Optogenetic stimulation of MCH neurons increases sleep

Targeting MCH Neuroendocrine Circuit in Lateral Hypothalamus to Protect Against Skeletal Senescence

Neuroendocrine regulation is essential for maintaining metabolic homeostasis. However, whether neuroendocrine pathway influence bone metabolism and skeletal senescence is unelucidated. Here, a central neuroendocrine circuit is identified that directly controls osteogenesis. Using virus based tracing, this study is identified that melanin concentrating hormone (MCH) expressing neurons in the lateral hypothalamus (LH) are connected to the bone. Chemogenetic activation of MCH neurons in the LH induces osteogenesis, whereas inhibiting these neurons reduces osteogenesis. Meanwhile, MCH is released into the circulation upon chemogenetic activation of these neurons. Single cell sequencing reveals that blocking MCH neurons in the LH diminishes osteogenic differentiation of bone marrow stromal cells (BMSCs) and induces senescence. Mechanistically, MCH promotes BMSC differentiation by activating MCHR1 via PKA signaling, and activating MCHR1 by MCH agonists attenuate skeletal senescence in mice. By elucidating a brain-bone connection that autonomously enhances osteogenesis, these findings uncover the neuroendocrinological mechanisms governing bone mass regulation and protect against skeletal senescence.

Ethnic and region-specific genetic risk variants of stroke and its comorbid conditions can define the variations in the burden of stroke and its phenotypic traits

Burden of stroke differs by region, which could be attributed to differences in comorbid conditions and ethnicity. Genomewide variation acts as a proxy marker for ethnicity, and comorbid conditions. We present an integrated approach to understand this variation by considering prevalence and mortality rates of stroke and its comorbid risk for 204 countries from 2009 to 2019, and Genome-wide association studies (GWAS) risk variant for all these conditions. Global and regional trend analysis of rates using linear regression, correlation, and proportion analysis, signifies ethnogeographic differences. Interestingly, the comorbid conditions that act as risk drivers for stroke differed by regions, with more of metabolic risk in America and Europe, in contrast to high systolic blood pressure in Asian and African regions. GWAS risk loci of stroke and its comorbid conditions indicate distinct population stratification for each of these conditions, signifying for population-specific risk. Unique and shared genetic risk variants for stroke, and its comorbid and followed up with ethnic-specific variation can help in determining regional risk drivers for stroke. Unique ethnic-specific risk variants and their distinct patterns of linkage disequilibrium further uncover the drivers for phenotypic variation. Therefore, identifying population- and comorbidity-specific risk variants might help in defining the threshold for risk, and aid in developing population-specific prevention strategies for stroke.

Is melanin-concentrating hormone in the medial preoptic area a signal for the decline of maternal care in late postpartum?

This manuscript proposes that melanin-concentrating hormone (MCH) in the medial preoptic area (MPOA) is an neurochemical signal evolved to trigger the declining process of maternal care. MCH in the MPOA appears only after parturition and is progressively increased with the progression of lactation, while maternal behavior declines progressively. Intra-MPOA injection of MCH decreases active maternal responses. MCH is also highly responsive to infant characteristics and maternal condition. Behavioral changes induced by MCH in late postpartum period are conducive to the decline of infant-directed maternal behavior. The MPOA MCH system may mediate the maternal behavior decline by suppressing the maternal approach motivation and/or increasing maternal withdrawal via its inhibitory action onto the mesolimbic dopamine D1/D2 receptors and its stimulating action on serotonin 5-HT2C receptors in the ventral tegmental area. Research into the MCH maternal effects will enhance our understanding of the neurochemical mechanisms underlying the maternal behavior decline.

The pulse of sleep: novel interventions in understanding the sleep-cardiovascular connection: a literature review

Introduction

Sleep disorders represent common complaints in different medical illnesses. They encompass a risk for diverse inflammatory, metabolic, and cardiovascular diseases. Sleep disorders include disorders of hypersomnolence, insomnia, parasomnias, sleep-related movement disorders, circadian rhythm sleep-wake-disorders, and sleep-related breathing disorders, each one of which was associated with increased cardiovascular disease risk in a different mechanism. In this review, the authors address the most recent research on the correlation between sleep and CVD.

Methods

The literature on sleep disorders and their potential links to various cardiovascular diseases was reviewed in narrative form. For the published papers up to June 2023, the authors searched the databases of PubMed and Google Scholar. Literature demonstrating the relationship between these illnesses, pathophysiological mechanisms, diagnosis, and various therapeutic approaches was included.

Results

Sleep disorders were significantly linked to heart rate variability, hypertension, and obesity, which can eventually result in cardiovascular consequences and affect mortality and morbidity. The disruption in sleep cycles, which can be noticed in different sleep disorders, can obviously result in blood pressure, heart rate, and other cardiac functions. The clinical assessment acts as the cornerstone in the diagnosis of different spectrums of sleep disorders. The management of sleep disorders ranges from cognitive-behavioral therapy to continuous positive airway pressure (CPAP).

Conclusion

Additional research on the topic is needed to pinpoint any potential links and pathological processes. To improve clinical treatment and preventive measures, further observational studies should emphasize the reliability of early diagnostic signs.

Searching for sleep in all the right places: My career in sleep research

My research has always focused on sleep, whether monitoring neural activity (microwires, c-Fos, calcium imaging), triggering it with optogenetics or pharmacologically (anandamide, cholinergic agonists), or measuring levels of endogenous sleep agents such as adenosine. A recurring theme of my research is to use new tools to find the sweet spot in the brain where the signal to sleep begins. My goal is to identify the circuit, determine whether it degrades with age or disease, and repair the circuit when it fails. I am deeply grateful to my mentors for introducing me to the science of sleep, to my students and colleagues for helping me in my quest, and to the NIH and VA Research for supporting the research. Because of the collective efforts of sleep researchers, the public is more aware of the importance of sleep to a healthy lifestyle.

Neuronal network controlling REM sleep

Rapid eye movement sleep is a state characterized by concomitant occurrence of rapid eye movements, electroencephalographic activation and muscle atonia. In this review, we provide up to date knowledge on the neuronal network controlling its onset and maintenance. It is now accepted that muscle atonia during rapid eye movement sleep is due to activation of glutamatergic neurons localized in the pontine sublaterodorsal tegmental nucleus. These neurons directly project and excite glycinergic/γ-aminobutyric acid-ergic pre-motoneurons localized in the ventromedial medulla. The sublaterodorsal tegmental nucleus rapid eye movement-on neurons are inactivated during wakefulness and non-rapid eye movement by rapid eye movement-off γ-aminobutyric acid-ergic neurons localized in the ventrolateral periaqueductal grey and the adjacent dorsal deep mesencephalic reticular nucleus. Melanin-concentrating hormone and γ-aminobutyric acid-ergic rapid eye movement sleep-on neurons localized in the lateral hypothalamus would inhibit these rapid eye movement sleep-off neurons initiating the state. Finally, the activation of a few limbic cortical structures during rapid eye movement sleep by the claustrum and the supramammillary nucleus as well as that of the basolateral amygdala would be involved in the function(s) of rapid eye movement sleep. In summary, rapid eye movement sleep is generated by a brainstem generator controlled by forebrain structures involved in autonomic control.

