The central circadian timing system

Grape Seed Proanthocyanidin Extract Attenuates Cafeteria-Diet-Induced Liver Metabolic Disturbances in Rats: Influence of Photoperiod

This study investigated the influence of photoperiod (day length) on the efficacy of grape seed proanthocyanidin extract (GSPE) in mitigating metabolic disorders in obese rats fed a cafeteria diet. Rats were exposed to standard (L12), long (L18), or short (L6) photoperiods and treated with GSPE or vehicle. In the standard photoperiod, GSPE reduced body weight gain (50.5%), total cholesterol (37%), and triglycerides (34.8%), while increasing the expression of hepatic metabolic genes. In the long photoperiod, GSPE tended to decrease body weight gain, increased testosterone levels (68.3%), decreased liver weight (12.4%), and decreased reverse serum amino acids. In the short photoperiod, GSPE reduced glycemia (~10%) and lowered triglyceride levels (38.5%), with effects modified by diet. The standard photoperiod showed the greatest efficacy against metabolic syndrome-associated diseases. The study showed how day length affects GSPE's benefits and underscores considering biological rhythms in metabolic disease therapies.

Neuronal reprogramming of mouse and human fibroblasts using transcription factors involved in suprachiasmatic nucleus development

The hypothalamic suprachiasmatic nucleus (SCN) is composed of heterogenous populations of neurons that express signaling peptides such as vasoactive intestinal polypeptide (VIP) and arginine vasopressin (AVP) and regulate circadian rhythms in behavior and physiology. SCN neurons acquire functional and morphological specializations from waves of transcription factors (TFs) that are expressed during neurogenesis. However, the in vitro generation of SCN neurons has never been achieved. Here we supplemented a highly efficient neuronal conversion protocol with TFs that are expressed during SCN neurogenesis, namely Six3, Six6, Dlx2, and Lhx1. Neurons induced from mouse and human fibroblasts predominantly exhibited neuronal properties such as bipolar or multipolar morphologies, GABAergic neurons with expression of VIP. Our study reveals a critical contribution of these TFs to the development of vasoactive intestinal peptide (Vip) expressing neurons in the SCN, suggesting the regenerative potential of neuronal subtypes contained in the SCN for future SCN regeneration and in vitro disease remodeling.

Potential neural substrates underlying circadian and olfactory disruptions in preclinical Alzheimer's disease

Alzheimer's disease (AD) is the leading cause of dementia, with over 45 million patients worldwide, and poses significant economic and emotional burdens to both patients and caregivers, significantly raising the number of those affected. Unfortunately, much of the existing research on the disease only addresses a small subset of associated symptomologies and pathologies. In this review, we propose to target the earliest stages of the disease, when symptomology first arises. In these stages, before the onset of hallmark symptoms of AD such as cognitive impairments and memory loss, circadian and olfactory disruptions arise and are detectable. Functional similarities between circadian and olfactory systems provide a basis upon which to seek out common mechanisms in AD which may target them early on in the disease. Existing studies of interactions between these systems, while intriguing, leave open the question of the neural substrates underlying them. Potential substrates for such interactions are proposed in this review, such as indirect projections that may functionally connect the two systems and dopaminergic signaling. These substrates may have significant implications for mechanisms underlying disruptions to circadian and olfactory function in early stages of AD. In this review, we propose early detection of AD using a combination of circadian and olfactory deficits and subsequent early treatment of these deficits may provide profound benefits to both patients and caregivers. Additionally, we suggest that targeting research toward the intersection of these two systems in AD could uncover mechanisms underlying the broader set of symptoms and pathologies that currently elude researchers.

A brainstem to circadian system circuit links Tau pathology to sundowning-related disturbances in an Alzheimer's disease mouse model

Alzheimer's disease (AD) patients exhibit progressive disruption of entrained circadian rhythms and an aberrant circadian input pathway may underlie such dysfunction. Here we examine AD-related pathology and circadian dysfunction in the APPSwe-Tau (TAPP) model of AD. We show these mice exhibit phase delayed body temperature and locomotor activity with increases around the active-to-rest phase transition. Similar AD-related disruptions are associated with sundowning, characterized by late afternoon and early evening agitation and aggression, and we show TAPP mice exhibit increased aggression around this transition. We show such circadian dysfunction and aggression coincide with hyperphosphorylated Tau (pTau) development in lateral parabrachial (LPB) neurons, with these disturbances appearing earlier in females. Finally, we show LPB neurons, including those expressing dynorphin (LPBdyn), project to circadian structures and are affected by pTau, and LPBdyn ablations partially recapitulate the hyperthermia of TAPP mice. Altogether we link pTau in a brainstem circadian input pathway to AD-related disturbances relevant to sundowning.

Retinorecipient areas in the common marmoset (Callithrix jacchus): An image-forming and non-image forming circuitry

The mammalian retina captures a multitude of diverse features from the external environment and conveys them via the optic nerve to a myriad of retinorecipient nuclei. Understanding how retinal signals act in distinct brain functions is one of the most central and established goals of neuroscience. Using the common marmoset (Callithrix jacchus), a monkey from Northeastern Brazil, as an animal model for parsing how retinal innervation works in the brain, started decades ago due to their marmoset's small bodies, rapid reproduction rate, and brain features. In the course of that research, a large amount of new and sophisticated neuroanatomical techniques was developed and employed to explain retinal connectivity. As a consequence, image and non-image-forming regions, functions, and pathways, as well as retinal cell types were described. Image-forming circuits give rise directly to vision, while the non-image-forming territories support circadian physiological processes, although part of their functional significance is uncertain. Here, we reviewed the current state of knowledge concerning retinal circuitry in marmosets from neuroanatomical investigations. We have also highlighted the aspects of marmoset retinal circuitry that remain obscure, in addition, to identify what further research is needed to better understand the connections and functions of retinorecipient structures.

To sleep or not to sleep - Effects on memory in normal aging and disease

Sleep behavior undergoes significant changes across the lifespan, and aging is associated with marked alterations in sleep amounts and quality. The primary sleep changes in healthy older adults include a shift in sleep timing, reduced slow-wave sleep, and impaired sleep maintenance. However, neurodegenerative and psychiatric disorders are more common among the elderly, which further worsen their sleep health. Irrespective of the cause, insufficient sleep adversely affects various bodily functions including energy metabolism, mood, and cognition. In this review, we will focus on the cognitive changes associated with inadequate sleep during normal aging and the underlying neural mechanisms.

A chemical-genetic investigation of BDNF-NtrkB signaling in mammalian sleep

STUDY OBJECTIVES

The neurotrophin brain derived neurotrophic factor (BDNF) is hypothesized to be a molecular mediator of mammalian sleep homeostasis. This hypothesis is supported by correlational findings and results obtained from pharmacology. BDNF binds with high affinity to the membrane bound receptor Neurotrophin Tyrosine Kinase Receptor B (NtrkB), which triggers several intracellular signaling cascades. It is therefore possible that BDNF's role in sleep homeostasis is mediated via NtrkB. We examined this hypothesis using a chemical-genetic technique that allows for rapid and selective inhibition of NtrkB in vivo.

METHODS

We used mutant mice bearing a point mutation in the NtrkB that allows for selective and reversible inactivation in the presence of a small binding molecule (1-NM-PP1). Using a cross-over design, we determined the effects of NtrkB inhibition on baseline sleep architecture and sleep homeostasis.

