The hypothalamic link between arousal and sleep homeostasis in mice

Variability in sleep architecture and alterations in circadian rhythms in patients with acute cerebral infarction accompanied by sleep-disordered breathing

PURPOSE

To continuously and dynamically monitor the sleep status of patients in the acute phase of cerebral infarction, and to investigate the characteristics of acute cerebral infarction(ACI)associated with sleep-disordered breathing (SDB), variations in sleep structure, and changes in sleep circadian rhythms.

METHODS

Patients with ACI within 48 h of onset who were admitted to the Department of Neurology at Kailuan General Hospital from November 2020 to December 2022 were selected. Detailed baseline information such as age, gender, smoking history, drinking history, were recorded for the selected participants. From the beginning of their hospitalization, the selected participants were monitored for their sleep status continuously for 5 days using the Intelligent Mattress-based Sleep Monitoring Platform System(IMSMPS). Based on the heart rate data obtained from the monitoring, the interdaily stability (IS) and intradaily variability (IV) of the sleep circadian rhythm were calculated.

RESULTS

1,367 patients with ACI were selected. Monitoring results over 5 days indicated 147 cases (10.75%) without SDB, and 1,220 cases (89.25%) with SDB. Among the group with SDB, there were 248 cases (18.14%) with continuous mild SDB, 395 cases (28.90%) with moderate SDB, 295 cases (21.58%) with severe SDB, and 282 cases (20.63%) that fluctuated between different severity levels. Within this fluctuating group, 152 cases (53.90%) fluctuated between two severity levels, 120 cases (42.55%) between three levels, and 10 cases (3.55%) among all four levels. There were statistically significant differences (P < 0.05) in the sleep latency, sleep efficiency, non-rapid eye movement stages 1-2, rapid eye movement, proportion of non-rapid eye movement, proportion of rapid eye movement, wake after sleep onset, time out of bed, number of awakenings, respiratory variability index, and heart rate variability index among patients with ACI monitored from day 1 to 5. However, other monitored sleep structure parameters did not show statistically significant differences (P > 0.05). The coefficient of variation for all sleep monitoring parameters ranged between 14.54 and 36.57%. The IV in the SDB group was higher than in the group without SDB (P < 0.05), and the IS was lower than in the group without SDB (P < 0.05).

CONCLUSION

Patients in the acute phase of cerebral infarction have a high probability of accompanying SDB. The sleep structure of these patients shows significant variability based on the onset time of the stroke, and some patients experience fluctuations among different severity levels of SDB. ACI accompanied by SDB can further reduce the IS of a patient's sleep circadian rhythm and increase its IV.

Noradrenergic tone is not required for neuronal activity-induced rebound sleep in zebrafish

Sleep pressure builds during wakefulness, but the mechanisms underlying this homeostatic process are poorly understood. One zebrafish model suggests that sleep pressure increases as a function of global neuronal activity, such as during sleep deprivation or acute exposure to drugs that induce widespread brain activation. Given that the arousal-promoting noradrenergic system is important for maintaining heightened neuronal activity during wakefulness, we hypothesised that genetic and pharmacological reduction of noradrenergic tone during drug-induced neuronal activation would dampen subsequent rebound sleep in zebrafish larvae. During stimulant drug treatment, dampening noradrenergic tone with the α2-adrenoceptor agonist clonidine unexpectedly enhanced subsequent rebound sleep, whereas enhancing noradrenergic signalling with a cocktail of α1- and β-adrenoceptor agonists did not enhance rebound sleep. Similarly, CRISPR/Cas9-mediated elimination of the dopamine β-hydroxylase (dbh) gene, which encodes an enzyme required for noradrenalin synthesis, enhanced baseline sleep in larvae but did not prevent additional rebound sleep following acute induction of neuronal activity. Across all drug conditions, c-fos expression immediately after drug exposure correlated strongly with the amount of induced rebound sleep, but was inversely related to the strength of noradrenergic modulatory tone. These results are consistent with a model in which increases in neuronal activity, as reflected by brain-wide levels of c-fos induction, drive a sleep pressure signal that promotes rebound sleep independently of noradrenergic tone.

