A specific circuit in the midbrain detects stress and induces restorative sleep

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.

Sleep and the recovery from stress

The relationship between stress and sleep is multifaceted, with stress capable of both disrupting and promoting sleep depending on the nature, intensity, and duration of the stressor. While stress commonly leads to sleep fragmentation and arousal in both humans and animals, certain selective stressors, such as immune challenges and psychosocial stress, promote sleep in rodent models. Specific neural circuits, such as those involving the ventral tegmental area and lateral habenula, mediate this stress-induced sleep. Post-stress sleep may facilitate recovery, reduce anxiety, and enhance stress resilience, but the extent to which sleep versus wakefulness post-stress aids long-term adaptation is unclear. Both human and animal studies highlight a bidirectional relationship, where stress-induced changes in sleep architecture may have adaptive or maladaptive consequences. Here, we propose that post-stress sleep contributes to resilience and discuss potential mechanisms underlying this process. A deeper understanding of these pathways may provide new strategies for enhancing stress recovery and improving mental health outcomes.

Antianxiety effects of dexmedetomidine: systematic review and meta-analysis

BACKGROUND

Despite numerous studies of the anxiolytic effects of dexmedetomidine compared with those of other drugs or saline, the results have been inconsistent. Here we report a systematic review and meta-analysis to comprehensively evaluate the evidence of the anxiolytic effects of dexmedetomidine.

METHODS

This research has been registered in the International Prospective Register of Systematic Reviews. The PubMed, Embase, Cochrane Library, Web of Science, and ClinicalTrials.gov database were searched for clinical trials that compared the anxiolytic effects of dexmedetomidine with those of a control group with valid anxiety scores from inception to December 29, 2024.

RESULTS

Overall, this systematic review and meta-analysis included 25 clinical studies with 2159 participants who underwent surgery. The primary outcome revealed that patients who were treated with dexmedetomidine had significantly lower anxiety scores than others did overall (MD = - 1.73, 95% CI = [ - 2.33, - 1.13], p < 0.00001, I2 = 86.5%). Dexmedetomidine was found to be more effective than benzodiazepines in relieving anxiety (MD = - 1.34, 95% CI = [ - 2.08, - 0.60], p = 0.0004, I2 = 83.3%). The secondary outcomes revealed no significant differences in satisfaction, pain level, sedation scores or the risk of postoperative nausea and vomiting between patients who were treated with dexmedetomidine and controls. However, the occurrence of bradycardia was more common in the dexmedetomidine groups.

CONCLUSIONS

Overall, this meta-analysis provided evidence of the potential of dexmedetomidine for relieving anxiety among patients who undergo surgery, with superior antianxiety effects compared with those of benzodiazepines.

Free water imaging reveals asynchronous dopaminergic degeneration in substantia nigra and ventral tegmental area in prodromal and early Parkinson's disease

PURPOSE

The ventral tegmental area (VTA), which is rich in dopaminergic neurons, may play a role in influencing clinical symptoms in Parkinson's Disease (PD). However, the degeneration dynamics of the VTA during the early and prodromal stages of PD remain unclear. This study aims to explore microstructural changes in the VTA among prodromal PD patients with idiopathic REM sleep behavior disorder (iRBD) and early-stage PD patients using free water imaging (FWI) to assess free water (FW) and its correlation with clinical symptoms.

METHOD

Diffusion tensor imaging data from 238 participants, including 69 healthy controls (HC), 54 iRBD patients, and 115 PD patients. FW values were computed using a bi-tensor model, and comparisons were done between the HC, iRBD, and PD groups. Additionally, the relationship between FW values in the VTA and substantia nigra pars compacta (SNc) and clinical symptoms was explored through baseline assessments and longitudinal tracking of iRBD patients.

RESULTS

FW values in the SNc significantly increased in iRBD and PD patients compared to HC, with the PD group exhibiting even higher FW values. Initially, the FW values in the VTA in iRBD patients did not significantly differ from those of HC but increased in early PD, correlating with anxiety and motor deficits. Longitudinal tracking revealed FW increases in the SNc and VTA in iRBD patients over time.

CONCLUSION

The present findings revealed a desynchronized degeneration pattern between the VTA and SNc, with no degeneration observed in the prodromal phase but gradual changes over time, leading to pronounced VTA degeneration in early PD. This underscores the impact of early VTA changes on PD symptoms, contributing to understanding of PD pathophysiology.

Subtle behavioral alterations in the spontaneous behaviors of MPTP mouse model of Parkinson's disease

Midbrain dopamine (DA) neurons are essential for regulating movement, emotion, and reward, with their dysfunction closely linked to Parkinson's disease (PD). While DA neurons in the substantia nigra pars compacta (SNc) and ventral tegmental area (VTA) have known overlapping roles in behaviors such as depression and reward, their distinct contributions to subtle spontaneous behaviors remain insufficiently understood. In this study, we utilized a 3D behavioral analysis platform powered by machine learning to explore motor and nuanced behavioral changes in a subacute MPTP mouse model of PD. This investigative approach was combined with cell-type-specific genetic ablation of DA neurons in both the SNc and VTA. Our findings highlight significant deficits in rearing, walking, and hunching behaviors correlated with the loss of SNc DA neurons, but not VTA DA neurons, alongside increased overall movement, reduced movement precision, and pronounced right-sided lateralization. These subtle features, particularly rearing deficits and lateralization, emerge as critical behavioral biomarkers of SNc DA neuron loss, thereby enhancing the translational relevance of PD models.

Decreased gut microbiome-derived indole-3-propionic acid mediates the exacerbation of myocardial ischemia/reperfusion injury following depression via the brain-gut-heart axis

Despite the increasing recognition of the interplay between depression and cardiovascular disease (CVD), the precise mechanisms by which depression contributes to the pathogenesis of cardiovascular disease remain inadequately understood. The involvement of gut microbiota and their metabolites to health and disease susceptibility has been gaining increasing attention. In this study, it was found that depression exacerbated cardiac injury, impaired cardiac function (EF%: P < 0.01; FS%: P < 0.05), hindered long-term survival (P < 0.01), and intensified adverse cardiac remodeling (WGA: P < 0.01; MASSON: P < 0.0001) after myocardial ischemia/reperfusion (MI/R) in mice. Then we found that mice receiving microbiota transplants from chronic social defeat stress (CSDS) mice exhibited worse cardiac function (EF%: P < 0.01; FS%: P < 0.01) than those receiving microbiota transplants from non-CSDS mice after MI/R injury. Moreover, impaired tryptophan metabolism due to alterations in gut microbiota composition and structure was observed in the CSDS mice. Mechanistically, we analyzed the metabolomics of fecal and serum samples from CSDS mice and identified indole-3-propionic acid (IPA) as a protective agent for cardiomyocytes against ferroptosis after MI/R via NRF2/System xc-/GPX4 axis, played a role in mediating the detrimental influence of depression on MI/R. Our findings provide new insights into the role of the gut microbiota and IPA in depression and CVD, forming the basis of intervention strategies aimed at mitigating the deterioration of cardiac function following MI/R in patients experiencing depression.