RESULTS

We find that NtrkB inhibition reduced REM sleep time and increased state-transitions but had no effect on sleep homeostasis.

CONCLUSIONS

These findings suggest that BDNF-NtrkB receptor signaling has relatively subtle roles in sleep architecture, but no role in sleep homeostasis.

Human circadian variations

Circadian rhythms, present in most phyla across life, are biological oscillations occurring on a daily cycle. Since the discovery of their molecular foundations in model organisms, many inputs that modify this tightly controlled system in humans have been identified. Polygenic variations and environmental factors influence each person's circadian rhythm, contributing to the trait known as chronotype, which manifests as the degree of morning or evening preference in an individual. Despite normal variation in chronotype, much of society operates on a "one size fits all" schedule that can be difficult to adjust to, especially for certain individuals whose endogenous circadian phase is extremely advanced or delayed. This is a public health concern, as phase misalignment in humans is associated with a number of adverse health outcomes. Additionally, modern technology (such as electric lights and computer, tablet, and phone screens that emit blue light) and lifestyles (such as shift or irregular work schedules) are disrupting circadian consistency in an increasing number of people. Though medical and lifestyle interventions can alleviate some of these issues, growing research on endogenous circadian variability and sensitivity suggests that broader social changes may be necessary to minimize the impact of circadian misalignment on health.

Systems and Circuits Linking Chronic Pain and Circadian Rhythms

Research over the last 20 years regarding the link between circadian rhythms and chronic pain pathology has suggested interconnected mechanisms that are not fully understood. Strong evidence for a bidirectional relationship between circadian function and pain has been revealed through inflammatory and immune studies as well as neuropathic ones. However, one limitation of many of these studies is a focus on only a few molecules or cell types, often within only one region of the brain or spinal cord, rather than systems-level interactions. To address this, our review will examine the circadian system as a whole, from the intracellular genetic machinery that controls its timing mechanism to its input and output circuits, and how chronic pain, whether inflammatory or neuropathic, may mediate or be driven by changes in these processes. We will investigate how rhythms of circadian clock gene expression and behavior, immune cells, cytokines, chemokines, intracellular signaling, and glial cells affect and are affected by chronic pain in animal models and human pathologies. We will also discuss key areas in both circadian rhythms and chronic pain that are sexually dimorphic. Understanding the overlapping mechanisms and complex interplay between pain and circadian mediators, the various nuclei they affect, and how they differ between sexes, will be crucial to move forward in developing treatments for chronic pain and for determining how and when they will achieve their maximum efficacy.

Chronic lead exposure alters photic entrainment of locomotor activity rhythm and neuronal photoactivation in the suprachiasmatic nucleus of the adult rat

Chronic lead (Pb) exposure affects the circadian physiological processes regulated by suprachiasmatic nucleus (SCN), which is synchronized (entrainment) by light. Disorders in the entrainment capacity of an organism alter its performance to interact with the environment, thus affecting its health status. The objectives of the present study were to evaluate whether chronic early Pb exposure affects the entrainment of the circadian rhythm of locomotor activity by light and to explore the possible mechanisms involved. Adult male Wistar rats, control and chronically exposed to Pb (320 ppm) in drinking water from gestation to adult age, were used. Assessment of the metal level showed a significant increase of Pb in the blood, hypothalamus and prefrontal cortex of the experimental rats. Continuous registrations of locomotor activity (12 h:12 h light-dark cycle) depicted that Pb induces important delay of this activity when the light was turned off. The Pb exposed animals entrained faster with a photoperiod delay of 6 h, (lights on at 13:00 h), and maintained the significant delay in the onset of activity at lights out. In continuous darkness, the animals were exposed to a light pulse at circadian time 23. This resulted in a significant decrease of photo-stimulated neurons (immunoreactivity to c-Fos) in the SCN of the metal-exposed animals. These results show that chronic early Pb exposure alters the photic entrainment of the rhythm of locomotor activity, which is evidenced by a significant decrease in both the number of photo-stimulated neurons and neuronal population (Nissl stain) of the SCN.

[Sleep and Sleep Disturbance in Subjetcs with Dementia]

Treating sleep disorders is a challenge in individuals with dementia. A precondition for treatment success is thorough diagnostics of sleep disorders. Sleep diaries and observational questionnairs represent important diagnostic tools. In addition to general treatment strategies including optimal treatment of comorbidities, behavioral therapy is a main intervention. Drugs for the treatment of a sleep disorder should only be prescribed with a clear indication and prolongation of prescription should regularly be checked. The active search for and the treatment of sleep disorders should always be performed in individuals with dementia.

The connections of Locus Coeruleus with hypothalamus: potential involvement in Alzheimer's disease

The hypothalamus and Locus Coeruleus (LC) share a variety of functions, as both of them take part in the regulation of the sleep/wake cycle and in the modulation of autonomic and homeostatic activities. Such a functional interplay takes place due to the dense and complex anatomical connections linking the two brain structures. In Alzheimer's disease (AD), the occurrence of endocrine, autonomic and sleep disturbances have been associated with the disruption of the hypothalamic network; at the same time, in this disease, the occurrence of LC degeneration is receiving growing attention for the potential roles it may have both from a pathophysiological and pathogenetic point of view. In this review, we summarize the current knowledge on the anatomical and functional connections between the LC and hypothalamus, to better understand whether the impairment of the former may be responsible for the pathological involvement of the latter, and whether the disruption of their interplay may concur to the pathophysiology of AD. Although only a few papers specifically explored this topic, intriguingly, some pre-clinical and post-mortem human studies showed that aberrant protein spreading and neuroinflammation may cause hypothalamus degeneration and that these pathological features may be linked to LC impairment. Moreover, experimental studies in rodents showed that LC plays a relevant role in modulating the hypothalamic sleep/wake cycle regulation or neuroendocrine and systemic hormones; in line with this, the degeneration of LC itself may partly explain the occurrence of hypothalamic-related symptoms in AD.

The aging brain: sleep, the circadian clock and exercise

Aging is a multifactorial process likely stemming from damage accumulation and/or a decline in maintenance and repair mechanisms in the organisms that eventually determine their lifespan. In our review, we focus on the morphological and functional alterations that the aging brain undergoes affecting sleep and the circadian clock in both human and rodent models. Although both species share mammalian features, differences have been identified on several experimental levels, which we outline in this review. Additionally, we delineate some challenges on the preferred analysis and we suggest that a uniform route is followed so that findings can be smoothly compared. We conclude by discussing potential interventions and highlight the influence of physical exercise as a beneficial lifestyle intervention, and its effect on healthy aging and longevity. We emphasize that even moderate age-matched exercise is able to ameliorate several aging characteristics as far as sleep and circadian rhythms are concerned, independent of the species studied.

Sleep, Narcolepsy, and Sodium Oxybate

Sodium oxybate (SO) has been in use for many decades to treat narcolepsy with cataplexy. It functions as a weak GABAB agonist but also as an energy source for the brain as a result of its metabolism to succinate and as a powerful antioxidant because of its capacity to induce the formation of NADPH. Its actions at thalamic GABAB receptors can induce slow-wave activity, while its actions at GABAB receptors on monoaminergic neurons can induce or delay REM sleep. By altering the balance between monoaminergic and cholinergic neuronal activity, SO uniquely can induce and prevent cataplexy. The formation of NADPH may enhance sleep’s restorative process by accelerating the removal of the reactive oxygen species (ROS), which accumulate during wakefulness. SO improves alertness in normal subjects and in patients with narcolepsy. SO may allay severe psychological stress - an inflammatory state triggered by increased levels of ROS and characterized by cholinergic supersensitivity and monoaminergic deficiency. SO may be able to eliminate the inflammatory state and correct the cholinergic/ monoaminergic imbalance.