Glutamatergic signaling from melanin-concentrating hormone-producing neurons: A requirement for memory regulation, but not for metabolism control

Melanin-concentrating hormone-producing neurons (MCH neurons), found mainly in the lateral hypothalamus and surrounding areas, play essential roles in various brain functions, including sleep and wakefulness, reward, metabolism, learning, and memory. These neurons coexpress several neurotransmitters and act as glutamatergic neurons. The contribution of glutamate from MCH neurons to memory- and metabolism-related functions has not been fully investigated. In a mouse model, we conditionally knocked out Slc17a6 gene, which encodes for vesicular glutamate transporter 2 (vGlut2), in the MCH neurons exclusively by using two different methods: the Cre recombinase/loxP system and in vivo genome editing using CRISPR/Cas9. Then, we evaluated several aspects of memory and measured metabolic rates using indirect calorimetry. We found that mice with MCH neuron-exclusive vGlut2 ablation had higher discrimination ratios between novel and familiar stimuli for novel object recognition, object location, and three-chamber tests. In contrast, there was no significant change in body weight, food intake, oxygen consumption, respiratory quotient, or locomotor activity. These findings suggest that glutamatergic signaling from MCH neurons is required to regulate memory, but its role in regulating metabolic rate is negligible.

Exploratory Rearing Is Governed by Hypothalamic Melanin-Concentrating Hormone Neurons According to Locus Ceruleus

Information seeking, such as standing on tiptoes to look around in humans, is observed across animals and helps survival. Its rodent analog-unsupported rearing on hind legs-was a classic model in deciphering neural signals of cognition and is of intense renewed interest in preclinical modeling of neuropsychiatric states. Neural signals and circuits controlling this dedicated decision to seek information remain largely unknown. While studying subsecond timing of spontaneous behavioral acts and activity of melanin-concentrating hormone (MCH) neurons (MNs) in behaving male and female mice, we observed large MN activity spikes that aligned to unsupported rears. Complementary causal, loss and gain of function, analyses revealed specific control of rear frequency and duration by MNs and MCHR1 receptors. Activity in a key stress center of the brain-the locus ceruleus noradrenaline cells-rapidly inhibited MNs and required functional MCH receptors for its endogenous modulation of rearing. By defining a neural module that both tracks and controls rearing, these findings may facilitate further insights into biology of information seeking.

The wake- and sleep-modulating neurons of the lateral hypothalamic area demonstrate a differential pattern of degeneration in Alzheimers disease

BACKGROUND

Sleep-wake dysfunction is an early and common event in Alzheimer's disease (AD). The lateral hypothalamic area (LHA) regulates the sleep and wake cycle through wake-promoting orexinergic neurons (OrxN) and sleep-promoting melanin-concentrating hormone or MCHergic neurons (MCHN). These neurons share close anatomical proximity with functional reciprocity. This study investigated LHA OrxN and MCHN loss patterns in AD individuals. Understanding the degeneration pattern of these neurons will be instrumental in designing potential therapeutics to slow down the disease progression and remediate the sleep-wake dysfunction in AD.

METHODS

Postmortem human brain tissue from donors with AD (across progressive stages) and controls were examined using unbiased stereology. Formalin-fixed, celloidin-embedded hypothalamic sections were stained with Orx-A/MCH, p-tau (CP13), and counterstained with gallocyanin. Orx or MCH-positive neurons with or without CP13 inclusions and gallocyanin-stained neurons were considered for stereology counting. Additionally, we extracted RNA from the LHA using conventional techniques. We used customized Neuropathology and Glia nCounter (Nanostring) panels to study gene expression. Wald statistical test was used to compare the groups, and the genes were considered differentially expressed when the p-value was <.05.

RESULTS

We observed a progressive decline in OrxN alongside a relative preservation of MCHN. OrxN decreased by 58% (p=0.03) by Braak stages (BB) 1-2 and further declined to 81% (p=0.03) by BB 5-6. Conversely, MCHN demonstrated a non-statistical significant decline (27%, p=0.1088) by BB 6. We observed a progressive increase in differentially expressed genes (DEGs), starting with glial profile changes in BB2. While OrxN loss was observed, Orx-related genes showed upregulation in BB 3-4 compared to BB 0-1. GO and KEGG terms related to neuroinflammatory pathways were mainly enriched.

CONCLUSIONS

To date, OrxN loss in the LHA represents the first neuronal population to die preceding the loss of LC neurons. Conversely, MCHN shows resilience to AD p-tau accumulation across Braak stages. The initial loss of OrxN correlates with specific neuroinflammation, glial profile changes, and an overexpression of HCRT, possibly due to hyperexcitation following compensation mechanisms. Interventions preventing OrxN loss and inhibiting p-tau accumulation in the LHA could prevent neuronal loss in AD and, perhaps, the progression of the disease.

Most dynorphin neurons in the zona incerta-perifornical area are active in waking relative to non-rapid-eye movement and rapid-eye movement sleep

Dynorphin is an endogenous opiate localized in many brain regions and spinal cord, but the activity of dynorphin neurons during sleep is unknown. Dynorphin is an inhibitory neuropeptide that is coreleased with orexin, an excitatory neuropeptide. We used microendoscopy to test the hypothesis that, like orexin, the dynorphin neurons are wake-active. Dynorphin-cre mice (n = 3) were administered rAAV8-Ef1a-Con/Foff 2.0-GCaMP6M into the zona incerta-perifornical area, implanted with a GRIN lens (gradient reflective index), and electrodes to the skull that recorded sleep. One month later, a miniscope imaged calcium fluorescence in dynorphin neurons during multiple bouts of wake, non-rapid-eye movement (NREM), and rapid-eye movement (REM) sleep. Unbiased data analysis identified changes in calcium fluorescence in 64 dynorphin neurons. Most of the dynorphin neurons (72%) had the highest fluorescence during bouts of active and quiet waking compared to NREM or REM sleep; a subset (20%) were REM-max. Our results are consistent with the emerging evidence that the activity of orexin neurons can be classified as wake-max or REM-max. Since the two neuropeptides are coexpressed and coreleased, we suggest that dynorphin-cre-driven calcium sensors could increase understanding of the role of this endogenous opiate in pain and sleep.