Cross-species dissection of the modular role of the ventral tegmental area in depressive disorders

Depressive disorders, including major depressive disorder (MDD), represent one of the most prevalent set of disorders worldwide. MDD is characterized by a range of cognitive, behavioral, and neurobiological changes that contribute to the vast array of symptom profiles that make this disorder particularly difficult to treat. A multitude of established evidence suggests a role for the dopamine system, stemming in part from the ventral tegmental area (VTA), in mediating symptoms and behavioral changes that underlie depression. Developments in cutting-edge technologies in pre-clinical models of depressive phenotypes, such as retrograde tracing, electrophysiological recordings, immunohistochemistry, and molecular profiling, have allowed a deeper characterization of singular VTA neuron molecular, physiological, and projection properties. These developments have highlighted that the VTA is not a homogenous cell population but instead comprises vast cellular diversity that underscores its modular role across various functions related to reward processing, aversion, salience processing, learning and motivation. In this review, we begin by introducing the various cell types and brain regions that comprise the VTA circuitry. Then, we introduce the role of the VTA in reward processing as it compares to aversion processing. Next, we characterize distinct neural pathways within the VTA circuitry to understand the effects of chronic social and non-social stress and tie together how these neurobiological changes manifest into specific behavioral phenotypes. Finally, we relate these preclinical findings to clinical findings to parse the heterogeneity of depressive phenotypes and explain the efficacy of recent novel pharmacological interventions that may target the VTA in MDD.

Glia: the cellular glue that binds circadian rhythms and sleep

Glia are increasingly appreciated as serving an important function in the control of sleep and circadian rhythms. Glial cells in Drosophila and mammals regulate daily rhythms of locomotor activity and sleep as well as homeostatic rebound following sleep deprivation. In addition, they contribute to proposed functions of sleep, with different functions mapping to varied glial subtypes. Here, we discuss recent findings in Drosophila and rodent models establishing a role of glia in circadian or sleep regulation of synaptic plasticity, brain metabolism, removal of cellular debris, and immune challenges. These findings underscore the relevance of glia for benefits attributed to sleep and have implications for understanding the neurobiological mechanisms underlying sleep and associated disorders.

Dopamine Drives Feedforward Inhibition to Orexin Feeding System, Mediating Weight Loss Induced by Morphine Addiction

Feeding behavior changes induced by opioid addiction significantly contribute to the worsening opioid crisis. Activation of the reward system has shown to provoke binge eating disorder in individuals with opioid use disorder, whereas prolonged opioid exposure leads to weight loss. Understanding the mechanisms underlying these phenomena is essential for addressing this pressing societal issue. This study demonstrates that weight loss resulting from feeding behavior changes during morphine addiction requires the activation of the ventral tegmental area dopamine (DA) system, which suppresses the orexin feeding center. Specifically, DA exerts an inhibitory effect on orexin neurons in the lateral hypothalamus area (LHA) through a feedforward inhibition mediated by GABA neurons in the LHA, involving D1 receptors (D1R) and T-type Ca2+ channels. Moreover, the morphine addiction-induced reduction in body weight and food intake can be reversed by the D1R antagonist SCH23390 and chemogenetic silencing of GABA neurons in the LHA. These findings delineate a neuromodulatory mechanism underlying morphine addiction-associated feeding behavior changes and weight loss.

Hierarchical behavioral analysis framework as a platform for standardized quantitative identification of behaviors

Behavior is composed of modules that operate based on inherent logic. Understanding behavior and its neural mechanisms is facilitated by clear structural behavioral analysis. Here, we developed a hierarchical behavioral analysis framework (HBAF) that efficiently reveals the organizational logic of these modules by analyzing high-dimensional behavioral data. By creating a spontaneous behavior atlas for male and female mice, we discovered that spontaneous behavior patterns are hardwired, with sniffing serving as the hub node for movement transitions. The sniffing-to-grooming ratio accurately distinguished the spontaneous behavioral states in a high-throughput manner. These states are influenced by emotional status, circadian rhythms, and lighting conditions, leading to unique behavioral characteristics, spatiotemporal features, and dynamic patterns. By implementing the straightforward and achievable spontaneous behavior paradigm, HBAF enables swift and accurate assessment of animal behavioral states and bridges the gap between a theoretical understanding of the behavioral structure and practical analysis using comprehensive multidimensional behavioral information.

Understanding the connection between stress and sleep: From underlying mechanisms to therapeutic solutions

The objective of this chapter is to navigate through the nexus between stress and sleep, highlighting the neurobiological systems that connect them. Starting with an overview of neuroanatomy and physiology of stress and sleep, with a further detailed breakdown of sleep stages and key neuroanatomical centers that are responsible for sleep and wakefulness. Starting with suprachiasmatic nuclei (SCN) in circadian rhythm and sleep regulation overview, with a center point on the molecular systems including the CLOCK/CRY and BMAL1/2/PER1/2 feedback loops. Following this is the neurobiological of stress, specifically the hypothalamic-pituitary-adrenal (HPA) axis and sympathetic-adrenal (SPA) axis and influence on sleep. Vital neural circuits connecting stress and sleep are examined with the attention of the ventral tegmental area (VTA) GABA-somatostatin neurons and the locus coerules in sleep regulation in response to stress. In addition, neuroinflammation's role occurs through the cytokines IL-1β and TNF-α are investigated as a mediator of sleep disturbances caused by stress. It concludes by summarizing the implications of neuroinflammatory modulation in stress-related psychopathologies, emphasizing the opening this provides for interventions that target this inflammation helping to lighten sleep disorder.

Dopaminergic modulation of propofol-induced activation in VLPO neurons: the role of D1 receptors in sleep-promoting neural circuits

Background

The ventrolateral preoptic nucleus (VLPO) is a crucial regulator of sleep, and its neurons are implicated in both sleep-wake regulation and anesthesia-induced loss of consciousness. Propofol (PRO), a widely used intravenous anesthetic, modulates the activity of VLPO neurons, but the underlying mechanisms, particularly the role of dopaminergic receptors, remain unclear.

Objective

This study aimed to investigate the effects of PRO on NA (-) neurons in the VLPO and to determine the involvement of D1 and D2 dopaminergic receptors in mediating these effects.

Methods

Using in vitro patch-clamp techniques, we identified and characterized NA (-) and NA (+) neurons in the VLPO based on their morphological, pharmacological, and electrophysiological properties. We assessed the effects of PRO on spontaneous excitatory postsynaptic currents (sEPSCs) and inhibitory postsynaptic currents (sIPSCs) in NA (-) neurons, both in the presence and absence of dopaminergic receptor modulators.

Results

PRO significantly increased the firing frequency of NA (-) neurons while decreasing the firing frequency of NA (+) neurons. This activation of NA (-) neurons was mediated through GABA_A receptors, as evidenced by the increased frequency of sEPSCs and altered sIPSCs dynamics. Dopamine (DA) attenuated the PRO-induced increase in sEPSCs frequency and suppression of sIPSCs frequency in NA (-) neurons via D1 receptors, but not D2 receptors. Blocking D1 receptors with SCH23390 reversed the effects of DA on PRO-induced changes, while D2 receptor antagonist sulpiride had minimal impact.

