schedules followed by a 30-min middle cerebral artery occlusion, then reperfusion and 3-day recovery. A history of weekly phase advances resulted in an increased infarct volume versus the control lighting schedule. These effects were shift-direction specific, nonpermanent, and required multiple shifts to occur. In a separate cohort, stereotaxic injections of lipopolysaccharide were given bilaterally after exposure to 1 of 3 different lighting schedules. Ratios of pro- to anti-inflammatory cytokine expression show dysregulated responses after a history of phase advances. We conclude that chronic circadian disruption leads to worsened stroke outcome in a direction- and schedule-specific manner likely because of priming of the inflammatory response in the brain. These pieces of evidence suggest that the health impacts of shift work may be improved by targeting shift work scheduling, inflammatory mediators, or both.

Circadian regulation of sleep in a pre-clinical model of Dravet syndrome: dynamics of sleep stage and siesta re-entrainment

STUDY OBJECTIVES

Sleep disturbances are common co-morbidities of epileptic disorders. Dravet syndrome (DS) is an intractable epilepsy accompanied by disturbed sleep. While there is evidence that daily sleep timing is disrupted in DS, the difficulty of chronically recording polysomnographic sleep from patients has left our understanding of the effect of DS on circadian sleep regulation incomplete. We aim to characterize circadian sleep regulation in a mouse model of DS.

METHODS

Here we exploit long-term electrocorticographic recordings of sleep in a mouse model of DS in which one copy of the Scn1a gene is deleted. This model both genocopies and phenocopies the disease in humans. We test the hypothesis that the deletion of Scn1a in DS mice is associated with impaired circadian regulation of sleep.

RESULTS

We find that DS mice show impairments in circadian sleep regulation, including a fragmented rhythm of non-rapid eye movement (NREM) sleep and an elongated circadian period of sleep. Next, we characterize re-entrainment of sleep stages and siesta following jet lag in the mouse. Strikingly, we find that re-entrainment of sleep following jet lag is normal in DS mice, in contrast to previous demonstrations of slowed re-entrainment of wheel-running activity. Finally, we report that DS mice are more likely to have an absent or altered daily "siesta".

CONCLUSIONS

Our findings support the hypothesis that the circadian regulation of sleep is altered in DS and highlight the value of long-term chronic polysomnographic recording in studying the role of the circadian clock on sleep/wake cycles in pre-clinical models of disease.

Conceptual Models of Entrainment, Jet Lag, and Seasonality

Understanding entrainment of circadian rhythms is a central goal of chronobiology. Many factors, such as period, amplitude, Zeitgeber strength, and daylength, govern entrainment ranges and phases of entrainment. We have tested whether simple amplitude-phase models can provide insight into the control of entrainment phases. Using global optimization, we derived conceptual models with just three free parameters (period, amplitude, and relaxation rate) that reproduce known phenotypic features of vertebrate clocks: phase response curves (PRCs) with relatively small phase shifts, fast re-entrainment after jet lag, and seasonal variability to track light onset or offset. Since optimization found multiple sets of model parameters, we could study this model ensemble to gain insight into the underlying design principles. We found complex associations between model parameters and entrainment features. Arnold onions of representative models visualize strong dependencies of entrainment on periods, relative Zeitgeber strength, and photoperiods. Our results support the use of oscillator theory as a framework for understanding the entrainment of circadian clocks.

Intraindividual variability of sleep/wake patterns in adolescents with and without attention-deficit/hyperactivity disorder

BACKGROUND

Prior studies examining the sleep of adolescents with and without attention-deficit/hyperactivity disorder (ADHD) have relied on mean values such as average sleep duration, which masks intraindividual variability (IIV). The objective was to investigate whether adolescents with ADHD have greater IIV of sleep/wake patterns than adolescents without ADHD using actigraphy and daily sleep diaries.

METHOD

Adolescents (ages 13.17 ± 0.40 years; 45% female) with (n = 162) and without (n = 140) ADHD were recruited from middle schools at two sites. Participants wore actigraphs and completed sleep diaries for an average of 2 weeks.

RESULTS

Multilevel models were conducted with sex, sleep medication use, ADHD medication use, number of days with data, and social jetlag controlled for in analyses. For actigraphy, adolescents with ADHD had greater variability for time in bed, sleep onset and offset, and wake after sleep onset than adolescents without ADHD. For sleep diary data, adolescents with ADHD had greater variability in bedtime, wake time, sleep duration, sleep onset latency, sleep quality, and night wakings than adolescents without ADHD. Social jetlag was a significant predictor of variability in sleep measures based on both actigraph and daily diaries; however, ADHD status was not associated with social jetlag.

