The hypothalamic integrator for circadian rhythms

Slumber under pressure: REM sleep and stress response

Sleep, a state of reduced responsiveness and distinct brain activity, is crucial across the animal kingdom. This review explores the potential adaptive functions of REM sleep in adapting to stress, emphasizing its role in memory consolidation, emotional regulation, and threat processing. We further explore the underlying neural mechanisms linking stress responses to REM sleep. By synthesizing current findings, we propose that REM sleep allows animals to "rehearse" or simulate responses to danger in a secure, offline state, while also maintaining emotional balance. Environmental factors, such as predation risk and social dynamics, further influence REM sleep. This modulation may enhance survival by optimizing stress responses while fulfilling physiological needs in animals. Insights into REM sleep's role in animals may shed light on human sleep in the context of modern stressors and sleep disruptions. This review also explores the complex interplay between stress, immunity, sleep disruptions-particularly involving REM sleep-and their evolutionary underpinnings.

Effects of menopause on temperature regulation

Changes in thermoregulation, notably the emergence of hot flashes, occur during the menopause transition in association with reproductive hormonal changes. Hot flashes constitute the most characteristic symptom of menopause (prevalence of 50-80%), and have a substantial negative effect on quality of life. Here, we review the endocrine changes associated with menopause and the thermoregulatory system and its sensitivity to female sex hormones. We then review current knowledge on the underlying neural mechanisms of hot flashes and how the reproductive and thermoregulatory systems interact in females. We consider the kisspeptin-neurokinin B-dynorphin (KNDy) neuron complex, which becomes hyperactive when estradiol levels decrease. KNDy neurons project from the arcuate nucleus to thermoregulatory areas within the hypothalamic preoptic area, where heat loss mechanisms are triggered, including cutaneous vasodilation and sweating - characteristics of the hot flash. We describe the physiology and measurement of hot flashes and discuss the mixed research findings about thresholds for sweating in symptomatic individuals. We consider the unique situation of hot flashes that arise during sleep, and discuss the relationships between the environment, exercise, and body mass index with hot flashes. We also discuss the unique situation of surgical menopause (with oophorectomy) and cancer therapy, conditions that are associated with frequent, severe, hot flashes. We then provide an overview of treatments of hot flashes, including hormone therapy and targeted neurokinin B-antagonists, recently developed to target the neural mechanism of hot flashes. Finally, we highlight gaps in knowledge about menopausal thermoregulation and hot flashes and suggest future directions for research.

Melatonin's Role in Hair Follicle Growth and Development: A Cashmere Goat Perspective

Hair follicles, unique skin appendages, undergo cyclic phases (anagen, catagen, telogen) governed by melatonin and associated molecular pathways. Melatonin, synthesized in the pineal gland, skin, and gut, orchestrates these cycles through antioxidant activity and signaling cascades (e.g., Wnt, BMP). This review examines melatonin's biosynthesis across tissues, its regulation of cashmere growth patterns, and its interplay with non-coding RNAs and the gut-skin axis. Recent advances highlight melatonin's dual role in enhancing antioxidant capacity (via Keap1-Nrf2) and modulating gene expression (e.g., Wnt10b, CTNNB1) to promote hair follicle proliferation. By integrating multi-omics insights, we construct a molecular network of melatonin's regulatory mechanisms, offering strategies to improve cashmere yield and quality while advancing therapies for human alopecia.

Acute and circadian feedforward regulation of agouti-related peptide hunger neurons

When food is freely available, eating occurs without energy deficit. While agouti-related peptide (AgRP) neurons are likely involved, their activation is thought to require negative energy balance. To investigate this, we implemented long-term, continuous in vivo fiber-photometry recordings in mice. We discovered new forms of AgRP neuron regulation, including fast pre-ingestive decreases in activity and unexpectedly rapid activation by fasting. Furthermore, AgRP neuron activity has a circadian rhythm that peaks concurrent with the daily feeding onset. Importantly, this rhythm persists when nutrition is provided via constant-rate gastric infusions. Hence, it is not secondary to a circadian feeding rhythm. The AgRP neuron rhythm is driven by the circadian clock, the suprachiasmatic nucleus (SCN), as SCN ablation abolishes the circadian rhythm in AgRP neuron activity and feeding. The SCN activates AgRP neurons via excitatory afferents from thyrotrophin-releasing hormone-expressing neurons in the dorsomedial hypothalamus (DMHTrh neurons) to drive daily feeding rhythms.

Chronodisruption that dampens output of the central clock abolishes rhythms in metabolome profiles and elevates acylcarnitine levels in the liver of female rats

AIM

Exposure to light at night and meal time misaligned with the light/dark (LD) cycle-typical features of daily life in modern 24/7 society-are associated with negative effects on health. To understand the mechanism, we developed a novel protocol of complex chronodisruption (CD) in which we exposed female rats to four weekly cycles consisting of 5-day intervals of constant light and 2-day intervals of food access restricted to the light phase of the 12:12 LD cycle.

METHODS

We examined the effects of CD on behavior, estrous cycle, sleep patterns, glucose homeostasis and profiles of clock- and metabolism-related gene expression (using RT qPCR) and liver metabolome and lipidome (using untargeted metabolomic and lipidomic profiling).

RESULTS

CD attenuated the rhythmic output of the central clock in the suprachiasmatic nucleus via Prok2 signaling, thereby disrupting locomotor activity, the estrous cycle, sleep patterns, and mutual phase relationship between the central and peripheral clocks. In the periphery, CD abolished Per1,2 expression rhythms in peripheral tissues (liver, pancreas, colon) and worsened glucose homeostasis. In the liver, it impaired the expression of NAD+, lipid, and cholesterol metabolism genes and abolished most of the high-amplitude rhythms of lipids and polar metabolites. Interestingly, CD abolished the circadian rhythm of Cpt1a expression and increased the levels of long-chain acylcarnitines (ACar 18:2, ACar 16:0), indicating enhanced fatty acid oxidation in mitochondria.

CONCLUSION

Our data show the widespread effects of CD on metabolism and point to ACars as biomarkers for CD due to misaligned sleep and feeding patterns.

Effects of light on biological functions and human sleep

The nonvisual effects of light in humans are mainly conveyed by a subset of retinal ganglion cells that contain the pigment melanopsin which renders them intrinsically photosensitive (= intrinsically photosensitive retinal ganglion cells, ipRGCs). They have direct connections to the main circadian clock in the suprachiasmatic nuclei (SCN) of the hypothalamus and modulate a variety of physiological processes, pineal melatonin secretion, autonomic functions, cognitive processes such as attention, and behavior, including sleep and wakefulness. This is because efferent projections from the SCN reach other hypothalamic nuclei, the pineal gland, thalamus, basal forebrain, and the brainstem. The ipRGCs also directly impact the prefrontal cortex and the perihabenular nucleus (mood). In particular, light suppresses the secretion of melatonin in a dose-dependent manner, mainly depending on irradiance and spectral composition of light. There is evidence that exposure to light-emitting devices from luminaires and screens before bedtime can impact on sleep onset latency, sleep duration, and sleep quality. Likewise, light exposure during daytime modulates sleep architecture, duration, and sleep quality during the subsequent night. Therefore, the integration of acute, circadian, and long-term effects of light together influence sleep-wake quality and behavior in healthy individuals, as well as in patients with psychiatric or medical disorders.