Conclusion

Our findings demonstrate that PRO excites sleep-promoting NA (-) neurons in the VLPO, primarily through GABA_A receptors, with dopaminergic modulation occurring via D1 receptors. These results provide new insights into the neural mechanisms underlying general anesthesia and highlight the potential role of dopaminergic signaling in modulating anesthetic effects on sleep-related neural circuits.

Role of the ventral tegmental area in general anesthesia

The ventral tegmental area (VTA), located in the midbrain, plays a pivotal role in the regulation of many important behaviors, such as reward, addiction, aversion, memory, learning, and sleep-wakefulness cycles. The majority of VTA neurons are dopaminergic neurons, although there is a significant proportion of GABAergic neurons and few glutamatergic neurons. These neuronal types project to different brain regions, thus mediating various biological functions. Therefore, the diverse roles of the VTA might depend on its heterogeneous neuronal types and projecting circuits. General anesthesia and sleep-wakefulness cycles share the feature of reversible loss of consciousness, and several common neural mechanisms underlie these two conditions. In addition to the well-known regulatory role of VTA in sleep-wakefulness, emerging evidence has demonstrated that VTA activity is also associated with promoting emergence from general anesthesia. Herein, we reviewed the literature and summarized the evidence regarding the modulation of the VTA by general anesthesia in rodents, which will improve the understanding of the modulatory mechanism of the VTA in general anesthesia.

Triphala ameliorates cognitive deficits and anxiety via activation of the Nrf2/HO-1 axis in chronic sleep-deprived mice

Triphala is renowned for its curative attributes and has been utilized for centuries to address diverse health ailments. Moreover, the active component of Triphala, polyphenols, is widely recognized for its excellent pharmacological activities, such as anti-inflammatory properties, and has been utilized as a potential natural remedy. However, the precise mechanism through which Triphala alleviates cognitive dysfunction and anxiety induced by chronic sleep deprivation (SD) remains restricted. The objective of this investigation is to examine and clarify the potential mechanism of action that underlies the therapeutic benefits of Triphala in addressing cognitive dysfunction and anxiety induced by chronic SD. Our results demonstrated that Triphala significantly alleviates chronic SD-induced behavioral abnormalities. Additionally, Triphala was highly effective at preventing histopathological or morphological damage to neurons located in the hippocampus. The therapeutic effects of Triphala in treating cognitive dysfunction and anxiety induced by chronic SD involve the modulation of several biological pathways, including inflammation and immune responses, oxidative stress, cell growth and differentiation, metabolism, and neurotransmitter communication. Moreover, our study illustrated that Triphala increased the nuclear translocation of nuclear factor erythroid 2-related factor 2 (Nrf2) and significantly activated the Nrf2/hemeoxygenase-1 (HO-1) axis. Additionally, the neuroprotective properties of Triphala were found to be counteracted by the Nrf2 inhibitor ML385. Our study represented the first to unveil that Triphala exerts therapeutic benefits in alleviating chronic SD-induced cognitive deficits and anxiety by activation of the Nrf2/HO-1 axis. Triphala emerges as a promising nutraceutical ingredient for mitigating cognitive deficits and anxiety linked to chronic SD.

Engrailed1 in Parvalbumin-Positive Neurons Regulates Eye-Specific Retinogeniculate Segregation and Visual Function

Homeobox transcription factor Engrailed1 (En1) is expressed in the ectoderm and mediates the establishment of retinotectal topography, but its role in eye-specific retinogeniculate segregation and visual function remains unclear. Parvalbumin (PV) neurons, which are widely distributed in the visual pathway, play a crucial role in visual development and function. In this study, we conditionally knocked out En1 gene in PV neurons and found an expansion of the ipsilateral eye projection, while no significant effects were observed in the contralateral eye projection. Additionally, we observed a decrease in the number of PV neurons in PV-Cre:En1fl/fl mice, accompanied by an increased level of cleaved caspase-3 in PV neurons. Furthermore, the genetic ablation of PV neurons in the retina through intraocular AAV-DIO-Caspase3 injection in PV-Cre mice was sufficient to disrupt retinogeniculate segregation. Finally, we observed that PV-Cre:En1fl/fl mice exhibited enhanced visual depth perception in the visual cliff test. These results demonstrate that En1 in PV neurons participates in eye-specific retinogeniculate segregation through cell survival and regulates binocular vision.

Distinct circuits and molecular targets of the paraventricular hypothalamus decode visceral and somatic pain

Visceral and somatic pain serve as protective mechanisms against external threats. Accumulated evidence has confirmed that the paraventricular hypothalamus (PVH) plays an important role in the perception of visceral and somatic pain, whereas the exact neural pathways and molecules distinguishing them remain unclear. Here, we report distinct neuronal ensembles within the PVH dedicated to processing visceral and somatic pain signals. An essential discovery is the distinct expression of P2X3R and VIPR2 in visceral and somatic pain-activated PVH neuronal ensembles. Furthermore, visceral pain- and somatic pain-responsive PVH neuronal ensembles project to specific downstream regions, the ventral part of the lateral septal nucleus (LSV) and the caudal part of the zona incerta (ZIC), respectively. These findings unveil that the PVH acts as a pain sorting center that distinctly processes visceral and somatic pain, identifying potential molecular targets for specific pain processing and providing a new framework for comprehending how the brain processes nociceptive information.

Black tea extracts enhance stress-induced sleep of Caenorhabditis elegans to resist UV damage

Black tea is believed to strengthen the ability of the body to defend itself against external stimuli. Here, by examining Caenorhabditis elegans (C. elegans) locomotor behavior over a short period after UV stress, we found that feeding black tea extract (BTE) caused worms to enter a superior stress-induced sleep (SIS) state, which potentially boosting organismal recovery. BTE enhances SIS through KIN-29 mediated epidermal growth factor signaling and modulation of sleep by specific interneurons ALA and RIS. It also inhibits lipid degradation during sleep. These functions were also observed when theaflavins (TFs) were fed. In conclusion, our results describe a new way for BTE-enhanced damage repair in C. elegans after UV stress that relies on enhanced SIS, and confirm the contribution of TFs therein.

Nucleus Accumbens Corticotropin-Releasing Hormone Neurons Projecting to the Bed Nucleus of the Stria Terminalis Promote Wakefulness and Positive Affective State

The nucleus accumbens (NAc) plays an important role in various emotional and motivational behaviors that rely on heightened wakefulness. However, the neural mechanisms underlying the relationship between arousal and emotion regulation in NAc remain unclear. Here, we investigated the roles of a specific subset of inhibitory corticotropin-releasing hormone neurons in the NAc (NAcCRH) in regulating arousal and emotional behaviors in mice. We found an increased activity of NAcCRH neurons during wakefulness and rewarding stimulation. Activation of NAcCRH neurons converts NREM or REM sleep to wakefulness, while inhibition of these neurons attenuates wakefulness. Remarkably, activation of NAcCRH neurons induces a place preference response (PPR) and decreased basal anxiety level, whereas their inactivation induces a place aversion response and anxious state. NAcCRH neurons are identified as the major NAc projection neurons to the bed nucleus of the stria terminalis (BNST). Furthermore, activation of the NAcCRH-BNST pathway similarly induced wakefulness and positive emotional behaviors. Taken together, we identified a basal forebrain CRH pathway that promotes the arousal associated with positive affective states.

