The Serotonergic Raphe Promote Sleep in Zebrafish and Mice

A REM-active basal ganglia circuit that regulates anxiety

Rapid eye movement (REM) sleep has been hypothesized to promote emotional resilience, but any neuronal circuits mediating this have not been identified. We find that in mice, somatostatin (Som) neurons in the entopeduncular nucleus (EPSom)/internal globus pallidus are predominantly active during REM sleep. This unique REM activity is both necessary and sufficient for maintaining normal REM sleep. Inhibiting or exciting EPSom neurons reduced or increased REM sleep duration, respectively. Activation of the sole downstream target of EPSom neurons, Vglut2 cells in the lateral habenula (LHb), increased sleep via the ventral tegmental area (VTA). A simple chemogenetic scheme to periodically inhibit the LHb over 4 days selectively removed a significant amount of cumulative REM sleep. Chronic, but not acute, REM reduction correlated with mice becoming anxious and more sensitive to aversive stimuli. Therefore, we suggest that cumulative REM sleep, in part generated by the EP → LHb → VTA circuit identified here, could contribute to stabilizing reactions to habitual aversive stimuli.

Impact of Serotonin Deficiency on Circadian Dopaminergic Rhythms

Physiology and behavior are structured temporally to anticipate daily cycles of light and dark, ensuring fitness and survival. Neuromodulatory systems in the brain-including those involving serotonin and dopamine-exhibit daily oscillations in neural activity and help shape circadian rhythms. Disrupted neuromodulation can cause circadian abnormalities that are thought to underlie several neuropsychiatric disorders, including bipolar mania and schizophrenia, for which a mechanistic understanding is still lacking. Here, we show that genetically depleting serotonin in Tph2 knockout mice promotes manic-like behaviors and disrupts daily oscillations of the dopamine biosynthetic enzyme tyrosine hydroxylase (TH) in midbrain dopaminergic nuclei. Specifically, while TH mRNA and protein levels in the Substantia Nigra (SN) and Ventral Tegmental Area (VTA) of wild-type mice doubled between the light and dark phase, TH levels were high throughout the day in Tph2 knockout mice, suggesting a hyperdopaminergic state. Analysis of TH expression in striatal terminal fields also showed blunted rhythms. Additionally, we found low abundance and blunted rhythmicity of the neuropeptide cholecystokinin (Cck) in the VTA of knockout mice, a neuropeptide whose downregulation has been implicated in manic-like states in both rodents and humans. Altogether, our results point to a previously unappreciated serotonergic control of circadian dopamine signaling and propose serotonergic dysfunction as an upstream mechanism underlying dopaminergic deregulation and ultimately maladaptive behaviors.

Visual light flicker stimulation: enhancing alertness in sleep-deprived rats

Introduction

In the evolving field of neurophysiological research, visual light flicker stimulation is recognized as a promising non-invasive intervention for cognitive enhancement, particularly in sleep-deprived conditions.

Methods

This study explored the effects of specific flicker frequencies (40 Hz and 20-30 Hz random flicker) on alertness recovery in sleep-deprived rats. We employed a multidisciplinary approach that included behavioral assessments with the Y-maze, in vivo electrophysiological recordings, and molecular analyses such as c-FOS immunohistochemistry and hormone level measurements.

Results

Both 40 Hz and 20-30 Hz flicker significantly enhanced behavioral performance in the Y-maze test, suggesting an improvement in alertness. Neurophysiological data indicated activation of neural circuits in key brain areas like the thalamus and hippocampus. Additionally, flicker exposure normalized cortisol and serotonin levels, essential for stress response and mood regulation. Notably, increased c-FOS expression in brain regions related to alertness and cognitive functions suggested heightened neural activity.

Discussion

These findings underscore the potential of light flicker stimulation not only to mitigate the effects of sleep deprivation but also to enhance cognitive functions. The results pave the way for future translational research into light-based therapies in human subjects, with possible implications for occupational health and cognitive ergonomics.

Elevated sleep quota in a stress-resilient Drosophila species

Sleep is broadly conserved across the animal kingdom but can vary widely between species. It is currently unclear which selective pressures and regulatory mechanisms influence differences in sleep between species. The fruit fly Drosophila melanogaster has become a successful model system for examining sleep regulation and function, but little is known about the sleep patterns in many related fly species. Here, we find that fly species with adaptations to extreme desert environments, including D. mojavensis, exhibit strong increases in baseline sleep compared with D. melanogaster. Long-sleeping D. mojavensis show intact homeostasis, indicating that desert flies carry an elevated drive for sleep. In addition, D. mojavensis exhibit altered abundance or distribution of several sleep/wake-related neuromodulators and neuropeptides that are consistent with their reduced locomotor activity and increased sleep. Finally, we find that in a nutrient-deprived environment, the sleep patterns of individual D. mojavensis are strongly correlated with their survival time and that disrupting sleep via constant light stimulation renders D. mojavensis more sensitive to starvation. Our results demonstrate that D. mojavensis is a novel model for studying organisms with high sleep drive and for exploring sleep strategies that provide resilience in extreme environments.

Single-nucleus RNA-seq identifies one galanin neuronal subtype in mouse preoptic hypothalamus activated during recovery from sleep deprivation

The preoptic area of the hypothalamus (POA) is essential for sleep regulation. However, the cellular makeup of the POA is heterogeneous, and the molecular identities of the sleep-promoting cells remain elusive. To address this question, this study compares mice during recovery sleep following sleep deprivation to mice allowed extended sleep. Single-nucleus RNA sequencing (single-nucleus RNA-seq) identifies one galanin inhibitory neuronal subtype that shows upregulation of rapid and delayed activity-regulated genes during recovery sleep. This cell type expresses higher levels of growth hormone receptor and lower levels of estrogen receptor compared to other galanin subtypes. single-nucleus RNA-seq also reveals cell-type-specific upregulation of purinergic receptor (P2ry14) and serotonin receptor (Htr2a) during recovery sleep in this neuronal subtype, suggesting possible mechanisms for sleep regulation. Studies with RNAscope validate the single-nucleus RNA-seq findings. Thus, the combined use of single-nucleus RNA-seq and activity-regulated genes identifies a neuronal subtype functionally involved in sleep regulation.

Shen Yuan extract exerts a hypnotic effect via the tryptophan/5-hydroxytryptamine/melatonin pathway in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Sleep plays a critical role in several physiologic processes, and sleep disorders increase the risk of depression, dementia, stroke, cancer, and other diseases. Stress is one of the main causes of sleep disorders. Ginseng Radix et Rhizoma and Polygalae Radix have been reported to have effects of calming the mind and intensifying intelligence in Chinese Pharmacopoeia. Traditional Chinese medicine prescriptions composed of Ginseng Radix et Rhizoma and Polygalae Radix (Shen Yuan, SY) are commonly used to treat insomnia, depression, and other psychiatric disorders in clinical practice. Unfortunately, the underlying mechanisms of the SY extract's effect on sleep are still unknown.

AIM OF THE STUDY

This study aimed to investigate the hypnotic effect of the SY extract in normal mice and mice with chronic restraint stress (CRS)-induced sleep disorders and elucidate the underlying mechanisms.

MATERIALS AND METHODS

The SY extract (0.5 and 1.0 g/kg) was intragastrically administered to normal mice for 1, 14, and 28 days and to CRS-treated mice for 28 days. The open field test (OFT) and pentobarbital sodium-induced sleep test (PST) were used to evaluate the hypnotic effect of the SY extract. Liquid chromatography-tandem mass spectrometry and enzyme-linked immunosorbent assay were utilized to detect the levels of neurotransmitters and hormones. Molecular changes at the mRNA and protein levels were determined using real-time quantitative polymerase chain reaction and Western blot analysis to identify the mechanisms by which SY improves sleep disorders.