Neuropathology of the Brainstem to Mechanistically Understand and to Treat Alzheimer's Disease

Alzheimer’s disease (AD) is a devastating neurodegenerative disorder as yet without effective therapy. Symptoms of this disorder typically reflect cortical malfunction with local neurohistopathology, which biased investigators to search for focal triggers and molecular mechanisms. Cortex, however, receives massive afferents from caudal brain structures, which do not only convey specific information but powerfully tune ensemble activity. Moreover, there is evidence that the start of AD is subcortical. The brainstem harbors monoamine systems, which establish a dense innervation in both allo- and neocortex. Monoaminergic synapses can co-release neuropeptides either by precisely terminating on cortical neurons or, when being “en passant”, can instigate local volume transmission. Especially due to its early damage, malfunction of the ascending monoaminergic system emerges as an early sign and possible trigger of AD. This review summarizes the involvement and cascaded impairment of brainstem monoaminergic neurons in AD and discusses cellular mechanisms that lead to their dysfunction. We highlight the significance and therapeutic challenges of transmitter co-release in ascending activating system, describe the role and changes of local connections and distant afferents of brainstem nuclei in AD, and summon the rapidly increasing diagnostic window during the last few years.

Challenging sleep homeostasis

In this commentary, I play the Devil’s advocate and assume the title of High Contrarian. I intend to be provocative to challenge long-standing ideas about sleep. I blame all on Professor Craig Heller, who taught me to think this way as a graduate student in his laboratory. Scientists should fearlessly jump into the foaming edge of what we know, but also consider how safe are their intellectual harbors. There are many ideas we accept as ‘known’: that sleep is ubiquitous in the animal kingdom, that it serves vital functions, that it plays an essential role in brain plasticity. All of this could be wrong. As one example, I reexamine the idea that sleep is regulated by a mysterious ‘homeostat’ that determines sleep need based on prior wake time.

The Effect of Cannabinoids on the Brain's Circadian Clock

The circadian rhythm is without a doubt the main element influencing the way human lead their lives. Emerging evidence indicate that cannabinoids affect these routines by regulating neuronal firing within the suprachiasmatic nucleus, the master circadian pacemaker in the brain. These actions of cannabinoids on the brain's clock may also underlie time-wraps commonly experienced by marijuana users.

The circadian system in Parkinson's disease, multiple system atrophy, and progressive supranuclear palsy

Circadian organization of physiology and behavior is an important biologic process that allows organisms to anticipate and prepare for predictable changes in the environment. Circadian disruptions are associated with a wide range of health issues. In patients with neurodegenerative diseases, alterations of circadian rhythms are among the most common and debilitating symptoms. Although a growing awareness of these symptoms has occurred during the last decade, their underlying neuropathophysiologic circuitry remains poorly understood and, consequently, no effective therapeutic strategies are available to alleviate these health issues. Recent studies have examined the neuropathologic status of the different neural components of the circuitry governing the generation of circadian rhythms in neurodegenerative diseases. In this review, we will dissect the potential contribution of dysfunctions in the different nodes of this circuitry to circadian alterations in patients with parkinsonism-linked neurodegenerative diseases (namely, Parkinson's disease, multiple system atrophy, and progressive supranuclear palsy). A deeper understanding of these mechanisms will provide not only a better understanding of disease neuropathophysiology but also holds promise for the development of more effective and mechanisms-based therapies.

Hypothalamic α-synuclein and its relation to autonomic symptoms and neuroendocrine abnormalities in Parkinson disease

Parkinson's disease (PD) is a complex neurodegenerative disorder presenting with defining motor features and a variable combination of nonmotor symptoms. There is growing evidence suggesting that hypothalamic involvement in PD may contribute to the pathogenesis of nonmotor symptoms. Initial neuropathologic studies demonstrated histologic involvement of hypothalamic nuclei by Lewy pathology, i.e., neuronal aggregates including Lewy bodies (round eosinophilic inclusions with a halo found in the neuronal perikarya) and other inclusions in neuronal processes such as Lewy neurites. Recent studies using more sensitive immunohistochemistry have shown that synuclein deposition is common in all hypothalamic nuclei and can happen at preclinical stages of the disease. Several neuropathologic changes, including synuclein deposition, neuronal loss, and adaptative morphologic changes, have been described in neurochemically defined specific hypothalamic cell populations with a potential role in the pathogenesis of nonmotor symptoms such as autonomic dysfunction, blood pressure control, circadian rhythms, sleep, and body weight regulation. The clinical implications of these hypothalamic neuropathologic changes are not fully understood and a direct clinical correlation may be challenging due to the multifactorial pathogenesis of the symptomatology and the additional involvement of other peripheral regulatory mechanisms. Future neuropathologic research using histological and functional assessments should establish the potential role of hypothalamic dysfunction on clinical burden, symptomatic therapies, and disease biomarkers in PD.

Traumatic stress and the circadian system: neurobiology, timing and treatment of posttraumatic chronodisruption

Background: Humans have an evolutionary need for a well-preserved internal 'clock', adjusted to the 24-hour rotation period of our planet. This intrinsic circadian timing system enables the temporal organization of numerous physiologic processes, from gene expression to behaviour. The human circadian system is tightly and bidirectionally interconnected to the human stress system, as both systems regulate each other's activity along the anticipated diurnal challenges. The understanding of the temporal relationship between stressors and stress responses is critical in the molecular pathophysiology of stress-and trauma-related diseases, such as posttraumatic stress disorder (PTSD). Objectives/Methods: In this narrative review, we present the functional components of the stress and circadian system and their multilevel interactions and discuss how traumatic stress can affect the harmonious interplay between the two systems. Results: Circadian dysregulation after trauma exposure (posttraumatic chronodisruption) may represent a core feature of trauma-related disorders mediating enduring neurobiological correlates of traumatic stress through a loss of the temporal order at different organizational levels. Posttraumatic chronodisruption may, thus, affect fundamental properties of neuroendocrine, immune and autonomic systems, leading to a breakdown of biobehavioral adaptive mechanisms with increased stress sensitivity and vulnerability. Given that many traumatic events occur in the late evening or night hours, we also describe how the time of day of trauma exposure can differentially affect the stress system and, finally, discuss potential chronotherapeutic interventions. Conclusion: Understanding the stress-related mechanisms susceptible to chronodisruption and their role in PTSD could deliver new insights into stress pathophysiology, provide better psychochronobiological treatment alternatives and enhance preventive strategies in stress-exposed populations.

[Neuroendocrine and metabolic impairments in patients with Parkinson's disease]

ABSRACT

Neuroendocrine and neurometabolic disorders, although occasionally noted in Parkinson's disease (PD), existed in the shadow of motor and non-motor symptoms (hypokinesia, rigidity, tremor, depression, constipation, etc.). In recent years, they are increasingly being diagnosed and are the subject of special research. These include, in particular, disorders of carbohydrate metabolism, changes in body weight, metabolic disorders in bone tissue, secretion, as well as the secretion of neurohormones, such as melatonin. They are associated with other non-motor symptoms, negatively affect patients' general condition and quality of life, but can be treatable. At the same time, treatment of neuroendocrine and neurometabolic disorders can favorably influence the rate of progression of the disease as a whole. This review discusses the pathophysiological mechanisms, clinical consequences, as well as pharmacological and non-pharmacological approaches to the treatment of neuroendocrine and neurometabolic disorders arising in PD, which have been relatively rarely covered in literature.