An Electroencephalogram Signature of Melanin-Concentrating Hormone Neuron Activities Predicts Cocaine Seeking

BACKGROUND

Identifying biomarkers that predict substance use disorder propensity may better strategize antiaddiction treatment. Melanin-concentrating hormone (MCH) neurons in the lateral hypothalamus critically mediate interactions between sleep and substance use; however, their activities are largely obscured in surface electroencephalogram (EEG) measures, hindering the development of biomarkers.

METHODS

Surface EEG signals and real-time calcium (Ca2+) activities of lateral hypothalamus MCH neurons (Ca2+MCH) were simultaneously recorded in male and female adult rats. Mathematical modeling and machine learning were then applied to predict Ca2+MCH using EEG derivatives. The robustness of the predictions was tested across sex and treatment conditions. Finally, features extracted from the EEG-predicted Ca2+MCH either before or after cocaine experience were used to predict future drug-seeking behaviors.

RESULTS

An EEG waveform derivative-a modified theta-delta-theta peak ratio (EEGTDT ratio)-accurately tracked real-time Ca2+MCH in rats. The prediction was robust during rapid eye movement sleep (REMS), persisted through vigilance states, sleep manipulations, and circadian phases, and was consistent across sex. Moreover, cocaine self-administration and long-term withdrawal altered EEGTDT ratio, suggesting shortening and circadian redistribution of synchronous MCH neuron activities. In addition, features of EEGTDT ratio indicative of prolonged synchronous MCH neuron activities predicted lower subsequent cocaine seeking. EEGTDT ratio also exhibited advantages over conventional REMS measures for the predictions.

CONCLUSIONS

The identified EEGTDT ratio may serve as a noninvasive measure for assessing MCH neuron activities in vivo and evaluating REMS; it may also serve as a potential biomarker for predicting drug use propensity.

Which structure generates paradoxical (REM) sleep: The brainstem, the hypothalamus, the amygdala or the cortex?

Paradoxical or Rapid eye movement (REM) sleep (PS) is a state characterized by REMs, EEG activation and muscle atonia. In this review, we discuss the contribution of brainstem, hypothalamic, amygdalar and cortical structures in PS genesis. We propose that muscle atonia during PS is due to activation of glutamatergic neurons localized in the pontine sublaterodorsal tegmental nucleus (SLD) projecting to glycinergic/GABAergic pre-motoneurons localized in the ventro-medial medulla (vmM). The SLD PS-on neurons are inactivated during wakefulness and slow-wave sleep by PS-off GABAergic neurons localized in the ventrolateral periaqueductal gray (vPAG) and the adjacent deep mesencephalic reticular nucleus. Melanin concentrating hormone (MCH) and GABAergic PS-on neurons localized in the posterior hypothalamus would inhibit these PS-off neurons to initiate the state. Finally, the activation of a few limbic cortical structures during PS by the claustrum and the supramammillary nucleus as well as that of the basolateral amygdala would also contribute to PS expression. Accumulating evidence indicates that the activation of these limbic structures plays a role in memory consolidation and would communicate to the PS-generating structures the need for PS to process memory. In summary, PS generation is controlled by structures distributed from the cortex to the medullary level of the brain.

An EEG Signature of MCH Neuron Activities Predicts Cocaine Seeking

Background

Identifying biomarkers that predict substance use disorder (SUD) propensity may better strategize anti-addiction treatment. The melanin-concentrating hormone (MCH) neurons in the lateral hypothalamus (LH) critically mediates interactions between sleep and substance use; however, their activities are largely obscured in surface electroencephalogram (EEG) measures, hindering the development of biomarkers.

Methods

Surface EEG signals and real-time Ca2+ activities of LH MCH neurons (Ca2+MCH) were simultaneously recorded in male and female adult rats. Mathematical modeling and machine learning were then applied to predict Ca2+MCH using EEG derivatives. The robustness of the predictions was tested across sex and treatment conditions. Finally, features extracted from the EEG-predicted Ca2+MCH either before or after cocaine experience were used to predict future drug-seeking behaviors.

Results

An EEG waveform derivative - a modified theta-to-delta ratio (EEG Ratio) - accurately tracks real-time Ca2+MCH in rats. The prediction was robust during rapid eye movement sleep (REMS), persisted through REMS manipulations, wakefulness, circadian phases, and was consistent across sex. Moreover, cocaine self-administration and long-term withdrawal altered EEG Ratio suggesting shortening and circadian redistribution of synchronous MCH neuron activities. In addition, features of EEG Ratio indicative of prolonged synchronous MCH neuron activities predicted lower subsequent cocaine seeking. EEG Ratio also exhibited advantages over conventional REMS measures for the predictions.

Conclusions

The identified EEG Ratio may serve as a non-invasive measure for assessing MCH neuron activities in vivo and evaluating REMS; it may also serve as a potential biomarker predicting drug use propensity.

Unilateral optogenetic stimulation of Lhx6 neurons in the zona incerta increases REM sleep

To determine how a waking brain falls asleep researchers have monitored and manipulated activity of neurons and glia in various brain regions. While imaging Gamma-Aminobutyric Acid (GABA) neurons in the zona incerta (ZI) we found a subgroup that anticipates onset of NREM sleep (Blanco-Centurion C, Luo S, Vidal-Ortiz A, Swank C, Shiromani PJ. Activity of a subset of vesicular GABA-transporter neurons in the ventral ZI anticipates sleep onset. Sleep. 2021;44(6):zsaa268. doi:10.1093/sleep/zsaa268.). To differentiate the GABA subtype we now image and optogenetically manipulate the ZI neurons containing the transcription factor, Lhx6. In the first study, Lhx6-cre mice (n = 5; female = 4) were given rAAV-DJ-EF1a-DIO-GCaMP6M into the ZI (isofluorane anesthesia), a GRIN lens implanted, and 21days later sleep and fluorescence in individual Lhx6 neurons were recorded for 4 hours. Calcium fluorescence was detected in 132 neurons. 45.5% of the Lhx6 neurons were REM-max; 30.3% were wake-max; 11.4% were wake + REM max; 9% were NREM-max; and 3.8% had no change. The NREM-max group of neurons fluoresced 30 seconds ahead of sleep onset. The second study tested the effects of unilateral optogenetic stimulation of the ZI Lhx6 neurons (n = 14 mice) (AAV5-Syn-FLEX-rc[ChrimsonR-tdTomato]. Stimulation at 1 and 5 Hz (1 minute on- 4 minutes off) significantly increased percent REM sleep during the 4 hours stimulation period (last half of day cycle). The typical experimental approach is to stimulate neurons in both hemispheres, but here we found that low-frequency stimulation of ZI Lhx6 neurons in one hemisphere is sufficient to shift states of consciousness. Detailed mapping combined with mechanistic testing is necessary to identify local nodes that can shift the brain between wake-sleep states.

