Disruption of circadian clocks has ramifications for metabolism, brain, and behavior. Proc Natl Acad Sci U S A. 2011;108:1657-1662. [PMID: 21220317 DOI: 10.1073/pnas.1018375108]

Are Owls and Larks Different When it Comes to Aggression? Genetics, Neurobiology, and Behavior

This review focuses on the contribution of circadian rhythms to aggression with a multifaceted approach incorporating genetics, neural networks, and behavior. We explore the hypothesis that chronic circadian misalignment is contributing to increased aggression. Genes involved in both circadian rhythms and aggression are discussed as a possible mechanism for increased aggression that might be elicited by circadian misalignment. We then discuss the neural networks underlying aggression and how dysregulation in the interaction of these networks evoked by circadian rhythm misalignment could contribute to aggression. The last section of this review will present recent human correlational data demonstrating the association between chronotype and/or circadian misalignment with aggression. With circadian rhythms and aggression being a burgeoning area of study, we hope that this review initiates more interest in this promising and topical area.

Longitudinal Characterization and Biomarkers of Age and Sex Differences in the Decline of Spatial Memory

The current longitudinal study examined factors (sex, physical function, response to novelty, ability to adapt to a shift in light/dark cycle, brain connectivity), which might predict the emergence of impaired memory during aging. Male and female Fisher 344 rats were tested at 6, 12, and 18 months of age. Impaired spatial memory developed in middle-age (12 months), particularly in males, and the propensity for impairment increased with advanced age. A reduced response to novelty was observed over the course of aging, which is inconsistent with cross-sectional studies. This divergence likely resulted from differences in the history of environmental enrichment/impoverishment for cross-sectional and longitudinal studies. Animals that exhibited lower level exploration of the inner region on the open field test exhibited better memory at 12 months. Furthermore, males that exhibited a longer latency to enter a novel environment at 6 months, exhibited better memory at 12 months. For females, memory at 12 months was correlated with the ability to behaviorally adapt to a shift in light/dark cycle. Functional magnetic resonance imaging of the brain, conducted at 12 months, indicated that the decline in memory was associated with altered functional connectivity within different memory systems, most notably between the hippocampus and multiple regions such as the retrosplenial cortex, thalamus, striatum, and amygdala. Overall, some factors, specifically response to novelty at an early age and the capacity to adapt to shifts in light cycle, predicted spatial memory in middle-age, and spatial memory is associated with corresponding changes in brain connectivity. We discuss similarities and differences related to previous longitudinal and cross-sectional studies, as well as the role of sex differences in providing a theoretical framework to guide future longitudinal research on the trajectory of cognitive decline. In addition to demonstrating the power of longitudinal studies, these data highlight the importance of middle-age for identifying potential predictive indicators of sexual dimorphism in the trajectory in brain and cognitive aging.

The fluctuations of metabotropic glutamate receptor subtype 5 (mGluR5) in the amygdala in fear conditioning model of male Wistar rats following sleep deprivation, reverse circadian and napping

Sleep is involved in metabolic system, mental health and cognitive functions. Evidence shows that sleep deprivation (SD) negatively affects mental health and impairs cognitive functions, including learning and memory. Furthermore, the metabotropic glutamate receptor subtype 5 (mGluR5) is a metabolic biomarker, which is affected by various conditions, including stress, sleep deprivation, and cognitive and psychiatric disorders. In this research, we investigated the effect of SD and reverse circadian (RC), and two models of napping (continuous and non-continuous) combined with SD or RC on fear-conditioning memory, anxiety-like behavior and mGluR5 fluctuations in the amygdala. 64 male Wistar rats were used in this study. The water box apparatus was used to induce SD/RC for 48 h, and fear-conditioning memory apparatus was used to assess fear memory. The results showed, fear-conditioning memory was impaired following SD and RC, especially in contextual stage. However, anxiety-like behavior was increased. Furthermore, mGluR5 was increased in the left amygdala more than the right amygdala. Additionally, continuous napping significantly improved fear-conditioning memory, especially freezing behavior. In conclusion, following SD and RC, fear-conditioning memory in contextual stage is more vulnerable than in auditory stage. Furthermore, increase in anxiety-like behavior is related to increase in the activity of left amygdala and mGluR5 receptors.

Adverse Effects of Circadian Disorganization on Mood and Molecular Rhythms in the Prefrontal Cortex of Mice

Disturbance of the daily cycles in sleep and wakefulness induced by conditions such as shift work and jet lag can increase the risk of affective disorders including anxiety and depression. The way such circadian disorganization disrupts the regulation of mood, however, is not well understood. More specifically, the impact of circadian disorganization on the daily rhythms of the neuronal function that controls mood remains unclear. We therefore investigated the effects of circadian disorganization on expression rhythms of clock genes as well as immediate early genes (IEGs) in several mood-controlling regions of the brain. To introduce circadian disorganization of behaviors, we exposed male C57BL/6J mice to chronic reversal of the light-dark cycle and we found a marked negative mood phenotype in these mice. Importantly, the most adverse effect of circadian disorganization on expression rhythms of clock and IEGs was observed in the prefrontal cortex (PFC) when compared to that in other mood-related areas of the brain. Dysregulation of molecular rhythms in the PFC is therefore suggested to be associated with the development of mood disorders in conditions including shift work and jet lag.

Chronic stress, physiological adaptation and developmental programming of the neuroendocrine stress system

Chronic stress undermines physical and mental health, in part via dysregulation of the neuroendocrine stress system. Key to understand this dysregulation is recognizing that the problem is not stress per se, but rather its chronicity. The optimally functioning stress system is highly dynamic, and negative feedback regulation enforces transient responses to acute stressors. Chronic stress overrides this, and adaptation to the chronicity can result in persistent dysregulation by altering sensitivity thresholds critical for control of system dynamics. Such adaptation involves plasticity within the central nervous system (CNS) as well as epigenetic regulation. When it occurs during development, it can have persistent effects on neuroendocrine regulation. Understanding how chronic stress programs development of the neuroendocrine stress system requires elucidation of stress-responsive gene regulatory networks that control CNS plasticity and development.

Circadian rhythm disruption and mental health

Circadian rhythms are internal manifestations of the solar day that permit adaptations to predictable environmental temporal changes. These ~24-h rhythms are controlled by molecular clockworks within the brain that are reset daily to precisely 24 h by exposure to the light-dark cycle. Information from the master clock in the mammalian hypothalamus conveys temporal information to the entire body via humoral and neural communication. A bidirectional relationship exists between mood disorders and circadian rhythms. Mood disorders are often associated with disrupted circadian clock-controlled responses, such as sleep and cortisol secretion, whereas disruption of circadian rhythms via jet lag, night-shift work, or exposure to artificial light at night, can precipitate or exacerbate affective symptoms in susceptible individuals. Evidence suggests strong associations between circadian rhythms and mental health, but only recently have studies begun to discover the direct interactions between the circadian system and mood regulation. This review provides an overview of disrupted circadian rhythms and the relationship to behavioral health and psychiatry. The focus of this review is delineating the role of disruption of circadian rhythms on mood disorders using human night shift studies, as well as jet lag studies to identify links. We also review animal models of disrupted circadian rhythms on affective responses. Lastly, we propose low-cost behavioral and lifestyle changes to improve circadian rhythms and presumably behavioral health.