Methods to estimate body temperature and energy expenditure dynamics in fed and fasted laboratory mice: effects of sleep deprivation and light exposure

Monitoring body temperature and energy expenditure in freely-moving laboratory mice remains a powerful methodology used widely across a variety of disciplines-including circadian biology, sleep research, metabolic phenotyping, and the study of body temperature regulation. Some of the most pronounced changes in body temperature are observed when small heterothermic species reduce their body temperature during daily torpor. Daily torpor is an energy saving strategy characterized by dramatic reductions in body temperature employed by mice and other species when challenged to meet energetic demands. Typical measurements used to describe daily torpor are the measurement of core body temperature and energy expenditure. These approaches can have drawbacks and developing alternatives for these techniques provides options that can be beneficial both from an animal-welfare and study-complexity perspective. First, this paper presents and assesses a method to estimate core body temperature based on measurements of subcutaneous body temperature, and second, a separate approach to better estimate energy expenditure during daily torpor based on core body temperature. Third, the effects of light exposure during the habitual dark phase and sleep deprivation during the light period on body temperature dynamics were tested preliminary in fed and fasted mice. Together, the here-published approaches and datasets can be used in the future to assess body temperature and metabolism in freely-moving laboratory mice.

The genetic architecture of the human hypothalamus and its involvement in neuropsychiatric behaviours and disorders

Despite its crucial role in the regulation of vital metabolic and neurological functions, the genetic architecture of the hypothalamus remains unknown. Here we conducted multivariate genome-wide association studies (GWAS) using hypothalamic imaging data from 32,956 individuals to uncover the genetic underpinnings of the hypothalamus and its involvement in neuropsychiatric traits. There were 23 significant loci associated with the whole hypothalamus and its subunits, with functional enrichment for genes involved in intracellular trafficking systems and metabolic processes of steroid-related compounds. The hypothalamus exhibited substantial genetic associations with limbic system structures and neuropsychiatric traits including chronotype, risky behaviour, cognition, satiety and sympathetic-parasympathetic activity. The strongest signal in the primary GWAS, the ADAMTS8 locus, was replicated in three independent datasets (N = 1,685-4,321) and was strengthened after meta-analysis. Exome-wide association analyses added evidence to the association for ADAMTS8, and Mendelian randomization showed lower ADAMTS8 expression with larger hypothalamic volumes. The current study advances our understanding of complex structure-function relationships of the hypothalamus and provides insights into the molecular mechanisms that underlie hypothalamic formation.

Somnotate: A probabilistic sleep stage classifier for studying vigilance state transitions

Electrophysiological recordings from freely behaving animals are a widespread and powerful mode of investigation in sleep research. These recordings generate large amounts of data that require sleep stage annotation (polysomnography), in which the data is parcellated according to three vigilance states: awake, rapid eye movement (REM) sleep, and non-REM (NREM) sleep. Manual and current computational annotation methods ignore intermediate states because the classification features become ambiguous, even though intermediate states contain important information regarding vigilance state dynamics. To address this problem, we have developed "Somnotate"-a probabilistic classifier based on a combination of linear discriminant analysis (LDA) with a hidden Markov model (HMM). First we demonstrate that Somnotate sets new standards in polysomnography, exhibiting annotation accuracies that exceed human experts on mouse electrophysiological data, remarkable robustness to errors in the training data, compatibility with different recording configurations, and an ability to maintain high accuracy during experimental interventions. However, the key feature of Somnotate is that it quantifies and reports the certainty of its annotations. We leverage this feature to reveal that many intermediate vigilance states cluster around state transitions, whereas others correspond to failed attempts to transition. This enables us to show for the first time that the success rates of different types of transition are differentially affected by experimental manipulations and can explain previously observed sleep patterns. Somnotate is open-source and has the potential to both facilitate the study of sleep stage transitions and offer new insights into the mechanisms underlying sleep-wake dynamics.