RESULTS

The SY extract decreased sleep latency and increased sleep duration in normal mice. Similarly, the sleep duration of mice subjected to CRS was increased by administering SY. The SY extract increased the levels of tryptophan (Trp) and 5-hydroxytryptamine (5-HT) and the expression of tryptophan hydroxylase 2 (TPH2) in the cortex of normal mice. The SY extract increased the Trp level, transcription and expression of estrogen receptor beta and TPH2 in the cortex in mice with sleep disorders by decreasing the serum corticosterone level, which promoted the synthesis of 5-HT. Additionally, the SY extract enhanced the expression of arylalkylamine N-acetyltransferase, which increased the melatonin level and upregulated the expressions of melatonin receptor-2 (MT2) and Cryptochrome 1 (Cry1) in the hypothalamus of mice with sleep disorders.

CONCLUSIONS

The SY extract exerted a hypnotic effect via the Trp/5-HT/melatonin pathway, which augmented the synthesis of 5-HT and melatonin and further increased the expressions of MT2 and Cry1.

Guhan Yangsheng Jing mitigates hippocampal neuronal pyroptotic injury and manifies learning and memory capabilities in sleep deprived mice via the NLRP3/Caspase1/GSDMD signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Guhan Yangsheng Jing (GHYSJ) is a traditional Chinese patent medicine, that has the function of nourishing the kidney and replenishing the essence, invigorating the brain and calming the mind. It is often used to treat dizziness, memory loss, sleep disorders, fatigue, and weakness, etc. However, its mechanism for improving sleep has not yet been determined.

AIM OF THE STUDY

This study aims to explore the effects of GHYSJ on Sleep Deprivation (SD)-induced hippocampal neuronal pyroptotic injury, learning and cognitive abilities, and sleep quality in mice.

METHODS

In this study, a PCPA-induced SD mouse model was established. We assessed the influence of GHYSJ on sleep quality and mood by using the pentobarbital-induced sleep test (PIST) and sucrose preference test (SPT). The pharmacological effects of GHYSJ on learning and memory impairment were evaluated by the Morris Water Maze (MWM) and Open Field Test (OFT). Pathological changes in the hippocampal tissue of the SD rats were observed via HE staining and Nissl staining. The severity of neuronal damage was evaluated by detecting the expression of the neuronal marker Microtubule-associated protein 2 (MAP2), via immunohistochemistry and immunofluorescence. Furthermore, the levels of neurotransmitter 5-hydroxytryptophan (5-HTP), 5-hydroxy tryptamine (5-HT), γ-aminobutyric acid (GABA), and Glutamic acid (Glu) in hippocampal tissues, as well as the expression of inflammatory factors Interleukin-1β (IL-1β) and Interleukin-18 (IL-18) in serum, were determined by ELISA. The expressions of mRNA and protein NOD-like receptor thermal protein domain associated protein 3 (NLRP3), Gasdermin D (GSDMD), Cysteinyl aspartate specific proteinase1 (Caspase1), High mobility group box-1 protein (HMGB1) and Apoptosis-associated speck-like protein containing CARD (ASC) related to the cellular ferroptosis pathway were tested and analyzed by RT-PCR and WB respectively.

RESULTS

PCPA significantly diminishes the sleep span of experimental animals by expediting the expenditure of 5-HT, consequently establishing an essentially direct SD model. The intervention of GHYSJ displays remarkable efficacy in mitigating insomnia symptoms, encompassing difficulties in initiating sleep and insufficient sleep duration. Likewise, it ameliorates memory function impairments induced by sleep deprivation, along with symptoms such as fatigue and depletion of vitality. GHYSJ exerts a protective influence on hippocampal neurons facilitated by inhibiting the down regulation of MAP2 and maintaining the equilibrium of neurotransmitters (5-HTP, 5-HT, GABA, and Glu). It diminishes the expression of intracellular pyroptosis-associated inflammatory factors (IL-1β and IL-18) and curbs the activation of the NLRP3/Caspase1/GSDMD pyroptosis-related signaling pathways, thereby alleviating the damage caused by hippocampal neuronal pyroptosis.

Optogenetic activation of dorsal raphe serotonin neurons induces brain-wide activation

Serotonin is a neuromodulator that affects multiple behavioral and cognitive functions. Nonetheless, how serotonin causes such a variety of effects via brain-wide projections and various receptors remains unclear. Here we measured brain-wide responses to optogenetic stimulation of serotonin neurons in the dorsal raphe nucleus (DRN) of the male mouse brain using functional MRI with an 11.7 T scanner and a cryoprobe. Transient activation of DRN serotonin neurons caused brain-wide activation, including the medial prefrontal cortex, the striatum, and the ventral tegmental area. The same stimulation under anesthesia with isoflurane decreased brain-wide activation, including the hippocampal complex. These brain-wide response patterns can be explained by DRN serotonergic projection topography and serotonin receptor expression profiles, with enhanced weights on 5-HT1 receptors. Together, these results provide insight into the DR serotonergic system, which is consistent with recent discoveries of its functions in adaptive behaviors.

Comprehensive mapping of histamine H1 receptor mRNA in the mouse brain

Histamine H1 receptor (H1R) in the central nervous system plays an important role in various functions, including learning and memory, aggression, feeding behaviors, and wakefulness, as evidenced by studies utilizing H1R knockout mice and pharmacological interventions. Although previous studies have reported the widespread distribution of H1R in the brains of rats, guinea pigs, monkeys, and humans, the detailed distribution in the mouse brain remains unclear. This study provides a comprehensive description of the distribution of H1R mRNA in the mouse brain using two recently developed techniques: RNAscope and in situ hybridization chain reaction, both of which offer enhanced sensitivity and resolution compared to traditional methodologies such as radioisotope labeling, which were used in previous studies. The H1R mRNA expression was observed throughout the entire brain, including key regions implicated in sleep-wake regulatory functions, such as the pedunculopontine tegmental nucleus and dorsal raphe. Additionally, strong H1R mRNA signals were identified in the paraventricular hypothalamus and ventromedial hypothalamus, which may explain the potential mechanisms underlying histamine-mediated feeding regulation. Notably, we identified strong H1R mRNA expression in previously unreported cerebral regions, such as the dorsal endopiriform nucleus, bed nucleus of the accessory olfactory tract, and postsubiculum. These findings significantly contribute to our understanding of the multifaceted roles of H1R in diverse brain functions.

Serotonergic dysfunction may mediate the relationship between alcohol consumption and Alzheimer's disease

The impact of Alzheimer's disease (AD) and its related dementias is rapidly expanding, and its mitigation remains an urgent social and technical challenge. To date there are no effective treatments or interventions for AD, but recent studies suggest that alcohol consumption is correlated with the risk of developing dementia. In this review, we synthesize data from preclinical, clinical, and epidemiological models to evaluate the combined role of alcohol consumption and serotonergic dysfunction in AD, underscoring the need for further research on this topic. We first discuss the limitations inherent to current data-collection methods, and how neuropsychiatric symptoms common among AD, alcohol use disorder, and serotonergic dysfunction may mask their co-occurrence. We additionally describe how excess alcohol consumption may accelerate the development of AD via direct effects on serotonergic function, and we explore the roles of neuroinflammation and proteostasis in mediating the relationship between serotonin, alcohol consumption, and AD. Lastly, we argue for a shift in current research to disentangle the pathogenic effects of alcohol on early-affected brainstem structures in AD.