Salivary cortisol as a non-invasive window on the brain

The validation of accurate and meaningful assessment of cortisol in saliva samples has proved revolutionary in stress research. Its many advantages have expanded the scope of investigation from traditional laboratory and clinical settings to include multidisciplinary and community-based research. These developments have given rise to a wealth insight into the links between stress and health. Here we highlight the potential of salivary cortisol as both a product and mediator of brain function, instrumental in disturbing brain health. However, the subtleties of salivary cortisol as a measure can be underestimated, leading to misinterpretation of findings. These issues are explored, with a particular emphasis on necessary methodological rigor. Notwithstanding great promise, there is undeniably more to learn so we conclude by making recommendations for future research including use of salivary cortisol in the development of integrative predictive models of stress-related risk factors and resilience across the life course.

Circadian disruption: What do we actually mean?

The circadian system regulates physiology and behavior. Acute challenges to the system, such as those experienced when traveling across time zones, will eventually result in re-synchronization to local environmental time cues, but this re-synchronization is oftentimes accompanied by adverse short-term consequences. When such challenges are experienced chronically, adaptation may not be achieved, as for example in the case of rotating night shift workers. The transient and chronic disturbance of the circadian system is most frequently referred to as "circadian disruption", but many other terms have been proposed and used to refer to similar situations. It is now beyond doubt that the circadian system contributes to health and disease, emphasizing the need for clear terminology when describing challenges to the circadian system and their consequences. The goal of this review is to provide an overview of the terms used to describe disruption of the circadian system, discuss proposed quantifications of disruption in experimental and observational settings with a focus on human research, and highlight limitations and challenges of currently available tools. For circadian research to advance as a translational science, clear, operationalizable, and scalable quantifications of circadian disruption are key, as they will enable improved assessment and reproducibility of results, ideally ranging from mechanistic settings, including animal research, to large-scale randomized clinical trials.

The hypothalamic-pituitary-adrenal axis as a substrate for stress resilience: Interactions with the circadian clock

Stress, primarily processed via the hypothalamic-pituitary-adrenal (HPA) axis, engages biological pathways throughout the brain and body which promote adaptation and survival to changing environmental demands. Adaptation to environmental challenges is compromised when these pathways are no longer functioning optimally. The physiological and behavioral mechanisms through which HPA axis function influences stress adaptation and resilience are not fully elucidated. Our understanding of stress biology and disease must take into account the complex interactions between the endocrine system, neural circuits, and behavioral coping strategies. In addition, further consideration must be taken concerning influences of other aspects of physiology, including the circadian clock which is critical for regulation of daily changes in HPA activity. While adding a layer of complexity, it also offers targets for intervention. Understanding the role of HPA function in mediating these diverse biological responses will lead to important insights about how to bolster successful stress adaptation and promote stress resilience.

DAILY-A Personalized Circadian Zeitgeber Therapy as an Adjunctive Treatment for Alcohol Use Disorder Patients: Study Protocol for a Randomized Controlled Trial

Background: Hallmarks of alcohol use disorder (AUD) are disturbances of circadian rhythms and everyday structures. While circadian rhythms dictate the timing of daily recurring activities such as sleep, activity, and meals, conversely, these activities represent time cues, so called Zeitgebers, that the circadian system uses to synchronize with the environment. Here we present a study protocol for our newly developed therapy approach for AUD patients, in which we take advantage of this mutual influence and stabilize and strengthen their circadian system by creating strict daily schedules for daily Zeitgeber activities. Since every person has a circadian system with its own characteristics and is subject to social obligations, the daily plans are personalized for each test person. Our hypothesis is that a regular exposure to Zeitgebers stabilizes behavioral and physiological circadian rhythms and thereby reduces the risk of alcohol relapses and depressive symptoms and facilitates physical recovery in AUD patients during the 1st weeks of their addiction therapy. Methods/design: The study is a 6-weeks single site trial with a controlled, randomized, single-blinded, parallel-group design including patients with a diagnosis of AUD. The study runs parallel to the standard addiction therapy of the clinic. Patients are randomly assigned to either an intervention group (DAILY) or a sham control group (placebo treatment). Questionnaires and physiological assessments of both groups are conducted before and immediately after the intervention or control treatment. According to our hypothesis, the primary outcomes of this study are improvements of regularity, alcohol consumption, and relapse rate in AUD patients compared to AUD patients receiving control treatment. Secondary outcomes are reduced depressive symptoms and increased physical recovery. Discussion: This study is a randomized controlled trial to investigate the efficacy of a personalized circadian Zeitgeber therapy as an adjunctive treatment for alcohol use disorder patients. The overall goal of this and more extended future studies is the development of an adjunctive therapy for AUD patients that is uncomplicated in its use and easy to implement in the clinical and everyday routine. Trial registration: This study is registered at the German Clinical Trial Register with the trial number DRKS00019093 on November 28, 2019.

Stress and glucocorticoid modulation of feeding and metabolism

This perspective highlights research presented as part of the symposium entitled, "Stress and Glucocorticoid Modulation of Feeding and Metabolism" at the 2018 Neurobiology of Stress Workshop held in Banff, AB, Canada. The symposium comprised five researchers at different career stages who each study different aspects of the interaction between the stress response and metabolic control. Their collective results reveal the complexity of this relationship in terms of behavioural and physiological outcomes. Their work emphasizes the need to consider the level of interaction (cellular, tissue, systems) as well as the timing and context in which the interaction is studied. Rather than a comprehensive review on the work presented at the Symposium, here we discuss recurring themes that emerged at the biennial workshop, which address new avenues of research that will drive the field forward.

Circadian Rhythm Disruption Aggravates DSS-Induced Colitis in Mice with Fecal Calprotectin as a Marker of Colitis Severity

BACKGROUND

Inflammatory bowel disease (IBD) is a chronic immunologically mediated pathology that remains a major health burden. Circadian rhythm disruption leads to a deregulation in the immune system which is a major risk factor for IBD.

AIMS

Since fecal calprotectin (FC) has been a useful tool for monitoring IBD, we aimed to evaluate the effect of circadian rhythm alteration on gut inflammation status and whether FC is associated with the severity of colitis.

METHODS

C57BL/6J mice were exposed to circadian shifts for 3 months, and then colitis was induced by 2% dextran sulfate sodium (DSS). Colitis was evaluated according to clinical symptoms and histological scoring. Plasma and intestinal inflammatory and permeability markers as well as fecal and intestinal calprotectin were assessed.

RESULTS

Circadian shifts aggravated DSS-induced colitis with increased diarrhea, flatulence, and fecal blood associated with decreased colon length. In addition, intestinal cryptic architecture was lost with the presence of increased inflammation, mucosal muscle thickening, and cryptic abscesses. Plasma tumor necrosis factor alpha, interleukin 1 beta, interleukin 6, and C-reactive protein upregulations were paralleled by the deterioration of intestinal permeability. Calprotectin expression and distribution increased in the intestines and feces of shifted animals, and levels highly correlated with the increases in intestinal inflammation and permeability.