Crosstalk between the subiculum and sleep-wake regulation: A review

The circuitry underlying the initiation, maintenance, and coordination of wakefulness, rapid eye movement sleep, and non-rapid eye movement sleep is not thoroughly understood. Sleep is thought to arise due to decreased activity in the ascending reticular arousal system, which originates in the brainstem and awakens the thalamus and cortex during wakefulness. Despite the conventional association of sleep-wake states with hippocampal rhythms, the mutual influence of the hippocampal formation in regulating vigilance states has been largely neglected. Here, we focus on the subiculum, the main output region of the hippocampal formation. The subiculum, particulary the ventral part, sends extensive monosynaptic projections to crucial regions implicated in sleep-wake regulation, including the thalamus, lateral hypothalamus, tuberomammillary nucleus, basal forebrain, ventrolateral preoptic nucleus, ventrolateral tegmental area, and suprachiasmatic nucleus. Additionally, second-order projections from the subiculum are received by the laterodorsal tegmental nucleus, locus coeruleus, and median raphe nucleus, suggesting the potential involvement of the subiculum in the regulation of the sleep-wake cycle. We also discuss alterations in the subiculum observed in individuals with sleep disorders and in sleep-deprived mice, underscoring the significance of investigating neuronal communication between the subiculum and pathways promoting both sleep and wakefulness.

Brain Circuits Underlying Narcolepsy

Narcolepsy is a sleep disorder manifesting symptoms such as excessive daytime sleepiness and often cataplexy, a sudden and involuntary loss of muscle activity during wakefulness. The underlying neuropathological basis of narcolepsy is the loss of orexin neurons from the lateral hypothalamus. To date numerous animal models of narcolepsy have been produced in the laboratory, being invaluable tools for delineating the brain circuits of narcolepsy. This review will examine the evidence regarding the function of the orexin system, and how loss of this wake-promoting system manifests in excessive daytime sleepiness. This review will also outline the brain circuits controlling cataplexy, focusing on the contribution of orexin signaling loss in narcolepsy. Although our understanding of the brain circuits of narcolepsy has made great progress in recent years, much remains to be understood.

Sleep and the hypothalamus

Neural substrates of wakefulness, rapid eye movement sleep (REMS), and non-REMS (NREMS) in the mammalian hypothalamus overlap both anatomically and functionally with cellular networks that support physiological and behavioral homeostasis. Here, we review the roles of sleep neurons of the hypothalamus in the homeostatic control of thermoregulation or goal-oriented behaviors during wakefulness. We address how hypothalamic circuits involved in opposing behaviors such as core body temperature and sleep compute conflicting information and provide a coherent vigilance state. Finally, we highlight some of the key unresolved questions and challenges, and the promise of a more granular view of the cellular and molecular diversity underlying the integrative role of the hypothalamus in physiological and behavioral homeostasis.

Characterizing brain stage-dependent pupil dynamics based on lateral hypothalamic activity

Pupil dynamics presents varied correlation features with brain activity under different vigilant levels. The modulation of brain dynamic stages can arise from the lateral hypothalamus (LH), where diverse neuronal cell types contribute to arousal regulation in opposite directions via the anterior cingulate cortex (ACC). However, the relationship of the LH and pupil dynamics has seldom been investigated. Here, we performed local field potential (LFP) recordings at the LH and ACC, and whole-brain fMRI with simultaneous fiber photometry Ca2+ recording in the ACC, to evaluate their correlation with brain state-dependent pupil dynamics. Both LFP and functional magnetic resonance imaging (fMRI) data showed various correlations to pupil dynamics across trials that span negative, null, and positive correlation values, demonstrating brain state-dependent coupling features. Our results indicate that the correlation of pupil dynamics with ACC LFP and whole-brain fMRI signals depends on LH activity, suggesting a role of the latter in brain dynamic stage regulation.

Orexin and MCH neurons: regulators of sleep and metabolism

Sleep-wake and fasting-feeding are tightly coupled behavioral states that require coordination between several brain regions. The mammalian lateral hypothalamus (LH) is a functionally and anatomically complex brain region harboring heterogeneous cell populations that regulate sleep, feeding, and energy metabolism. Significant attempts were made to understand the cellular and circuit bases of LH actions. Rapid advancements in genetic and electrophysiological manipulation help to understand the role of discrete LH cell populations. The opposing action of LH orexin/hypocretin and melanin-concentrating hormone (MCH) neurons on metabolic sensing and sleep-wake regulation make them the candidate to explore in detail. This review surveys the molecular, genetic, and neuronal components of orexin and MCH signaling in the regulation of sleep and metabolism.

Differentiation, Transcriptomic Profiling, and Calcium Imaging of Human Hypothalamic Neurons

Neurons in the hypothalamus orchestrate homeostatic physiological processes and behaviors essential for life. Human pluripotent stem cells (hPSCs) can be differentiated into many types of hypothalamic neurons, progenitors, and glia. This updated unit includes published studies and protocols with new advances in the differentiation, maturation, and interrogation by transcriptomic profiling and calcium imaging of human hypothalamic cell populations. Specifically, new methods to freeze and thaw hypothalamic progenitors after they have been patterned and before substantial neurogenesis has occurred are provided that will facilitate experimental flexibility and planning. Also included are updated recipes and protocols for neuronal maturation, with details on the equipment and methods for examining their transcriptomic response and cell-autonomous properties in culture in the presence of synaptic blockers. Together, these protocols facilitate the adoption and use of this model system for fundamental biological discovery and therapeutic translation to human diseases such as obesity, diabetes, sleep disorders, infertility, and chronic stress. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: hPSC maintenance Basic Protocol 2: Hypothalamic neuron differentiation Support Protocol 1: Cortical neuron (control) differentiation Basic Protocol 3: Neuronal maturation Support Protocol 2: Cryopreservation and thawing of neuronal progenitors Support Protocol 3: Quality control: Confirmation of hypothalamic patterning and neurogenesis Support Protocol 4: Bulk RNA sequencing of hypothalamic cultures Basic Protocol 4: Calcium imaging of hypothalamic neurons using Fura-2 AM Alternate Protocol: Calcium imaging of green fluorescent hypothalamic neurons using Rhod-3 AM.