Understanding zebrafish sleep and wakefulness physiology as an experimental model for biomedical research

Sleep is a globally observable fact, or period of reversible distracted rest, that can be distinguished from arousal by various behavioral criteria. Although the function of sleep is an evolutionarily conserved behavior, its mechanism is not yet clear. The zebrafish (Danio rerio) has become a valuable model for neurobehavioral studies such as studying learning, memory, anxiety, and depression. It is characterized by a sleep-like state and circadian rhythm, making it comparable to mammals. Zebrafish are a good model for behavioral studies because they share genetic similarities with humans. A number of neurotransmitters are involved in sleep and wakefulness. There is a binding between melatonin and the hypocretin system present in zebrafish. The full understanding of sleep and wakefulness physiology in zebrafish is still unclear among researchers. Therefore, to make a clear understanding of the sleep/wake cycle in zebrafish, this article covers the mechanism involved behind it, and the role of the neuromodulator system followed by the mechanism of the HPA axis.

Mapping the 5-HTergic neural pathways in perimenopausal mice and elucidating the role of oestrogen receptors in 5-HT neurotransmission

Perimenopausal syndrome (PMS) encompasses neuropsychiatric symptoms, such as hot flashes and depression, which are associated with alterations in the 5-HTergic neural pathway in the brain. However, the specific changes and mechanisms underlying these alterations remain unclear. In this study, ovariectomized mice were used to successfully establish a perimenopause model, and the changes in the expression of 5-HT and its receptors (5-HT1AR and 5-HT2AR) across 72 brain regions in these ovariectomized mice were assessed by immunohistochemistry. Although both 5-HT and 5-HT1AR were widely expressed throughout the brain, only a limited number of regions expressed 5-HT2AR. Notably, decreased expression of 5-HT was observed across almost all brain regions in the ovariectomy (OVX) group compared with the Sham group. Altered expression of both receptors was found within areas related to hot flashes (the preoptic area) or mood disorders (the amygdala). Additionally, reduced oestrogen receptor (ER)α/β expression was detected in cells in the raphe nucleus (RN), an area known to regulate body temperature. Results showed that ERα/β positively regulate the transcriptional activity of the enzymes TPH2/MAOA, which are involved in serotonin metabolism during perimenopause. This study revealed the changes in 5-HT neuropathways (5-HT, 5-HT1AR and 5-HT2AR) in perimenopausal mice, mainly in brain regions related to regulation of the body temperature, mood, sleep and memory. This study clarified that the expression of oestrogen receptor decreased in perimenopause, which regulated the transcription levels of TPH2 and MAOA, and ultimately led to the reduction of 5-HT content, providing a new target for clinical diagnosis and treatment of perimenopausal diseases.

A midbrain GABAergic circuit constrains wakefulness in a mouse model of stress

Enhancement of wakefulness is a prerequisite for adaptive behaviors to cope with acute stress, but hyperarousal is associated with impaired behavioral performance. Although the neural circuitries promoting wakefulness in acute stress conditions have been extensively identified, less is known about the circuit mechanisms constraining wakefulness to prevent hyperarousal. Here, we found that chemogenetic or optogenetic activation of GAD2-positive GABAergic neurons in the midbrain dorsal raphe nucleus (DRNGAD2) decreased wakefulness, while inhibition or ablation of these neurons produced an increase in wakefulness along with hyperactivity. Surprisingly, DRNGAD2 neurons were paradoxically wakefulness-active and were further activated by acute stress. Bidirectional manipulations revealed that DRNGAD2 neurons constrained the increase of wakefulness and arousal level in a mouse model of stress. Circuit-specific investigations demonstrated that DRNGAD2 neurons constrained wakefulness via inhibition of the wakefulness-promoting paraventricular thalamus. Therefore, the present study identified a wakefulness-constraining role DRNGAD2 neurons in acute stress conditions.

Serotonergic modulation of vigilance states in zebrafish and mice

Vigilance refers to being alertly watchful or paying sustained attention to avoid potential threats. Animals in vigilance states reduce locomotion and have an enhanced sensitivity to aversive stimuli so as to react quickly to dangers. Here we report that an unconventional 5-HT driven mechanism operating at neural circuit level which shapes the internal state underlying vigilance behavior in zebrafish and male mice. The neural signature of internal vigilance state was characterized by persistent low-frequency high-amplitude neuronal synchrony in zebrafish dorsal pallium and mice prefrontal cortex. The neuronal synchronization underlying vigilance was dependent on intense release of 5-HT induced by persistent activation of either DRN 5-HT neuron or local 5-HT axon terminals in related brain regions via activation of 5-HTR7. Thus, we identify a mechanism of vigilance behavior across species that illustrates the interplay between neuromodulators and neural circuits necessary to shape behavior states.

Serotonergic regulation of cortical neurovascular coupling and hemodynamics upon awakening from sleep in mice

Neurovascular coupling (NVC) is the functional hyperemia of the brain responding to local neuronal activity. It is mediated by astrocytes and affected by subcortical ascending pathways in the cortex that convey information, such as sensory stimuli and the animal condition. Here, we investigate the influence of the raphe serotonergic system, a subcortical ascending arousal system in animals, on the modulation of cortical NVC and cerebral blood flow (CBF). Raphe serotonergic neurons were optogenically activated for 30 s, which immediately awakened the mice from non-rapid eye movement sleep. This caused a biphasic cortical hemodynamic change: a transient increase for a few seconds immediately after photostimulation onset, followed by a large progressive decrease during the stimulation period. Serotonergic neuron activation increased intracellular Ca2+ levels in cortical pyramidal neurons and astrocytes, demonstrating its effect on the NVC components. Pharmacological inhibition of cortical neuronal firing activity and astrocyte metabolic activity had small hypovolemic effects on serotonin-induced biphasic CBF changes, while blocking 5-HT1B receptors expressed primarily in cerebral vasculature attenuated the decreasing CBF phase. This suggests that serotonergic neuron activation leading to animal awakening could allow the NVC to exert a hyperemic function during a biphasic CBF response, with a predominant decrease in the cortex.

Diving into the zebrafish brain: exploring neuroscience frontiers with genetic tools, imaging techniques, and behavioral insights

The zebrafish (Danio rerio) is increasingly used in neuroscience research. Zebrafish are relatively easy to maintain, and their high fecundity makes them suitable for high-throughput experiments. Their small, transparent embryos and larvae allow for easy microscopic imaging of the developing brain. Zebrafish also share a high degree of genetic similarity with humans, and are amenable to genetic manipulation techniques, such as gene knockdown, knockout, or knock-in, which allows researchers to study the role of specific genes relevant to human brain development, function, and disease. Zebrafish can also serve as a model for behavioral studies, including locomotion, learning, and social interactions. In this review, we present state-of-the-art methods to study the brain function in zebrafish, including genetic tools for labeling single neurons and neuronal circuits, live imaging of neural activity, synaptic dynamics and protein interactions in the zebrafish brain, optogenetic manipulation, and the use of virtual reality technology for behavioral testing. We highlight the potential of zebrafish for neuroscience research, especially regarding brain development, neuronal circuits, and genetic-based disorders and discuss its certain limitations as a model.