Reshaping circadian metabolism in the suprachiasmatic nucleus and prefrontal cortex by nutritional challenge

Food is a powerful entrainment cue for circadian clocks in peripheral tissues, and changes in the composition of nutrients have been demonstrated to metabolically reprogram peripheral clocks. However, how food challenges may influence circadian metabolism of the master clock in the suprachiasmatic nucleus (SCN) or in other brain areas is poorly understood. Using high-throughput metabolomics, we studied the circadian metabolome profiles of the SCN and medial prefrontal cortex (mPFC) in lean mice compared with mice challenged with a high-fat diet (HFD). Both the mPFC and the SCN displayed a robust cyclic metabolism, with a strikingly high sensitivity to HFD perturbation in an area-specific manner. The phase and amplitude of oscillations were drastically different between the SCN and mPFC, and the metabolic pathways impacted by HFD were remarkably region-dependent. Furthermore, HFD induced a significant increase in the number of cycling metabolites exclusively in the SCN, revealing an unsuspected susceptibility of the master clock to food stress.

Dual-Color Single-Cell Imaging of the Suprachiasmatic Nucleus Reveals a Circadian Role in Network Synchrony

The suprachiasmatic nucleus (SCN) acts as a master pacemaker driving circadian behavior and physiology. Although the SCN is small, it is composed of many cell types, making it difficult to study the roles of particular cells. Here we develop bioluminescent circadian reporter mice that are Cre dependent, allowing the circadian properties of genetically defined populations of cells to be studied in real time. Using a Color-Switch PER2::LUCIFERASE reporter that switches from red PER2::LUCIFERASE to green PER2::LUCIFERASE upon Cre recombination, we assess circadian rhythms in two of the major classes of peptidergic neurons in the SCN: AVP (arginine vasopressin) and VIP (vasoactive intestinal polypeptide). Surprisingly, we find that circadian function in AVP neurons, not VIP neurons, is essential for autonomous network synchrony of the SCN and stability of circadian rhythmicity.

Potential Pathways for Circadian Dysfunction and Sundowning-Related Behavioral Aggression in Alzheimer's Disease and Related Dementias

Patients with Alzheimer's disease (AD) and related dementias are commonly reported to exhibit aggressive behavior and other emotional behavioral disturbances, which create a tremendous caretaker burden. There has been an abundance of work highlighting the importance of circadian function on mood and emotional behavioral regulation, and recent evidence demonstrates that a specific hypothalamic pathway links the circadian system to neurons that modulate aggressive behavior, regulating the propensity for aggression across the day. Such shared circuitry may have important ramifications for clarifying the complex interactions underlying "sundowning syndrome," a poorly understood (and even controversial) clinical phenomenon in AD and dementia patients that is characterized by agitation, aggression, and delirium during the late afternoon and early evening hours. The goal of this review is to highlight the potential output and input pathways of the circadian system that may underlie circadian dysfunction and behavioral aggression associated with sundowning syndrome, and to discuss possible ways these pathways might inform specific interventions for treatment. Moreover, the apparent bidirectional relationship between chronic disruptions of circadian and sleep-wake regulation and the pathology and symptoms of AD suggest that understanding the role of these circuits in such neurobehavioral pathologies could lead to better diagnostic or even preventive measures.

Impaired function of the suprachiasmatic nucleus rescues the loss of body temperature homeostasis caused by time-restricted feeding

The suprachiasmatic nucleus (SCN) is the master circadian pacemaker that drives body temperature rhythm. Time-restricted feeding (TRF) has potential as a preventative or therapeutic approach against many diseases. The potential side effects of TRF remain unknown. Here we show that a 4-hour TRF stimulus in mice can severely impair body temperature homeostasis and can result in lethality. Nearly half of the mice died at 21 °C, and all mice died at 18 °C during 4-hour TRF. Moreover, this effect was modulated by the circadian clock and was associated with severe hypothermia due to loss of body temperature homeostasis, which is different from "torpor", an adaptive response under food deprivation. Disrupting the circadian clock by the SCN lesions or a non-invasive method (constant light) which disrupts circadian clock rescued lethality during TRF. Analysis of circadian gene expression in the dorsomedial hypothalamus (DMH) demonstrated that TRF reprograms rhythmic transcriptome in DMH and suppresses expression of genes, such as Ccr5 and Calcrl, which are involved in thermoregulation. We demonstrate a side effect of 4-hour TRF on the homeostasis of body temperature and a rescue function by impairing the SCN function. Altogether, our results suggested that constructing a circadian arrhythmicity may have a beneficial effect on the host response to an acute stress.

Circadian alterations in patients with neurodegenerative diseases: Neuropathological basis of underlying network mechanisms

Circadian organization of physiology and behavior is an important biological process that allows organisms to anticipate and prepare for daily changes and demands. Disruptions in this system precipitates a wide range of health issues. In patients with neurodegenerative diseases, alterations of circadian rhythms are among the most common and debilitating symptoms. Although a growing awareness of these symptoms has occurred during the last decade, their underlying neuropathophysiological circuitry remains poorly understood and consequently no effective therapeutic strategies are available to alleviate these health issues. Recent studies have examined the neuropathological status of the different neural components of the circuitry governing the generation of circadian rhythms in neurodegenerative diseases. In this review, we will dissect the potential contribution of dysfunctions in the different nodes of this circuitry to circadian alterations in patients with neurodegenerative diseases. A deeper understanding of these mechanisms will provide not only a better understanding of disease neuro-pathophysiology, but also hold the promise for developing effective and mechanisms-based therapies.

Light-resetting impact on behavior and the central circadian clock in two vole species (genus: Lasiopodomys)

The behavioral circadian rhythms of subterranean rodents show intra- and interspecies diversity in terms of adaptation to dark underground environments, but the endogenous molecular mechanism of rhythm regulation in the suprachiasmatic nuclei (SCN) is stable to many species. In this study, we sought to determine the rhythms of behavior and central molecular regulatory mechanisms in the SCN of the subterranean Mandarin voles (Lasiopodomys mandarinus) compared with a related aboveground species, Brandt's voles (Lasiopodomys brandtii). Both species were reared under a 12 L:12 D cycle or in continuous darkness for 4 weeks. The pattern of wheel-running activity was similar in both species and had a periodicity of almost 24 h regardless of rearing conditions. However, the intensity of daily activity in Brandt's voles decreased markedly in darkness, while there was no significant difference in activity intensity in mandarin voles under different light regimes. In both vole species, all tested genes in the SCN showed significant time-dependent expression regardless of rearing conditions, and the expression levels of most genes did not differ significantly between different species and conditions. However, the peak phase shift in gene expression differed between the two species. In conclusion, behavioral patterns in mandarin and Brandt's voles were regulated by a stable molecular endogenous biological clock. The observed differences in activity intensity and phase shift suggest that different mechanisms regulate circadian rhythms in different living environments.