CONCLUSIONS

Circadian rhythm disruption aggravates DSS-induced colitis, whereas fecal and intestinal calprotectin associates with the severity of disease. Calprotectin might be a useful marker and tool for assessing patients at risk of IBD due to lifestyles with disruptive sleep patterns.

CRISPR/Cas-mediated Fubp1 silencing disrupts circadian oscillation of Per1 protein via downregulating Syncrip expression

Most living organisms have physiological and behavioral circadian rhythms controlled by molecular clocks. In mammals, several core clock genes show self-perpetuating oscillation profiles of their messenger RNAs (mRNAs) and proteins through an auto-regulatory transcription-translation feedback loop (TTFL). As a critical component in the molecular clock system, Period 1 (Per1) contributes to the maintenance of circadian rhythm duration predominantly in peripheral clocks. Alterations in Per1 expression and oscillating patterns lead to the development of cancers as well as circadian rhythm abnormalities. In this study, we demonstrate that the phasic profile of Per1 protein was clearly disrupted in CRISPR/Cas-mediated Fubp1-deficient cells. Although Fubp1 does not show rhythmic expression, Fubp1 upregulates the mRNA and protein level of Syncrip, the main post-transcriptional regulator of Per1 protein oscillation. In addition to the diverse physiological functions of Fubp1, including cell-cycle regulation and cellular metabolic control, our results suggest new roles for Fubp1 in the molecular clock system.

Lifetime coffee consumption, pineal gland volume, and sleep quality in late life

Study Objectives

Previous studies have shown that coffee consumption may suppress the production of melatonin in pinealocytes through competitive inhibition of adenosine A2 receptors by caffeine. We investigated the impact of lifetime coffee consumption on pineal gland volume and the resulting effects on sleep quality.

Methods

We enrolled 162 cognitively normal elderly individuals among the participants in the Korean Longitudinal Study on Cognitive Aging and Dementia. We evaluated the patterns and amounts of coffee consumption using a study-specific standardized interview and assessed sleep quality using the Pittsburgh Sleep Quality Index. We measured the volume of pineal parenchyma (VPP) by manually segmenting the pineal gland on high-resolution three-dimensional T1-weighted magnetic resonance images. We examined the impact of lifetime coffee consumption on the VPP and the resulting effects on sleep quality using analysis of covariance, multiple linear regression, and mediation analyses.

Results

We found that smaller VPP was associated with higher cumulative lifetime coffee consumption. Participants who consumed more than 60 cup-years of coffee had VPPs that were smaller by about 20% than individuals who consumed less than 60 cup-years of coffee. The VPP mediated the association between lifetime coffee consumption and sleep efficiency and quality.

Conclusions

Our findings suggest that high lifetime coffee consumption may reduce VPP, and that this reduction in VPP may impair the quality of sleep in late life.

Circadian Rest-Activity Pattern Changes in Aging and Preclinical Alzheimer Disease

Importance

Circadian rhythm disturbances occur in symptomatic Alzheimer disease (AD) and have been hypothesized to contribute to disease pathogenesis. However, it is unknown whether circadian changes occur during the presymptomatic phase of the disease.

Objective

To examine the associations between circadian function, aging, and preclinical AD pathology in cognitively normal adults.

Design, Setting, and Participants

This cross-sectional study was conducted using community volunteers from the Knight Alzheimer's Disease Research Center at Washington University in St Louis. Cognitively normal participants (n = 205) underwent 7 to 14 days of actigraphy in their home environment between 2010 and 2012, in addition to clinical assessment, amyloid imaging with Pittsburgh Compound B (PiB), and cerebrospinal fluid biomarker collection. Data collected from 3 years before to 6 months after actigraphy were included. Sixteen participants were excluded owing to incomplete data collection.

Main Outcomes and Measures

Circadian rhythm analysis was performed on actigraphy data using 3 methods: cosinor, nonparametric, and empirical mode decomposition. Preclinical AD was assessed by longitudinal clinical assessment, amyloid imaging with PiB, and cerebrospinal fluid biomarker collection.

Results

Data from 189 participants were included in the analyses. The mean (SD) age was 66.6 (8.3) years, and 121 participants (64%) were women. Older age (β = .247; P = .003) and male sex (β = .170; P = .04), in the absence of amyloid pathology, were associated with a significant increase in intradaily variability, a nonparametric measure of rest-activity rhythm fragmentation, as well as decreased amplitude by several measures. After correction for age and sex, the presence of preclinical amyloid plaque pathology, assessed by positive PiB imaging (mean [SD], 0.804 [0.187] for PiB negative vs 0.875 [0.178] for PiB positive; P = .05) or increasing cerebrospinal fluid phosphorylated-tau to amyloid β 42 ratio (β = .231; P = .008), was associated with increased intradaily variability, indicating rest-activity rhythm fragmentation.

Conclusions and Relevance

Preclinical AD is associated with rest-activity rhythm fragmentation, independent of age or sex. Aging was also associated with circadian dysfunction independently of preclinical AD pathology, particularly in men. The presence of circadian rhythm abnormalities in the preclinical phase of AD suggests that circadian dysfunction could contribute to early disease pathogenesis or serve as a biomarker of preclinical disease.

The Role of the Molecular Clock in Promoting Skeletal Muscle Growth and Protecting against Sarcopenia

The circadian clock has a critical role in many physiological functions of skeletal muscle and is essential to fully understand the precise underlying mechanisms involved in these complex interactions. The importance of circadian expression for structure, function and metabolism of skeletal muscle is clear when observing the muscle phenotype in models of molecular clock disruption. Presently, the maintenance of circadian rhythms is emerging as an important new factor in human health, with disruptions linked to ageing, as well as to the development of many chronic diseases, including sarcopenia. Therefore, the aim of this review is to present the latest findings demonstrating how circadian rhythms in skeletal muscle are important for maintenance of the cellular physiology, metabolism and function of skeletal muscle. Moreover, we will present the current knowledge about the tissue-specific functions of the molecular clock in skeletal muscle.

Enhanced Circadian Entrainment in Mice and Its Utility under Human Shiftwork Schedules

The circadian system is generally considered to be incapable of adjusting to rapid changes in sleep/work demands. In shiftworkers this leads to chronic circadian disruption and sleep loss, which together predict underperformance at work and negative health consequences. Two distinct experimental protocols have been proposed to increase circadian flexibility in rodents using dim light at night: rhythm bifurcation and T-cycle (i.e., day length) entrainment. Successful translation of such protocols to human shiftworkers could facilitate alignment of internal time with external demands. To assess entrainment flexibility following bifurcation and exposure to T-cycles, mice in Study 1 were repeatedly phase-shifted. Mice from experimental conditions rapidly phase-shifted their activity, while control mice showed expected transient misalignment. In Study 2 and 3, mice followed a several weeks-long intervention designed to model a modified DuPont or Continental shiftwork schedule, respectively. For both schedules, bifurcation and nocturnal dim lighting reduced circadian misalignment. Together, these studies demonstrate proof of concept that mammalian circadian systems can be rendered sufficiently flexible to adapt to multiple, rapidly changing shiftwork schedules. Flexible adaptation to exotic light-dark cycles likely relies on entrainment mechanisms that are distinct from traditional entrainment.