Deciphering prefrontal circuits underlying stress and depression: exploring the potential of volume electron microscopy

Adapting to environmental changes and formulating behavioral strategies are central to the nervous system, with the prefrontal cortex being crucial. Chronic stress impacts this region, leading to disorders including major depression. This review discusses the roles for prefrontal cortex and the effects of stress, highlighting similarities and differences between human/primates and rodent brains. Notably, the rodent medial prefrontal cortex is analogous to the human subgenual anterior cingulate cortex in terms of emotional regulation, sharing similarities in cytoarchitecture and circuitry, while also performing cognitive functions similar to the human dorsolateral prefrontal cortex. It has been shown that chronic stress induces atrophic changes in the rodent mPFC, which mirrors the atrophy observed in the subgenual anterior cingulate cortex and dorsolateral prefrontal cortex of depression patients. However, the precise alterations in neural circuitry due to chronic stress are yet to be fully unraveled. The use of advanced imaging techniques, particularly volume electron microscopy, is emphasized as critical for the detailed examination of synaptic changes, providing a deeper understanding of stress and depression at the molecular, cellular and circuit levels. This approach offers invaluable insights into the alterations in neuronal circuits within the medial prefrontal cortex caused by chronic stress, significantly enriching our understanding of stress and depression pathologies.

Reduced hepatic AdipoR2 by increased glucocorticoid mediates effect of psychosocial stress to elevate serum cholesterol

Understanding the effects of psychosocial stress on serum cholesterol may offer valuable insights into the relationship between psychological disorders and endocrine diseases. However, these effects and their underlying mechanisms have not been elucidated yet. Here we show that serum corticosterone, total cholesterol and low-density lipoprotein cholesterol (LDL-C) are elevated in a mouse model of psychosocial stress. Furthermore, alterations occur in AdipoR2-mediated AMPK and PPARα signaling pathways in liver, accompanied by a decrease in LDL-C clearance and an increase in cholesterol synthesis. These changes are further verified in wild-type and AdipoR2 overexpression HepG2 cells incubated with cortisol and AdipoR agonist, and are finally confirmed by treating wild-type and hepatic-specific AdipoR2 overexpression mice with corticosterone. We conclude that increased glucocorticoid mediates the effects of psychosocial stress to elevate serum cholesterol by inhibiting AdipoR2-mediated AMPK and PPARα signaling to decrease LDL-C clearance and increase cholesterol synthesis in liver.

Establishing connectivity through microdissections of midbrain stimulation-related neural circuits

Comprehensive understanding of the neural circuits involving the ventral tegmental area is essential for elucidating the anatomofunctional mechanisms governing human behaviour, in addition to the therapeutic and adverse effects of deep brain stimulation for neuropsychiatric diseases. Although the ventral tegmental area has been targeted successfully with deep brain stimulation for different neuropsychiatric diseases, the axonal connectivity of the region is not fully understood. Here, using fibre microdissections in human cadaveric hemispheres, population-based high-definition fibre tractography and previously reported deep brain stimulation hotspots, we find that the ventral tegmental area participates in an intricate network involving the serotonergic pontine nuclei, basal ganglia, limbic system, basal forebrain and prefrontal cortex, which is implicated in the treatment of obsessive-compulsive disorder, major depressive disorder, Alzheimer's disease, cluster headaches and aggressive behaviours.

A hypothalamus-lateral periaqueductal gray GABAergic neural projection facilitates arousal following sevoflurane anesthesia in mice

BACKGROUND

The lateral hypothalamus (LHA) is an evolutionarily conserved structure that regulates basic functions of an organism, particularly wakefulness. To clarify the function of LHAGABA neurons and their projections on regulating general anesthesia is crucial for understanding the excitatory and inhibitory effects of anesthetics on the brain. The aim of the present study is to investigate whether LHAGABA neurons play either an inhibitory or a facilitatory role in sevoflurane-induced anesthetic arousal regulation.

METHODS

We used fiber photometry and immunofluorescence staining to monitor changes in neuronal activity during sevoflurane anesthesia. Opto-/chemogenetic modulations were employed to study the effect of neurocircuit modulations during the anesthesia. Anterograde tracing was used to identify a GABAergic projection from the LHA to a periaqueductal gray (PAG) subregion.

RESULTS

c-Fos staining showed that LHAGABA activity was inhibited by induction of sevoflurane anesthesia. Anterograde tracing revealed that LHAGABA neurons project to multiple arousal-associated brain areas, with the lateral periaqueductal gray (LPAG) being one of the dense projection areas. Optogenetic experiments showed that activation of LHAGABA neurons and their downstream target LPAG reduced the burst suppression ratio (BSR) during continuous sevoflurane anesthesia. Chemogenetic experiments showed that activation of LHAGABA and its projection to LPAG neurons prolonged the anesthetic induction time and promoted wakefulness.

CONCLUSIONS

In summary, we show that an inhibitory projection from LHAGABA to LPAGGABA neurons promotes arousal from sevoflurane-induced loss of consciousness, suggesting a complex control of wakefulness through intimate interactions between long-range connections.

Mental health: The REM sleep paradox in depression

The relationship between mental disorders and sleep remains unclear. Two new studies show that the lateral habenula, a brain region associated with value-guided behavior, controls REM sleep and promotes emotional stability but also contributes to REM sleep disinhibition in depression.

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.

Regulation of stress-induced sleep perturbations by dorsal raphe VGLUT3 neurons in male mice

Exposure to stressors has profound effects on sleep that have been linked to serotonin (5-HT) neurons of the dorsal raphe nucleus (DR). However, the DR also comprises glutamatergic neurons expressing vesicular glutamate transporter type 3 (DRVGLUT3), leading us to examine their role. Cell-type-specific tracing revealed that DRVGLUT3 neurons project to brain areas regulating arousal and stress. We found that chemogenetic activation of DRVGLUT3 neurons mimics stress-induced sleep perturbations. Furthermore, deleting VGLUT3 in the DR attenuated stress-induced sleep perturbations, especially after social defeat stress. In the DR, VGLUT3 is found in subsets of 5-HT and non-5-HT neurons. We observed that both populations are activated by acute stress, including those projecting to the ventral tegmental area. However, deleting VGLUT3 in 5-HT neurons minimally affected sleep regulation. These findings suggest that VGLUT3 expression in the DR drives stress-induced sleep perturbations, possibly involving non-5-HT DRVGLUT3 neurons.

Divergent evolution of sleep in Drosophila species

Living organisms synchronize their biological activities with the earth's rotation through the circadian clock, a molecular mechanism that regulates biology and behavior daily. This synchronization factually maximizes positive activities (e.g., social interactions, feeding) during safe periods, and minimizes exposure to dangers (e.g., predation, darkness) typically at night. Beyond basic circadian regulation, some behaviors like sleep have an additional layer of homeostatic control, ensuring those essential activities are fulfilled. While sleep is predominantly governed by the circadian clock, a secondary homeostatic regulator, though not well-understood, ensures adherence to necessary sleep amounts and hints at a fundamental biological function of sleep beyond simple energy conservation and safety. Here we explore sleep regulation across seven Drosophila species with diverse ecological niches, revealing that while circadian-driven sleep aspects are consistent, homeostatic regulation varies significantly. The findings suggest that in Drosophilids, sleep evolved primarily for circadian purposes. The more complex, homeostatically regulated functions of sleep appear to have evolved independently in a species-specific manner, and are not universally conserved. This laboratory model may reproduce and recapitulate primordial sleep evolution.