Epigenetic events influencing the biological clock: Panacea for neurodegeneration

The human biological clock is the 24-h internal molecular network of circadian genes in synchronization with other cells in response to external stimuli. The rhythmicity of the clock genes is maintained by positive and negative transcriptional feedback loops coordinating the 24-h oscillation in different tissues. The superchiasmatic nucleus, the central pacemaker of the biological clock diminishes with aging causing alterations in the clock rhythmicity leading to the onset of neurodegenerative diseases mainly Alzheimer's disease, Parkinson's disease, and Huntington's disease. Studies have shown that brain and muscle Arnt -like 1 (Bmal1) and Circadian Locomotor Output Cycles Kaput (Clock) gene expression is altered in the onset of neurodegeneration. One of the major symptoms of neurodegeneration is changes in the sleep/wake cycle. Moreover, variations in circadian clock oscillations can happen due to lifestyle changes, addiction to alcohol, cocaine, drugs, smoking, food habits and most importantly eating and sleep/awake cycle patterns which can significantly impact the expression of circadian genes. Recent studies have focused on the molecular function of clock genes affected due to environmental cues. Epigenetic modifications are influenced by the external environmental factors. This review aims to focus on the principal mechanism of epigenetics influencing circadian rhythm disruption leading to neurodegeneration and as well as targeting the epigenetic modulators could be a novel therapeutic approach to combat neurodegenerative disorders.

Circadian Clock and Body Temperature

The circadian fluctuation of body temperature is one of the most prominent and stable outputs of the circadian clock and plays an important role in maintaining optimal day-night energy homeostasis. The body temperature of homothermic animals is not strictly constant, but it shows daily oscillation within a range of 1-3 °C, which is sufficient to synchronize the clocks of peripheral tissues throughout the body. The thermal entrainment mechanisms of the clock are partly mediated by the action of the heat shock transcription factor and cold-inducible RNA-binding protein-both have the ability to affect clock gene expression. Body temperature in the poikilotherms is not completely passive to the ambient temperature change; they can travel to the place of preferred temperature in a manner depending on the time of their endogenous clock. Based on this behavior-level thermoregulation, flies exhibit a clear body temperature cycle. Noticeably, flies and mice share the same molecular circuit for the controlled body temperature; in both species, the calcitonin receptors participate in the formation of body temperature rhythms during the active phase and exhibit rather specific expression in subsets of clock neurons in the brain. We summarize knowledge on mutual relationships between body temperature regulation and the circadian clock.

The SCN-HPA-Periphery Circadian Timing System: Mathematical Modeling of Clock Synchronization and the Effects of Photoperiod on Jetlag Adaptation

Synchronizing the circadian timing system (CTS) to external light/dark cycles is crucial for homeostasis maintenance and environmental adaptation. The CTS is organized hierarchically, with the central pacemaker located in the suprachiasmatic nuclei (SCN) generating coherent oscillations that are entrained to light/dark cycles. These oscillations regulate the release of glucocorticoids by the hypothalamus-pituitary-adrenal (HPA) axis, which acts as a systemic entrainer of peripheral clocks throughout the body. The SCN adjusts its network plasticity in response to variations in photoperiod, leading to changes in the rhythmic release of glucocorticoids and ultimately impacting peripheral clocks. However, the effects of photoperiod-induced variations of glucocorticoids on the synchronization of peripheral clocks are not fully understood, and the interaction between jetlag adaption and photoperiod changes is unclear. This study presents a semi-mechanistic mathematical model to investigate how the CTS responds to changes in photoperiod. Specifically, the study focuses on the entrainment properties of a system composed of the SCN, HPA axis, and peripheral clocks. The results show that high-amplitude glucocorticoid rhythms lead to a more coherent phase distribution in the periphery. In addition, our study investigates the effect of photoperiod exposure on jetlag recovery time and phase shift, proposing different interventional strategies for eastward and westward jetlag. The findings suggest that decreasing photic exposure before jetlag during eastward traveling and after jetlag during westward traveling can accelerate jetlag readaptation. The study provides insights into the mechanisms of CTS organization and potential recovery strategies for transitions between time zones and lighting zones.

Twenty-four-hour rhythmicities in disorders of consciousness are associated with a favourable outcome

Fluctuations of consciousness and their rhythmicities have been rarely studied in patients with a disorder of consciousness after acute brain injuries. 24-h assessment of brain (EEG), behaviour (eye-opening), and circadian (clock-controlled hormones secretion from urine) functions was performed in acute brain-injured patients. The distribution, long-term predictability, and rhythmicity (circadian/ultradian) of various EEG features were compared with the initial clinical status, the functional outcome, and the circadian rhythmicities of behaviour and clock-controlled hormones. Here we show that more physiological and favourable patterns of fluctuations are associated with a higher 24 h predictability and sharp up-and-down shape of EEG switches, reminiscent of the Flip-Flop model of sleep. Multimodal rhythmic analysis shows that patients with simultaneous circadian rhythmicity for brain, behaviour, and hormones had a favourable outcome. Finally, both re-emerging EEG fluctuations and homogeneous 24-h cycles for EEG, eye-opening, and hormones appeared as surrogates for preserved functionality in brainstem and basal forebrain, which are key prognostic factors for later improvement. While the recovery of consciousness has previously been related to a high short-term complexity, we suggest in this exploratory study the importance of the high predictability of the 24 h long-term generation of brain rhythms and highlight the importance of circadian body-brain rhythms in awakening.

Light modulates task-dependent thalamo-cortical connectivity during an auditory attentional task

Exposure to blue wavelength light stimulates alertness and performance by modulating a widespread set of task-dependent cortical and subcortical areas. How light affects the crosstalk between brain areas to trigger this stimulating effect is not established. Here we record the brain activity of 19 healthy young participants (24.05±2.63; 12 women) while they complete an auditory attentional task in darkness or under an active (blue-enriched) or a control (orange) light, in an ultra-high-field 7 Tesla MRI scanner. We test if light modulates the effective connectivity between an area of the posterior associative thalamus, encompassing the pulvinar, and the intraparietal sulcus (IPS), key areas in the regulation of attention. We find that only the blue-enriched light strengthens the connection from the posterior thalamus to the IPS. To the best of our knowledge, our results provide the first empirical data supporting that blue wavelength light affects ongoing non-visual cognitive activity by modulating task-dependent information flow from subcortical to cortical areas.

Molecular and Neural Mechanisms of Temperature Preference Rhythm in Drosophila melanogaster

Temperature influences animal physiology and behavior. Animals must set an appropriate body temperature to maintain homeostasis and maximize survival. Mammals set their body temperatures using metabolic and behavioral strategies. The daily fluctuation in body temperature is called the body temperature rhythm (BTR). For example, human body temperature increases during wakefulness and decreases during sleep. BTR is controlled by the circadian clock, is closely linked with metabolism and sleep, and entrains peripheral clocks located in the liver and lungs. However, the underlying mechanisms of BTR are largely unclear. In contrast to mammals, small ectotherms, such as Drosophila, control their body temperatures by choosing appropriate environmental temperatures. The preferred temperature of Drosophila increases during the day and decreases at night; this pattern is referred to as the temperature preference rhythm (TPR). As flies are small ectotherms, their body temperature is close to that of the surrounding environment. Thus, Drosophila TPR produces BTR, which exhibits a pattern similar to that of human BTR. In this review, we summarize the regulatory mechanisms of TPR, including recent studies that describe neuronal circuits relaying ambient temperature information to dorsal neurons (DNs). The neuropeptide diuretic hormone 31 (DH31) and its receptor (DH31R) regulate TPR, and a mammalian homolog of DH31R, the calcitonin receptor (CALCR), also plays an important role in mouse BTR regulation. In addition, both fly TPR and mammalian BTR are separately regulated from another clock output, locomotor activity rhythms. These findings suggest that the fundamental mechanisms of BTR regulation may be conserved between mammals and flies. Furthermore, we discuss the relationships between TPR and other physiological functions, such as sleep. The dissection of the regulatory mechanisms of Drosophila TPR could facilitate an understanding of mammalian BTR and the interaction between BTR and sleep regulation.