Early alterations in the MCH system link aberrant neuronal activity and sleep disturbances in a mouse model of Alzheimer's disease

Early Alzheimer's disease (AD) is associated with hippocampal hyperactivity and decreased sleep quality. Here we show that homeostatic mechanisms transiently counteract the increased excitatory drive to CA1 neurons in App^NL-G-F mice, but that this mechanism fails in older mice. Spatial transcriptomics analysis identifies Pmch as part of the adaptive response in App^NL-G-F mice. Pmch encodes melanin-concentrating hormone (MCH), which is produced in sleep-active lateral hypothalamic neurons that project to CA1 and modulate memory. We show that MCH downregulates synaptic transmission, modulates firing rate homeostasis in hippocampal neurons and reverses the increased excitatory drive to CA1 neurons in App^NL-G-F mice. App^NL-G-F mice spend less time in rapid eye movement (REM) sleep. App^NL-G-F mice and individuals with AD show progressive changes in morphology of CA1-projecting MCH axons. Our findings identify the MCH system as vulnerable in early AD and suggest that impaired MCH-system function contributes to aberrant excitatory drive and sleep defects, which can compromise hippocampus-dependent functions.

Projections from LIM homeobox 6 (Lhx6) + zona incerta neurons to the cholinergic or monoaminergic nuclei of the rat

A recent report suggested that LIM homeobox 6 (Lhx6) + GABA-releasing neurons of the ventral zona incerta (VZI) promote sleep, particularly paradoxical sleep (PS). While their potential involvement in sleep still needs to be firmly confirmed, little is known about their specific input/output connections with widespread brain regions, including those involved in sleep. Thus, the present study was designed to examine whether Lhx6-expressing neurons (in parallel to intermingled MCH-expressing ones) may send efferent projections to cholinergic and/or monoaminergic nuclei from basal forebrain (BF) to brainstem (BS). Based on the present observations, the proportions of Lhx6+ neuronal projection to the BF and BS cholinergic nuclei over the total number of Lhx6+ VZI cells were approximately 5.9% and 6.9%, respectively. Likewise, the proportions of Lhx6+ neuronal projection to the dorsal raphe and locus coeruleus over the total number of Lhx6+ VZI cells were about 4.3% and 3.9%, respectively. In addition, Lhx6+ cells projecting to the cholinergic or monoaminergic nuclei were scattered along the entire dorsal-to-ventral extent of the VZI. Based on the present as well as our previous observations, it is suggested that Lhx6+ VZI neurons might play an important role in the regulation of PS, partly via the neural network involving the cholinergic as well as monoaminergic nuclei of the rat.

Activity of GABA neurons in the zona incerta and ventral lateral periaqueductal grey is biased towards sleep

STUDY OBJECTIVES

As in various brain regions the activity of gamma-aminobutyric acid (GABA) neurons is largely unknown, we measured in vivo changes in calcium fluorescence in GABA neurons in the zona incerta (ZI) and the ventral lateral periaqueductal grey (vlPAG), two areas that have been implicated in regulating sleep.

METHODS

vGAT-Cre mice were implanted with sleep electrodes, microinjected with rAAV-DIO-GCaMP6 into the ZI (n = 6) or vlPAG (n = 5) (isoflurane anesthesia) and a GRIN (Gradient-Index) lens inserted atop the injection site. Twenty-one days later, fluorescence in individual vGAT neurons was recorded over multiple REM cycles. Regions of interest corresponding to individual vGAT somata were automatically extracted with PCA-ICA analysis.

RESULTS

In the ZI, 372 neurons were identified. Previously, we had recorded the activity of 310 vGAT neurons in the ZI and we combined the published dataset with the new dataset to create a comprehensive dataset of ZI vGAT neurons (total neurons = 682; mice = 11). In the vlPAG, 169 neurons (mice = 5) were identified. In both regions, most neurons were maximally active in REM sleep (R-Max; ZI = 51.0%, vlPAG = 60.9%). The second most abundant group was W-Max (ZI = 23.9%, vlPAG = 25.4%). In the ZI, but not in vlPAG, there were neurons that were NREMS-Max (11.7%). vlPAG had REMS-Off neurons (8.3%). In both areas, there were two minor classes: wake/REMS-Max and state indifferent. In the ZI, the NREMS-Max neurons fluoresced 30 s ahead of sleep onset.

CONCLUSIONS

These descriptive data show that the activity of GABA neurons is biased in favor of sleep in two brain regions implicated in sleep.

Activation of the rostral nucleus accumbens shell by optogenetics induces cataplexy-like behavior in orexin neuron-ablated mice

Cataplexy is one of the symptoms of type 1 narcolepsy, characterized by a sudden loss of muscle tone. It can be seen as a behavioral index of salience, predominantly positive emotion, since it is triggered by laughter in humans and palatable foods in mice. In our previous study using chemogenetic techniques in narcoleptic mice (orexin neuron-ablated mice), we found that the rostral nucleus accumbens (NAc) shell is needed for chocolate-induced cataplexy. In this study, we investigated whether a short-lasting stimulation/inhibition of the NAc by optogenetics led to a similar result. Photo-illumination to the NAc in the channel rhodopsin-expressing mice showed a higher incidence (34.9 ± 5.1%) of cataplexy-like behavior than the control mice (17.8 ± 3.1%, P = 0.0056). Meanwhile, inactivation with archaerhodopsin did not affect incidence. The episode duration of cataplexy-like behavior was not affected by activation or inactivation. Immunohistochemical analysis revealed that photo-illumination activated channel rhodopsin-expressing NAc shell neurons. Thus, activation of the NAc, whether transient (light stimulation) or longer-lasting (chemical stimulation in our previous study), facilitates cataplexy-like behaviors and contributes to the induction but not maintenance in them. On the other hand, our study's result from optogenetic inhibition of the NAc (no effect) was different from chemogenetic inhibition (reduction of cataplexy-like behavior) in our previous study. We propose that the initiation of cataplexy-like behavior is facilitated by activation of the NAc, while NAc-independent mechanisms determine the termination of the behavior.

Sleep-mediated regulation of reward circuits: implications in substance use disorders

Our modern society suffers from both pervasive sleep loss and substance abuse-what may be the indications for sleep on substance use disorders (SUDs), and could sleep contribute to the individual variations in SUDs? Decades of research in sleep as well as in motivated behaviors have laid the foundation for us to begin to answer these questions. This review is intended to critically summarize the circuit, cellular, and molecular mechanisms by which sleep influences reward function, and to reveal critical challenges for future studies. The review also suggests that improving sleep quality may serve as complementary therapeutics for treating SUDs, and that formulating sleep metrics may be useful for predicting individual susceptibility to SUDs and other reward-associated psychiatric diseases.