Mitochondria, Metabolism, and Redox Mechanisms in Psychiatric Disorders

Significance: Our current knowledge of the pathophysiology and molecular mechanisms causing psychiatric disorders is modest, but genetic susceptibility and environmental factors are central to the etiology of these conditions. Autism, schizophrenia, bipolar disorder and major depressive disorder show genetic gene risk overlap and share symptoms and metabolic comorbidities. The identification of such common features may provide insights into the development of these disorders. Recent Advances: Multiple pieces of evidence suggest that brain energy metabolism, mitochondrial functions and redox balance are impaired to various degrees in psychiatric disorders. Since mitochondrial metabolism and redox signaling can integrate genetic and environmental environmental factors affecting the brain, it is possible that they are implicated in the etiology and progression of psychiatric disorders. Critical Issue: Evidence for direct links between cellular mitochondrial dysfunction and disease features are missing. Future Directions: A better understanding of the mitochondrial biology and its intracellular connections to the nuclear genome, the endoplasmic reticulum and signaling pathways, as well as its role in intercellular communication in the organism, is still needed. This review focuses on the findings that implicate mitochondrial dysfunction, the resultant metabolic changes and oxidative stress as important etiological factors in the context of psychiatric disorders. We also propose a model where specific pathophysiologies of psychiatric disorders depend on circuit-specific impairments of mitochondrial dysfunction and redox signaling at specific developmental stages.

Lifespan is unaffected by size and direction of daily phase shifts in Nasonia, a hymenopteran insect with strong circadian light resetting

Most organisms have an endogenous circadian clock with a period length of approximately 24 h that enables adaptation, synchronization and anticipation to environmental cycles. The circadian system (circa = about or around, diem = a day) may provide evolutionary benefits when entrained to the 24-h light-dark cycle. The more the internal circadian period (τ) deviates from the external light-dark cycle, the larger the daily phase shifts need to be to synchronize to the environment. In some species, large daily phase shifts reduce survival rate. Here we tested this 'resonance fitness hypothesis' on the diurnal wasp Nasonia vitripennis, which exhibits a large latitudinal cline in free-running period with longer circadian period lengths in the north than in the south. Longevity was measured in northern and southern wasps placed into light-dark cycles (T-cycles) with periods ranging from 20 h to 28 h. Further, locomotor activity was recorded to estimate range and phase angle of entrainment under these various T-cycles. A light pulse induced phase response curve (PRC) was measured in both lines to understand entrainment results. We expected a concave survival curve with highest longevity at T = τ and a reduction in longevity the further τ deviates from T (τ/T<>1). Our results do not support this resonance fitness hypothesis. We did not observe a reduction in longevity when τ deviates from T. Our results may be understood by the strong circadian light resetting mechanism (type 0 PRC) to single light pulses that we measured in Nasonia, resulting in: (1) the broad range of entrainment, (2) the wide natural variation in circadian free-running period, and (3) the lack of reduced survival when τ/T ratio's deviates from 1. Together this indicates that circadian adaption to latitude may lead to changes in circadian period and light response, without negative influences on survival.

Circadian Rhythms and Measures of CNS/Autonomic Interaction

The physiological role and relevance of the mechanisms sustaining circadian rhythms have been acknowledged. Abnormalities of the circadian and/or sleep-wakefulness cycles can result in major metabolic disorders or behavioral/professional inadequacies and stand as independent risk factors for metabolic, psychiatric, and cerebrovascular disorders and early markers of disease. Neuroimaging and clinical evidence have documented functional interactions between autonomic (ANS) and CNS structures that are described by a concept model (Central Autonomic Network) based on the brain-heart two-way interplay. The circadian rhythms of autonomic function, ANS-mediated processes, and ANS/CNS interaction appear to be sources of variability adding to a variety of environmental factors, and may become crucial when considering the ANS major role in internal environment constancy and adaptation that are fundamental to homeostasis. The CNS/ANS interaction has not yet obtained full attention and systematic investigation remains overdue.

Circadian regulation of depression: A role for serotonin

Synchronizing circadian (24 h) rhythms in physiology and behavior with the environmental light-dark cycle is critical for maintaining optimal health. Dysregulation of the circadian system increases susceptibility to numerous pathological conditions including major depressive disorder. Stress is a common etiological factor in the development of depression and the circadian system is highly interconnected to stress-sensitive neurotransmitter systems such as the serotonin (5-hydroxytryptamine, 5-HT) system. Thus, here we propose that stress-induced perturbation of the 5-HT system disrupts circadian processes and increases susceptibility to depression. In this review, we first provide an overview of the basic components of the circadian system. Next, we discuss evidence that circadian dysfunction is associated with changes in mood in humans and rodent models. Finally, we provide evidence that 5-HT is a critical factor linking dysregulation of the circadian system and mood. Determining how these two systems interact may provide novel therapeutic targets for depression.

The role of sleep deprivation and circadian rhythm disruption as risk factors of Alzheimer's disease

Emerging evidence suggests that sleep deprivation (SD) and circadian rhythm disruption (CRD) may interact and increase the risk for the development of Alzheimer's disease (AD). This review inspects different pathophysiological aspects of SD and CRD, and shows that the two may impair the glymphatic-vascular-lymphatic clearance of brain macromolecules (e.g., β-amyloid and microtubule associated protein tau), increase local brain oxidative stress and diminish circulatory melatonin levels. Lastly, this review looks into the potential association between sleep and circadian rhythm with stress granule formation, which might be a new mechanism along the AD pathogenic pathway. In summary, SD and CRD is likely to be associated with a positive risk in developing Alzheimer's disease in humans.

Sustained rescue of prefrontal circuit dysfunction by antidepressant-induced spine formation

The neurobiological mechanisms underlying the induction and remission of depressive episodes over time are not well understood. Through repeated longitudinal imaging of medial prefrontal microcircuits in the living brain, we found that prefrontal spinogenesis plays a critical role in sustaining specific antidepressant behavioral effects and maintaining long-term behavioral remission. Depression-related behavior was associated with targeted, branch-specific elimination of postsynaptic dendritic spines on prefrontal projection neurons. Antidepressant-dose ketamine reversed these effects by selectively rescuing eliminated spines and restoring coordinated activity in multicellular ensembles that predict motivated escape behavior. Prefrontal spinogenesis was required for the long-term maintenance of antidepressant effects on motivated escape behavior but not for their initial induction.