Blue-light background impairs visual exogenous attention shift

Previous research into the effects of blue light on visual-spatial attention has yielded mixed results due to a lack of properly controlling critical factors like S-cone stimulation, ipRGCs stimulation, and color. We adopted the clock paradigm and systematically manipulated these factors to see how blue light impacts the speed of exogenous and endogenous attention shifts. Experiments 1 and 2 revealed that, relative to the control light, exposure to the blue-light background decreased the speed of exogenous (but not endogenous) attention shift to external stimuli. To further clarify the contribution(s) of blue-light sensitive photoreceptors (i.e., S-cone and ipRGCs), we used a multi-primary system that could manipulate the stimulation of a single type of photoreceptor without changing the stimulation of other photoreceptors (i.e., the silent substitution method). Experiments 3 and 4 revealed that stimulation of S-cones and ipRGCs did not contribute to the impairment of exogenous attention shift. Our findings suggest that associations with blue colors, such as the concept of blue light hazard, cause exogenous attention shift impairment. Some of the previously documented blue-light effects on cognitive performances need to be reevaluated and reconsidered in light of our findings.

The Mammalian Circadian Time-Keeping System

Our physiology and behavior follow precise daily programs that adapt us to the alternating opportunities and challenges of day and night. Under experimental isolation, these rhythms persist with a period of approximately one day (circadian), demonstrating their control by an internal autonomous clock. Circadian time is created at the cellular level by a transcriptional/translational feedback loop (TTFL) in which the protein products of the Period and Cryptochrome genes inhibit their own transcription. Because the accumulation of protein is slow and delayed, the system oscillates spontaneously with a period of ∼24 hours. This cell-autonomous TTFL controls cycles of gene expression in all major tissues and these cycles underpin our daily metabolic programs. In turn, our innumerable cellular clocks are coordinated by a central pacemaker, the suprachiasmatic nucleus (SCN) of the hypothalamus. When isolated in slice culture, the SCN TTFL and its dependent cycles of neural activity persist indefinitely, operating as "a clock in a dish". In vivo, SCN time is synchronized to solar time by direct innervation from specialized retinal photoreceptors. In turn, the precise circadian cycle of action potential firing signals SCN-generated time to hypothalamic and brain stem targets, which co-ordinate downstream autonomic, endocrine, and behavioral (feeding) cues to synchronize and sustain the distributed cellular clock network. Circadian time therefore pervades every level of biological organization, from molecules to society. Understanding its mechanisms offers important opportunities to mitigate the consequences of circadian disruption, so prevalent in modern societies, that arise from shiftwork, aging, and neurodegenerative diseases, not least Huntington's disease.

The Molecular Relationship between Stress and Insomnia

The bi-directional relationship between sleep and stress has been actively researched as sleep disturbances and stress have become increasingly common in society. Interestingly, the brain and underlying neural circuits important for sleep regulation may respond uniquely to stress that leads to post-traumatic stress disorder (PTSD) and stress that does not. In stress that does not lead to PTSD, the hypothalamic-pituitary-adrenal axis (HPA) pathway is activated normally that results in sympathetic nervous system activation that allows the brain and body to return to baseline functioning. However, exposure to stress that leads to PTSD, causes enhanced negative feedback of this same pathway and results in long-term physiological and psychological changes. In this review, how stress regulates glucocorticoid signaling pathways in brain glial cells called astrocytes, and then mediates stress-induced insomnia are examined. Astrocytes are critical sleep regulatory cells and their connections to sleep and stress due to disturbed glucocorticoid signaling provide a novel mechanism to explain how stress leads to insomnia. This review will examine the interactions of stress neurobiology, astrocytes, sleep, and glucocorticoid signaling pathways and will examine the how stress that leads to PTSD and stress that does not impacts sleep-regulatory processes.

Mammalian circadian networks mediated by the suprachiasmatic nucleus

The brain has a complex structure composed of hundreds of regions, forming networks to cooperate body functions. Therefore, understanding how various brain regions communicate with each other and with peripheral organs is important to understand human physiology. The suprachiasmatic nucleus (SCN) in the brain is the circadian pacemaker. The SCN receives photic information from the environment and conveys this to other parts of the brain and body to synchronize all circadian clocks. The circadian clock is an endogenous oscillator that generates daily rhythms in metabolism and physiology in almost all cells via a conserved transcriptional-translational negative feedback loop. So, the information flow from the environment to the SCN to other tissues synchronizes locally distributed circadian clocks to maintain homeostasis. Thus, understanding the circadian networks and how they adjust to environmental changes will better understand human physiology. This review will focus on circadian networks mediated by the SCN to understand how the environment, brain, and peripheral tissues form networks for cooperation.

Physiological and pharmacological perspectives of melatonin

The pineal gland is a interface between light-dark cycle and shows neuro-endocrine functions. Melatonin is the primary hormone of pineal gland, secreted at night. The night-time melatonin peak regulates the physiological functions at dark. Melatonin has several unique features as it synchronises internal rhythm with daily and seasonal variations, regulates circadian rhythm and sleep-wake cycle. Physiologically melatonin involves in detoxification of free radicals, immune functions, neuro-protection, oncostatic effects, cardiovascular functions, reproduction, and foetal development. The precise functions of melatonin are exhibited by specific receptors. In relation to pathophysiology, impaired melatonin secretion promotes sleep disorder, cancer progression, type-2 diabetes, and neurodegenerative diseases. Several reports have highlighted the therapeutic benefits of melatonin specially related to cancer protection, sleep disorder, psychiatric disorders, and jet lag problems. This review will touch the most of the area of melatonin-oriented health impacts and its therapeutic aspects.

Convergence of monosynaptic inputs from neurons in the brainstem and forebrain on parabrachial neurons that project to the paraventricular nucleus of the thalamus

The paraventricular nucleus of the thalamus (PVT) projects to areas of the forebrain involved in regulating behavior. Homeostatic challenges and salient cues activate the PVT and evidence shows that the PVT regulates appetitive and aversive responses. The brainstem is a source of afferents to the PVT and the present study was done to determine if the lateral parabrachial nucleus (LPB) is a relay for inputs to the PVT. Retrograde tracing experiments with cholera toxin B (CTB) demonstrate that the LPB contains more PVT projecting neurons than other regions of the brainstem including the catecholamine cell groups. The hypothesis that the LPB is a relay for signals to the PVT was assessed using an intersectional monosynaptic rabies tracing approach. Sources of inputs to LPB included the reticular formation; periaqueductal gray (PAG); nucleus cuneiformis; and superior and inferior colliculi. Distinctive clusters of input cells to LPB-PVT projecting neurons were also found in the dorsolateral bed nucleus of the stria terminalis (BSTDL) and the lateral central nucleus of the amygdala (CeL). Anterograde viral tracing demonstrates that LPB-PVT neurons densely innervate all regions of the PVT in addition to providing collateral innervation to the preoptic area, lateral hypothalamus, zona incerta and PAG but not the BSTDL and CeL. The paper discusses the anatomical evidence that suggests that the PVT is part of a network of interconnected neurons involved in arousal, homeostasis, and the regulation of behavioral states with forebrain regions potentially providing descending modulation or gating of signals relayed from the LPB to the PVT.