Rapid Eye Movement Sleep Engages Melanin-Concentrating Hormone Neurons to Reduce Cocaine Seeking

BACKGROUND

Persistent sleep disruptions following withdrawal from abused drugs may hold keys to battle drug relapse. It is posited that there may be sleep signatures that predict relapse propensity, identifying which may open new avenues for treating substance use disorders.

METHODS

We trained male rats (approximately postnatal day 56) to self-administer cocaine. After long-term drug withdrawal (approximately postnatal day 100), we examined the correlations between the intensity of cocaine seeking and key sleep features. To test for causal relationships, we then used behavioral, chemogenetic, or optogenetic methods to selectively increase rapid eye movement sleep (REMS) and measured behavioral and electrophysiological outcomes to probe for cellular and circuit mechanisms underlying REMS-mediated regulation of cocaine seeking.

RESULTS

A selective set of REMS features was preferentially associated with the intensity of cue-induced cocaine seeking after drug withdrawal. Moreover, selectively increasing REMS time and continuity by environmental warming attenuated a withdrawal time-dependent intensification of cocaine seeking, or incubation of cocaine craving, suggesting that REMS may benefit withdrawal. Warming increased the activity of lateral hypothalamic melanin-concentrating hormone (MCH) neurons selectively during prolonged REMS episodes and counteracted cocaine-induced synaptic accumulation of calcium-permeable AMPA receptors in the nucleus accumbens-a critical substrate for incubation. Finally, the warming effects were partly mimicked by chemogenetic or optogenetic stimulations of MCH neurons during sleep, or intra-accumbens infusions of MCH peptide during the rat's inactive phase.

CONCLUSIONS

REMS may encode individual vulnerability to relapse, and MCH neuron activities can be selectively targeted during REMS to reduce drug relapse.

Regulation of wakefulness by astrocytes in the lateral hypothalamus

The lateral hypothalamus (LH) is an important brain region mediating sleep-wake behavior. Recent evidence has shown that central nervous system astrocytes modulate the activity of adjacent neurons and participate in several physiological functions. However, the role of LH astrocytes in sleep-wake regulation remains unclear. Here, using synchronous recording of electroencephalogram/electromyogram in mice and calcium signals in LH astrocytes, we show that the activity of LH astrocytes is significantly increased during non-rapid eye movement (NREM) sleep-to-wake transitions and decreased during wake-to-NREM sleep transitions. Chemogenetic activation of LH astrocytes potently promotes wakefulness and maintains long-term arousal, while chemogenetic inhibition of LH astrocytes decreases the total amount of wakefulness in mice. Moreover, by combining chemogenetics with fiber photometry, we show that activation of LH astrocytes significantly increases the calcium signals of adjacent neurons, especially among GABAergic neurons. Taken together, our results clearly illustrate that LH astrocytes are a key neural substrate regulating wakefulness and encode this behavior through surrounding GABAergic neurons. Our findings raise the possibility that overactivity of LH astrocytes may be an underlying mechanism of clinical sleep disorders.

Carbohydrate and sleep: An evaluation of putative mechanisms

Sleep problems are extremely common in industrialized countries and the possibility that diet might be used to improve sleep has been considered. The topic has been reviewed many times, resulting in the frequent suggestion that carbohydrate increases the uptake of tryptophan by the brain, where it is metabolized into serotonin and melatonin, with the suggestion that this improves sleep. An alternative mechanism was proposed based on animal literature that has been largely ignored by those considering diet and sleep. The hypothesis was that, as in the hypothalamus there are glucose-sensing neurons associated with the sleep-wake cycle, we should consider the impact of carbohydrate-induced changes in the level of blood glucose. A meta-analysis found that after consuming a lower amount of carbohydrate, more time was spent in slow-wave sleep (SWS) and less in rapid-eye-movement sleep. As the credibility of alternative mechanisms has tended not to have been critically evaluated, they were considered by examining their biochemical, nutritional, and pharmacological plausibility. Although high carbohydrate consumption can increase the uptake of tryptophan by the brain, it only occurs with such low levels of protein that the mechanism is not relevant to a normal diet. After entering the brain tryptophan is converted to serotonin, a neurotransmitter known to influence so many different aspects of sleep and wakefulness, that it is not reasonable to expect a uniform improvement in sleep. Some serotonin is converted to melatonin, although the exogenous dose of melatonin needed to influence sleep cannot be credibly provided by the diet. This review was registered in the International Prospective Register of Systematic Reviews (CRD42020223560).

The melanin-concentrating hormone system as a target for the treatment of sleep disorders

Given the widespread prevalence of sleep disorders and their impacts on health, it is critical that researchers continue to identify and evaluate novel avenues of treatment. Recently the melanin-concentrating hormone (MCH) system has attracted commercial and scientific interest as a potential target of pharmacotherapy for sleep disorders. This interest emerges from basic scientific research demonstrating a role for MCH in regulating sleep, and particularly REM sleep. In addition to this role in sleep regulation, the MCH system and the MCH receptor 1 (MCHR1) have been implicated in a wide variety of other physiological functions and behaviors, including feeding/metabolism, reward, anxiety, depression, and learning. The basic research literature on sleep and the MCH system, and the history of MCH drug development, provide cause for both skepticism and cautious optimism about the prospects of MCH-targeting drugs in sleep disorders. Extensive efforts have focused on developing MCHR1 antagonists for use in obesity, however, few of these drugs have advanced to clinical trials, and none have gained regulatory approval. Additional basic research will be needed to fully characterize the MCH system’s role in sleep regulation, for example, to fully differentiate between MCH-neuron and peptide/receptor-mediated functions. Additionally, a number of issues relating to drug design will continue to pose a practical challenge for novel pharmacotherapies targeting the MCH system.

Motivational and Valence-Related Modulation of Sleep/Wake Behavior are Mediated by Midbrain Dopamine and Uncoupled from the Homeostatic and Circadian Processes

Motivation and its hedonic valence are powerful modulators of sleep/wake behavior, yet its underlying mechanism is still poorly understood. Given the well-established role of midbrain dopamine (mDA) neurons in encoding motivation and emotional valence, here, neuronal mechanisms mediating sleep/wake regulation are systematically investigated by DA neurotransmission. It is discovered that mDA mediates the strong modulation of sleep/wake states by motivational valence. Surprisingly, this modulation can be uncoupled from the classically employed measures of circadian and homeostatic processes of sleep regulation. These results establish the experimental foundation for an additional new factor of sleep regulation. Furthermore, an electroencephalographic marker during wakefulness at the theta range is identified that can be used to reliably track valence-related modulation of sleep. Taken together, this study identifies mDA signaling as an important neural substrate mediating sleep modulation by motivational valence.