Role of the substantia nigra pars reticulata in sleep-wakefulness: A review of research progress

Sleep is a complex physiological process that includes two main stages: non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. During mammalian sleep, especially REM sleep, skeletal muscles are suppressed to varying degrees, and corresponding movements are inhibited. The synchronous occurrence of sleep and motor inhibition suggests they may share the same neural circuits. Recently, the substantia nigra pars reticulata (SNr) has attracted attention for its potential dual role in regulating sleep-wake cycles and movement. In this review, the SNr's role is surveyed by examining existing research reports regarding its involvement in sleep-wake regulation and motor control. By focusing on the SNr, the goal is to shed light on its dual role intricacies and stimulate further inquiry into potential interactions between sleep and movement regulation, thus aiming to explore sleep-wake regulatory mechanisms and offer novel directions for subsequent scientific investigation.

Penguins snatch seconds-long microsleeps

Chinstrap penguins fall asleep thousands of times per day in the wild.

Whole-brain monosynaptic inputs to lateral periaqueductal gray glutamatergic neurons in mice

OBJECTIVE

The lateral periaqueductal gray (LPAG), which mainly contains glutamatergic neurons, plays an important role in social responses, pain, and offensive and defensive behaviors. Currently, the whole-brain monosynaptic inputs to LPAG glutamatergic neurons are unknown. This study aims to explore the structural framework of the underlying neural mechanisms of LPAG glutamatergic neurons.

METHODS

This study used retrograde tracing systems based on the rabies virus, Cre-LoxP technology, and immunofluorescence analysis.

RESULTS

We found that 59 nuclei projected monosynaptic inputs to the LPAG glutamatergic neurons. In addition, seven hypothalamic nuclei, namely the lateral hypothalamic area (LH), lateral preoptic area (LPO), substantia innominata (SI), medial preoptic area, ventral pallidum, posterior hypothalamic area, and lateral globus pallidus, projected most densely to the LPAG glutamatergic neurons. Notably, we discovered through further immunofluorescence analysis that the inputs to the LPAG glutamatergic neurons were colocalized with several markers related to important neurological functions associated with physiological behaviors.

CONCLUSION

The LPAG glutamatergic neurons received dense projections from the hypothalamus, especially nuclei such as LH, LPO, and SI. The input neurons were colocalized with several markers of physiological behaviors, which show the pivotal role of glutamatergic neurons in the physiological behaviors regulation by LPAG.

Sleep dysfunction mediates the relationship between hypothalamic-insula connectivity and anxiety-depression symptom severity bidirectionally in young adults

BACKGROUND

The hypothalamus plays a crucial role in regulating sleep-wake cycle and motivated behavior. Sleep disturbance is associated with impairment in cognitive and affective functions. However, how hypothalamic dysfunction may contribute to inter-related sleep, cognitive, and emotional deficits remain unclear.

METHODS

We curated the Human Connectome Project dataset and investigated how hypothalamic resting state functional connectivities (rsFC) were associated with sleep dysfunction, as evaluated by the Pittsburgh Sleep Quality Index (PSQI), cognitive performance, and subjective mood states in 687 young adults (342 women). Imaging data were processed with published routines and evaluated with a corrected threshold. We examined the inter-relationship amongst hypothalamic rsFC, PSQI score, and clinical measures with mediation analyses.

RESULTS

In whole-brain regressions with age and drinking severity as covariates, men showed higher hypothalamic rsFC with the right insula in correlation with PSQI score. No clusters were identified in women at the same threshold. Both hypothalamic-insula rsFC and PSQI score were significantly correlated with anxiety and depression scores in men. Further, mediation analyses showed that PSQI score mediated the relationship between hypothalamic-insula rsFC and anxiety/depression symptom severity bidirectionally in men.

CONCLUSIONS

Sleep dysfunction is associated with negative emotions and hypothalamic rsFC with the right insula, a core structure of the interoceptive circuits. Notably, anxiety-depression symptom severity and altered hypothalamic-insula rsFC are related bidirectionally by poor sleep quality. These findings are specific to men, suggesting potential sex differences in the neural circuits regulating sleep and emotional states that need to be further investigated.