Neural cell-types and circuits linking thermoregulation and social behavior

Understanding how social and affective behavioral states are controlled by neural circuits is a fundamental challenge in neurobiology. Despite increasing understanding of central circuits governing prosocial and agonistic interactions, how bodily autonomic processes regulate these behaviors is less resolved. Thermoregulation is vital for maintaining homeostasis, but also associated with cognitive, physical, affective, and behavioral states. Here, we posit that adjusting body temperature may be integral to the appropriate expression of social behavior and argue that understanding neural links between behavior and thermoregulation is timely. First, changes in behavioral states-including social interaction-often accompany changes in body temperature. Second, recent work has uncovered neural populations controlling both thermoregulatory and social behavioral pathways. We identify additional neural populations that, in separate studies, control social behavior and thermoregulation, and highlight their relevance to human and animal studies. Third, dysregulation of body temperature is linked to human neuropsychiatric disorders. Although body temperature is a "hidden state" in many neurobiological studies, it likely plays an underappreciated role in regulating social and affective states.

Dexmedetomidine Inhibits Paraventricular Corticotropin-releasing Hormone Neurons that Attenuate Acute Stress-induced Anxiety-like Behavior in Mice

BACKGROUND

Dexmedetomidine has repeatedly shown to improve anxiety, but the precise neural mechanisms underlying this effect remain incompletely understood. This study aims to explore the role of corticotropin-releasing hormone-producing hypothalamic paraventricular nucleus (CRHPVN) neurons in mediating the anxiolytic effects of dexmedetomidine.

METHODS

A social defeat stress mouse model was used to evaluate the anxiolytic effects induced by dexmedetomidine through the elevated plus maze, open-field test, and measurement of serum stress hormone levels. In vivo Ca2+ signal fiber photometry and ex vivo patch-clamp recordings were used to determine the excitability of CRHPVN neurons and investigate the specific mechanism involved. CRHPVN neuron modulation was achieved through chemogenetic activation or inhibition.

RESULTS

Compared with saline, dexmedetomidine (40 µg/kg) alleviated anxiety-like behaviors. Additionally, dexmedetomidine reduced CRHPVN neuronal excitability. Chemogenetic activation of CRHPVN neurons decreased the time spent in the open arms of the elevated plus maze and in the central area of the open-field test. Conversely, chemogenetic inhibition of CRHPVN neurons had the opposite effect. Moreover, the suppressive impact of dexmedetomidine on CRHPVN neurons was attenuated by the α2-receptor antagonist yohimbine.

CONCLUSIONS

The results indicate that the anxiety-like effects of dexmedetomidine are mediated via α2-adrenergic receptor-triggered inhibition of CRHPVN neuronal excitability in the hypothalamus.

EDITOR’S PERSPECTIVE

Extracting Stress-Related EEG Patterns From Pre-Sleep EEG for Forecasting Slow-Wave Sleep Deficiency

Sleep is vital to our daily activity. Lack of proper sleep can impair functionality and overall health. While stress is known for its detrimental impact on sleep quality, the precise effect of pre-sleep stress on subsequent sleep structure remains unknown. This study introduced a novel approach to study the pre-sleep stress effect on sleep structure, specifically slow-wave sleep (SWS) deficiency. To achieve this, we selected forehead resting EEG immediately before and upon sleep onset to extract stress-related neurological markers through power spectra and entropy analysis. These markers include beta/delta correlation, alpha asymmetry, fuzzy entropy (FuzzEn) and spectral entropy (SpEn). Fifteen subjects were included in this study. Our results showed that subjects lacking SWS often exhibited signs of stress in EEG, such as an increased beta/delta correlation, higher alpha asymmetry, and increased FuzzEn in frontal EEG. Conversely, individuals with ample SWS displayed a weak beta/delta correlation and reduced FuzzEn. Finally, we employed several supervised learning models and found that the selected neurological markers can predict subsequent SWS deficiency. Our investigation demonstrated that the classifiers could effectively predict varying levels of slow-wave sleep (SWS) from pre-sleep EEG segments, achieving a mean balanced accuracy surpassing 0.75. The SMOTE-Tomek resampling method could improve the performance to 0.77. This study suggests that stress-related neurological markers derived from pre-sleep EEG can effectively predict SWS deficiency. Such information can be integrated with existing sleep-improving techniques to provide a personalized sleep forecasting and improvement solution.

Microglia modulate sleep/wakefulness under baseline conditions and under acute social defeat stress in adult mice

Although sleep is tightly regulated by multiple neuronal circuits in the brain, nonneuronal cells such as glial cells have been increasingly recognized as crucial sleep regulators. Recent studies have shown that microglia may act to maintain wakefulness. Here, we investigated the possible involvement of microglia in the regulation of sleep quantity and quality under baseline and stress conditions through electroencephalography (EEG)/electromyography (EMG) recordings, and by employing pharmacological methods to eliminate microglial cells in the adult mouse brain. We found that severe microglial depletion induced by the colony-stimulating factor 1 receptor (CSF1R) antagonist PLX5622 (PLX) reversibly decreased the total wake time and the wake episode duration and increased the EEG slow-wave power during wakefulness under baseline conditions. To examine the role of microglia in sleep/wake regulation under mental stress, we used the acute social defeat stress (ASDS) paradigm, an ethological model for psychosocial stress. Sleep analysis under ASDS revealed that microglial depletion exacerbated the stress-induced decrease in the total wake time and increase in anxiety-like behaviors in the open field test. These results demonstrate that microglia actively modulate sleep quantity and architecture under both baseline and stress conditions. Our findings suggest that microglia may potentially provide resilience against acute psychosocial stress by regulating restorative sleep.

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.

The missing hallmark of health: psychosocial adaptation

The eight biological hallmarks of health that we initially postulated (Cell. 2021 Jan 7;184(1):33-63) include features of spatial compartmentalization (integrity of barriers, containment of local perturbations), maintenance of homeostasis over time (recycling & turnover, integration of circuitries, rhythmic oscillations) and an array of adequate responses to stress (homeostatic resilience, hormetic regulation, repair & regeneration). These hallmarks affect all eight somatic strata of the human body (molecules, organelles, cells, supracellular units, organs, organ systems, systemic circuitries and meta-organism). Here we postulate that mental and socioeconomic factors must be added to this 8×8 matrix as an additional hallmark of health ("psychosocial adaptation") and as an additional stratum ("psychosocial interactions"), hence building a 9×9 matrix. Potentially, perturbation of each of the somatic hallmarks and strata affects psychosocial factors and vice versa. Finally, we discuss the (patho)physiological bases of these interactions and their implications for mental health improvement.