Sleep-Wake Neurochemistry

Behavioral states naturally alternate between wakefulness and the sleep phases rapid eye movement and nonrapid eye movement sleep. Waking and sleep states are complex processes that are elegantly orchestrated by spatially fine-tuned neurochemical changes of neurotransmitters and neuromodulators including glutamate, acetylcholine, γ-aminobutyric acid, norepinephrine, dopamine, serotonin, histamine, hypocretin, melanin concentrating hormone, adenosine, and melatonin. However, as highlighted in this brief overview, no single neurotransmitter or neuromodulator, but rather their complex interactions within organized neuronal ensembles, regulate waking and sleep states. The neurochemical pathways presented here are aimed to provide a conceptual framework for the understanding of the effects of currently used sleep medications.

Translational Approaches to Influence Sleep and Arousal

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

Roles of Neuropeptides in Sleep-Wake Regulation

Sleep and wakefulness are basic behavioral states that require coordination between several brain regions, and they involve multiple neurochemical systems, including neuropeptides. Neuropeptides are a group of peptides produced by neurons and neuroendocrine cells of the central nervous system. Like traditional neurotransmitters, neuropeptides can bind to specific surface receptors and subsequently regulate neuronal activities. For example, orexin is a crucial component for the maintenance of wakefulness and the suppression of rapid eye movement (REM) sleep. In addition to orexin, melanin-concentrating hormone, and galanin may promote REM sleep. These results suggest that neuropeptides play an important role in sleep–wake regulation. These neuropeptides can be divided into three categories according to their effects on sleep–wake behaviors in rodents and humans. (i) Galanin, melanin-concentrating hormone, and vasoactive intestinal polypeptide are sleep-promoting peptides. It is also noticeable that vasoactive intestinal polypeptide particularly increases REM sleep. (ii) Orexin and neuropeptide S have been shown to induce wakefulness. (iii) Neuropeptide Y and substance P may have a bidirectional function as they can produce both arousal and sleep-inducing effects. This review will introduce the distribution of various neuropeptides in the brain and summarize the roles of different neuropeptides in sleep–wake regulation. We aim to lay the foundation for future studies to uncover the mechanisms that underlie the initiation, maintenance, and end of sleep–wake states.

Characterization of Hypothalamic MCH Neuron Development in a 3D Differentiation System of Mouse Embryonic Stem Cells

Hypothalamic melanin-concentrating hormone (MCH) neurons are important regulators of multiple physiological processes, such as sleep, feeding, and memory. Despite the increasing interest in their neuronal functions, the molecular mechanism underlying MCH neuron development remains poorly understood. We report that a three-dimensional culture of mouse embryonic stem cells (mESCs) can generate hypothalamic-like tissues containing MCH-positive neurons, which reproduce morphologic maturation, neuronal connectivity, and neuropeptide/neurotransmitter phenotype of native MCH neurons. Using this in vitro system, we demonstrate that Hedgehog (Hh) signaling serves to produce major neurochemical subtypes of MCH neurons characterized by the presence or absence of cocaine- and amphetamine-regulated transcript (CART). Without exogenous Hh signals, mESCs initially differentiated into dorsal hypothalamic/prethalamic progenitors and finally into MCH⁺CART⁺ neurons through a specific intermediate progenitor state. Conversely, activation of the Hh pathway specified ventral hypothalamic progenitors that generate both MCH⁺CART⁻ and MCH⁺CART⁺ neurons. These results suggest that in vivo MCH neurons may originate from multiple cell lineages that arise through early dorsoventral patterning of the hypothalamus. Additionally, we found that Hh signaling supports the differentiation of mESCs into orexin/hypocretin neurons, a well-defined cell group intermingled with MCH neurons in the lateral hypothalamic area (LHA). The present study highlights and improves the utility of mESC culture in the analysis of the developmental programs of specific hypothalamic cell types.

How REM sleep shapes hypothalamic computations for feeding behavior

The electrical activity of diverse brain cells is modulated across states of vigilance, namely wakefulness, non-rapid eye movement (NREM) sleep, and rapid eye movement (REM) sleep. Enhanced activity of neuronal circuits during NREM sleep impacts on subsequent awake behaviors, yet the significance of their activation, or lack thereof, during REM sleep remains unclear. This review focuses on feeding-promoting cells in the lateral hypothalamus (LH) that express the vesicular GABA and glycine transporter (vgat) as a model to further understand the impact of REM sleep on neural encoding of goal-directed behavior. It emphasizes both spatial and temporal aspects of hypothalamic cell dynamics across awake behaviors and REM sleep, and discusses a role for REM sleep in brain plasticity underlying energy homeostasis and behavioral optimization.

Neurobiology of cataplexy

Cataplexy is the pathognomonic and the most striking symptom of narcolepsy. It has originally been, and still is now, widely considered as an abnormal manifestation of rapid eye movement (REM) sleep during wakefulness due to the typical muscle atonia. The neurocircuits of cataplexy, originally confined to the brainstem as those of REM sleep atonia, now include the hypothalamus, dorsal raphe (DR), amygdala and frontal cortex, and its neurochemistry originally focused on catecholamines and acetylcholine now extend to hypocretin (HCRT) and other neuromodulators. Here, we review the neuroanatomy and neurochemistry of cataplexy and propose that cataplexy is a distinct brain state that, despite similarities with REM sleep, involves cataplexy-specific features.

Tau-driven degeneration of sleep- and wake-regulating neurons in Alzheimer's disease

Disturbances of the sleep/wake cycle in Alzheimer's disease (AD) are common, frequently precede cognitive decline, and tend to worsen with disease progression. Sleep is critical to the maintenance of homeostatic and circadian function, and chronic sleep disturbances have significant cognitive and physical health consequences that likely exacerbate disease severity. Sleep-wake cycles are regulated by neuromodulatory centers located in the brainstem, the hypothalamus, and the basal forebrain, many of which are vulnerable to the accumulation of abnormal protein deposits associated with neurodegenerative conditions. In AD, while sleep disturbances are commonly attributed to the accumulation of amyloid beta, patients often first experience sleep issues prior to the appearance of amyloid beta plaques, on a timeline that more closely corresponds to the first appearance of abnormal tau neurofibrillary tangles in sleep/wake regulating areas of the brainstem. Sleep disturbances also occur in pure tauopathies, providing further support that tau is a major contributor. Here, we provide an overview of the neuroanatomy of sleep/wake centers discovered in animal models, and review the evidence that tau-driven neuropathology is a primary driver of sleep disturbance in AD.