Fast and slow: Recording neuromodulator dynamics across both transient and chronic time scales

Neuromodulators transform animal behaviors. Recent research has demonstrated the importance of both sustained and transient change in neuromodulators, likely due to tonic and phasic neuromodulator release. However, no method could simultaneously record both types of dynamics. Fluorescence lifetime of optical reporters could offer a solution because it allows high temporal resolution and is impervious to sensor expression differences across chronic periods. Nevertheless, no fluorescence lifetime change across the entire classes of neuromodulator sensors was previously known. Unexpectedly, we find that several intensity-based neuromodulator sensors also exhibit fluorescence lifetime responses. Furthermore, we show that lifetime measures in vivo neuromodulator dynamics both with high temporal resolution and with consistency across animals and time. Thus, we report a method that can simultaneously measure neuromodulator change over transient and chronic time scales, promising to reveal the roles of multi-time scale neuromodulator dynamics in diseases, in response to therapies, and across development and aging.

Synthetic surprise as the foundation of the psychedelic experience

Psychedelic agents, such as LSD and psilocybin, induce marked alterations in consciousness via activation of the 5-HT2A receptor (5-HT2ARs). We hypothesize that psychedelics enforce a state of synthetic surprise through the biased activation of the 5-HTRs system. This idea is informed by recent insights into the role of 5-HT in signaling surprise. The effects on consciousness, explained by the cognitive penetrability of perception, can be described within the predictive coding framework where surprise corresponds to prediction error, the mismatch between predictions and actual sensory input. Crucially, the precision afforded to the prediction error determines its effect on priors, enabling a dynamic interaction between top-down expectations and incoming sensory data. By integrating recent findings on predictive coding circuitry and 5-HT2ARs transcriptomic data, we propose a biological implementation with emphasis on the role of inhibitory interneurons. Implications arise for the clinical use of psychedelics, which may rely primarily on their inherent capacity to induce surprise in order to disrupt maladaptive patterns.

All-optical interrogation of brain-wide activity in freely swimming larval zebrafish

We introduce an all-optical technique that enables volumetric imaging of brain-wide calcium activity and targeted optogenetic stimulation of specific brain regions in unrestrained larval zebrafish. The system consists of three main components: a 3D tracking module, a dual-color fluorescence imaging module, and a real-time activity manipulation module. Our approach uses a sensitive genetically encoded calcium indicator in combination with a long Stokes shift red fluorescence protein as a reference channel, allowing the extraction of Ca2+ activity from signals contaminated by motion artifacts. The method also incorporates rapid 3D image reconstruction and registration, facilitating real-time selective optogenetic stimulation of different regions of the brain. By demonstrating that selective light activation of the midbrain regions in larval zebrafish could reliably trigger biased turning behavior and changes of brain-wide neural activity, we present a valuable tool for investigating the causal relationship between distributed neural circuit dynamics and naturalistic behavior.

Effects of BXSMD on ESR1 and ESR2 expression in CSD female mice

ETHNIC PHARMACOLOGICAL RELEVANCE

Due to the rapid pace of modern society, chronic insomnia has become universal phenomenon. In China, Banxia Shumi Decoction (BXSMD) has been used in treating chronic insomnia for thousands of years, but its chemical composition and action mechanism are still unknown.

AIM OF THE STUDY

This study aims to explore the chemical composition of BXSMD and its effects on Estrogen receptor 1 (ESR1) and Estrogen receptor 2 (ESR2) in mice with chronic sleep deprivation (CSD).

MATERIALS AND METHODS

UHPLC-Q-Orbitrap-MS/MS was applied in determining the chemical composition of BXSMD. After 21-day sleep deprivation (SD) in platform water environment, CSD mice model was prepared. By conducting open field test, 24-h autonomic diurnal and nocturnal activity of mice in each group was detected. ELISA was employed to measure the contents of 5-HT, DA, NE, GABA, Glu, and MT. With RT-PCR, Western blot (WB), and immunohistochemistry (IHC), mRNA and protein expressions of ESR1 and ESR2 in the hypothalamus and hippocampus were tested.

RESULTS

BXSMD included ferulic acid, kaverol, daidzein, apigenin, berberine, adenosine, aesculin, vanillin, naringin, and glycine, which might constitute the material basis forthe improvement of chronic insomnia. With BXSMD, the total moving distance and the rest time in dark period of CSD mice were shortened, while its rest time in light period was increased. Besides, BXSMD enhanced the contents of 5-HT, GABA, and MT in CSD mice, and decreased the contents of Glu, NE, and DA. BXSMD elevated the mRNA of Esr1 and Esr2, and elevated the protein expressions of ESR1 and ESR2 in the hypothalamus and hippocampus of CSD mice.

CONCLUSIONS

BXSMD contains various chemical components for sleep-wake regulation, with the mechanism of stimulating estrogen signaling pathway by regulating the expressions of ESR1 and ESR2, ultimately realizing the regulation to sleep-wake disorder caused by CSD.

Gut microbiota intervention attenuates thermogenesis in broilers exposed to high temperature through modulation of the hypothalamic 5-HT pathway

BACKGROUND

Broilers have a robust metabolism and high body temperature, which make them less tolerant to high-temperature (HT) environments and more susceptible to challenges from elevated temperatures. Gut microbes, functioning as symbionts within the host, possess the capacity to significantly regulate the physiological functions and environmental adaptability of the host. This study aims to investigate the effects of gut microbial intervention on the body temperature and thermogenesis of broilers at different ambient temperatures, as well as the underlying mechanism involving the "gut-brain" axis.

METHODS

Broilers were subjected to gut microbiota interference with or without antibiotics (control or ABX) starting at 1 day of age. At 21 day of age, they were divided into 4 groups and exposed to different environments for 7 d: The control and ABX groups at room temperature (RT, 24 ± 1 °C, 60% relative humidity (RH), 24 h/d) and the control-HT and ABX-HT groups at high temperature (HT, 32 ± 1 °C, 60% RH, 24 h/d). RESULTS : The results demonstrated that the antibiotic-induced gut microbiota intervention increased body weight and improved feed conversion in broiler chickens (P < 0.05). Under HT conditions, the microbiota intervention reduced the rectal temperature of broiler chickens (P < 0.05), inhibited the expression of avUCP and thermogenesis-related genes in breast muscle and liver (P < 0.05), and thus decreased thermogenesis capacity. Furthermore, the gut microbiota intervention blunted the hypothalamic‒pituitary‒adrenal axis and hypothalamic-pituitary-thyroid axis activation induced by HT conditions. By analyzing the cecal microbiota composition of control and ABX chickens maintained under HT conditions, we found that Alistipes was enriched in control chickens. In contrast, antibiotic-induced gut microbiota intervention resulted in a decrease in the relative abundance of Alistipes (P < 0.05). Moreover, this difference was accompanied by increased hypothalamic 5-hydroxytryptamine (5-HT) content and TPH2 expression (P < 0.05).

CONCLUSIONS

These findings underscore the critical role of the gut microbiota in regulating broiler thermogenesis via the gut-brain axis and suggest that the hypothalamic 5-HT pathway may be a potential mechanism by which the gut microbiota affects thermoregulation in broilers.

Serotonin

Serotonin, also known as 5-hydroxytryptamine or 5-HT, is a neuromodulator widely recognized for its role in various psychoactive drugs. These drugs can exhibit antidepressant, antipsychotic, anxiolytic, empathogenic, or psychedelic effects, depending on their specific interactions with the serotonin system as well as other neuromodulators such as noradrenaline, dopamine, and oxytocin. This has led to a widespread belief that the neurochemical processes taking place deep inside our brains affect our subjective experiences and mental health. However, a scientific understanding of how neuromodulators' functions relate to drug effects remains elusive.