Psychological stress-induced microbial metabolite indole-3-acetate disrupts intestinal cell lineage commitment

The brain and gut are intricately connected and respond to various stimuli. Stress-induced brain-gut communication is implicated in the pathogenesis and relapse of gut disorders. The mechanism that relays psychological stress to the intestinal epithelium, resulting in maladaptation, remains poorly understood. Here, we describe a stress-responsive brain-to-gut metabolic axis that impairs intestinal stem cell (ISC) lineage commitment. Psychological stress-triggered sympathetic output enriches gut commensal Lactobacillus murinus, increasing the production of indole-3-acetate (IAA), which contributes to a transferrable loss of intestinal secretory cells. Bacterial IAA disrupts ISC mitochondrial bioenergetics and thereby prevents secretory lineage commitment in a cell-intrinsic manner. Oral α-ketoglutarate supplementation bolsters ISC differentiation and confers resilience to stress-triggered intestinal epithelial injury. We confirm that fecal IAA is higher in patients with mental distress and is correlated with gut dysfunction. These findings uncover a microbe-mediated brain-gut pathway that could be therapeutically targeted for stress-driven gut-brain comorbidities.

Does sleep promote adaptation to acute stress: An experimental study

Objectives

Evidence of the impact of chronic stress on sleep is abundant, yet experimental sleep studies with a focus on acute stress are scarce and the results are mixed. Our study aimed to fill this gap by experimentally investigating the effects of pre-sleep social stress on sleep dynamics during the subsequent night, as measured with polysomnography (PSG).

Methods

Thirty-four healthy individuals (65% females, Mage = 25.76 years SD = 3.35) underwent a stress-inducing (SC) or neutral control condition (CC) in virtual reality (VR). We used overnight EEG measurements to analyze the basic sleep parameters and power spectral density (PSD) across the sleep cycles, and measured heart rate and its variability (HRV), skin electrodermal activity (EDA), and salivary cortisol to capture physiological arousal during the VR task and the pre-sleep period.

Results

Following acute stress (SC), the amount of slow-wave sleep (SWS) was higher and N2 sleep lower relative to CC, specifically in the first sleep cycle. In SC, PSD was elevated in the beta-low (16-24 Hz) and beta-high (25-35 Hz) frequency ranges during both stages N2 and SWS over the entire night.

Conclusions

Sleep promoted adaptation to acute social stress by a longer duration of SWS in the subsequent sleep period, especially in early sleep. A similar homeostatic effect towards restorative sleep is well-evidenced in animal model stress studies but has not been previously reported in experimental human studies. Whether the high-frequency PSD activity during stages N2 and SWS also serves in the resolution of transient stress, remains open.

Relationship between bedtime, nighttime sleep duration, and anxiety symptoms in preschoolers in China

Background

Sleep problems in preschoolers are becoming increasingly prominent, and the association between sleep status and anxiety symptoms has attracted growing attention. However, studies investigating the relationship between bedtime and nighttime sleep duration in preschoolers and their anxiety symptoms remain scant. We used the large sample data from the Longhua Cohort Study of Children in Shenzhen, China (LCCS) to analyze the association between bedtime and sleep in preschoolers and their anxiety symptoms.

Methods

A cross-sectional study of 69,138 preschoolers in Longhua District, Shenzhen, China was conducted in 2022. Data on sociodemographic characteristics of families, bedtime, nighttime sleep duration of preschoolers, and their anxiety symptoms (measured by the Spence Preschool Children Anxiety Scale) were collected through a structured questionnaire completed by the parents. Using binary logistic regression models, the relationship between bedtime, nighttime sleep duration, and childhood anxiety symptoms was examined.

Results

The bedtimes of preschoolers were concentrated between 21:01-22:00 (52.41%). Among the preschoolers, 38.70% had bedtimes later than 22:00, and 75.49% had insufficient nighttime sleep duration. The positive screening rate for anxiety symptoms among preschoolers was 3.50%. After adjusting for confounding factors using binary logistic regression models, compared with preschoolers with bedtime ≤21:00, The OR (95%CI) values of anxiety in preschoolers with bedtime ≥23:01, 22:01-23:00 and 21:01-22:00 were 2.86 (2.21-3.69), 1.51 (1.27-1.79) and 1.48 (1.26-1.76), respectively. Compared with those with sufficient nighttime sleep duration, the OR (95%CI) of children with nighttime sleep duration less than 9 h was 1.36 (1.23-1.51).

Conclusion

An association exists between bedtime and nighttime sleep duration in preschoolers and their anxiety symptoms. Preschoolers with 21:00 for bedtime and a nighttime sleep duration of 10 h may have lower anxiety symptoms. These findings support the importance of adequate sleep for preventing anxiety symptoms in children.

Effects of thermal exposure to disposable plastic tableware on human gut microbiota and metabolites: A quasi-experimental study

The aim of this quasi-experimental study was to determine the alterations in gut microbiota and metabolism in humans who consume hot food served in disposable plastic tableware (DPT). Participants in the exposure and control groups were provided three hot meals in DPT (n = 30) or non-DPT (n = 30), respectively. After a month of observation, individuals in the exposure group discontinued the three meals provided in DPT (n = 27) for 1 month as the post-exposure group. Fecal samples were collected and tested for microplastics (MPs) detection using LDIR and gut microbiota identification based on the 16 S rRNA. Urine samples were used for metabolite analysis using LC-MS/MS. Results showed that the level of MPs in feces was lower in the post-exposure group compared with the exposure group. Furthermore, the abundance of the phyla Actinobacteria, Proteobacteria, Firmicutes, and Bacteroidota in the exposure and post-exposure groups were significantly different compared with the control group. Changes in microbiota abundance and metabolite levels were mainly associated with central nervous system effects, energy metabolism, and inflammation, suggesting that thermal exposure to DPT for 1 month has considerable health effects.

Hidden variables in stress neurobiology research

Among the central goals of stress neurobiology research is to understand the mechanisms by which stressors change neural circuit function to precipitate or exacerbate psychiatric symptoms. Yet despite decades of effort, psychiatric medications that target the biological substrates of the stress response are largely lacking. We propose that the clinical advancement of stress response-based therapeutics for psychiatric disorders may be hindered by 'hidden variables' in stress research, including considerations of behavioral study design (stressors and outcome measures), individual variability, sex differences, and the interaction of the body's stress hormone system with endogenous circadian and ultradian rhythms. We highlight key issues and suggest ways forward in stress neurobiology research that may improve the ability to assess stress mechanisms and translate preclinical findings.

The different cell-specific mechanisms of voluntary exercise and forced exercise in the nucleus accumbens

Physical inactivity is a global epidemic. People who take the initiative to exercise will feel pleasure during the exercise process and stick with it for a long time, while people who passively ask for exercise will feel pain and cannot stick with it. However, the neural mechanisms underlying voluntary and forced exercise remain unclear. Here, we report that voluntary running increased the frequency and amplitude of miniature excitatory postsynaptic currents (mEPSC) but decreased membrane excitability in D1R-MSNs, whereas D2R-MSNs did not change in mEPSC and membrane excitability. Forced running increased the frequency of mEPSC and membrane excitability in D2R-MSNs, but D1R-MSNs did not change, which may be the mechanism by which forced exercise has a non-rewarding effect. These findings provide new insights into how voluntary and forced exercise mediate reward and non-reward effects.