Effects of 50 Hz magnetic fields on circadian rhythm control in mice

Artificial light and power frequency magnetic fields are ubiquitous in the built environment. Light is a potent zeitgeber but it is unclear whether power frequency magnetic fields can influence circadian rhythm control. To study this possibility, 8-12-week-old male C57BL/6J mice were exposed for 30 min starting at zeitgeber time 14 (ZT14, 2 h into the dark period of the day) to 50 Hz magnetic fields at 580 μT using a pair of Helmholtz coils and/or a blue LED light at 700 lux or neither. Our experiments revealed an acute adrenal response to blue light, in terms of increased adrenal per1 gene expression, increased serum corticosterone levels, increased time spent sleeping, and decreased locomotor activity (in all cases, P < 0.0001) compared to an unexposed control group. There appeared to be no modulating effect of the magnetic fields on the response to light, and there was also no effect of the magnetic fields alone (in both cases, P > 0.05) except for a decrease in locomotor activity (P < 0.03). Gene expression of the cryptochromes cry1 and cry2 in the adrenals, liver, and hippocampus was also not affected by exposures (in all cases, P > 0.05). In conclusion, these results suggest that 50 Hz magnetic fields do not significantly affect the acute light response to a degree that can be detected in the adrenal response. Bioelectromagnetics. 2019;9999:XX-XX. © 2019 Bioelectromagnetics Society.

Meal Timing, Aging, and Metabolic Health

A growing body of evidence suggests that meal timing is an important factor for metabolic regulation and that the circadian clock tightly interacts with metabolic functions. The proper functioning of the circadian clock is critical for maintaining metabolic health. Therefore, chrononutrition, a novel discipline which investigates the relation between circadian rhythms, nutrition, and metabolism, has attracted increasing attention in recent years. Circadian rhythms are strongly affected by obesity, type 2 diabetes, and other dietary-induced metabolic diseases. With increasing age, the circadian system also undergoes significant changes which contribute to the dysregulation of metabolic rhythms. Metabolic diseases are a major health concern, particularly in light of a growing aging population, and effective approaches for their prevention and treatment are urgently needed. Recently, animal studies have impressively shown beneficial effects of several dietary patterns (e.g., caloric restriction or time-restricted feeding) on circadian rhythms and metabolic outcomes upon nutritional challenges. Whether these dietary patterns show the same beneficial effects in humans is, however, less well studied. As indicated by recent studies, dietary approaches might represent a promising, attractive, and easy-to-adapt strategy for the prevention and therapy of circadian and metabolic disturbances in humans of different age.

The physiological significance of the circadian dynamics of the HPA axis: Interplay between circadian rhythms, allostasis and stress resilience

Circadian time-keeping mechanisms preserve homeostasis by synchronizing internal physiology with predictable variations in the environment and temporally organize the activation of physiological signaling mechanisms to promote survival and optimize the allocation of energetic resources. In this paper, we highlight the importance of the robust circadian dynamics of allostatic mediators, with a focus on the hypothalamic-pituitary-adrenal (HPA) axis, for the optimal regulation of host physiology and in enabling organisms to adequately respond and adapt to physiological stressors. We review studies showing how the chronic disruption of circadian rhythms can result in the accumulation of allostatic load, which impacts the appropriate functioning of physiological systems and diminishes the resilience of internal systems to adequately respond to subsequent stressors. A careful consideration of circadian rhythm dynamics leads to a more comprehensive characterization of individual variability in allostatic load and stress resilience. Finally, we suggest that the restoration of circadian rhythms after pathological disruption can enable the re-engagement of allostatic mechanisms and re-establish stress resilience.

The Clock Mechanism Influences Neurobiology and Adaptations to Heart Failure in Clock∆19/∆19 Mice With Implications for Circadian Medicine

In this study we investigated the role of the circadian mechanism on cognition-relevant brain regions and neurobiological impairments associated with heart failure (HF), using murine models. We found that the circadian mechanism is an important regulator of healthy cognitive system neurobiology. Normal Clock∆19/∆19 mice had neurons with smaller apical dendrite trees in the medial prefrontal cortex (mPFC), and hippocampus, showed impaired visual-spatial memory, and exhibited lower cerebrovascular myogenic tone, versus wild types (WT). We then used the left anterior descending coronary artery ligation model to investigate adaptations in response to HF. Intriguingly, adaptations to neuron morphology, memory, and cerebrovascular tone occurred in differing magnitude and direction between Clock∆19/∆19 and WT mice, ultimately converging in HF. To investigate this dichotomous response, we performed microarrays and found genes crucial for growth and stress pathways that were altered in Clock∆19/∆19 mPFC and hippocampus. Thus these data demonstrate for the first time that (i) the circadian mechanism plays a role in neuron morphology and function; (ii) there are changes in neuron morphology and function in HF; (iii) CLOCK influences neurobiological gene adaptations to HF at a cellular level. These findings have clinical relevance as patients with HF often present with concurrent neurocognitive impairments. There is no cure for HF, and new understanding is needed to reduce morbidity and improve the quality of life for HF patients.

The pathogenesis of obesity

Body fat mass increases when energy intake exceeds energy expenditure. In the long term, a positive energy balance will result in obesity. The worldwide prevalence of obesity has increased dramatically, posing a serious threat to human health. Therefore, insight in the pathogenesis of obesity is important to identify novel prevention and treatment strategies. This review describes the physiology of energy expenditure and energy intake in the context of body weight gain in humans. We focus on the components of energy expenditure and the regulation of energy intake. Finally, we describe rare monogenetic causes leading to an impairment in central regulation of food intake and obesity.

Retrospective Analysis of the Effects of Identification Procedures and Cage Changing by Using Data from Automated, Continuous Monitoring

Many variables can influence animal behavior and physiology, potentially affecting scientific study outcomes. Laboratory and husbandry procedures-including handling, cage cleaning, injections, blood collection, and animal identification-may produce a multitude of effects. Previous studies have examined the effects of such procedures by making behavioral and physiologic measurements at specific time points; this approach can be disruptive and limits the frequency or duration of observations. Because these procedures can have both acute and long-term effects, the behavior and physiology of animals should be monitored continuously. We performed a retrospective data analysis on the effects of 2 routine procedures, animal identification and cage changing, on motion and breathing rates of mice continuously monitored in the home cage. Animal identification, specifically tail tattooing and ear tagging, as well as cage changing, produced distinct and reproducible postprocedural changes in spontaneous motion and breathing rate patterns. Behavioral and physiologic changes lasted approximately 2 d after tattooing or ear tagging and 2 to 4 d for cage changing. Furthermore, cage changes showed strain-, sex-, and time-of-day-dependent responses but not age-dependent differences. Finally, by reviewing data from a rodent model of multiple sclerosis as a retrospective case study, we documented that cage changing inadvertently affected experimental outcomes. In summary, we demonstrate how retrospective analysis of data collected continuously can provide high-throughput, meaningful, and longitudinal insights in to how animals respond to routine procedures.