What is sleep exactly? Global and local modulations of sleep oscillations all around the clock

Wakefulness, non-rapid eye-movement (NREM) and rapid eye-movement (REM) sleep differ from each other along three dimensions: behavioral, phenomenological, physiological. Although these dimensions often fluctuate in step, they can also dissociate. The current paradigm that views sleep as made of global NREM and REM states fail to account for these dissociations. This conundrum can be dissolved by stressing the existence and significance of the local regulation of sleep. We will review the evidence in animals and humans, healthy and pathological brains, showing different forms of local sleep and the consequences on behavior, cognition, and subjective experience. Altogether, we argue that the notion of local sleep provides a unified account for a host of phenomena: dreaming in REM and NREM sleep, NREM and REM parasomnias, intrasleep responsiveness, inattention and mind wandering in wakefulness. Yet, the physiological origins of local sleep or its putative functions remain unclear. Exploring further local sleep could provide a unique and novel perspective on how and why we sleep.

The States of Different 5-HT Receptors Located in the Dorsal Raphe Nucleus Are Crucial for Regulating the Awakening During General Anesthesia

General anesthesia is widely used in various clinical practices due to its ability to cause loss of consciousness. However, the exact mechanism of anesthesia-induced unconsciousness remains unclear. It is generally thought that arousal-related brain nuclei are involved. 5-Hydroxytryptamine (5-HT) is closely associated with sleep arousal. Here, we explore the role of the 5-HT system in anesthetic awakening through pharmacological interventions and optogenetic techniques. Our data showed that exogenous administration of 5-hydroxytryptophan (5-HTP) and optogenetic activation of 5-HT neurons in the dorsal raphe nucleus (DR) could significantly shorten the emergence time of sevoflurane anesthesia in mice, suggesting that regulation of the 5-HT system using both endogenous and exogenous approaches could mediate delayed emergence. In addition, we first discovered that the different 5-HT receptors located in the DR, known as 5-HT autoreceptors, are essential for the regulation of general anesthetic awakening, with 5-HT1A and 5-HT2A/C receptors playing a regulatory role. These results can provide a reliable theoretical basis as well as potential targets for clinical intervention to prevent delayed emergence and some postoperative risks.

Mass spectrum oriented metabolomics for evaluating the efficacy and discovering the metabolic mechanism of Naoling Pian for insomnia

Insomnia is an accompanying symptom of many diseases and is closely associated with neurodegenerative diseases. Naoling Pian (NLP) is a patented Chinese medicine mainly used to treat insomnia. To evaluate the sedative and hypnotic effects of NLP and its modulatory effects on biological metabolites and metabolic pathways, rats with p-chlorophenylalanine (PCPA)-induced insomnia were given different doses of NLP by oral gavage for seven days. Diazepam (DZP) served as a positive control. Behavior was measured using the open field test, and neurotransmitter levels in the brain tissue related to sleep were measured using ELISA. The metabolic profiles and biomarkers of PCPA-induced insomnia in rats before and after NLP administration were analyzed using UPLC-Q/TOF-MS combined with multivariate data analysis. The results showed that the levels of 5-hydroxytryptamine, gamma-aminobutyric acid, norepinephrine, and dopamine in the brain tissue were significantly recovered in the NLP treatment groups, demonstrating similar or even superior therapeutic effects compared to the DZP group. The behavior of the PCPA-model rats partially recovered to normal levels after seven days of treatment. Metabolomics identified 30 metabolites in the urine as potential biomarkers of insomnia, and NLP significantly altered 25 of these, involving 21 metabolic pathways. NLP has a remarkable effect on insomnia, the therapeutic effects of which may be largely due to the rectification of metabolic disturbances. This is the first study of the sedative and hypnotic effects of NLP from a metabolomic perspective.

Single-cell RNAseq analysis of spinal locomotor circuitry in larval zebrafish

Identification of the neuronal types that form the specialized circuits controlling distinct behaviors has benefited greatly from the simplicity offered by zebrafish. Electrophysiological studies have shown that in addition to connectivity, understanding of circuitry requires identification of functional specializations among individual circuit components, such as those that regulate levels of transmitter release and neuronal excitability. In this study, we use single-cell RNA sequencing (scRNAseq) to identify the molecular bases for functional distinctions between motoneuron types that are causal to their differential roles in swimming. The primary motoneuron, in particular, expresses high levels of a unique combination of voltage-dependent ion channel types and synaptic proteins termed functional 'cassettes.' The ion channel types are specialized for promoting high-frequency firing of action potentials and augmented transmitter release at the neuromuscular junction, both contributing to greater power generation. Our transcriptional profiling of spinal neurons further assigns expression of this cassette to specific interneuron types also involved in the central circuitry controlling high-speed swimming and escape behaviors. Our analysis highlights the utility of scRNAseq in functional characterization of neuronal circuitry, in addition to providing a gene expression resource for studying cell type diversity.

Sex-specific modulation of the medial prefrontal cortex by glutamatergic median raphe neurons

A substantial proportion of raphe neurons are glutamatergic. However, little is known about how these glutamatergic neurons modulate the forebrain. We investigated how glutamatergic median raphe nucleus (MRN) input modulates the medial prefrontal cortex (mPFC), a critical component of fear circuitry. We show that vesicular glutamate transporter 3 (VGLUT3)-expressing MRN neurons activate VGLUT3- and somatostatin-expressing neurons in the mPFC. Consistent with this modulation of mPFC GABAergic neurons, activation of MRN (VGLUT3) neurons enhances GABAergic transmission in mPFC pyramidal neurons and attenuates fear memory in female but not male mice. Serotonin plays a key role in MRN (VGLUT3) neuron-mediated GABAergic plasticity in the mPFC. In agreement with these female-specific effects, we observed sex differences in glutamatergic transmission onto MRN (VGLUT3) neurons and in mPFC (VGLUT3) neuron-mediated dual release of glutamate and GABA. Our results demonstrate a cell type-specific modulation of the mPFC by MRN (VGLUT3) neurons and reveal a sex-specific role of this neuromodulation in mPFC synaptic plasticity.

Utility of the Zebrafish Model for Studying Neuronal and Behavioral Disturbances Induced by Embryonic Exposure to Alcohol, Nicotine, and Cannabis

It is estimated that 5% of pregnant women consume drugs of abuse during pregnancy. Clinical research suggests that intake of drugs during pregnancy, such as alcohol, nicotine and cannabis, disturbs the development of neuronal systems in the offspring, in association with behavioral disturbances early in life and an increased risk of developing drug use disorders. After briefly summarizing evidence in rodents, this review focuses on the zebrafish model and its inherent advantages for studying the effects of embryonic exposure to drugs of abuse on behavioral and neuronal development, with an emphasis on neuropeptides known to promote drug-related behaviors. In addition to stimulating the expression and density of peptide neurons, as in rodents, zebrafish studies demonstrate that embryonic drug exposure has marked effects on the migration, morphology, projections, anatomical location, and peptide co-expression of these neurons. We also describe studies using advanced methodologies that can be applied in vivo in zebrafish: first, to demonstrate a causal relationship between the drug-induced neuronal and behavioral disturbances and second, to discover underlying molecular mechanisms that mediate these effects. The zebrafish model has great potential for providing important information regarding the development of novel and efficacious therapies for ameliorating the effects of early drug exposure.