ASMT determines gut microbiota and increases neurobehavioral adaptability to exercise in female mice

N-acetylserotonin O-methyltransferase (ASMT) is responsible for melatonin biosynthesis. The Asmt gene is located on the X chromosome, and its genetic polymorphism is associated with depression in humans. However, the underlying mechanism remains unclear. Here, we use CRISPR/Cas9 to delete 20 bp of exon 2 of Asmt, and construct C57BL/6J mouse strain with Asmt frameshift mutation (Asmtft/ft). We show that female Asmtft/ft mice exhibit anxiety- and depression-like behaviors, accompanied by an obvious structural remodeling of gut microbiota. These behavioral abnormalities are not observed in male. Moreover, female Asmtft/ft mice show a lower neurobehavioral adaptability to exercise, while wild-type shows a "higher resilience". Cross-sectional and longitudinal analysis indicates that the structure of gut microbiota in Asmtft/ft mice is less affected by exercise. These results suggests that Asmt maintains the plasticity of gut microbiota in female, thereby enhancing the neurobehavioral adaptability to exercise.

Acute or Chronic Exposure to Corticosterone Promotes Wakefulness in Mice

Elevated glucocorticoid levels triggered by stress potentially contribute to sleep disturbances in stress-induced depression. However, sleep changes in response to elevated corticosterone (CORT), the major glucocorticoid in rodents, remain unclear. Here, we investigated the effects of acute or chronic CORT administration on sleep using electroencephalogram (EEG) and electromyography (EMG) recordings in freely moving mice. Acute CORT exposure rapidly promoted wakefulness, marked by increased episodes and enhanced EEG delta power, while simultaneously suppressing rapid eye movement (REM) and non-rapid eye movement (NREM) sleep, with the latter marked by decreased mean duration and reduced delta power. Prolonged 28-day CORT exposure led to excessive wakefulness and REM sleep, characterized by higher episodes, and decreased NREM sleep, characterized by higher episodes and reduced mean duration. EEG theta activity during REM sleep and delta activity during NREM sleep were attenuated following 28-day CORT exposure. These effects persisted, except for REM sleep amounts, even 7 days after the drug withdrawal. Elevated plasma CORT levels and depressive phenotypes were identified and correlated with observed sleep changes during and after administration. Fos expression significantly increased in the lateral habenula, lateral hypothalamus, and ventral tegmental area following acute or chronic CORT treatment. Our findings demonstrate that CORT exposure enhanced wakefulness, suppressed and fragmented NREM sleep, and altered EEG activity across all stages. This study illuminates sleep alterations during short or extended periods of heightened CORT levels in mice, providing a neural link connecting insomnia and depression.

Melatonin alleviates depression-like behaviors and cognitive dysfunction in mice by regulating the circadian rhythm of AQP4 polarization

Depression is a common chronic psychiatric illness, which is resistant to medical treatments. While melatonin may alleviate certain depression symptoms, evidence for its efficacy against core symptoms is lacking. Here, we tested a mechanism whereby melatonin rescues the behavioral outcomes of the chronic unpredictable mild stress (CUMS) mouse model of depression. CUMS mice showed depressive behaviors to tail suspension, open field behavior, and sucrose preference test, and cognitive dysfunction in the Morris water maze. Impairments in these measures were relieved by melatonin treatment. Moreover, CUMS mice had impaired glymphatic function across the sleep-wake cycle due to the astrocytic loss and disturbance of circadian regulation of the polarized expression of aquaporin-4 (AQP4) water channels in perivascular astrocytes. EEG results in CUMS mice showed a reduced total sleep time and non-rapid eye movement (NREM) sleep, due to sleep fragmentation in the light phase. CUMS mice lost the normal rhythmic expressions of circadian proteins Per2, Cry2, Bmal1, Clock, and Per1. However, the melatonin treatment restored glymphatic system function and the polarization of AQP4, while improving sleep structure, and rectifying the abnormal expression of Per2, Bmal1, Clock, and Per1 in CUMS mice. Interestingly, Per2 expression correlated negatively with the polarization of AQP4. Further studies demonstrated that Per2 directed the location of AQP4 expression via interactions with the α-dystrobrevin (Dtna) subunit of AQP4 in primary cultured astrocytes. In conclusion, we report a new mechanism whereby melatonin improves depression outcomes by regulating the expression of the circadian protein Per2, maintaining the circadian rhythm of astrocytic AQP4 polarization, and restoring glymphatic function.

Somatostatin neurons in prefrontal cortex initiate sleep-preparatory behavior and sleep via the preoptic and lateral hypothalamus

The prefrontal cortex (PFC) enables mammals to respond to situations, including internal states, with appropriate actions. One such internal state could be 'tiredness'. Here, using activity tagging in the mouse PFC, we identified particularly excitable, fast-spiking, somatostatin-expressing, γ-aminobutyric acid (GABA) (PFCSst-GABA) cells that responded to sleep deprivation. These cells projected to the lateral preoptic (LPO) hypothalamus and the lateral hypothalamus (LH). Stimulating PFCSst-GABA terminals in the LPO hypothalamus caused sleep-preparatory behavior (nesting, elevated theta power and elevated temperature), and stimulating PFCSst-GABA terminals in the LH mimicked recovery sleep (non-rapid eye-movement sleep with higher delta power and lower body temperature). PFCSst-GABA terminals had enhanced activity during nesting and sleep, inducing inhibitory postsynaptic currents on diverse cells in the LPO hypothalamus and the LH. The PFC also might feature in deciding sleep location in the absence of excessive fatigue. These findings suggest that the PFC instructs the hypothalamus to ensure that optimal sleep takes place in a suitable place.

Ventrolateral periaqueductal gray GABAergic neurons promote arousal of sevoflurane anesthesia through cortico-midbrain circuit

The mechanism of general anesthesia remains elusive. The ventrolateral periaqueductal gray (vlPAG) in the midbrain regulates sleep and awake states. However, the role of vlPAG and its circuits in anesthesia is unclear. We utilized opto/chemogenetics, righting reflex, and electroencephalographic recording to assess consciousness changes. We employed fiber photometry to measure the activity of neurons and neurotransmitters. As a result, photometry recording showed that the activity of GABA neurons in vlPAG decreased during sevoflurane anesthesia and was reactivated after anesthesia. Activating GABAergic neurons in vlPAG promoted arousal during anesthesia, while inhibiting them delayed this process. Furthermore, medial prefrontal cortex (mPFC) to vlPAG pyramidal neurons projections and vlPAG to ventral tegmental area (VTA) GABAergic projections played a prominent role in the anesthesia-awake transition. GABA neurotransmitter activity of VTA synchronized with mPFC-vlPAG pyramidal neuron projections. Therefore, the cortico-midbrain circuits centered on vlPAG GABAergic neurons exert an arousal-promoting effect during sevoflurane anesthesia.