Effects of high fat diet and chronic circadian challenge on glucocorticoid regulation in C57BL/6J mice

Both high-fat diet and chronic circadian disruption have been associated with increased incidence of obesity and type 2 diabetes in humans. Chronically elevated glucocorticoids, which have considerable impacts on physiological processes such as intermediary metabolism, inflammation, and fat metabolism, have also been implicated in insulin resistance associated with obesity and diabetes. In this study, the effects of high-fat diet (HFD) or chronic circadian challenge in C57BL/6J mice on basal and stress-induced corticosterone (CORT) and blood glucose levels were assessed. Baseline and stress-induced levels of CORT, insulin and glucose were measured before and after acute restraint stress at 4 different time points across the light-dark cycle (LD) in male C57BL/6J mice maintained for 8 weeks on HFD or regular chow. After 8 weeks on diet, baseline CORT levels in HFD mice were of similar magnitude but more variable than in mice on low-fat diet, rendering their daily fluctuations arrhythmic according to statistical analysis. Baseline glucose measures were unchanged despite significant 3-fold increases in baseline insulin levels in HFD mice at all time points sampled. Restraint stress yielded considerable decreases in insulin levels and increases in CORT and glucose levels that were significantly exaggerated in the early active period in mice on HFD. These results indicate a circadian influence on stress responses after prolonged consumption of high fat diet. In a separate experiment, C57BL/6J mice were subjected to 6 weeks of an alternating light-dark (LD) cycle comprised of 6 h advances and delays of phase every 5 days to keep the circadian system from establishing consistent circadian entrainment, with a control group of mice under a regular 12:12 LD cycle. While body weights were not significantly affected by chronic circadian challenge, the basal CORT rhythm in alternating-LD mice was significantly dampened. Stress-induced CORT in alternating LD were no different from regular LD group with the exception of ZT 18, at which time the stress response was moderately suppressed compared to controls. These results support that high-fat diet may be contributing to health disorders such as obesity and diabetes in a manner different from any effects of chronic circadian disruption.

Circadian misalignment has differential effects on affective behavior following exposure to controllable or uncontrollable stress

In modern 24 h society, circadian disruption is pervasive, arising from night shift work, air travel across multiple time zones, irregular sleep schedules, and exposure to artificial light at night. Disruption of the circadian system is associated with many adverse health consequences, including mood disorders. Here we investigate whether inducing circadian misalignment using a phase advance protocol interferes with the ability to cope with a stressor, thereby increasing susceptibility to the negative consequences of stress. Male rats were maintained on a standard 12:12 light: dark (LD) cycle or subjected to a chronic phase advance (CPA) protocol involving 4 weekly 6 h phase shifts (earlier light onset) of the LD cycle. Rats were then exposed to escapable stress (ES), inescapable stress (IS), or no stress (home cage control; HC) and performance on juvenile social exploration and active escape learning in the two-way shuttlebox test was assessed 24 h and 48 h following stress, respectively. CPA alone had no effect on pre-stress juvenile social exploration, and it also did not interfere with the protective effect of ES on the stress-induced reduction in juvenile social exploration. In contrast, CPA impaired escape learning in the two-way shuttlebox to the same extent as IS in all subjects, regardless of stress history. Additionally, CPA produced somatic alterations that included increased body mass, increased epididymal adiposity, and decreased adrenal mass. These data indicate that CPA differentially modulated the stress-protective effects of behavioral control depending on the type of affective behavior examined.

Alterations of circadian rhythms and their impact on obesity, metabolic syndrome and cardiovascular diseases

Circadian system is comprised by central circadian pacemaker and several peripheral clocks that receive information from the external environment, synchronizing the circadian clocks. It is widely known that physiology is rhythmic and that the rupture of this rhythmicity can generate serious consequences. Circadian clocks, led by suprachiasmatic nucleus (SCN) in the central nervous system, are the responsible for generating this biological rhythmicity. These clocks are affected by external signals such as light (changes between day and night) and feeding rhythms. In this review, the basic principles of the circadian system and current knowledge of biological clocks are addressed, analyzing the relationship between circadian system, food intake, nutrition, and associated metabolic processes. In addition, the consequences occurring when these systems are not well coordinated with each other, such as the development of cardiovascular and metabolic pathologies, will be thoroughly discussed.

Circadian Etiology of Type 2 Diabetes Mellitus

The epidemic of Type 2 diabetes mellitus necessitates development of novel therapeutic and preventative strategies to attenuate expansion of this debilitating disease. Evidence links the circadian system to various aspects of diabetes pathophysiology and treatment. The aim of this review will be to outline the rationale for therapeutic targeting of the circadian system in the treatment and prevention of Type 2 diabetes mellitus and consequent metabolic comorbidities.

Misaligned core body temperature rhythms impact cognitive performance of hospital shift work nurses

Circadian rhythms greatly influence 24-h variation in cognition in nearly all organisms, including humans. Circadian clock impairment and sleep disruption are detrimental to hippocampus-dependent memory and negatively influence the acquisition and recall of learned behaviors. The circadian clock can become out of sync with the environment during circadian misalignment. Shift work represents a real-world model of circadian misalignment that can be studied for its physiological implications. The present study aimed to test the hypothesis that circadian misalignment disrupts vigilance and cognitive performance on occupationally relevant tasks using shift work as a model. As such, we sought to (1) explore the general effects of night- and day-shift worker schedules on sleep-wake parameters and core body temperature (CBT) phase, and (2) determine whether shift-type and CBT phase impact cognitive performance and vigilance at the end of a 12-h shift. We observed a sample of day-shift and night-shift hospital nurses over a 10-day period. At the end of three, consecutive, 12-h shifts (7 pm-7am or 7am-7 pm), participants completed a cognitive battery assessing vigilance, cognitive throughput, and medication calculation fluency (via an investigator developed and tested metric). Night-shift nurses exhibited significantly greater sleep fragmentation as well as a greater disparity between their wake-time and time of CBT minimum compared to day-shift nurses. Night-shift nurses exhibited significantly slower cognitive proficiency at the end of their shifts, even after adjustment for CBT phase. These results suggest that circadian disruption and reduced sleep quality both contribute to cognitive functioning and performance.

Multilevel Interactions of Stress and Circadian System: Implications for Traumatic Stress

The dramatic fluctuations in energy demands by the rhythmic succession of night and day on our planet has prompted a geophysical evolutionary need for biological temporal organization across phylogeny. The intrinsic circadian timing system (CS) represents a highly conserved and sophisticated internal "clock," adjusted to the 24-h rotation period of the earth, enabling a nyctohemeral coordination of numerous physiologic processes, from gene expression to behavior. The human CS is tightly and bidirectionally interconnected to the stress system (SS). Both systems are fundamental for survival and regulate each other's activity in order to prepare the organism for the anticipated cyclic challenges. Thereby, the understanding of the temporal relationship between stressors and stress responses is critical for the comprehension of the molecular basis of physiology and pathogenesis of disease. A critical loss of the harmonious timed order at different organizational levels may affect the fundamental properties of neuroendocrine, immune, and autonomic systems, leading to a breakdown of biobehavioral adaptative mechanisms with increased stress sensitivity and vulnerability. In this review, following an overview of the functional components of the SS and CS, we present their multilevel interactions and discuss how traumatic stress can alter the interplay between the two systems. Circadian dysregulation after traumatic stress exposure may represent a core feature of trauma-related disorders mediating enduring neurobiological correlates of trauma through maladaptive stress regulation. Understanding the mechanisms susceptible to circadian dysregulation and their role in stress-related disorders could provide new insights into disease mechanisms, advancing psychochronobiological treatment possibilities and preventive strategies in stress-exposed populations.