Translational Approaches to Influence Sleep and Arousal

Sleep disorders are widespread in society and are prevalent in military personnel and in Veterans. Disturbances of sleep and arousal mechanisms are common in neuropsychiatric disorders such as schizophrenia, post-traumatic stress disorder, anxiety and affective disorders, traumatic brain injury, dementia, and substance use disorders. Sleep disturbances exacerbate suicidal ideation, a major concern for Veterans and in the general population. These disturbances impair quality of life, affect interpersonal relationships, reduce work productivity, exacerbate clinical features of other disorders, and impair recovery. Thus, approaches to improve sleep and modulate arousal are needed. Basic science research on the brain circuitry controlling sleep and arousal led to the recent approval of new drugs targeting the orexin/hypocretin and histamine systems, complementing existing drugs which affect GABA_A receptors and monoaminergic systems. Non-invasive brain stimulation techniques to modulate sleep and arousal are safe and show potential but require further development to be widely applicable. Invasive viral vector and deep brain stimulation approaches are also in their infancy but may be used to modulate sleep and arousal in severe neurological and psychiatric conditions. Behavioral, pharmacological, non-invasive brain stimulation and cell-specific invasive approaches covered here suggest the potential to selectively influence arousal, sleep initiation, sleep maintenance or sleep-stage specific phenomena such as sleep spindles or slow wave activity. These manipulations can positively impact the treatment of a wide range of neurological and psychiatric disorders by promoting the restorative effects of sleep on memory consolidation, clearance of toxic metabolites, metabolism, and immune function and by decreasing hyperarousal.

Circadian clocks, cognition, and Alzheimer's disease: synaptic mechanisms, signaling effectors, and chronotherapeutics

Modulation of basic biochemical and physiological processes by the circadian timing system is now recognized as a fundamental feature of all mammalian organ systems. Within the central nervous system, these clock-modulating effects are reflected in some of the most complex behavioral states including learning, memory, and mood. How the clock shapes these behavioral processes is only now beginning to be realized. In this review we describe recent findings regarding the complex set of cellular signaling events, including kinase pathways, gene networks, and synaptic circuits that are under the influence of the clock timing system and how this, in turn, shapes cognitive capacity over the circadian cycle. Further, we discuss the functional roles of the master circadian clock located in the suprachiasmatic nucleus, and peripheral oscillator populations within cortical and limbic circuits, in the gating of synaptic plasticity and memory over the circadian cycle. These findings are then used as the basis to discuss the connection between clock dysregulation and cognitive impairments resulting from Alzheimer's disease (AD). In addition, we discuss the conceptually novel idea that in AD, there is a selective disruption of circadian timing within cortical and limbic circuits, and that it is the disruption/desynchronization of these regions from the phase-entraining effects of the SCN that underlies aspects of the early- and mid-stage cognitive deficits in AD. Further, we discuss the prospect that the disruption of circadian timing in AD could produce a self-reinforcing feedback loop, where disruption of timing accelerates AD pathogenesis (e.g., amyloid deposition, oxidative stress and cell death) that in turn leads to a further disruption of the circadian timing system. Lastly, we address potential therapeutic approaches that could be used to strengthen cellular timing networks and, in turn, how these approaches could be used to improve cognitive capacity in Alzheimer's patients.

Orexin enhances neuronal synchronization in adult rat hypothalamic culture: a model to study hypothalamic function

The regulation of sleep/wake behavior and energy homeostasis is maintained in part by the hypothalamic neuropeptide orexin A (OXA, hypocretin). Reduction in orexin signaling is associated with sleep disorders and obesity, whereas higher lateral hypothalamic (LH) orexin signaling and sensitivity promotes obesity resistance. Similarly, dysregulation of hypothalamic neural networks is associated with onset of age-related diseases, including obesity and several neurological diseases. Despite the association of obesity and aging, and that adult populations are the target for the majority of pharmaceutical and obesity studies, conventional models for neuronal networks utilize embryonic neural cultures rather than adult neurons. Synchronous activity describes correlated changes in neuronal activity between neurons and is a feature of normal brain function, and is a measure of functional connectivity and final output from a given neural structure. Earlier studies show alterations in hypothalamic synchronicity following behavioral perturbations in embryonic neurons obtained from obesity-resistant rats and following application of orexin onto embryonic hypothalamic cultures. Synchronous network dynamics in adult hypothalamic neurons remain largely undescribed. To address this, we established an adult rat hypothalamic culture in multi-electrode-array (MEA) dishes and recorded the field potentials. Then we studied the effect of exogenous orexin on network synchronization of these adult hypothalamic cultures. In addition, we studied the wake promoting effects of orexin in vivo when directly injected into the lateral hypothalamus (LH). Our results showed that the adult hypothalamic cultures are viable for nearly 3 mo in vitro, good quality MEA recordings can be obtained from these cultures in vitro, and finally, that cultured adult hypothalamus is responsive to orexin. These results support that adult rat hypothalamic cultures could be used as a model to study the neural mechanisms underlying obesity. In addition, LH administration of OXA enhanced wakefulness in rats, indicating that OXA enhances wakefulness partly by promoting neural synchrony in the hypothalamus.NEW & NOTEWORTHY This study, for the first time, demonstrates that adult hypothalamic cultures are viable in vitro for a prolonged duration and are electrophysiologically active. In addition, the study shows that orexin enhances neural synchronization in adult hypothalamic cultures.

Dorsal clock networks drive temperature preference rhythms in Drosophila

Animals display a body temperature rhythm (BTR). Little is known about the mechanisms by which a rhythmic pattern of BTR is regulated and how body temperature is set at different times of the day. As small ectotherms, Drosophila exhibit a daily temperature preference rhythm (TPR), which generates BTR. Here, we demonstrate dorsal clock networks that play essential roles in TPR. Dorsal neurons 2 (DN2s) are the main clock for TPR. We find that DN2s and posterior DN1s (DN1ps) contact and the extent of contacts increases during the day and that the silencing of DN2s or DN1ps leads to a lower temperature preference. The data suggest that temporal control of the microcircuit from DN2s to DN1ps contributes to TPR regulation. We also identify anterior DN1s (DN1as) as another important clock for TPR. Thus, we show that the DN networks predominantly control TPR and determine both a rhythmic pattern and preferred temperatures.

Median preoptic GABA and glutamate neurons exert differential control over sleep behavior

Previous studies suggest that the median preoptic nucleus (MnPO) of the hypothalamus plays an important role in regulating the wake-sleep cycle and, in particular, homeostatic sleep drive. However, the precise cellular phenotypes, targets, and central mechanisms by which the MnPO neurons regulate the wake-sleep cycle remain unknown. Both excitatory and inhibitory MnPO neurons innervate brain regions implicated in sleep promotion and maintenance, suggesting that both cell types may participate in sleep control. Using genetically targeted approaches, we investigated the role of the MnPO GABAergic (MnPO^Vgat) and glutamatergic (MnPO^Vglut2) neurons in modulating wake-sleep behavior of mice. We found that both neuron populations differentially participate in wake-sleep control, with MnPO^Vgat neurons being involved in sleep homeostasis and MnPO^Vglut2 neurons facilitating sleep during allostatic (stressful) challenges.