Bright light treatment counteracts stress-induced sleep alterations in mice, via a visual circuit related to the rostromedial tegmental nucleus

Light in the environment greatly impacts a variety of brain functions, including sleep. Clinical evidence suggests that bright light treatment has a beneficial effect on stress-related diseases. Although stress can alter sleep patterns, the effect of bright light treatment on stress-induced sleep alterations and the underlying mechanism are poorly understood. Here, we show that bright light treatment reduces the increase in nonrapid eye movement (NREM) sleep induced by chronic stress through a di-synaptic visual circuit consisting of the thalamic ventral lateral geniculate nucleus and intergeniculate leaflet (vLGN/IGL), lateral habenula (LHb), and rostromedial tegmental nucleus (RMTg). Specifically, chronic stress causes a marked increase in NREM sleep duration and a complementary decrease in wakefulness time in mice. Specific activation of RMTg-projecting LHb neurons or activation of RMTg neurons receiving direct LHb inputs mimics the effects of chronic stress on sleep patterns, while inhibition of RMTg-projecting LHb neurons or RMTg neurons receiving direct LHb inputs reduces the NREM sleep-promoting effects of chronic stress. Importantly, we demonstrate that bright light treatment reduces the NREM sleep-promoting effects of chronic stress through the vLGN/IGL-LHb-RMTg pathway. Together, our results provide a circuit mechanism underlying the effects of bright light treatment on sleep alterations induced by chronic stress.

GABAergic modulation of sleep-wake states

Benzodiazepine, a classical medication utilized in the treatment of insomnia, operates by augmenting the activity of the GABAA receptor. This underscores the significance of GABAergic neurotransmission in both the initiation and maintenance of sleep. Nevertheless, an increasing body of evidence substantiates the notion that GABA-mediated neurotransmission also assumes a vital role in promoting wakefulness in specific neuronal circuits. Despite the longstanding belief in the pivotal function of GABA in regulating the sleep-wake cycle, there exists a dearth of comprehensive documentation regarding the specific regions within the central nervous system where GABAergic neurons are crucial for these functions. In this review, we delve into the involvement of GABAergic neurons in the regulation of sleep-wake cycles, with particular focus on those located in the preoptic area (POA) and ventral tegmental area (VTA). Recent research, including our own, has further underscored the importance of GABAergic neurotransmission in these areas for the regulation of sleep-wake cycles.

Somatostatin-Expressing Neurons in the Ventral Tegmental Area Innervate Specific Forebrain Regions and Are Involved in Stress Response

Expanding knowledge about the cellular composition of subcortical brain regions demonstrates large heterogeneity and differences from the cortical architecture. Previously we described three subtypes of somatostatin-expressing (Sst) neurons in the mouse ventral tegmental area (VTA) and showed their local inhibitory action on the neighboring dopaminergic neurons (Nagaeva et al., 2020). Here, we report that Sst+ neurons especially from the anterolateral part of the mouse VTA also project far outside the VTA and innervate forebrain regions that are mainly involved in the regulation of emotional behavior, including the ventral pallidum, lateral hypothalamus, the medial part of the central amygdala, anterolateral division of the bed nucleus of stria terminalis, and paraventricular thalamic nucleus. Deletion of these VTASst neurons in mice affected several behaviors, such as home cage activity, sensitization of locomotor activity to morphine, fear conditioning responses, and reactions to the inescapable stress of forced swimming, often in a sex-dependent manner. Together, these data demonstrate that VTASst neurons have selective projection targets distinct from the main targets of VTA dopamine neurons. VTASst neurons are involved in the regulation of behaviors primarily associated with the stress response, making them a relevant addition to the efferent VTA pathways and stress-related neuronal network.

Contribution of activating lateral hypothalamus-lateral habenula circuit to nerve trauma-induced neuropathic pain in mice

Neuropathic pain, a severe clinical symptom, significantly affects the quality of life in the patients. The molecular mechanisms underlying neuropathic pain have been the focus of research in recent decades; however, the neuronal circuit-mediated mechanisms associated with this disorder remain poorly understood. Here, we report that a projection from the lateral hypothalamus (LH) glutamatergic neurons to the lateral habenula (LHb), an excitatory LH-LHb neuronal circuit, participates in nerve injury-induced nociceptive hypersensitivity. LH glutamatergic neurons are activated and display enhanced responses to normally non-noxious stimuli following chronic constriction injury. Chemogenetic inhibition of LH glutamatergic neurons or excitatory LH-LHb circuit blocked CCI-induced nociceptive hypersensitivity. Activation of the LH-LHb circuit led to augmented responses to mechanical and thermal stimuli in mice without nerve injury. These findings suggest that LH neurons and their triggered LH-LHb circuit participate in central mechanisms underlying neuropathic pain and may be targets for the treatment of this disorder.

β-asarone prolongs sleep via regulating the level of glutamate in the PVN

People of all ages could suffer from sleep disorders, which are increasingly recognized as common manifestations of neurologic disease. Acorus tatarinowii is a herb that has been used in traditional medicine to promote sleep. β-asarone, as the main component of volatile oil obtained from Acorus tatarinowii, may be the main contributor to the sleeping-promoting efficacy of Acorus tatarinowii. In the study, adult male C57BL/6 mice were administered β-asarone at 12.5 mg/kg, 25 mg/kg, and 50 mg/kg. Behavioral experiments showed that β-asarone at 25 mg/kg could significantly improve sleep duration. It was also observed that the proportion of NREM (Non-Rapid Eye Movement) sleep increased considerably after administration of β-asarone. In the PVN (paraventricular nucleus of hypothalamus) region of the hypothalamus, it was observed that the glutamate content decreased after β-asarone treatment. At the same time, the expression of VGLUT2 (vesicular glutamate transporters 2) decreased while the expression of GAD65 (glutamic acid decarboxylase 65) and GABARAP (GABA Type A Receptor-Associated Protein) increased in the hypothalamus, suggesting that β-asarone may suppress arousal by reducing glutamate and promoting transformation of glutamate to the inhibitory neurotransmitter GABA (γ-aminobutyric acid). This study is the first to focus on the association between β-asarone and sleep, shedding perspectives for pharmacological applications of β-asarone and providing a new direction for future research.

The stress of losing sleep: Sex-specific neurobiological outcomes

Sleep is a vital and evolutionarily conserved process, critical to daily functioning and homeostatic balance. Losing sleep is inherently stressful and leads to numerous detrimental physiological outcomes. Despite sleep disturbances affecting everyone, women and female rodents are often excluded or underrepresented in clinical and pre-clinical studies. Advancing our understanding of the role of biological sex in the responses to sleep loss stands to greatly improve our ability to understand and treat health consequences of insufficient sleep. As such, this review discusses sex differences in response to sleep deprivation, with a focus on the sympathetic nervous system stress response and activation of the hypothalamic-pituitary-adrenal (HPA) axis. We review sex differences in several stress-related consequences of sleep loss, including inflammation, learning and memory deficits, and mood related changes. Focusing on women's health, we discuss the effects of sleep deprivation during the peripartum period. In closing, we present neurobiological mechanisms, including the contribution of sex hormones, orexins, circadian timing systems, and astrocytic neuromodulation, that may underlie potential sex differences in sleep deprivation responses.