Optogenetic control of neural activity: The biophysics of microbial rhodopsins in neuroscience

Optogenetics, the use of microbial rhodopsins to make the electrical activity of targeted neurons controllable by light, has swept through neuroscience, enabling thousands of scientists to study how specific neuron types contribute to behaviors and pathologies, and how they might serve as novel therapeutic targets. By activating a set of neurons, one can probe what functions they can initiate or sustain, and by silencing a set of neurons, one can probe the functions they are necessary for. We here review the biophysics of these molecules, asking why they became so useful in neuroscience for the study of brain circuitry. We review the history of the field, including early thinking, early experiments, applications of optogenetics, pre-optogenetics targeted neural control tools, and the history of discovering and characterizing microbial rhodopsins. We then review the biophysical attributes of rhodopsins that make them so useful to neuroscience - their classes and structure, their photocycles, their photocurrent magnitudes and kinetics, their action spectra, and their ion selectivity. Our hope is to convey to the reader how specific biophysical properties of these molecules made them especially useful to neuroscientists for a difficult problem - the control of high-speed electrical activity, with great precision and ease, in the brain.

The claustrum and consciousness: An update

The seminal paper of Crick and Koch (2005) proposed that the claustrum, an enigmatic and thin grey matter structure that lies beside the insular cortex, may be involved in the processing of consciousness. As a result, this otherwise obscure structure has received ever-increasing interest in the search for neural correlates of consciousness. Here we review theories of consciousness and discuss the possible relationship between the claustrum and consciousness. We review relevant experimental evidence collected since the Crick and Koch (2005) paper and consider whether these findings support or contradict their hypothesis. We also explore how future experimental work can be designed to clarify how consciousness emerges from neural activity and to understand the role of the claustrum in consciousness.

Single cell RNA-seq analysis of spinal locomotor circuitry in larval zebrafish

Identification of the neuronal types that form the specialized circuits controlling distinct behaviors has benefited greatly from the simplicity offered by zebrafish. Electrophysiological studies have shown that additional to connectivity, understanding of circuitry requires identification of functional specializations among individual circuit components, such as those that regulate levels of transmitter release and neuronal excitability. In this study we use single cell RNA sequencing (scRNAseq) to identify the molecular bases for functional distinctions between motoneuron types that are causal to their differential roles in swimming. The primary motoneuron (PMn) in particular, expresses high levels of a unique combination of voltage-dependent ion channel types and synaptic proteins termed functional 'cassettes'. The ion channel types are specialized for promoting high frequency firing of action potentials and augmented transmitter release at the neuromuscular junction, both contributing to greater power generation. Our transcriptional profiling of spinal neurons further assigns expression of this cassette to specific interneuron types also involved in the central circuitry controlling high speed swimming and escape behaviors. Our analysis highlights the utility of scRNAseq in functional characterization of neuronal circuitry, in addition to providing a gene expression resource for studying cell type diversity.

Brain regulation of gastric dysfunction induced by stress

Psychological and physical stressors have been implicated in gastric disorders in humans. The mechanism coupling the brain to the stomach underlying stress-induced gastric dysfunction has remained elusive. Here, we show that the stomach directly receives acetylcholinergic inputs from the dorsal motor nucleus of the vagus (AChDMV), which are innervated by serotonergic neurons in the dorsal raphe nucleus (5-HTDRN). Microendoscopic calcium imaging and multi-tetrode electrophysiological recordings reveal that the 5-HTDRN → AChDMV → stomach circuit is inhibited with chronic stress accompanied by hypoactivate gastric function. Artificial activation of this circuit reverses the gastric dysfunction induced by chronic stress in both male and female mice. Our study demonstrates that this 5-HTDRN → AChDMV → stomach axis drives gastric dysfunction associated with stress, thus providing insights into the circuit basis for brain regulation of the stomach.

The zebrafish mutant dreammist implicates sodium homeostasis in sleep regulation

Sleep is a nearly universal feature of animal behaviour, yet many of the molecular, genetic, and neuronal substrates that orchestrate sleep/wake transitions lie undiscovered. Employing a viral insertion sleep screen in larval zebrafish, we identified a novel gene, dreammist (dmist), whose loss results in behavioural hyperactivity and reduced sleep at night. The neuronally expressed dmist gene is conserved across vertebrates and encodes a small single-pass transmembrane protein that is structurally similar to the Na+,K+-ATPase regulator, FXYD1/Phospholemman. Disruption of either fxyd1 or atp1a3a, a Na+,K+-ATPase alpha-3 subunit associated with several heritable movement disorders in humans, led to decreased night-time sleep. Since atpa1a3a and dmist mutants have elevated intracellular Na+ levels and non-additive effects on sleep amount at night, we propose that Dmist-dependent enhancement of Na+ pump function modulates neuronal excitability to maintain normal sleep behaviour.

The Underlying Mechanisms of Sleep Deprivation Exacerbating Neuropathic Pain

Pain disrupts sleep, and sleep deprivation or interference can alter pain perception in animals and humans, for example by increasing sensitivity to pain. However, the mechanism by which sleep affects neuropathic pain remains unclear. In this review, we discuss the available evidence from the epidemiologic, clinical, and human, as well as laboratory studies. In previous studies, we have found that sleep deprivation affects various injurious systems, including opioids, dopaminergic, immune, orexins, hypothalamic-pituitary-adrenal axis, and adenosine. At the same time, these systems play a crucial role in neuropathic pain regulation. In the complex interactions between these neurobiological systems, there may be potential regulatory pathways through which sleep deprivation amplifies neuropathic pain. Because of the impact sleep problems and neuropathic pain can have on the patients' quality of life, studying the link between sleep and neuropathic pain is important for neuropathic pain prevention and public health.

A brain-wide analysis maps structural evolution to distinct anatomical module

The vertebrate brain is highly conserved topologically, but less is known about neuroanatomical variation between individual brain regions. Neuroanatomical variation at the regional level is hypothesized to provide functional expansion, building upon ancestral anatomy needed for basic functions. Classically, animal models used to study evolution have lacked tools for detailed anatomical analysis that are widely used in zebrafish and mice, presenting a barrier to studying brain evolution at fine scales. In this study, we sought to investigate the evolution of brain anatomy using a single species of fish consisting of divergent surface and cave morphs, that permits functional genetic testing of regional volume and shape across the entire brain. We generated a high-resolution brain atlas for the blind Mexican cavefish Astyanax mexicanus and coupled the atlas with automated computational tools to directly assess variability in brain region shape and volume across all populations. We measured the volume and shape of every grossly defined neuroanatomical region of the brain and assessed correlations between anatomical regions in surface fish, cavefish, and surface × cave F2 hybrids, whose phenotypes span the range of surface to cave. We find that dorsal regions of the brain are contracted, while ventral regions have expanded, with F2 hybrid data providing support for developmental constraint along the dorsal-ventral axis. Furthermore, these dorsal-ventral relationships in anatomical variation show similar patterns for both volume and shape, suggesting that the anatomical evolution captured by these two parameters could be driven by similar developmental mechanisms. Together, these data demonstrate that A. mexicanus is a powerful system for functionally determining basic principles of brain evolution and will permit testing how genes influence early patterning events to drive brain-wide anatomical evolution.

Elevated sleep need in a stress-resilient Drosophila species

Sleep is broadly conserved across the animal kingdom, but can vary widely between species. It is currently unclear which types of selective pressures and sleep regulatory mechanisms influence differences in sleep between species. The fruit fly Drosophila melanogaster has become a successful model system for examining sleep regulation and function, but little is known about the sleep patterns and need for sleep in many related fly species. Here, we find that Drosophila mojavensis, a fly species that has adapted to extreme desert environments, exhibits strong increases in sleep compared to D. melanogaster. Long-sleeping D. mojavensis show intact sleep homeostasis, indicating that these flies carry an elevated need for sleep. In addition, D. mojavensis exhibit altered abundance or distribution of several sleep/wake related neuromodulators and neuropeptides that are consistent with their reduced locomotor activity, and increased sleep. Finally, we find that in a nutrient-deprived environment, the sleep responses of individual D. mojavensis are correlated with their survival time. Our results demonstrate that D. mojavensis is a novel model for studying organisms with high sleep need, and for exploring sleep strategies that provide resilience in extreme environments.