An Edge Computing and Ambient Data Capture System for Clinical and Home Environments

The non-contact patient monitoring paradigm moves patient care into their homes and enables long-term patient studies. The challenge, however, is to make the system non-intrusive, privacy-preserving, and low-cost. To this end, we describe an open-source edge computing and ambient data capture system, developed using low-cost and readily available hardware. We describe five applications of our ambient data capture system. Namely: (1) Estimating occupancy and human activity phenotyping; (2) Medical equipment alarm classification; (3) Geolocation of humans in a built environment; (4) Ambient light logging; and (5) Ambient temperature and humidity logging. We obtained an accuracy of 94% for estimating occupancy from video. We stress-tested the alarm note classification in the absence and presence of speech and obtained micro averaged F1 scores of 0.98 and 0.93, respectively. The geolocation tracking provided a room-level accuracy of 98.7%. The root mean square error in the temperature sensor validation task was 0.3°C and for the humidity sensor, it was 1% Relative Humidity. The low-cost edge computing system presented here demonstrated the ability to capture and analyze a wide range of activities in a privacy-preserving manner in clinical and home environments and is able to provide key insights into the healthcare practices and patient behaviors.

Therapeutic Effect and Mechanism of Acupuncture in Autoimmune Diseases

Autoimmune diseases (AIDs) are conditions arising from abnormal immune reactions to autoantigens, which can be defined as the loss of immune tolerance to autoantigens, causing the production of autoantibodies and subsequent inflammation and tissue injury. The etiology of AIDs remains elusive, which may involve both genetic and environmental factors, such as diet, drugs, and infections. Despite rapid progress in the treatment of autoimmune diseases over the past few decades, there is still no approach that can cure AIDs. As an alternative approach, traditional Chinese medicine (TCM) such as acupuncture has been used in an attempt to treat AIDs including multiple sclerosis (MS), rheumatoid arthritis (RA), and inflammatory bowel disease (IBD), and the results have proven to be quite promising, despite the fact that its mechanism is still not fully understood. In this review, the present knowledge regarding mechanisms of acupuncture in the treatment of AIDs has been summarized, and deeper insights will be provided in order to better understand how acupuncture may regulate immune responses during AIDs.

Systematic review of drugs that modify the circadian system's phase-shifting responses to light exposure

We searched PubMed for primary research quantifying drug modification of light-induced circadian phase-shifting in rodents. This search, conducted for work published between 1960 and 2018, yielded a total of 146 papers reporting results from 901 studies. Relevant articles were those with any extractable data on phase resetting in wildtype (non-trait selected) rodents administered a drug, alongside a vehicle/control group, near or at the time of exposure. Most circadian pharmacology experiments were done using drugs thought to act directly on either the brain's central pacemaker, the suprachiasmatic nucleus (SCN), the SCN's primary relay, the retinohypothalamic tract, secondary pathways originating from the medial/dorsal raphe nuclei and intergeniculate leaflet, or the brain's sleep-arousal centers. While the neurotransmitter systems underlying these circuits were of particular interest, including those involving glutamate, gamma-aminobutyric acid, serotonin, and acetylcholine, other signaling modalities have also been assessed, including agonists and antagonists of receptors linked to dopamine, histamine, endocannabinoids, adenosine, opioids, and second-messenger pathways downstream of glutamate receptor activation. In an effort to identify drugs that unduly influence circadian responses to light, we quantified the net effects of each drug class by ratioing the size of the phase-shift observed after administration to that observed with vehicle in a given experiment. This allowed us to organize data across the literature, compare the relative efficacy of one mechanism versus another, and clarify which drugs might best suppress or potentiate phase resetting. Aggregation of the available data in this manner suggested that several candidates might be clinically relevant as auxiliary treatments to suppress ectopic light responses during shiftwork or amplify the circadian effects of timed bright light therapy. Future empirical research will be necessary to validate these possibilities.

Orexin, serotonin, and energy balance

The lateral hypothalamus is critical for the control of ingestive behavior and spontaneous physical activity (SPA), as lesion or stimulation of this region alters these behaviors. Evidence points to lateral hypothalamic orexin neurons as modulators of feeding and SPA. These neurons affect a broad range of systems, and project to multiple brain regions such as the dorsal raphe nucleus, which contains serotoninergic neurons (DRN) important to energy homeostasis. Physical activity is comprised of intentional exercise and SPA. These are opposite ends of a continuum of physical activity intensity and structure. Non‐goal‐oriented behaviors, such as fidgeting, standing, and ambulating, constitute SPA in humans, and reflect a propensity for activity separate from intentional activity, such as high‐intensity voluntary exercise. In animals, SPA is activity not influenced by rewards such as food or a running wheel. Spontaneous physical activity in humans and animals burns calories and could theoretically be manipulated pharmacologically to expend calories and protect against obesity. The DRN neurons receive orexin inputs, and project heavily onto cortical and subcortical areas involved in movement, feeding and energy expenditure (EE). This review discusses the function of hypothalamic orexin in energy‐homeostasis, the interaction with DRN serotonin neurons, and the role of this orexin‐serotonin axis in regulating food intake, SPA, and EE. In addition, we discuss possible brain areas involved in orexin–serotonin cross‐talk; the role of serotonin receptors, transporters and uptake‐inhibitors in the pathogenesis and treatment of obesity; animal models of obesity with impaired serotonin‐function; single‐nucleotide polymorphisms in the serotonin system and obesity; and future directions in the orexin–serotonin field.

This article is categorized under:

Metabolic Diseases > Molecular and Cellular Physiology

Organizing a Rational Approach to Treatments of Disorders of Consciousness Using the Anterior Forebrain Mesocircuit Model

SUMMARY

Organizing a rational treatment strategy for patients with multifocal structural brain injuries and disorders of consciousness (DOC) is an important and challenging clinical goal. Among potential clinical end points, restoring elements of communication to DOC patients can support improved patient care, caregiver satisfaction, and patients' quality of life. Over the past decade, several studies have considered the use of the anterior forebrain mesocircuit model to approach this problem because this model proposes a supervening circuit-level impairment arising across DOC of varying etiologies. We review both the conceptual foundation of the mesocircuit model and studies of mechanisms underlying DOC that test predictions of this model. We consider how this model can guide therapeutic interventions and discuss a proposed treatment algorithm based on these ideas. Although the approach reviewed originates in the evaluation of patients with chronic DOC, we consider some emerging implications for patients in acute and subacute settings.

Infant diurnal cortisol predicts sleep

The sleep-wake system is immature at birth and develops in parallel with the hypothalamic-pituitary-adrenal axis, a biological stress system of which the end product is cortisol. Perturbations in one system during infancy can maladaptively influence the maturation of the other system, leading to lasting sleep and cortisol system dysregulation and heightening the risk of enduring health problems. To better understand the early interplay between these systems, we examined whether actigraphy-derived measures of night-time sleep duration and onset were associated with cumulative exposure to cortisol, indexed by hair cortisol concentration, in 12-month-old children. Overall, early sleep onset predicted lower hair cortisol above and beyond sleep duration, family income and chaos experienced at home. Furthermore, both sleep and cortisol levels vary day to day, and temporal dependencies between daily sleep and cortisol regulation are not well understood. Thus, we assessed how the sleep characteristics on a particular evening related to salivary cortisol levels the following day and how daytime and evening cortisol related to the sleep characteristics on the same night. Lower total exposure to cortisol on a particular day was related to longer night-time sleep duration the same night, but not sleep onset. Lower salivary cortisol levels on a given evening related to earlier sleep onset the same night, but not to night-time sleep duration. Sleep duration and onset on a given night were unrelated to total cortisol exposure the following day. Findings suggest that in early development, the day-to-day relation between sleep and cortisol is not bidirectional, but more driven by diurnal cortisol.