CONCLUSIONS

This is the first study to show that adolescents with ADHD have more variable sleep/wake patterns than their peers using both objective and subjective sleep measures. IIV of sleep/wake patterns may be important for clinicians to assess and monitor as part of treatment. Research is needed to understand the mechanisms underlying increased IIV of sleep/wake patterns in adolescents with ADHD and potential consequences for daytime functioning.

Out of your zone? 21 years of travel and performance in Super Rugby

The extent to which travel has affected Super Rugby teams' performances was analysed using outcomes of all matches played from the beginning of the competition in 1996 to the end of the 2016 season. Points difference and matches won or lost were predicted with general and generalized mixed linear models. The predictors were the linear effects of number of time zones crossed and travel duration based on the teams' locations for each match and their locations in the previous week. The away-match disadvantage was also estimated, along with trends in all these effects. In 1996 the predicted combined effect of eastward travel across 12 time zones was a reduction of 5.8 points scored per match, resulting in 4.1 more matches lost every 10 matches. Corresponding effects for westward travel were 6.4 points and 3.1 matches. In 2016 effects travelling eastward were 3.7 points and 2.3 matches, whereas travelling westward the effects were 3.7 points and 1.5 matches. These travel effects were due mainly to the away-match disadvantage: 5.7 points and 3.2 matches in 1996; 5.2 points and 2.3 matches in 2016. Teams in Super Rugby are dealing successfully with long-haul travel and should now focus on reducing the away-match disadvantage.

Exposure to jet lag aggravates depression-like behaviors and age-related phenotypes in rats subject to chronic corticosterone

Our previous finding demonstrated that chronic corticosterone (CORT) may be involved in mediating the pathophysiology of premature aging in rats. Frequent jet lag increases the risk for many diseases, including obesity and type 2 diabetes, and is associated with the aging processes. However, the effect of jet lag on CORT-induced depression and its association with aging phenotypes remain unclear. In this study, the rats were exposed to both CORT and jet lag treatment, and the differences were analyzed and compared to rats with single CORT treatment. Our results showed that jet lag treatment aggravated CORT-induced depression-like behavior evidenced by sucrose intake test, forced swimming test, and open field test. Additionally, this treatment aggravated the shortening of telomeres, which possibly resulted in decreased telomerase activity, and downregulated the expression of telomere-binding factor 2 (TRF2) and telomerase reverse transcriptase compared to that in CORT rats, as revealed by quantitative real-time-polymerase chain reaction and western blot analysis, respectively. The shortening of telomeres may have been caused by increased oxidative stress, which was associated with the inhibition of sirtuin 3. Exposure to jet lag also aggravated the degeneration of mitochondrial functions, as shown by the decreases in the mRNA expression of COX1, ND1, and Tfam. Our findings provide physiological evidence that jet lag exposure may worsen stress-induced depression and age-related abnormalities.

The longest journeys in Super Rugby: 11 years of travel and performance indicators

Regular air travel is common in sport. The aim of this study was to understand the extent to which travel has affected Super Rugby teams' performance from 2006, the first season with available Key Performance Indicators (KPIs), to 2016. Data were analysed with mixed linear models for the effects of number of time-zones crossed (east or west), travel duration, the away-match disadvantage, difference in ranking, a set of amendments to the laws of Rugby Union in 2008, a change in competition format (introduction of a conference system) in 2011, and a secular trend. In 2006, the predicted combined effects of travelling 24 h across 12 time-zones and playing away were trivial or small and negative but generally unclear for most of the KPIs in both directions of travel. In 2016 more effects were clear, small and negative for westward travel, while most effects for eastward travel were clear, small to moderate and negative. Most KPIs showed small to moderate increases over the 11 years, while difference in ranking, the introduction of new rules and game format led to mostly small changes. Changes in the physical demands of the game, and inadequate recovery time for long-haul travel can explain these effects.

Spike-Wave Discharges and Sleep-Wake States during Circadian Desynchronization: No Effects of Agomelatine upon Re-Entrainment

Rapid changes in the light-dark cycle cause circadian desynchronization between rhythms of spike-wave discharges (SWDs) and motor activity in genetic epileptic rats, and this is accompanied by an increase in epileptic activity. Given the close relationship between absence seizures and sleep-wake states, the present study assessed firstly a putative relationship between vigilance rhythms and SWDs during re-synchronization, and secondly sleep-wake patterns responsible for increased epileptic activity. Lastly, in a view of existing evidence that melatonin and its agonists accelerate re-synchronization, the effects of different doses of agomelatine upon the speed of re-synchronization of different sleep-wake states and SWDs were investigated. Simultaneous electroencephalographic and electromyographic recordings were made in symptomatic WAG/Rij rats, before, during and 10 days following an 8 h light phase delay. Agomelatine was orally administered acutely and sub-chronically, during 10 post-shift days. The magnitude of the advance after the shift and the speed of re-synchronization were specific for various rhythms. Most prominent change was the increase in REM sleep duration during the dark phase. A post-shift increase in passive wakefulness and a reduction in deep slow-wave sleep coincided with an aggravation of SWDs during the light phase. Agomelatine showed neither an effect on sleep-wake parameters and SWDs, nor affected re-synchronization. The same speed of re-synchronization of SWDs and light slow-wave sleep suggests that both are controlled by a common circadian mechanism. The redistribution of SWDs and their increase in the light phase after the shift may be of importance for patients with absence epilepsy planning long trans-meridian flight across time zones.