Alzheimer's disease phenotypes show different sleep architecture

INTRODUCTION

Sleep-wake disturbances are a prominent feature of Alzheimer's disease (AD). Atypical (non-amnestic) AD syndromes have different patterns of cortical vulnerability to AD. We hypothesized that atypical AD also shows differential vulnerability in subcortical nuclei that will manifest as different patterns of sleep dysfunction.

METHODS

Overnight electroencephalography monitoring was performed on 48 subjects, including 15 amnestic, 19 atypical AD, and 14 controls. AD was defined based on neuropathological or biomarker confirmation. We compared sleep architecture by visual scoring and spectral power analysis in each group.

RESULTS

Overall, AD cases showed increased sleep fragmentation and N1 sleep compared to controls. Compared to atypical AD groups, typical AD showed worse N3 sleep dysfunction and relatively preserved rapid eye movement (REM) sleep.

DISCUSSION

Results suggest differing effects of amnestic and atypical AD variants on slow wave versus REM sleep, respectively, corroborating the hypothesis of differential selective vulnerability patterns of the subcortical nuclei within variants. Optimal symptomatic treatment for sleep dysfunction in clinical phenotypes may differ.

HIGHLIGHTS

Alzheimer's disease (AD) variants show distinct patterns of sleep impairment. Amnestic/typical AD has worse N3 slow wave sleep (SWS) impairment compared to atypical AD. Atypical AD shows more rapid eye movement deficits than typical AD. Selective vulnerability patterns in subcortical areas may underlie sleep differences. Relatively preserved SWS may explain better memory scores in atypical versus typical AD.

Structure and Function of Neuronal Circuits Linking Ventrolateral Preoptic Nucleus and Lateral Hypothalamic Area

To understand how sleep-wakefulness cycles are regulated, it is essential to disentangle structural and functional relationships between the preoptic area (POA) and lateral hypothalamic area (LHA), since these regions play important yet opposing roles in the sleep-wakefulness regulation. GABA- and galanin (GAL)-producing neurons in the ventrolateral preoptic nucleus (VLPO) of the POA (VLPOGABA and VLPOGAL neurons) are responsible for the maintenance of sleep, while the LHA contains orexin-producing neurons (orexin neurons) that are crucial for maintenance of wakefulness. Through the use of rabies virus-mediated neural tracing combined with in situ hybridization (ISH) in male and female orexin-iCre mice, we revealed that the vesicular GABA transporter (Vgat, Slc32a1)- and galanin (Gal)-expressing neurons in the VLPO directly synapse with orexin neurons in the LHA. A majority (56.3 ± 8.1%) of all VLPO input neurons connecting to orexin neurons were double-positive for Vgat and Gal Using projection-specific rabies virus-mediated tracing in male and female Vgat-ires-Cre and Gal-Cre mice, we discovered that VLPOGABA and VLPOGAL neurons that send projections to the LHA received innervations from similarly distributed input neurons in many brain regions, with the POA and LHA being among the main upstream areas. Additionally, we found that acute optogenetic excitation of axons of VLPOGABA neurons, but not VLPOGAL neurons, in the LHA of male Vgat-ires-Cre mice induced wakefulness. This study deciphers the connectivity between the VLPO and LHA, provides a large-scale map of upstream neuronal populations of VLPO→LHA neurons, and reveals a previously uncovered function of the VLPOGABA→LHA pathway in the regulation of sleep and wakefulness.SIGNIFICANCE STATEMENT We identified neurons in the ventrolateral preoptic nucleus (VLPO) that are positive for vesicular GABA transporter (Vgat) and/or galanin (Gal) and serve as presynaptic partners of orexin-producing neurons in the lateral hypothalamic area (LHA). We depicted monosynaptic input neurons of GABA- and galanin-producing neurons in the VLPO that send projections to the LHA throughout the entire brain. Their input neurons largely overlap, suggesting that they comprise a common neuronal population. However, acute excitatory optogenetic manipulation of the VLPOGABA→LHA pathway, but not the VLPOGAL→LHA pathway, evoked wakefulness. This study shows the connectivity of major components of the sleep/wake circuitry in the hypothalamus and unveils a previously unrecognized function of the VLPOGABA→LHA pathway in sleep-wakefulness regulation. Furthermore, we suggest the existence of subpopulations of VLPOGABA neurons that innervate LHA.