Neural circuit mechanisms that govern inter-male attack in mice

Individuals of many species fight with conspecifics to gain access to or defend critical resources essential for survival and reproduction. Such intraspecific fighting is evolutionarily selected for in a species-, sex-, and environment-dependent manner when the value of resources secured exceeds the cost of fighting. One such example is males fighting for chances to mate with females. Recent advances in new tools open up ways to dissect the detailed neural circuit mechanisms that govern intraspecific, particularly inter-male, aggression in the model organism Mus musculus (house mouse). By targeting and functional manipulating genetically defined populations of neurons and their projections, these studies reveal a core neural circuit that controls the display of reactive male-male attacks in mice, from sensory detection to decision making and action selection. Here, we summarize these critical results. We then describe various modulatory inputs that route into the core circuit to afford state-dependent and top-down modulation of inter-male attacks. While reviewing these exciting developments, we note that how the inter-male attack circuit converges or diverges with neural circuits that mediate other forms of social interactions remain not fully understood. Finally, we emphasize the importance of combining circuit, pharmacological, and genetic analysis when studying the neural control of aggression in the future.

Mechanisms Driving Palmitate-Mediated Neuronal Dysregulation in the Hypothalamus

The hypothalamus maintains whole-body homeostasis by integrating information from circulating hormones, nutrients and signaling molecules. Distinct neuronal subpopulations that express and secrete unique neuropeptides execute the individual functions of the hypothalamus, including, but not limited to, the regulation of energy homeostasis, reproduction and circadian rhythms. Alterations at the hypothalamic level can lead to a myriad of diseases, such as type 2 diabetes mellitus, obesity, and infertility. The excessive consumption of saturated fatty acids can induce neuroinflammation, endoplasmic reticulum stress, and resistance to peripheral signals, ultimately leading to hyperphagia, obesity, impaired reproductive function and disturbed circadian rhythms. This review focuses on the how the changes in the underlying molecular mechanisms caused by palmitate exposure, the most commonly consumed saturated fatty acid, and the potential involvement of microRNAs, a class of non-coding RNA molecules that regulate gene expression post-transcriptionally, can result in detrimental alterations in protein expression and content. Studying the involvement of microRNAs in hypothalamic function holds immense potential, as these molecular markers are quickly proving to be valuable tools in the diagnosis and treatment of metabolic disease.

Changes of discharge properties of neurons from dorsomedial hypothalamic nuclei during aging in rats

The hypothalamus is a vital brain center that is participated in the integration of the endocrine and nervous systems and control of the homeostasis and aging. Spontaneous firing activity from single neurons of the dorsomedial hypothalamic nucleus (DMN) was studied extracellularly in vivo in urethane-anaesthetized rats. The discharge patterns of the majority of DMN neurons were irregular, including periods of relatively stable activity interrupted by pauses. Based on the features of interval interspike histogram, we have selected neurons with an irregular arrhythmic activity (50% in young, 46% in adult and 44% in aged rats), with a constant rhythmic activity (18% of neurons in young, 19% in adult and 23% in aged rats), with a wide interspike interval distribution (22% in young, 26% in adult and 25% in aged rats) and cells with bursts of two or three spikes (10% in young, 9% in adult and 8% in aged rats). The firing rate of DMN neurons was 2.5 ± 0.12 Hz in young and 2.4 ± 0.21 Hz in adult rats and significantly decreased to 1.8 ± 0.17 Hz in aged rats.

Timed daily exercise remodels circadian rhythms in mice

Regular exercise is important for physical and mental health. An underexplored and intriguing property of exercise is its actions on the body’s 24 h or circadian rhythms. Molecular clock cells in the brain’s suprachiasmatic nuclei (SCN) use electrical and chemical signals to orchestrate their activity and convey time of day information to the rest of the brain and body. To date, the long-lasting effects of regular physical exercise on SCN clock cell coordination and communication remain unresolved. Utilizing mouse models in which SCN intercellular neuropeptide signaling is impaired as well as those with intact SCN neurochemical signaling, we examined how daily scheduled voluntary exercise (SVE) influenced behavioral rhythms and SCN molecular and neuronal activities. We show that in mice with disrupted neuropeptide signaling, SVE promotes SCN clock cell synchrony and robust 24 h rhythms in behavior. Interestingly, in both intact and neuropeptide signaling deficient animals, SVE reduces SCN neural activity and alters GABAergic signaling. These findings illustrate the potential utility of regular exercise as a long-lasting and effective non-invasive intervention in the elderly or mentally ill where circadian rhythms can be blunted and poorly aligned to the external world.

Using mice with disrupted neuropeptide signaling, Hughes et al. show that daily scheduled voluntary exercise (SVE) promotes suprachiasmatic nuclei (SCN) clock cell synchrony and robust 24 h rhythms in behavior. This study suggests the potential utility of regular exercise as a non-invasive intervention for the elderly or mentally ill, where circadian rhythms can be poorly aligned to the external world.

Be cool to be far: Exploiting hibernation for space exploration

In mammals, torpor/hibernation is a state that is characterized by an active reduction in metabolic rate followed by a progressive decrease in body temperature. Torpor was successfully mimicked in non-hibernators by inhibiting the activity of neurons within the brainstem region of the Raphe Pallidus, or by activating the adenosine A1 receptors in the brain. This state, called synthetic torpor, may be exploited for many medical applications, and for space exploration, providing many benefits for biological adaptation to the space environment, among which an enhanced protection from cosmic rays. As regards the use of synthetic torpor in space, to fully evaluate the degree of physiological advantage provided by this state, it is strongly advisable to move from Earth-based experiments to 'in the field' tests, possibly on board the International Space Station.

Thermographic imaging of mouse across circadian time reveals body surface temperature elevation associated with non-locomotor body movements

Circadian clocks orchestrate multiple different physiological rhythms in a well-synchronized manner. However, how these separate rhythms are interconnected is not exactly understood. Here, we developed a method that allows for the real-time simultaneous measurement of locomotor activity and body temperature of mice using infrared video camera imaging. As expected from the literature, temporal profiles of body temperature and locomotor activity were positively correlated with each other. Basically, body temperatures were high when animals were in locomotion. However, interestingly, increases in body temperature were not always associated with the appearance of locomotor activity. Video imaging revealed that mice exhibit non-locomotor activities such as grooming and postural adjustments, which alone induce considerable elevation of body temperature. Noticeably, non-locomotor movements always preceded the initiation of locomotor activity. Nevertheless, non-locomotor movements were not always accompanied by locomotor movements, suggesting that non-locomotor movements provide a mechanism of thermoregulation independent of locomotor activity. In addition, in the current study, we also report the development of a machine learning-based recording method for the detection of circadian feeding and drinking behaviors of mice. Our data illustrate the potential utility of thermal video imaging in the investigation of different physiological rhythms.