A Systematic Review of Evidence for a Role of Rest-Activity Rhythms in Dementia

Background: Rest-activity rhythm (RAR) disruption may be a risk factor for dementia that can be objectively measured with wearable accelerometers. It is possible that risk monitoring and preventive interventions could be developed targeting RARs. To evaluate whether current evidence supports these applications, we systematically reviewed published studies linking RARs with dementia, its course, and mechanisms. Methods: Entering pre-defined search terms in PsycINFO, MEDLINE, and PubMed databases returned 192 unique titles. We identified 32 articles that met our primary inclusion criteria, namely, that they examined objective RAR measures in the context of dementia, cognition, or brain biomarkers. Results: Cross-sectional studies consistently found that people with dementia had less stable (5/6 studies), more fragmented (4/6 studies), lower amplitude rhythms (5/5 studies), that had a worse fit to 24-h models (3/3 studies). Findings from studies relating RARs to cognitive test performance (rather than diagnostic status) were more nuanced. RAR fragmentation was associated with neurodegeneration biomarkers in 2/2 studies; and 1/1 study found 24-h model fit related to hippocampal hyperactivation. Although 2/2 studies found RARs related to markers of cerebrovascular disease, the specific RARs and cerebrovascular disease measures were not consistent. Longitudinal studies (3/3 articles) reported that lower amplitude and worse 24-h rhythm fit predicted future cognitive impairment and executive function. However, interventions aimed at modifying RARs had mixed effects (e.g., 0/4 studies demonstrated effects of morning light on 24-h model fit; evening light was associated with improved 24-h fit in 2/2 studies reporting); these effects may be more evident in subgroups. Conclusions: Consistent evidence shows that dementia is associated with disrupted RARs. Importantly, recent studies have shown that RAR disruption is associated with dementia biomarkers and, prospectively, with the risk of cognitive impairment. Interventions mostly tried using bright light to modify RARs in people who already have dementia; these studies produced modest effects on RARs and did not show modification of dementia's course. Altogether, these findings suggest studies are needed to understand how RARs relate to changes in brain health earlier in the disease process. Better understanding of the biopsychosocial mechanisms linking RARs with future dementia risk can help further target intervention development.

Altered Regional Cerebral Blood Flow Associated with Mood and Sleep in Shift Workers: Cerebral Perfusion Magnetic Resonance Imaging Study

BACKGROUND AND PURPOSE

Shift work disrupts the body's circadian rhythms and increases the risk of health problems. Despite evidence of neuropsychological disturbances in shift workers (SW), the brain functional status as measured by brain perfusion in chronic shift work has not been evaluated previously. We investigated the regional cerebral blood flow (rCBF) in SW using perfusion MRI (pMRI) and evaluated the relationships between altered rCBF and sleep, mood, psychometric measures, and quality of life.

METHODS

Fifteen rotational SW and 15 day workers (DW) were enrolled. The participants were all female nurses working at a university-affiliated hospital. During 2 weeks of actigraphy they underwent pMRI scanning and psychometric testing on the last day immediately after working. Demographic characteristics, insomnia, daytime sleepiness, and mood were compared between the groups.

RESULTS

The participants were aged 35.3±2.9 years (mean±SD) and had been performing their current work for more than 2 years. The demographic characteristics did not differ between SW and DW, but the levels of insomnia, anxiety, depression, and hyperactivity-restlessness in psychometric measures were higher in SW than in DW. Cerebral perfusion in SW was significantly decreased in the cuneus, fusiform/parahippocampal gyri, and cerebellum of the right hemisphere, while it was increased in the inferior occipital gyrus of the left hemisphere. Perfusion changes in SW were significantly correlated with depression and insomnia severity. The onset and duration irregularity of sleep among SW were related to insomnia, mood, hyperactivity/ restlessness, and quality of life.

CONCLUSIONS

SW experience considerably more insomnia and mood disturbances than do DW, and this is significantly related to perfusion changes in multiple brain areas.

Coordination between Prefrontal Cortex Clock Gene Expression and Corticosterone Contributes to Enhanced Conditioned Fear Extinction Recall

Post-traumatic stress disorder (PTSD) is associated with impaired conditioned fear extinction learning, a ventromedial prefrontal cortex (vmPFC)-dependent process. PTSD is also associated with dysregulation of vmPFC, circadian, and glucocorticoid hormone function. Rats have rhythmic clock gene expression in the vmPFC that requires appropriate diurnal circulatory patterns of corticosterone (CORT), suggesting the presence of CORT-entrained intrinsic circadian clock function within the PFC. We examined the role of vmPFC clock gene expression and its interaction with CORT profiles in regulation of auditory conditioned fear extinction learning. Extinction learning and recall were examined in male rats trained and tested either in the night (active phase) or in the day (inactive phase). Using a viral vector strategy, Per1 and Per2 clock gene expression were selectively knocked down within the vmPFC. Circulating CORT profiles were manipulated via adrenalectomy (ADX) ± diurnal and acute CORT replacement. Rats trained and tested during the night exhibited superior conditioned fear extinction recall that was absent in rats that had knock-down of vmPFC clock gene expression. Similarly, the superior nighttime extinction recall was absent in ADX rats, but restored in ADX rats given a combination of a diurnal pattern of CORT and acute elevation of CORT during the postextinction training consolidation period. Thus, conditioned fear extinction learning is regulated in a diurnal fashion that requires normal vmPFC clock gene expression and a combination of circadian and training-associated CORT. Strategic manipulation of these factors may enhance the therapeutic outcome of conditioned fear extinction related treatments in the clinical setting.

Color matters: They would choose if they could (see)!

Concerning standardization of laboratory animal husbandry, only exiguous changes of habitat can potentially influence animal physiology or results of behavioral tests. Routinely, mice chow is dyed when different types of diets are dispensed. Given the fact that the dye itself has no effects on food odor or flavor, we wanted to test the hypothesis that the color of chow has an impact on food uptake in mice.

Twelve-week-old male mice of different strains (C57BL/6J, DBA/2J, C3H/HeJ, BALB/cJ; n = 12/strain) were single-housed in PhenoMaster® cages. After acclimatization standard mice chow in different colors was administered. Food intake was monitored as a two-alternative choice test of different color combinations.

All animals had an average food intake of 3 g/d and no preferences were observed when a combination of identically colored food was offered. Preference tests yielded significant aversion to blue food and significant attraction to yellow and green food in C57BL/6 and DBA/2J mice. In C3H/HeJ and BALB/cJ mice no color-related pattern occurred.

Selected mice strains have known differences concerning functionality of their visual sense. C57BL/6 and DBA/2 mice are considered to be normal sighted at testing age, BALB/c is representative for albino strains and C3H mice carry mutations resulting in retinal alterations. Results suggesting that normal-sighted mice would be selective concerning food color when given the choice. Nevertheless, this does not influence overall quantity of food intake when animals were provided solely with food colored with a single dye. Moreover, visually impaired mice showed no color-related food preferences.