Expression patterns of clock genes in the hypothalamus and eye of two Lasiopodomys species

To investigate the relationship between light sensing systems in the eye and circadian oscillators in the hypothalamus of subterranean rodents, we studied subterranean Mandarin voles (Lasiopodomys mandarinus) that spend their entire lives under dark conditions with degenerated eyes, and compared oscillatory expression patterns of clock genes in the hypothalamus and eye between Mandarin voles and their aboveground relatives, Brandt's voles (L. brandtii). Individuals of both vole species were kept under a 12-h light/12-h dark condition or continuous dark condition for 4 weeks. In both species, the expressions of most genes showed significant cosine rhythmicity in the hypothalamus but relatively weak rhythmicity in the eye. The number of rhythmic genes in the eye of Mandarin voles increased under the dark condition, but the opposite trend was observed in the eye of Brandt's voles. The expression levels of most clock genes in the hypothalamus of both vole species did not significantly differ between the two conditions, but unlike in Mandarin voles, these expression levels significantly decreased in the eye of Brandt's voles kept under the dark condition. In both vole species, the peak phase of most clock genes exhibited advanced or invariant change in the hypothalamus under the dark condition, and the peak phase of most clock genes showed consistent changes between the eye and hypothalamus of Mandarin voles. However, most clock genes in the eye showed a delayed phase in Brandt's voles kept under the dark condition. In conclusion, the hypothalamus plays an important role in both vole species irrespective of the light condition. However, the expression patterns of clock genes in the eye differed between the vole species, indicating that each species adapted differently to their environments.

Newly identified sleep-wake and circadian circuits as potential therapeutic targets

Optogenetics and chemogenetics are powerful tools, allowing the specific activation or inhibition of targeted neuronal subpopulations. Application of these techniques to sleep and circadian research has resulted in the unveiling of several neuronal populations that are involved in sleep-wake control, and allowed a comprehensive interrogation of the circuitry through which these nodes are coordinated to orchestrate the sleep-wake cycle. In this review, we discuss six recently described sleep-wake and circadian circuits that show promise as therapeutic targets for sleep medicine. The parafacial zone (PZ) and the ventral tegmental area (VTA) are potential druggable targets for the treatment of insomnia. The brainstem circuit underlying rapid eye movement sleep behavior disorder (RBD) offers new possibilities for treating RBD and neurodegenerative synucleinopathies, whereas the parabrachial nucleus, as a nexus linking arousal state control and breathing, is a promising target for developing treatments for sleep apnea. Therapies that act upon the hypothalamic circuitry underlying the circadian regulation of aggression or the photic regulation of arousal and mood pathway carry enormous potential for helping to reduce the socioeconomic burden of neuropsychiatric and neurodegenerative disorders on society. Intriguingly, the development of chemogenetics as a therapeutic strategy is now well underway and such an approach has the capacity to lead to more focused and less invasive therapies for treating sleep-wake disorders and related comorbidities.

Social stress and glucocorticoids alter PERIOD2 rhythmicity in the liver, but not in the suprachiasmatic nucleus

Circadian (~24 h) rhythms in behavior and physiological functions are under control of an endogenous circadian pacemaker in the suprachiasmatic nucleus (SCN) of the hypothalamus. The SCN directly drives some of these rhythms or serves as a coordinator of peripheral oscillators residing in other tissues and organs. Disruption of the circadian organization may contribute to disease, including stress-related disorders. Previous research indicates that the master clock in the SCN is resistant to stress, although it is unclear whether stress affects rhythmicity in other tissues, possibly mediated by glucocorticoids, released in stressful situations. In the present study, we examined the effect of uncontrollable social defeat stress and glucocorticoid hormones on the central and peripheral clocks, respectively in the SCN and liver. Transgenic PERIOD2::LUCIFERASE knock-in mice were used to assess the rhythm of the clock protein PERIOD2 (PER2) in SCN slices and liver tissue collected after 10 consecutive days of social defeat stress. The rhythmicity of PER2 expression in the SCN was not affected by stress exposure, whereas in the liver the expression showed a delayed phase in defeated compared to non-defeated control mice. In a second experiment, brain slices and liver samples were collected from transgenic mice and exposed to different doses of corticosterone. Corticosterone did not affect PER2 rhythm of the SCN samples, but caused a phase shift in PER2 expression in liver samples. This study confirms earlier findings that the SCN is resistant to stress and shows that clocks in the liver are affected by social stress, which might be due to the direct influence of glucocorticoids released from the adrenal gland.

Interaction Between Circadian Rhythms, Energy Metabolism, and Cognitive Function

The interaction between meal timing and light regulates circadian rhythms in mammals and not only determines the sleep-wake pattern but also the activity of the endocrine system. Related with that, the necessity to fulfill energy needs is a driving force that requires the participation of cognitive skills whose performance has been shown to undergo circadian variations. These facts have led to the concept that cognition and feeding behaviour can be analysed from a chronobiological perspective. In this context, research carried out during the last two decades has evidenced the link between feeding behaviour/nutritional habits and cognitive processes, and has highlighted the impact of circadian disorders on cognitive decline. All that has allowed hypothesizing a tight relationship between nutritional factors, chronobiology, and cognition. In this connection, experimental diets containing elevated amounts of fat and sugar (high-fat diets; HFDs) have been shown to alter in rodents the circadian distribution of meals, and to have a negative impact on cognition and motivational aspects of behaviour that disappear when animals are forced to adhere to a standard temporal eating pattern. In this review, we will present relevant studies focussing on the effect of HFDs on cognitive aspects of behaviour, paying particular attention to the influence that chronobiological alterations caused by these diets may have on hippocampaldependent cognition.

An overview of the neuroendocrine system in Parkinson's disease: what is the impact on diagnosis and treatment?

Introduction: A growing body of evidence indicates that neuroendocrine interactions may occur at all levels of the brain-gut-microbiota axis, which is directly involved in the pathogenesis of Parkinson's disease (PD).Areas covered: The review presents some current and emerging concepts regarding the organization and functioning of the neuroendocrine system as well as the role of neuroendocrine disturbances in the pathophysiology and symptomatology of PD. The concept of the brain-gut-microbiota triad interactions in the neuroendocrine system and PD is proposed. In PD, dysregulation of the main neuroendocrine axes coordinated by the hypothalamus is accompanied by disruptions at the peripheral level, which involve enteroendocrine cells producing numerous neuropeptides. Moreover, the important role of the gut microbiota as a main coordinator of immune and neuroendocrine interactions is discussed. The potential diagnostic and therapeutic implications in the context of the recent developments in the fields of neuroendocrinology and neurodegeneration are also presented.Expert opinion: Unraveling complex neuroendocrine interactions in the course of PD may provide crucial diagnostic implications and novel therapeutic approaches including the application of gut neuropeptides and gut microbiota modification.