Gestational jet lag predisposes to later-life skeletal and cardiac disease

Circadian rhythm disturbance (CRD) increases the risk of disease, e.g. metabolic syndrome, cardiovascular disease, and cancer. In the present study, we investigated later life adverse health effects triggered by repeated jet lag during gestation. Pregnant mice were subjected to a regular light-dark cycle (CTRL) or to a repeated delay (DEL) or advance (ADV) jet lag protocol. Both DEL and ADV offspring showed reduced weight gain. ADV offspring had an increased circadian period, and an altered response to a jet lag was observed in both DEL and ADV offspring. Analysis of the bones of adult male ADV offspring revealed reduced cortical bone mass and strength. Strikingly, analysis of the heart identified structural abnormalities and impaired heart function. Finally, DNA methylation analysis revealed hypermethylation of miR17-92 cluster and differential methylation within circadian clock genes, which correlated with altered gene expression. We show that developmental CRD affects the circadian system and predisposes to non-communicable disease in adult life.

Circadian rhythm bifurcation induces flexible phase resetting by reducing circadian amplitude

Shift-work and jet-lag-related disorders are caused by the limited flexibility of the suprachiasmatic nucleus (SCN), a master circadian clock in the hypothalamus, to adjust to new light-dark (LD) cycles. Recent findings confirmed here establish that behavioral jet lag after simulated time-zone travel is virtually eliminated following bifurcated circadian entrainment under a novel and atypical 24-h light:dark:light:dark (LDLD) cycle. To investigate the mechanisms of this fast resetting, we examined the oscillatory stability of the SCN and peripheral tissues in LDLD-bifurcated mice employing the dissection procedure as a perturbing resetting stimulus. SCN, lung, liver, and adrenal tissue were extracted at times throughout the day from female and male PER2::Luciferase knock-in mice entrained to either LDLD or a normal LD cycle. Except for adrenals, the phase of the cultured explants was more strongly set by dissection under LDLD than under normal LD. Acute bioluminescence levels of SCN explants indicate that the rhythm amplitude of PER2 is reduced and phase is altered in LDLD. Real-time quantitative PCR suggests that amplitude and rhythmicity of canonical clock genes in the lung, liver, and kidney are also significantly reduced in LDLD in vivo. Furthermore, spatiotemporal patterns of PER2 peak time in cultured SCN were altered in LDLD. These results suggest that altered gene expression patterns in the SCN caused by bifurcation likely result in fast resetting of behavior and cultured explants, consistent with previously reported mathematical models. Thus, non-invasive, simple light manipulations can make circadian rhythms more adaptable to abrupt shifts in the environmental LD cycle.

Effect of Daily Light on c-Fos Expression in the Suprachiasmatic Nucleus under Jet Lag Conditions

Jet-lag symptoms arise from temporal misalignment between the internal circadian clock and external solar time when traveling across multiple time zones. Light is known as a strong timing cue of the circadian clock. We here examined the effect of daily light on the process of jet lag by detecting c-Fos expression in the master clock neurons in the suprachiasmatic nucleus (SCN) under 8-hr phase-advanced jet lag condition. In WT mice, c-Fos-immunoreactivity was found at 1–2 hours on the first day after light/dark (LD) phase-advance. This induction was also observed on the second and third days, although their levels were diminished day by day. In contrast, c-Fos induction in the SCN of V1a^–/–V1b^–/– mice, which show virtually no jet lag symptoms even after 8-hr phase-advance, was only detected on the first day. These results indicate that external light has affected SCN neuronal activity for 3 days after LD phase-advance in WT mice suggesting the continuous progress of activity change of SCN neurons under jet lag conditions. Noteworthy, limited c-Fos induction in V1a^–/–V1b^–/– SCN is also consistent with the rapid reentrainment of the SCN clock in mutant mice after 8-hr LD phase-advance.