Subpopulations of hypocretin/orexin neurons differ in measures of their cell proliferation, dynorphin co-expression, projections, and response to embryonic ethanol exposure

Numerous studies in animals demonstrate that embryonic exposure to ethanol (EtOH) at low-moderate doses stimulates neurogenesis and increases the number of hypothalamic neurons expressing the peptide, hypocretin/orexin (Hcrt). A recent study in zebrafish showed that this effect on the Hcrt neurons in the anterior hypothalamus (AH) is area specific, evident in the anterior (aAH) but not posterior (pAH) part of this region. To understand specific factors that may determine the differential sensitivity to EtOH of these Hcrt subpopulations, we performed additional measures in zebrafish of their cell proliferation, co-expression of the opioid dynorphin (Dyn), and neuronal projections. In association with the increase in Hcrt neurons in the aAH but not pAH, EtOH significantly increased only in the aAH the proliferation of Hcrt neurons and their number lacking Dyn co-expression. The projections of these subpopulations differed markedly in their directionality, with those from the pAH primarily descending to the locus coeruleus and those from the aAH ascending to the subpallium, and they were both stimulated by EtOH, which induced specifically the most anterior subpallium-projecting Hcrt neurons to become ectopically expressed beyond the aAH. These differences between the Hcrt subpopulations suggest they are functionally distinct in their regulation of behavior.

Role of Chemokine Cxcl12a in Mediating the Stimulatory Effects of Ethanol on Embryonic Development of Subpopulations of Hypocretin/Orexin Neurons and Their Projections

Studies in zebrafish and rats show that embryonic ethanol exposure at low-moderate concentrations stimulates hypothalamic neurons expressing hypocretin/orexin (Hcrt) that promote alcohol consumption, effects possibly involving the chemokine Cxcl12 and its receptor Cxcr4. Our recent studies in zebrafish of Hcrt neurons in the anterior hypothalamus (AH) demonstrate that ethanol exposure has anatomically specific effects on Hcrt subpopulations, increasing their number in the anterior AH (aAH) but not posterior AH (pAH), and causes the most anterior aAH neurons to become ectopically expressed further anterior in the preoptic area (POA). Using tools of genetic overexpression and knockdown, our goal here was to determine whether Cxcl12a has an important function in mediating the specific effects of ethanol on these Hcrt subpopulations and their projections. The results demonstrate that the overexpression of Cxcl12a has stimulatory effects similar to ethanol on the number of aAH and ectopic POA Hcrt neurons and the long anterior projections from ectopic POA neurons and posterior projections from pAH neurons. They also demonstrate that knockdown of Cxcl12a blocks these effects of ethanol on the Hcrt subpopulations and projections, providing evidence supporting a direct role of this specific chemokine in mediating ethanol's stimulatory effects on embryonic development of the Hcrt system.

Sleep disturbances in autism spectrum disorder: Animal models, neural mechanisms, and therapeutics

Sleep is crucial for brain development. Sleep disturbances are prevalent in children with autism spectrum disorder (ASD). Strikingly, these sleep problems are positively correlated with the severity of ASD core symptoms such as deficits in social skills and stereotypic behavior, indicating that sleep problems and the behavioral characteristics of ASD may be related. In this review, we will discuss sleep disturbances in children with ASD and highlight mouse models to study sleep disturbances and behavioral phenotypes in ASD. In addition, we will review neuromodulators controlling sleep and wakefulness and how these neuromodulatory systems are disrupted in animal models and patients with ASD. Lastly, we will address how the therapeutic interventions for patients with ASD improve various aspects of sleep. Together, gaining mechanistic insights into the neural mechanisms underlying sleep disturbances in children with ASD will help us to develop better therapeutic interventions.

Structure and function in artificial, zebrafish and human neural networks

Network science provides a set of tools for the characterization of the structure and functional behavior of complex systems. Yet a major problem is to quantify how the structural domain is related to the dynamical one. In other words, how the diversity of dynamical states of a system can be predicted from the static network structure? Or the reverse problem: starting from a set of signals derived from experimental recordings, how can one discover the network connections or the causal relations behind the observed dynamics? Despite the advances achieved over the last two decades, many challenges remain concerning the study of the structure-dynamics interplay of complex systems. In neuroscience, progress is typically constrained by the low spatio-temporal resolution of experiments and by the lack of a universal inferring framework for empirical systems. To address these issues, applications of network science and artificial intelligence to neural data have been rapidly growing. In this article, we review important recent applications of methods from those fields to the study of the interplay between structure and functional dynamics of human and zebrafish brain. We cover the selection of topological features for the characterization of brain networks, inference of functional connections, dynamical modeling, and close with applications to both the human and zebrafish brain. This review is intended to neuroscientists who want to become acquainted with techniques from network science, as well as to researchers from the latter field who are interested in exploring novel application scenarios in neuroscience.

Human tau-overexpressing mice recapitulate brainstem involvement and neuropsychiatric features of early Alzheimer's disease

Alzheimer's disease (AD) poses an ever-increasing public health concern as the population ages, affecting more than 6 million Americans. AD patients present with mood and sleep changes in the prodromal stages that may be partly driven by loss of monoaminergic neurons in the brainstem, but a causal relationship has not been firmly established. This is due in part to a dearth of animal models that recapitulate early AD neuropathology and symptoms. The goal of the present study was to evaluate depressive and anxiety-like behaviors in a mouse model of AD that overexpresses human wild-type tau (htau) prior to the onset of cognitive impairments and assess these behavior changes in relationship to tau pathology, neuroinflammation, and monoaminergic dysregulation in the dorsal raphe nucleus (DRN) and locus coeruleus (LC). We observed depressive-like behaviors at 4 months in both sexes and hyperlocomotion in male htau mice. Deficits in social interaction persisted at 6 months and were accompanied by an increase in anxiety-like behavior in males. The behavioral changes at 4 months coincided with a lower density of serotonergic (5-HT) neurons, downregulation of 5-HT markers, reduced excitability of 5-HT neurons, and hyperphosphorylated tau in the DRN. Inflammatory markers were also upregulated in the DRN along with protein kinases and transglutaminase 2, which may promote tau phosphorylation and aggregation. Loss of 5-HT innervation to the entorhinal cortex and dentate gyrus of the hippocampus was also observed and may have contributed to depressive-like behaviors. There was also reduced expression of noradrenergic markers in the LC along with elevated phospho-tau expression, but this did not translate to a functional change in neuronal excitability. In total, these results suggest that tau pathology in brainstem monoaminergic nuclei and the resulting loss of serotonergic and/or noradrenergic drive may underpin depressive- and anxiety-like behaviors in the early stages of AD.

Brainstem serotonin neurons selectively gate retinal information flow to thalamus

Retinal ganglion cell (RGC) types relay parallel streams of visual feature information. We hypothesized that neuromodulators might efficiently control which visual information streams reach the cortex by selectively gating transmission from specific RGC axons in the thalamus. Using fiber photometry recordings, we found that optogenetic stimulation of serotonergic axons in primary visual thalamus of awake mice suppressed ongoing and visually evoked calcium activity and glutamate release from RGC boutons. Two-photon calcium imaging revealed that serotonin axon stimulation suppressed RGC boutons that responded strongly to global changes in luminance more than those responding only to local visual stimuli, while the converse was true for suppression induced by increases in arousal. Converging evidence suggests that differential expression of the 5-HT1B receptor on RGC presynaptic terminals, but not differential density of nearby serotonin axons, may contribute to the selective serotonergic gating of specific visual information streams before they can activate thalamocortical neurons.