A high-sucrose diet aggravates Alzheimer's disease pathology, attenuates hypothalamic leptin signaling, and impairs food-anticipatory activity in APPswe/PS1dE9 mice

High-fat and high-sugar diets contribute to the prevalence of type 2 diabetes and Alzheimer's disease (AD). Although the impact of high-fat diets on AD pathogenesis has been established, the effect of high-sucrose diets (HSDs) on AD pathogenesis remains unclear. This study sought to determine the impact of HSDs on AD-related pathologies. Male APPswe/PS1dE9 (APP/PS1) transgenic and wild-type mice were provided with HSD and their cognitive and hypothalamus-related noncognitive parameters, including feeding behaviors and glycemic regulation, were compared. HSD-fed APP/PS1 mice showed increased neuroinflammation, as well as increased cortical and serum levels of amyloid-β. HSD-fed APP/PS1 mice showed aggravated obesity, hyperinsulinemia, insulin resistance, and leptin resistance, but there was no induction of hyperphagia or hyperleptinemia. Leptin-induced phosphorylation of signal transducer and activator of transcription 3 in the dorsomedial and ventromedial hypothalamus was reduced in HSD-fed APP/PS1 mice, which might be associated with attenuated food-anticipatory activity, glycemic dysregulation, and AD-related noncognitive symptoms. Our study demonstrates that HSD aggravates metabolic stresses, increases AD-related pathologies, and attenuates hypothalamic leptin signaling in APP/PS1 mice.

The eIF2α Kinase GCN2 Modulates Period and Rhythmicity of the Circadian Clock by Translational Control of Atf4

The integrated stress response (ISR) is activated in response to diverse stress stimuli to maintain homeostasis in neurons. Central to this process is the phosphorylation of eukaryotic translation initiation factor 2 alpha (eIF2α). Here, we report a critical role for ISR in regulating the mammalian circadian clock. The eIF2α kinase GCN2 rhythmically phosphorylates eIF2α in the suprachiasmatic circadian clock. Increased eIF2α phosphorylation shortens the circadian period in both fibroblasts and mice, whereas reduced eIF2α phosphorylation lengthens the circadian period and impairs circadian rhythmicity in animals. Mechanistically, phosphorylation of eIF2α promotes mRNA translation of Atf4. ATF4 binding motifs are identified in multiple clock genes, including Per2, Per3, Cry1, Cry2, and Clock. ATF4 binds to the TTGCAGCA motif in the Per2 promoter and activates its transcription. Together, these results demonstrate a significant role for ISR in circadian physiology and provide a potential link between dysregulated ISR and circadian dysfunction in brain diseases.

A Histologic Study of the Circadian System in Parkinson Disease, Multiple System Atrophy, and Progressive Supranuclear Palsy

Importance

Circadian dysfunction may be associated with the symptoms and neurodegeneration in Parkinson disease (PD), multiple system atrophy (MSA), and progressive supranuclear palsy (PSP), although the underlying neuroanatomical site of disruption and pathophysiological mechanisms are not fully understood.

Objective

To perform a neuropathological analysis of disease-specific inclusions in the key structures of the circadian system in patients with PD, MSA, and PSP.

Design, Setting, and Participants

This investigation was a brain bank case-control study assessing neuropathological inclusions in the suprachiasmatic nucleus (SCN) of the hypothalamus and pineal gland in healthy controls, PD (Lewy pathology), MSA (glial cytoplasmic inclusions), and PSP (tau inclusions). The study analyzed 12 healthy control, 28 PD, 11 MSA, and 21 PSP samples from consecutive brain donations (July 1, 2010, to June 30, 2016) to the Queen Square Brain Bank for Neurological Disorders and the Parkinson's UK Brain Bank, London, United Kingdom. Cases were excluded if neither SCN nor pineal tissue was available.

Main Outcomes and Measures

Disease-specific neuropathological changes were graded using a standard semiquantitative scoring system (absent, mild, moderate, severe, or very severe) and compared between groups.

Results

Because of limited tissue availability, the following total samples were examined in a semiquantitative histologic analysis: 5 SCNs and 7 pineal glands in the control group (6 male; median age at death, 83.8 years; interquartile range [IQR], 78.2-88.0 years), 13 SCNs and 17 pineal glands in the PD group (22 male; median age at death, 78.8 years; IQR, 75.5-83.8 years), 5 SCNs and 6 pineal glands in the MSA group (7 male; median age at death, 69.5 years; IQR, 61.6-77.7 years), and 5 SCNs and 19 pineal glands in the PSP group (13 male; median age at death, 74.3 years; IQR, 69.7-81.1 years). No neuropathological changes were found in either the SCN or pineal gland in healthy controls or MSA cases. Nine PD cases had Lewy pathology in the SCN, and only 2 PD cases had Lewy pathology in the pineal gland. All PSP cases showed inclusions in the SCN, but no PSP cases had pathology in the pineal gland.

Conclusions and Relevance

Disease-related neuropathological changes were found in the SCN but not in the pineal gland in PD and PSP, while both structures were preserved in MSA, reflecting different pathophysiological mechanisms that may have important therapeutic implications.

Off the Clock: From Circadian Disruption to Metabolic Disease

Circadian timekeeping allows appropriate temporal regulation of an organism’s internal metabolism to anticipate and respond to recurrent daily changes in the environment. Evidence from animal genetic models and from humans under circadian misalignment (such as shift work or jet lag) shows that disruption of circadian rhythms contributes to the development of obesity and metabolic disease. Inappropriate timing of food intake and high-fat feeding also lead to disruptions of the temporal coordination of metabolism and physiology and subsequently promote its pathogenesis. This review illustrates the impact of genetically or environmentally induced molecular clock disruption (at the level of the brain and peripheral tissues) and the interplay between the circadian system and metabolic processes. Here, we discuss some mechanisms responsible for diet-induced circadian desynchrony and consider the impact of nutritional cues in inter-organ communication, with a particular focus on the communication between peripheral organs and brain. Finally, we discuss the relay of environmental information by signal-dependent transcription factors to adjust the timing of gene oscillations. Collectively, a better knowledge of the mechanisms by which the circadian clock function can be compromised will lead to novel preventive and therapeutic strategies for obesity and other metabolic disorders arising from circadian desynchrony.

Aging circadian rhythms and cannabinoids

Numerous aspects of mammalian physiology exhibit cyclic daily patterns known as circadian rhythms. However, studies in aged humans and animals indicate that these physiological rhythms are not consistent throughout the life span. The simultaneous development of disrupted circadian rhythms and age-related impairments suggests a shared mechanism, which may be amenable to therapeutic intervention. Recently, the endocannabinoid system has emerged as a complex signaling network, which regulates numerous aspects of circadian physiology relevant to the neurobiology of aging. Agonists of cannabinoid receptor-1 (CB1) have consistently been shown to decrease neuronal activity, core body temperature, locomotion, and cognitive function. Paradoxically, several lines of evidence now suggest that very low doses of cannabinoids are beneficial in advanced age. One potential explanation for this phenomenon is that these drugs exhibit hormesis-a biphasic dose-response wherein low doses produce the opposite effects of higher doses. Therefore, it is important to determine the dose-, age-, and time-dependent effects of these substances on the regulation of circadian rhythms and other processes dysregulated in aging. This review highlights 3 fields-biological aging, circadian rhythms, and endocannabinoid signaling-to critically assess the therapeutic potential of endocannabinoid modulation in aged individuals. If the hormetic properties of exogenous cannabinoids are confirmed, we conclude that precise administration of these compounds may bidirectionally entrain central and peripheral circadian clocks and benefit multiple aspects of aging physiology.