Complex interactions of circadian rhythms, eating behaviors, and the gastrointestinal microbiota and their potential impact on health

Human health is intricately intertwined with the composition and function of the trillions of microorganisms that make up the gastrointestinal (GI) microbiome. The GI microbiome is essentially a microbial organ that provides metabolic, immunologic, and protective functions for the host. Habitual diet, changes in macronutrient composition, and consumption of nondigestible dietary fibers have all been shown to impact the human GI microbiome. Intriguingly, the impact of diet on the microbiome may be related not only to what humans eat but also to the timing of food consumption. Emerging preclinical research suggests that gut microbes experience diurnal rhythms, and the health effects of eating patterns, including time-restricted feeding and meal frequency, may be related to the GI microbiome. Herein, the complex connections among circadian rhythms, eating behaviors, the GI microbiome, and health are reviewed, highlighting the need for additional translational research in this area.

Jet lag: Heuristics and therapeutics

Jet lag is one of those common medical problems, to which most people don’t give a serious thought. However, it is intricately intertwined with our normal circadian rhythm. It is classified as a sleep disorder. There is also a dearth of good scientific literature, not to mention clinical trials on the subject. Slowly but steadily, the scientific community is realizing the various deleterious health effects of jet lag and is devising innovative methods to counter them. This narrative review touches upon the etiopathogenesis, clinical manifestations and therapeutic strategies effective against the nagging problem of jet lag.

Human studies on hypothalamo-pituitary-adrenal (HPA) axis

The daily rhythm of the hypothalamo-pituitary-adrenal (HPA) axis is regulated by the central clock in the suprachiasmatic nucleus. Cortisol, a glucocorticoid, acts as a secondary messenger between the central clock and the peripheral tissues. Changes in clock time, as seen in shift workers, alters the HPA axis and results in metabolic disturbances associated with ill health. Depression, anorexia nervosa and obstructive sleep apnoea, are associated with cortisol rhythm phase shifts and increased cortisol exposure. Higher nocturnal cortisol exposure is observed in patients with Cushing's syndrome and adrenal incidentalomas with autonomous cortisol secretion and is associated with insulin resistance, and increased cardiovascular risk and mortality. A decrease in cortisol rhythm amplitude is seen in adrenal insufficiency, and despite replacement, patients have an impaired quality of life and increased mortality. Research on cortisol replacement has focused on replacing the cortisol daily rhythm by subcutaneous hydrocortisone infusions and oral modified release hydrocortisone formulations with the aim of improving disease control and quality of life.

Alcohol Intake Increases in Adolescent C57BL/6J Mice during Intermittent Cycles of Phase-Delayed, Long-Light Conditions

Adolescents naturally go to bed and awaken late, but are forced to awaken early for school and work. This leads to “social jetlag”, a state of circadian desynchrony (CD), in which internal biological rhythms are out of sync with behavioral rhythms. CD is associated with increased alcohol intake in adults, but has been less well-studied in adolescents. The goal of this study was to model adolescent alcohol intake during similar CD conditions in male C57BL/6J mice. Free access alcohol intake, water intake and wheel-running activity were measured during a normal 12HR photoperiod or during alternating photoperiod (Experiment 1: 12 h light for 4 days followed by 18 h light for 3 days, with dark (activity onset) delayed 9 h during the 18HR photoperiod; Experiment 2: 12 h light for 4 days followed by 6 h light for 3 days, with dark onset delayed 3 h during the 6HR photoperiod). In Experiment 1, CD produced a small but significant increase in the total alcohol intake per day as well as in intake in bouts, with the greatest increase over controls in the hours following the 6HR dark period. Additionally, the pattern of alcohol intake in bouts shifted to increase alcohol intake during the shorter dark period. In Experiment 2, the opposite effect occurred—the longer dark cycle led to lower alcohol drinking in the second half of the dark period. However, in Experiment 2, CD produced no significant changes in either total alcohol intake or alcohol intake in bouts. Conclusion: shifts in the light cycle that disrupt the regular pattern of day and night, and increase the length of the night phase, are sufficient to increase both drinking in bouts and restricted drinking in adolescent mice, modeling increased alcohol intake in adolescents during CD.

Direct Midbrain Dopamine Input to the Suprachiasmatic Nucleus Accelerates Circadian Entrainment

Dopamine (DA) neurotransmission controls behaviors important for survival, including voluntary movement, reward processing, and detection of salient events, such as food or mate availability. Dopaminergic tone also influences circadian physiology and behavior. Although the evolutionary significance of this input is appreciated, its precise neurophysiological architecture remains unknown. Here, we identify a novel, direct connection between the DA neurons of the ventral tegmental area (VTA) and the suprachiasmatic nucleus (SCN). We demonstrate that D1 dopamine receptor (Drd1) signaling within the SCN is necessary for properly timed resynchronization of activity rhythms to phase-shifted light:dark cycles and that elevation of DA tone through selective activation of VTA DA neurons accelerates photoentrainment. Our findings demonstrate a previously unappreciated role for direct DA input to the master circadian clock and highlight the importance of an evolutionarily significant relationship between the circadian system and the neuromodulatory circuits that govern motivational behaviors.