Sleep/Wake Disruption in a Mouse Model of BLOC-1 Deficiency

Mice lacking a functional Biogenesis of Lysosome-related Organelles Complex 1 (BLOC-1), such as those of the pallid line, display cognitive and behavioural impairments reminiscent of those presented by individuals with intellectual and developmental disabilities. Although disturbances in the sleep/wake cycle are commonly lamented by these individuals, the underlying mechanisms, including the possible role of the circadian timing system, are still unknown. In this paper, we have explored sleep/circadian malfunctions and underlying mechanisms in BLOC-1-deficient pallid mice. These mutants exhibited less sleep behaviour in the beginning of the resting phase than wild-type mice with a more broken sleeping pattern in normal light-dark conditions. Furthermore, the strength of the activity rhythms in the mutants were reduced with significantly more fragmentation and lower precision than in age-matched controls. These symptoms were accompanied by an abnormal preference for the open arm in the elevated plus maze in the day and poor performance in the novel object recognition at night. At the level of the central circadian clock (the suprachiasmatic nucleus, SCN), loss of BLOC-1 caused subtle morphological changes including a larger SCN and increased expression of the relative levels of the clock gene Per2 product during the day but did not affect the neuronal activity rhythms. In the hippocampus, the pallid mice presented with anomalies in the cytoarchitecture of the Dentate Gyrus granule cells, but not in CA1 pyramidal neurones, along with altered PER2 protein levels as well as reduced pCREB/tCREB ratio during the day. Our findings suggest that lack of BLOC-1 in mice disrupts the sleep/wake cycle and performance in behavioural tests associated with specific alterations in cytoarchitecture and protein expression.

Is chronodisruption a vulnerability factor to stress?

Since the circadian system seems to modulate stress responses, this study aimed to evaluate if the combination of circadian strain and stress amplifies changes expected from each factor alone. Control Balb/c mice (12:12-NS) kept in standard 12:12 light:dark cycles (LD) and submitted to no stress procedures (NS) were compared to groups submitted to shortened LD (10:10-NS), chronic mild stress (CMS) but no circadian strain (12:12-CMS), or shortened LD followed by CMS (10:10-CMS). Rest-activity/temperature rhythms and body weight were assessed throughout the experiments. In Experiment 1 mice were submitted to 3 weeks of CMS; in Experiment 2 sucrose preference and light-dark tests were performed. Also, blood samples were collected at the end of Experiment 2 to assess metabolic parameters. Relative amplitude of temperature after CMS was increased only in the 10:10-CMS group, while body weight change was reduced during CMS regardless of LD intervention. During the CMS, the relative amplitude of temperature was negatively correlated with body weight gain. No differences in behavior and metabolic parameters were seen among groups. Identifying suitable research designs to investigate our hypothesis that circadian disturbances may increase vulnerability to stress-induced depression and anxiety is warranted.

Rat Strain and Housing Conditions Alter Oxidative Stress and Hormone Responses to Chronic Intermittent Hypoxia

Sleep apnea has been associated with elevated risk for metabolic, cognitive, and cardiovascular disorders. Further, the role of hypothalamic–pituitary–adrenal (HPA) activation in sleep apnea has been controversial in human studies. Chronic intermittent hypoxia (CIH) is a rodent model, which mimics the hypoxemia experienced by patients with sleep apnea. Most studies of CIH in rats have been conducted in the Sprague Dawley rat strain. Previously published literature suggests different strains of rats exhibit various responses to disease models, and these effects can be further modulated by the housing conditions experienced by each strain. This variability in response is similar to what has been observed in clinical populations, especially with respect to the HPA system. To investigate if strain or housing (individual or pair-housed) can affect the results of CIH (AHI 8 or 10) treatment, we exposed individual and pair-housed Sprague Dawley and Long-Evans male rats to 7 days of CIH treatment. This was followed by biochemical analysis of circulating hormones, oxidative stress, and neurodegenerative markers. Both strain and housing conditions altered oxidative stress generation, hyperphosphorylated tau protein (tau tangles), circulating corticosterone and adrenocorticotropic hormone (ACTH), and weight metrics. Specifically, pair-housed Long-Evans rats were the most sensitive to CIH, which showed a significant association between oxidative stress generation and HPA activation under conditions of AHI of 8. These results suggest both strain and housing conditions can affect the outcomes of CIH.

The case for a chronobiological approach to neonatal care

Time of day is a critical factor for most biological functions, but concepts from the field of chronobiology have yet to be fully translated to clinical practice. Circadian rhythms, generated internally and synchronised to the external environment, promote function and support survival in almost every living species. Fetal circadian rhythms can be observed in utero from 30weeks gestation, coupled to the maternal rhythm, but synchronise to the external environment only after birth. Important cues for synchronisation include the light/dark cycle, the timing of feeding, and exposure to melatonin in breast milk. Disruption to these cues may occur during admission to the neonatal intensive care unit. This can impair the development of circadian rhythms, and influence survival and function in the neonatal period, with a potential to impact health and well-being throughout adult life. Here we outline the rationale and evidence to support a chronobiological approach to neonatal care.

Effects of circadian misalignment on sleep in mice

Circadian rhythms and sleep-wake history determine sleep duration and intensity, and influence subsequent waking. Previous studies have shown that T cycles - light-dark (LD) cycles differing from 24 h - lead to acute changes in the daily amount and distribution of waking and sleep. However, little is known about the long-term effects of T cycles. Here we performed continuous 10 day recording of electroencephalography (EEG), locomotor activity and core body temperature in C57BL/6 mice under a T20 cycle, to investigate spontaneous sleep and waking at baseline compared with when the circadian clock was misaligned and then re-aligned with respect to the external LD cycle. We found that the rhythmic distribution of sleep was abolished during misalignment, while the time course of EEG slow wave activity (1–4 Hz) was inverted compared to baseline. Although the typical light-dark distribution of NREM sleep was re-instated when animals were re-aligned, slow wave activity during NREM sleep showed an atypical increase in the dark phase, suggesting a long-term effect of T cycles on sleep intensity. Our data show that circadian misalignment results in previously uncharacterised long-term effects on sleep, which may have important consequences for behaviour.

Recurring circadian disruption alters circadian clock sensitivity to resetting

A single phase advance of the light:dark (LD) cycle can temporarily disrupt synchrony of neural circadian rhythms within the suprachiasmatic nucleus (SCN) and between the SCN and peripheral tissues. Compounding this, modern life can involve repeated disruptive light conditions. To model chronic disruption to the circadian system, we exposed male mice to more than a month of a 20-hr light cycle (LD10:10), which mice typically cannot entrain to. Control animals were housed under LD12:12. We measured locomotor activity and body temperature rhythms in vivo, and rhythms of PER2::LUC bioluminescence in SCN and peripheral tissues ex vivo. Unexpectedly, we discovered strong effects of the time of dissection on circadian phase of PER2::LUC bioluminescent rhythms, which varied across tissues. White adipose tissue was strongly reset by dissection, while thymus phase appeared independent of dissection timing. Prior light exposure impacted the SCN, resulting in strong resetting of SCN phase by dissection for mice housed under LD10:10, and weak phase shifts by time of dissection in SCN from control LD12:12 mice. These findings suggest that exposure to circadian disruption may desynchronize SCN neurons, increasing network sensitivity to perturbations. We propose that tissues with a weakened circadian network, such as the SCN under disruptive light conditions, or with little to no coupling, for example, some peripheral tissues, will show increased resetting effects. In particular, exposure to light at inconsistent circadian times on a recurring weekly basis disrupts circadian rhythms and alters sensitivity of the SCN neural pacemaker to dissection time.