Differences in twenty-four-hour profiles of blue-light exposure between day and night shifts in female medical staff

Light is the strongest zeitgeber currently known for the synchronization of the human circadian timing system. Especially shift workers are exposed to altered daily light profiles. Our objective is the characterization of differences in blue-light exposures between day and night shift taking into consideration modifying factors such as chronotype. We describe 24-hour blue-light profiles as measured with ambient light data loggers (LightWatcher) during up to three consecutive days with either day or night shifts in 100 female hospital staff including 511 observations. Linear mixed models were applied to analyze light profiles and to select time-windows for the analysis of associations between shift work, individual factors, and log mean light exposures as well as the duration of darkness per day. Blue-light profiles reflected different daily activities and were mainly influenced by work time. Except for evening (7-9 p.m.), all time windows showed large differences in blue-light exposures between day and night shifts. Night work reduced the duration of darkness per day by almost 4 h (β^ = -3:48 hh:mm, 95% CI (-4:27; -3.09)). Late chronotypes had higher light exposures in the morning and evening compared to women with intermediate chronotype (e.g. morning β^ = 0.50 log(mW/m²/nm), 95% CI (0.08; 0.93)). Women with children had slightly higher light exposures in the afternoon than women without children (β^ = 0.48, 95% CI (-0.10; 1,06)). Time windows for the description of light should be chosen carefully with regard to timing of shifts. Our results are helpful for future studies to capture relevant light exposure differences and potential collinearities with individual factors. Improvement of well-being of shift workers with altered light profiles may therefore require consideration of both - light at the workplace and outside working hours.

Real-time Mobile Monitoring of the Dynamic Associations Among Motor Activity, Energy, Mood, and Sleep in Adults With Bipolar Disorder

IMPORTANCE

Biologic systems involved in the regulation of motor activity are intricately linked with other homeostatic systems such as sleep, feeding behavior, energy, and mood. Mobile monitoring technology (eg, actigraphy and ecological momentary assessment devices) allows the assessment of these multiple systems in real time. However, most clinical studies of mental disorders that use mobile devices have not focused on the dynamic associations between these systems.

OBJECTIVES

To examine the directional associations among motor activity, energy, mood, and sleep using mobile monitoring in a community-identified sample, and to evaluate whether these within-day associations differ between people with a history of bipolar or other mood disorders and controls without mood disorders.

DESIGN, SETTING, AND PARTICIPANTS

This study used a nested case-control design of 242 adults, a subsample of a community-based sample of adults. Probands were recruited by mail from the greater Washington, DC, metropolitan area from January 2005 to June 2013. Enrichment of the sample for mood disorders was provided by volunteers or referrals from the National Institutes of Health Clinical Center or by participants in the National Institute of Mental Health Mood and Anxiety Disorders Program. The inclusion criteria were the ability to speak English, availability to participate, and consent to contact at least 2 living first-degree relatives. Data analysis was performed from June 2013 through July 2018.

MAIN OUTCOMES AND MEASURES

Motor activity and sleep duration data were obtained from minute-to-minute activity counts from an actigraphy device worn on the nondominant wrist for 2 weeks. Mood and energy levels were assessed by subjective analogue ratings on the ecological momentary assessment (using a personal digital assistant) by participants 4 times per day for 2 weeks.

RESULTS

Of the total 242 participants, 92 (38.1%) were men and 150 (61.9%) were women, with a mean (SD) age of 48 (16.9) years. Among the participants, 54 (22.3%) had bipolar disorder (25 with bipolar I; 29 with bipolar II), 91 (37.6%) had major depressive disorder, and 97 (40.1%) were controls with no history of mood disorders. A unidirectional association was found between motor activity and subjective mood level (β = -0.018, P = .04). Bidirectional associations were observed between motor activity (β = 0.176; P = .03) and subjective energy level (β = 0.027; P = .03) as well as between motor activity (β = -0.027; P = .04) and sleep duration (β = -0.154; P = .04). Greater cross-domain reactivity was observed in bipolar disorder across all outcomes, including motor activity, sleep, mood, and energy.

CONCLUSIONS AND RELEVANCE

These findings suggest that interventions focused on motor activity and energy may have greater efficacy than current approaches that target depressed mood; both active and passive tracking of multiple regulatory systems are important in designing therapeutic targets.

Developmental Trajectories of Early Life Stress and Trauma: A Narrative Review on Neurobiological Aspects Beyond Stress System Dysregulation

Early life stressors display a high universal prevalence and constitute a major public health problem. Prolonged psychoneurobiological alterations as sequelae of early life stress (ELS) could represent a developmental risk factor and mediate risk for disease, leading to higher physical and mental morbidity rates in later life. ELS could exert a programming effect on sensitive neuronal brain networks related to the stress response during critical periods of development and thus lead to enduring hyper- or hypo-activation of the stress system and altered glucocorticoid signaling. In addition, alterations in emotional and autonomic reactivity, circadian rhythm disruption, functional and structural changes in the brain, as well as immune and metabolic dysregulation have been lately identified as important risk factors for a chronically impaired homeostatic balance after ELS. Furthermore, human genetic background and epigenetic modifications through stress-related gene expression could interact with these alterations and explain inter-individual variation in vulnerability or resilience to stress. This narrative review presents relevant evidence from mainly human research on the ten most acknowledged neurobiological allostatic pathways exerting enduring adverse effects of ELS even decades later (hypothalamic-pituitary-adrenal axis, autonomic nervous system, immune system and inflammation, oxidative stress, cardiovascular system, gut microbiome, sleep and circadian system, genetics, epigenetics, structural, and functional brain correlates). Although most findings back a causal relation between ELS and psychobiological maladjustment in later life, the precise developmental trajectories and their temporal coincidence has not been elucidated as yet. Future studies should prospectively investigate putative mediators and their temporal sequence, while considering the potentially delayed time-frame for their phenotypical expression. Better screening strategies for ELS are needed for a better individual prevention and treatment.

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 time to fight: Circadian control of aggression and associated autonomic support

The central circadian clock, located in the suprachiasmatic nucleus of the mammalian hypothalamus (SCN), regulates daily behavioral rhythms including the temporal propensity for aggressive behavior. Such aggression propensity rhythms are regulated by a functional circuit from the SCN to neurons that drive attack behavior in the ventromedial hypothalamus (VMH), via a relay in the subparaventricular zone (SPZ). In addition to this pathway, the SCN also regulates sleep-wake and locomotor activity rhythms, via the SPZ, in a circuit to the dorsomedial hypothalamus (DMH), a structure that is also known to play a key role in autonomic function and the sympathetic "fight-or-flight" response (which prepares the body for action in stressful situations such as an agonistic encounter). While the autonomic nervous system is known to be under pronounced circadian control, it is less apparent how such autonomic rhythms and their underlying circuitry may support the temporal propensity for aggressive behavior. Additionally, it is unclear how circadian and autonomic dysfunction may contribute to aberrant social and emotional behavior, such as agitation and aggression. Here we review the literature concerning interactions between the circadian and autonomic systems and aggression, and we discuss the implications of these relationships for human neural and behavioral pathologies.

Early life stress and trauma: developmental neuroendocrine aspects of prolonged stress system dysregulation

Experience of early life stress (ELS) and trauma is highly prevalent in the general population and has a high public health impact, as it can trigger a health-related risk cascade and lead to impaired homeostatic balance and elevated cacostatic load even decades later. The prolonged neuropsychobiological impact of ELS can, thus, be conceptualized as a common developmental risk factor for disease associated with increased physical and mental morbidity in later life. ELS during critical periods of brain development with elevated neuroplasticity could exert a programming effect on particular neuronal networks related to the stress response and lead to enduring neuroendocrine alterations, i.e., hyper- or hypoactivation of the stress system, associated with adult hypothalamic-pituitary-adrenal axis and glucocorticoid signaling dysregulation. This paper reviews the pathophysiology of the human stress response and provides evidence from human research on the most acknowledged stress axis-related neuroendocrine pathways exerting the enduring adverse effects of ELS and mediating the cumulative long-term risk of disease vulnerability in adulthood.