Measuring body temperature of freely moving mice under an optogenetics-induced long-term hypothermic state

We present a protocol for inducing a hibernation-like state in free-moving mice using optogenetics. We have recently developed an optogenetic technique utilizing modified Opsin4, which is activated by weak blue light, resulting in prolonged neuronal excitation. We describe a protocol that includes detailed instructions for virus injection, implantation of optic fibers and temperature transmitters, photostimulation, and real-time recording of body temperature in mice. This method is valuable for investigating the mechanisms underlying torpor and thermoregulation in mice. For complete details on the use and execution of this protocol, please refer to Takahashi et al.¹.

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.

Neuroprotective effect of Ziziphi Spinosae Semen on rats with p-chlorophenylalanine-induced insomnia via activation of GABAA receptor

Ziziphus jujuba var. spinosa (Bunge) Hu ex H.F.Chow [Rhamnaceae; Ziziphi Spinosae Semen (ZSS)] has attracted extensive attention as the first choice of traditional Chinese medicine in the treatment of insomnia. However, recent studies on the sleep-improving mechanism of ZSS have mainly focused on the role of single components. Thus, to further reveal the potential mechanism of ZSS, an assessment of its multiple constituents is necessary. In this study, ZSS extract (ZSSE) was obtained from ZSS via detailed modern extraction, separation, and purification technologies. The chemical constituents of ZSSE were analyzed by high-performance liquid chromatography-mass spectrometry (HPLC-MS). For in vivo experiments, a rat model of insomnia induced by p-chlorophenylalanine (PCPA) was established to investigate the potential effect and corresponding mechanism of ZSSE on improving sleep. Hematoxylin-eosin staining (HE) results revealed that the drug group showed prominent advantages over the model group in improving sleep. Moreover, the brain levels of γ-aminobutyric acid (GABA), glutamic acid (Glu), 5-hydroxytryptamine (5-HT), and dopamine (DA) were monitored via enzyme-linked immunosorbent assay (ELISA) to further study the sleep-improving mechanism of ZSSE. We found that sleep was effectively improved via upregulation of GABA and 5-HT and downregulation of Glu and DA. In addition, molecular mechanisms of ZSSE in improving sleep were studied by immunohistochemical analysis. The results showed that sleep was improved by regulating the expression levels of GABA receptor subunit alpha-1 (GABAARα1) and GABA acid receptor subunit gamma-2 (GABAARγ2) receptors in the hypothalamus and hippocampus tissue sections. Therefore, this work not only identified the active ingredients of ZSSE but also revealed the potential pharmacological mechanism of ZSSE for improving sleep, which may greatly stimulate the prospective development and application of ZSSE.

Lateral septum modulates cortical state to tune responsivity to threat stimuli

Sudden unexpected environmental changes capture attention and, when perceived as potentially dangerous, evoke defensive behavioral states. Perturbations of the lateral septum (LS) can produce extreme hyperdefensiveness even to innocuous stimuli, but how this structure influences stimulus-evoked defensive responses and threat perception remains unclear. Here, we show that Crhr2-expressing neurons in mouse LS exhibit phasic activation upon detection of threatening but not rewarding stimuli. Threat-stimulus-driven activity predicts the probability but not vigor or type of defensive behavior evoked. Although necessary for and sufficient to potentiate stimulus-triggered defensive responses, LSCrhr2 neurons do not promote specific behaviors. Rather, their stimulation elicits negative valence and physiological arousal. Moreover, LSCrhr2 activity tracks brain state fluctuations and drives cortical activation and rapid awakening in the absence of threat. Together, our findings suggest that LS directs bottom-up modulation of cortical function to evoke preparatory defensive internal states and selectively enhance responsivity to threat-related stimuli.