Extensive divergence of projections to the forebrain from neurons in the paraventricular nucleus of the thalamus

Neurons in the paraventricular nucleus of the thalamus (PVT) respond to emotionally salient events and project densely to subcortical regions known to mediate adaptive behavioral responses. The areas of the forebrain most densely innervated by the PVT include striatal-like subcortical regions that consist of the shell of the nucleus accumbens (NAcSh), the dorsolateral region of the bed nucleus of the stria terminalis (BSTDL) and the lateral-capsular division of the central nucleus of the amygdala (CeL). A recent tracing experiment demonstrated that the PVT is composed of two intermixed populations of neurons that primarily project to either the dorsomedial (dmNAcSh) or ventromedial region of the NAcSh (vmNAcSh) with many of the vmNAcSh projecting neurons providing collateral innervation of the BSTDL and CeL. The present study used triple injections of the retrograde tracer cholera toxin B to provide a detailed map of the location of PVT neurons that provide collaterals to the vmNAcSh, BSTDL and CeL. These neurons were intermixed throughout the PVT and did not form uniquely localized subpopulations. An intersectional viral anterograde tracing approach was used to demonstrate that regardless of its presumed target of innervation (dmNAcSh, vmNAcSh, BSTDL, or CeL), most neurons in the PVT provide collateral innervation to a common set of forebrain regions. The paper shows that PVT-dmNAcSh projecting neurons provide the most divergent projection system and that these neurons express the immediate early gene product cFos following an aversive incident. We propose that the PVT may regulate a broad range of responses to physiological and psychological challenges by simultaneously influencing functionally diverse regions of the forebrain that include the cortex, striatal-like regions in the basal forebrain and a number of hypothalamic nuclei.

Circadian Rhythm Disorders and Corresponding Functional Brain Abnormalities in Young Female Nurses: A Preliminary Study

Objective: Shift work is associated with a decrease in melatonin level and perturbation of the circadian rhythm; however, it is unknown if these lead to functional brain changes. In this study, we investigated whether circadian rhythm disorders caused by shift work are related to changes in brain functional connectivity (FC) and regional homogeneity (ReHo) using whole-brain resting-state functional magnetic resonance imaging (fMRI).

Methods: This prospective case-control study included nine female night shift nurses and nine age-matched female day work nurses with normal sleep rhythms. To assess sleep quality and mood, participants were asked to complete questionnaires. Serum melatonin and cortisol levels were measured. ReHo of whole-brain resting-state function and seed-based FC of the bilateral hypothalamus were compared between groups. Variables that differed significantly between groups were used to examine the association between questionnaire scores and hormone levels and fMRI data.

Results: The night shift nurses had significantly lower sleep quality and melatonin levels; lower ReHo activation in the bilateral cerebellar hemisphere and higher ReHo in the bilateral occipital lobe and left parietal lobe; and higher FC from the hypothalamus to the right cingulate gyrus, right putamen, and vermis than did the day shift nurses. Activation of the right cerebellar hemisphere left superior parietal gyrus, and the right superior occipital gyrus was correlated with sleep quality scores. Moreover, activation of the right cerebellar hemisphere (r = 0.583, P = 0.011) was correlated with melatonin levels, and higher sleepiness scores were associated with stronger FC between the hypothalamus and vermis (r = 0.501, P = 0.034).

Conclusions: Circadian rhythm disorder caused by night shift work can lead to a decrease in sleep quality and melatonin level, as well as a series of changes in brain FC and ReHo.

Adult hypothalamic neurogenesis and sleep-wake dysfunction in aging

In the mammalian brain, adult neurogenesis has been extensively studied in the hippocampal sub-granular zone and the sub-ventricular zone of the anterolateral ventricles. However, growing evidence suggests that new cells are not only "born" constitutively in the adult hypothalamus, but many of these cells also differentiate into neurons and glia and serve specific functions. The preoptic-hypothalamic area plays a central role in the regulation of many critical functions, including sleep-wakefulness and circadian rhythms. While a role for adult hippocampal neurogenesis in regulating hippocampus-dependent functions, including cognition, has been extensively studied, adult hypothalamic neurogenic process and its contributions to various hypothalamic functions, including sleep-wake regulation are just beginning to unravel. This review is aimed at providing the current understanding of the hypothalamic adult neurogenic processes and the extent to which it affects hypothalamic functions, including sleep-wake regulation. We propose that hypothalamic neurogenic processes are vital for maintaining the proper functioning of the hypothalamic sleep-wake and circadian systems in the face of regulatory challenges. Sleep-wake disturbance is a frequent and challenging problem of aging and age-related neurodegenerative diseases. Aging is also associated with a decline in the neurogenic process. We discuss a hypothesis that a decrease in the hypothalamic neurogenic process underlies the aging of its sleep-wake and circadian systems and associated sleep-wake disturbance. We further discuss whether neuro-regenerative approaches, including pharmacological and non-pharmacological stimulation of endogenous neural stem and progenitor cells in hypothalamic neurogenic niches, can be used for mitigating sleep-wake and other hypothalamic dysfunctions in aging.

Resilience in the suprachiasmatic nucleus: Implications for aging and Alzheimer's disease

Many believe that the circadian impairments associated with aging and Alzheimer's disease are, simply enough, a byproduct of tissue degeneration within the central pacemaker, the suprachiasmatic nucleus (SCN). However, the findings that have accumulated to date examining the SCNs obtained postmortem from the brains of older individuals, or those diagnosed with Alzheimer's disease upon autopsy, suggest only limited atrophy. We review this literature as well as a complementary one concerning fetal-donor SCN transplant, which established that many circadian timekeeping functions can be maintained with rudimentary (structurally limited) representations of the SCN. Together, these corpora of data suggest that the SCN is a resilient brain region that cannot be directly (or solely) implicated in the behavioral manifestations of circadian disorganization often witnessed during aging as well as early and late progression of Alzheimer's disease. We complete our review by suggesting future directions of research that may bridge this conceptual divide and briefly discuss the implications of it for improving health outcomes in later adulthood.

Leptin receptor neurons in the dorsomedial hypothalamus regulate diurnal patterns of feeding, locomotion, and metabolism

The brain plays an essential role in driving daily rhythms of behavior and metabolism in harmony with environmental light-dark cycles. Within the brain, the dorsomedial hypothalamic nucleus (DMH) has been implicated in the integrative circadian control of feeding and energy homeostasis, but the underlying cell types are unknown. Here, we identify a role for DMH leptin receptor-expressing (DMH^LepR) neurons in this integrative control. Using a viral approach, we show that silencing neurotransmission in DMH^LepR neurons in adult mice not only increases body weight and adiposity but also phase-advances diurnal rhythms of feeding and metabolism into the light cycle and abolishes the normal increase in dark-cycle locomotor activity characteristic of nocturnal rodents. Finally, DMH^LepR-silenced mice fail to entrain to a restrictive change in food availability. Together, these findings identify DMH^LepR neurons as critical determinants of the daily time of feeding and associated metabolic rhythms.