Alteration of Circadian Rhythms in 2D2 Transgenic Mice

Background

Several immunological functions are dependent on circadian rhythms. However, there are still relatively few studies about circadian rhythms in neuromyelitis optica spectrum disorders (NMOSD) and 2D2 transgenic mice. We explore whether 2D2 mice have abnormalities in circadian rhythms and the potential underlying molecular mechanism.

Material/Methods

We first observed the wheel-running motion of the control and 2D2 mice using wheel-running measurements. The cytokine levels were also analyzed using enzyme-linked immunosorbent assay (ELISA), and the results of clock gene expressions in the suprachiasmatic nucleus (SCN) were investigated using real-time polymerase chain reaction (real-time PCR).

Results

The wheel-running rhythm in 2D2 mice differed from that of the controls. The TNF-α and IL-10 rhythms were disrupted in 2D2 mice. Additionally, the rhythm of the clock genes, Per1 and Per2, and expression in the SCN of 2D2 mice were also changed.

Conclusions

The results presented here indicate that alteration of circadian rhythms in 2D2 mice affects behavior and immune function, and the potential molecular mechanism might be the Per1 and Per2 expression disorders in the SCN. 2D2 mice might be a suitable model for studying circadian disruption in NMOSD.

Gene expression profiling of the SCN in young and old rhesus macaques

In mammals, the suprachiasmatic nucleus (SCN) is the location of a master circadian pacemaker. It receives photic signals from the environment via the retinal hypothalamic tract, which play a key role in synchronizing the body's endogenously generated circadian rhythms with the 24-h rhythm of the environment. Therefore, it is plausible that age-related changes within the SCN contribute to the etiology of perturbed activity-rest cycles that become prevalent in humans during aging. To test this hypothesis, we used gene arrays and quantitative RT-PCR to profile age-related gene expression changes within the SCN of male rhesus macaques - a pragmatic translational animal model of human aging, which similarly displays an age-related attenuation of daytime activity levels. As expected, the SCN showed high expression of arginine vasopressin, vasoactive intestinal polypeptide, calbindin and nuclear receptor subfamily 1, group D, member 1 (NR1D1) (also known as reverse strand of ERBA (REV-ERBα), both at the mRNA and protein level. However, no obvious difference was detected between the SCNs of young (7-12 years) and old animals (21-26 years), in terms of the expression of core clock genes or genes associated with SCN signaling and neurotransmission. These data demonstrate the resilience of the primate SCN to normal aging, at least at the transcriptional level and, at least in males, suggest that age-related disruption of activity-rest cycles in humans may instead stem from changes within other components of the circadian system, such as desynchronization of subordinate oscillators in other parts of the body.

Sleep and brain infections

Sleep is frequently altered in systemic infections as a component of sickness behavior in response to inflammation. Sleepiness in sickness behavior has been extensively investigated. Much less attention has instead been devoted to sleep and wake alterations in brain infections. Most of these, as other neuroinfections, are prevalent in sub-Saharan Africa. The present overview highlights the importance of this topic from both the clinical and pathogenetic points of view. Vigilance states and their regulation are first summarized, emphasizing that key nodes in this distributed brain system can be targeted by neuroinflammatory signaling. Sleep-wake changes in the parasitic disease human African trypanosomiasis (HAT) and its animal models are then reviewed and discussed. Experimental data have revealed that the suprachiasmatic nucleus, the master circadian pacemaker, and peptidergic cell populations of the lateral hypothalamus (the wake-promoting orexin neurons and the sleep-promoting melanin-concentrating hormone neurons) are targeted by African trypanosome infection. It is then discussed how prominent and disturbing are sleep changes in HIV/AIDS, also when the infection is cured with antiretroviral therapy. This recalls attention on the bidirectional interactions between sleep and immune system, including the specialized brain immune response of which microglial cells are protagonists. Sleep changes in an ancient viral disease, rabies, and in the emerging infection due to Zika virus which causes a congenital syndrome, are also dealt with. Altogether the findings indicate that sleep-wake regulation is targeted by brain infections caused by different pathogens and, although the relevant pathogenetic mechanisms largely remain to be clarified, these alterations differ from hypersomnia occurring in sickness behavior. Thus, brain infections point to the vulnerability of the neural network of sleep-wake regulation as a highly relevant clinical and basic science challenge.

A hypothalamic circuit for the circadian control of aggression

“Sundowning” in dementia and Alzheimer’s disease is characterized by early evening agitation and aggression. While such periodicity suggests a circadian origin, whether the circadian clock directly regulates aggressive behavior is unknown. We demonstrate that a daily rhythm in aggression propensity in male mice is gated by GABAergic subparaventricular zone (SPZ^GABA) neurons, the major postsynaptic targets of the central circadian clock, the suprachiasmatic nucleus (SCN). Optogenetic mapping revealed that SPZ^GABA neurons receive input from vasoactive intestinal polypeptide SCN neurons and innervate neurons in the ventrolateral part of the ventromedial hypothalamus (VMHvl) known to regulate aggression. Additionally, VMH-projecting dorsal SPZ neurons are more active during early day than early night, and acute chemogenetic inhibition of SPZ^GABA transmission phase-dependently increases aggression. Finally, SPZ^GABA-recipient central VMH neurons directly innervate VMHvl neurons and activation of this intra-VMH circuit drove attack behavior. Altogether, we reveal a functional polysynaptic circuit by which the SCN clock regulates aggression.

Hippocampal Neural Circuits Respond to Optogenetic Pacing of Theta Frequencies by Generating Accelerated Oscillation Frequencies

Biological oscillations can be controlled by a small population of rhythmic pacemaker cells, or in the brain, they also can emerge from complex cellular and circuit-level interactions. Whether and how these mechanisms are combined to give rise to oscillatory patterns that govern cognitive function are not well understood. For example, the activity of hippocampal networks is temporally coordinated by a 7- to 9-Hz local field potential (LFP) theta rhythm, yet many individual cells decouple from the LFP frequency to oscillate at frequencies ∼1 Hz higher. To better understand the network interactions that produce these complex oscillatory patterns, we asked whether the relative frequency difference between LFP and individual cells is retained when the LFP frequency is perturbed experimentally. We found that rhythmic optogenetic stimulation of medial septal GABAergic neurons controlled the hippocampal LFP frequency outside of the endogenous theta range, even during behavioral states when endogenous mechanisms would otherwise have generated 7- to 9-Hz theta oscillations. While the LFP frequency matched the optogenetically induced stimulation frequency, the oscillation frequency of individual hippocampal cells remained broadly distributed, and in a subset of cells including interneurons, it was accelerated beyond the new base LFP frequency. The inputs from septal GABAergic neurons to the hippocampus, therefore, do not appear to directly control the cellular oscillation frequency but rather engage cellular and circuit mechanisms that accelerate the rhythmicity of individual cells. Thus, theta oscillations are an example of cortical oscillations that combine inputs from a subcortical pacemaker with local computations to generate complex oscillatory patterns that support cognitive functions.