Shu-Xie decoction alleviates oxidative stress and colon injury in acute sleep-deprived mice by suppressing p62/KEAP1/NRF2/HO1/NQO1 signaling

Introduction: Sleep disorders are common clinical psychosomatic disorders that can co-exist with a variety of conditions. In humans and animal models, sleep deprivation (SD) is closely related with gastrointestinal diseases. Shu-Xie Decoction (SX) is a traditional Chinese medicine (TCM) with anti-nociceptive, anti-inflammatory, and antidepressant properties. SX is effective in the clinic for treating patients with abnormal sleep and/or gastrointestinal disorders, but the underlying mechanisms are not known. This study investigated the mechanisms by which SX alleviates SD-induced colon injury in vivo. Methods: C57BL/6 mice were placed on an automated sleep deprivation system for 72 h to generate an acute sleep deprivation (ASD) model, and low-dose SX (SXL), high-dose SX (SXH), or S-zopiclone (S-z) as a positive control using the oral gavage were given during the whole ASD-induced period for one time each day. The colon length was measured and the colon morphology was visualized using hematoxylin and eosin (H&E) staining. ROS and the redox biomarkers include reduced glutathione (GSH), malondialdehyde (MDA), and superoxide dismutase (SOD) were detected. Quantitative real-time PCR (qRT-PCR), molecular docking, immunofluorescence and western blotting assays were performed to detect the antioxidant signaling pathways. Results: ASD significantly increased FBG levels, decreased colon length, moderately increased the infiltration of inflammatory cells in the colon mucosa, altered the colon mucosal structure, increased the levels of ROS, GSH, MDA, and SOD activity compared with the controls. These adverse effects were significantly alleviated by SX treatment. ASD induced nuclear translocation of NRF2 in the colon mucosal cells and increased the expression levels of p62, NQO1, and HO1 transcripts and proteins, but these effects were reversed by SX treatment. Conclusion: SX decoction ameliorated ASD-induced oxidative stress and colon injury by suppressing the p62/KEAP1/NRF2/HO1/NQO1 signaling pathway. In conclusion, combined clinical experience, SX may be a promising drug for sleep disorder combined with colitis.

Meal Timing and Sleeping Energy Metabolism

There is a physiological link between sleep and eating. Insufficient sleep is a risk factor for overeating and excess body weight gain, and molecules such as orexin and insulin play a role in the control of sleep and energy intake. The effects of dietary timing on sleep and energy metabolism were examined in this review. First, we examined sleep energy metabolism and sleep quality under time-restricted eating, including skipping breakfast or dinner. Second, the mechanisms, benefits, and translational potential of the effects of time-restricted diets on sleep were discussed. Time-restricted eating under controlled conditions, in which daily caloric intake was kept constant, affected the time course of energy metabolism but did not affect total energy expenditure over 24 h. In free-living conditions, time-restricted eating for extended durations (4-16 weeks) decreased energy intake and body weight, and the effects of early time-restricted eating were greater than that of midday time-restricted eating. Although assessment of sleep by polysomnographic recording remains to be performed, no negative effects on the subjective quality of sleep have been observed.

Neuro-orchestration of sleep and wakefulness

Although considered an inactive state for centuries, sleep entails many active processes occurring at the cellular, circuit and organismal levels. Over the last decade, several key technological advances, including calcium imaging and optogenetic and chemogenetic manipulations, have facilitated a detailed understanding of the functions of different neuronal populations and circuits in sleep-wake regulation. Here, we present recent progress and summarize our current understanding of the circuitry underlying the initiation, maintenance and coordination of wakefulness, rapid eye movement sleep (REMS) and non-REMS (NREMS). We propose a de-arousal model for sleep initiation, in which the neuromodulatory milieu necessary for sleep initiation is achieved by engaging in repetitive pre-sleep behaviors that gradually reduce vigilance to the external environment and wake-promoting neuromodulatory tone. We also discuss how brain processes related to thermoregulation, hunger and fear intersect with sleep-wake circuits to control arousal. Lastly, we discuss controversies and lingering questions in the sleep field.

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.

Differential Serotonergic Modulation of Synaptic Inputs to the Olfactory Cortex

Serotonin (5-hydroxytriptamine, 5-HT) is an important monoaminergic neuromodulator involved in a variety of physiological and pathological functions. It has been implicated in the regulation of sensory functions at various stages of multiple modalities, but its mechanisms and functions in the olfactory system have remained elusive. Combining electrophysiology, optogenetics and pharmacology, here we show that afferent (feed-forward) pathway-evoked synaptic responses are boosted, whereas feedback responses are suppressed by presynaptic 5-HT_1B receptors in the anterior piriform cortex (aPC) in vitro. Blocking 5-HT_1B receptors also reduces the suppressive effects of serotonergic photostimulation of baseline firing in vivo. We suggest that by regulating the relative weights of synaptic inputs to aPC, 5-HT finely tunes sensory inputs in the olfactory cortex.

Serotonergic neurons control cortical neuronal intracellular energy dynamics by modulating astrocyte-neuron lactate shuttle

The central serotonergic system has multiple roles in animal physiology and behavior, including sleep-wake control. However, its function in controlling brain energy metabolism according to the state of animals remains undetermined. Through in vivo monitoring of energy metabolites and signaling, we demonstrated that optogenetic activation of raphe serotonergic neurons increased cortical neuronal intracellular concentration of ATP, an indispensable cellular energy molecule, which was suppressed by inhibiting neuronal uptake of lactate derived from astrocytes. Raphe serotonergic neuronal activation induced cortical astrocytic Ca²⁺ and cAMP surges and increased extracellular lactate concentrations, suggesting the facilitation of lactate release from astrocytes. Furthermore, chemogenetic inhibition of raphe serotonergic neurons partly attenuated the increase in cortical neuronal intracellular ATP levels as arousal increased in mice. Serotonergic neuronal activation promoted an increase in cortical neuronal intracellular ATP levels, partly mediated by the facilitation of the astrocyte-neuron lactate shuttle, contributing to state-dependent optimization of neuronal intracellular energy levels.

Understanding Sleep Regulation in Normal and Pathological Conditions, and Why It Matters

Sleep occupies a peculiar place in our lives and in science, being both eminently familiar and profoundly enigmatic. Historically, philosophers, scientists and artists questioned the meaning and purpose of sleep. If Shakespeare's verses from MacBeth depicting "Sleep that soothes away all our worries" and "relieves the weary laborer and heals hurt minds" perfectly epitomize the alleviating benefits of sleep, it is only during the last two decades that the growing understanding of the sophisticated sleep regulatory mechanisms allows us to glimpse putative biological functions of sleep. Sleep control brings into play various brain-wide processes occurring at the molecular, cellular, circuit, and system levels, some of them overlapping with a number of disease-signaling pathways. Pathogenic processes, including mood disorders (e.g., major depression) and neurodegenerative illnesses such Huntington's or Alzheimer's diseases, can therefore affect sleep-modulating networks which disrupt the sleep-wake architecture, whereas sleep disturbances may also trigger various brain disorders. In this review, we describe the mechanisms underlying sleep regulation and the main hypotheses drawn about its functions. Comprehending sleep physiological orchestration and functions could ultimately help deliver better treatments for people living with neurodegenerative diseases.