Characterization of mWake expression in the murine brain

Structure-function analyses of the mammalian brain have historically relied on anatomically-based approaches. In these investigations, physical, chemical, or electrolytic lesions of anatomical structures are applied, and the resulting behavioral or physiological responses assayed. An alternative approach is to focus on the expression pattern of a molecule whose function has been characterized and then use genetic intersectional methods to optogenetically or chemogenetically manipulate distinct circuits. We previously identified WIDE AWAKE (WAKE) in Drosophila, a clock output molecule that mediates the temporal regulation of sleep onset and sleep maintenance. More recently, we have studied the mouse homolog, mWAKE/ANKFN1, and our data suggest that its basic role in the circadian regulation of arousal is conserved. Here, we perform a systematic analysis of the expression pattern of mWake mRNA, protein, and cells throughout the adult mouse brain. We find that mWAKE labels neurons in a restricted, but distributed manner, in multiple regions of the hypothalamus (including the suprachiasmatic nucleus, dorsomedial hypothalamus, and tuberomammillary nucleus region), the limbic system, sensory processing nuclei, and additional specific brainstem, subcortical, and cortical areas. Interestingly, mWAKE is also observed in non-neuronal ependymal cells. In addition, to describe the molecular identities and clustering of mWake⁺ cells, we provide detailed analyses of single cell RNA sequencing data from the hypothalamus, a region with particularly significant mWAKE expression. These findings lay the groundwork for future studies into the potential role of mWAKE⁺ cells in the rhythmic control of diverse behaviors and physiological processes.

Association between circadian disruption and diseases: A narrative review

Circadian rhythms play an important role in a wide range of human physiology and pathology. Individuals increasingly experience situations such as night-shift work schedules, likely leading to circadian disruption. Recent studies have also demonstrated that patients with other diseases often show symptoms of circadian disruption as manifested by the sleep-wake cycle and other biological rhythms. Circadian disruption often results in changes to the phase, period, and amplitude of the sleep-wake cycle, melatonin rhythm, and core body temperature. Several cardiometabolic, psychiatric, and neurodegenerative diseases are closely related to circadian disruption. Several interventions are also available, including phototherapy, exogenous melatonin, and exercise. The cumulative findings suggest that circadian disruption can increase risk for some cardiometabolic diseases. Circadian disruption also acts as a concomitant symptom of several psychiatric and neurodegenerative diseases. More attention should be paid to evaluating the impact of circadian disruption on these related diseases, as well as the benefits of the mitigation interventions for both circadian disruption and related diseases.

The Potential Roles of Ghrelin in Metabolic Syndrome and Secondary Symptoms of Alzheimer's Disease

Although the major causative factors of Alzheimer's disease (AD) are the accumulation of amyloid β and hyperphosphorylated tau, AD can also be caused by metabolic dysfunction. The major clinical symptom of AD is cognitive dysfunction. However, AD is also accompanied by various secondary symptoms such as depression, sleep-wake disturbances, and abnormal eating behaviors. Interestingly, the orexigenic hormone ghrelin has been suggested to have beneficial effects on AD-related metabolic syndrome and secondary symptoms. Ghrelin improves lipid distribution and alters insulin sensitivity, effects that are hypothesized to delay the progression of AD. Furthermore, ghrelin can relieve depression by enhancing the secretion of hormones such as serotonin, noradrenaline, and orexin. Moreover, ghrelin can upregulate the expression of neurotrophic factors such as brain-derived neurotrophic factor and modulate the release of proinflammatory cytokines such as tumor necrosis factor α and interleukin 1β. Ghrelin alleviates sleep-wake disturbances by increasing the levels of melatonin, melanin-concentrating hormone. Ghrelin reduces the risk of abnormal eating behaviors by increasing neuropeptide Y and γ-aminobutyric acid. In addition, ghrelin increases food intake by inhibiting fatty acid biosynthesis. However, despite the numerous studies on the role of ghrelin in the AD-related pathology and metabolic disorders, there are only a few studies that investigate the effects of ghrelin on secondary symptoms associated with AD. In this mini review, our purpose is to provide the insights of future study by organizing the previous studies for the role of ghrelin in AD-related pathology and metabolic disorders.

[Relationship between circadian rhythm related brain dysfunction and bipolar disorder]

OBJECTIVE

To investigate the changes of functional connectivity (FC) in the suprachiasmatic nucleus (SCN) of patients with bipolar disorder and perform a cluster analysis of patients with bipolar disorder based on FC.

METHODS

The study recruited 138 patients with bipolar disorder (BD) diagnosed according to the 4th edition of Diagnostic and Statistical Manual of Mental Disorders IV (DSM-IV) and 150 healthy control subjects. All the participants underwent resting-state functional magnetic resonance brain scans. DPARSF software was used to generate the FC diagram of the SCN. Based on the FC data, principal components analysis (PCA) and k-means in scikit-learn 0.20.1 were used for cluster analysis of the patients with bipolar disorder.

RESULTS

Compared with the healthy controls, the patients showed enhanced functional connections between the SCN and the paraventricular nucleus and between the SCN and the dorsomedial hypothalamus nucleus. Based on these FC values, the optimal cluster of unsupervised k-means machine learning for bipolar disorder was 2, and the Silhouette coefficient was 0.49.

CONCLUSIONS

Patients with bipolar disorder have changes in the FC of the SCN, and the FC of the rhythm pathway can divide bipolar disorder into two subtypes, suggesting that biological rhythm is one of the potential biomarkers of bipolar disorder.

Eat, sleep, repeat: the role of the circadian system in balancing sleep-wake control with metabolic need

Feeding and sleep are behaviours fundamental to survival, and as such are subject to powerful homeostatic control. Of course, these are mutually exclusive behaviours, and therefore require coordinated temporal organisation to ensure that both energy demands and sleep need are met. Under optimal conditions, foraging/feeding and sleep can be simply partitioned to appropriate phases of the circadian cycle so that they are in suitable alignment with the external environment. However, under conditions of negative energy balance, increased foraging activity must be balanced against sleep requirements and energy conservation. In mammals and many other species, neural circuits that regulate sleep and energy balance are intimately and reciprocally linked. Here, we examine this circuitry, discuss how homeostatic regulation and temporal patterning of sleep are modulated by altered food availability, and describe the role of circadian system in adaptation to metabolic stress.

Deep brain stimulation of hypothalamus for narcolepsy-cataplexy in mice

BACKGROUND

Narcolepsy type 1 (NT1, narcolepsy with cataplexy) is a disabling neurological disorder caused by loss of excitatory orexin neurons from the hypothalamus and is characterized by decreased motivation, sleep-wake fragmentation, intrusion of rapid-eye-movement sleep (REMS) during wake, and abrupt loss of muscle tone, called cataplexy, in response to sudden emotions.

OBJECTIVE

We investigated whether subcortical stimulation, analogous to clinical deep brain stimulation (DBS), would ameliorate NT1 using a validated transgenic mouse model with postnatal orexin neuron degeneration.

METHODS

Using implanted electrodes in freely behaving mice, the immediate and prolonged effects of DBS were determined upon behavior using continuous video-electroencephalogram-electromyogram (video/EEG/EMG) and locomotor activity, and neural activation in brain sections, using immunohistochemical labeling of the immediate early gene product c-Fos.

RESULTS

Brief 10-s stimulation to the region of the lateral hypothalamus and zona incerta (LH/ZI) dose-responsively reversed established sleep and cataplexy episodes without negative sequelae. Continuous 3-h stimulation increased ambulation, improved sleep-wake consolidation, and ameliorated cataplexy. Brain c-Fos from mice sacrificed after 90 min of DBS revealed dose-responsive neural activation within wake-active nuclei of the basal forebrain, hypothalamus, thalamus, and ventral midbrain.

CONCLUSION

Acute and continuous LH/ZI DBS enhanced behavioral state control in a mouse model of NT1, supporting the feasibility of clinical DBS for NT1 and other sleep-wake disorders.