No loss of orexin/hypocretin, melanin-concentrating hormone or locus coeruleus noradrenergic neurons in a rat model of chronic sleep restriction

Chronic sleep restriction (CSR) is common in modern society, adversely affecting cognitive performance and health. Yet how it impacts neurons regulating sleep remains unclear. Several studies using mice reported substantial losses of wake-active orexin/hypocretin and locus coeruleus (LC) noradrenergic neurons, but not rapid eye movement sleep-active melanin-concentrating hormone (MCH) neurons, following CSR. Here, we used immunohistochemistry and stereology to examine orexin, MCH and LC noradrenergic neurons in a rat model of CSR that uses programmed wheel rotation (3 h on/1 h off; '3/1' protocol). Adult male Wistar rats underwent one or four cycles of the 4-day 3/1 CSR protocol, with 2-day recovery between cycles in home cages. Time-matched control rats were housed in locked wheels/home cages. We found no significant differences in the numbers of orexin, MCH and LC noradrenergic neurons following either one- or four-cycle CSR protocol compared to respective controls. Similarly, the four-cycle CSR protocol had no effect on the densities of orexin axon terminals in the LC, noradrenergic dendrites in the LC and noradrenergic axon terminals in the frontal cortex. Body weights, however, decreased after one cycle of CSR and then increased with diminishing slope over the next three cycles. Thus, we found no evidence for loss of orexin or LC noradrenergic neurons following one and four cycles of the 4-day 3/1 CSR protocol in rats. Differences in CSR protocols and/or possible species differences in neuronal vulnerability to sleep loss may account for the discrepancy between the current results in rats and previous findings in mice.

Cocaine-induced neural adaptations in the lateral hypothalamic melanin-concentrating hormone neurons and the role in regulating rapid eye movement sleep after withdrawal

Sleep abnormalities are often a prominent contributor to withdrawal symptoms following chronic drug use. Notably, rapid eye movement (REM) sleep regulates emotional memory, and persistent REM sleep impairment after cocaine withdrawal negatively impacts relapse-like behaviors in rats. However, it is not understood how cocaine experience may alter REM sleep regulatory machinery, and what may serve to improve REM sleep after withdrawal. Here, we focus on the melanin-concentrating hormone (MCH) neurons in the lateral hypothalamus (LH), which regulate REM sleep initiation and maintenance. Using adult male Sprague-Dawley rats trained to self-administer intravenous cocaine, we did transcriptome profiling of LH MCH neurons after long-term withdrawal using RNA-sequencing, and performed functional assessment using slice electrophysiology. We found that 3 weeks after withdrawal from cocaine, LH MCH neurons exhibit a wide range of gene expression changes tapping into cell membrane signaling, intracellular signaling, and transcriptional regulations. Functionally, they show reduced membrane excitability and decreased glutamatergic receptor activity, consistent with increased expression of voltage-gated potassium channel gene Kcna1 and decreased expression of metabotropic glutamate receptor gene Grm5. Finally, chemogenetic or optogenetic stimulations of LH MCH neural activity increase REM sleep after long-term withdrawal with important differences. Whereas chemogenetic stimulation promotes both wakefulness and REM sleep, optogenetic stimulation of these neurons in sleep selectively promotes REM sleep. In summary, cocaine exposure persistently alters gene expression profiles and electrophysiological properties of LH MCH neurons. Counteracting cocaine-induced hypoactivity of these neurons selectively in sleep enhances REM sleep quality and quantity after long-term withdrawal.

Activity of a subset of vesicular GABA-transporter neurons in the ventral zona incerta anticipates sleep onset

STUDY OBJECTIVES

Sleep and wake are opposing behavioral states controlled by the activity of specific neurons that need to be located and mapped. To better understand how a waking brain falls asleep it is necessary to identify activity of individual phenotype-specific neurons, especially neurons that anticipate sleep onset. In freely behaving mice, we used microendoscopy to monitor calcium (Ca2+) fluorescence in individual hypothalamic neurons expressing the vesicular GABA transporter (vGAT), a validated marker of GABA neurons.

METHODS

vGAT-Cre mice (male = 3; female = 2) transfected with rAAV-FLEX-GCaMP6M in the lateral hypothalamus were imaged 30 days later during multiple episodes of waking (W), non-rapid-eye movement sleep (NREMS) or REMS (REMS).

RESULTS

372 vGAT neurons were recorded in the zona incerta. 23.9% of the vGAT neurons showed maximal fluorescence during wake (classified as wake-max), 4% were NREM-max, 56.2% REM-max, 5.9% wake/REM max, while 9.9% were state-indifferent. In the NREM-max group, Ca2+ fluorescence began to increase before onset of NREM sleep, remained high throughout NREM sleep, and declined in REM sleep.

CONCLUSIONS

We found that 60.2% of the vGAT GABA neurons in the zona incerta had activity that was biased towards sleep (NREM and REMS). A subset of vGAT neurons (NREM-max) became active in advance of sleep onset and may induce sleep by inhibiting the activity of the arousal neurons. Abnormal activation of the NREM-max neurons may drive sleep attacks and hypersomnia.

Animal models of narcolepsy and the hypocretin/orexin system: Past, present, and future

Animal models have advanced not only our understanding of the etiology and phenotype of the sleep disorder narcolepsy but have also informed sleep/wake regulation more generally. The identification of an inheritable narcolepsy phenotype in dogs in the 1970s allowed the establishment of a breeding colony at Stanford University, resulting in studies that provided the first insights into the genetics and neurotransmitter systems that underlie cataplexy and rapid-eye movement sleep atonia. Although the discovery of the hypocretin/orexin neuropeptides in 1998 initially seemed unrelated to sleep/wake control, the description of the phenotype of the prepro-orexin knockout (KO) mouse as strongly resembling cataplexy, the pathognomonic symptom of narcolepsy, along with identification of a mutation in hypocretin receptor-2 gene as the source of canine narcolepsy, unequivocally established the relationship between this system and narcolepsy. The subsequent discovery of hypocretin neuron degeneration in human narcolepsy demystified a disorder whose etiology had been unknown since its initial description 120 years earlier. These breakthroughs prompted the development of numerous other animal models that have allowed manipulation of the hypocretin/orexin system, thereby advancing our understanding of sleep/wake circuitry. While animal models have greatly informed understanding of this fascinating disorder and the role of the hypocretin/orexin system in sleep/wake control, the question of why these neurons degenerate in human narcolepsy is only beginning to be understood. The development of new immune-mediated narcolepsy models are likely to further inform the etiology of this sleep disorder and animal models will undoubtedly play a critical role in the development of novel narcolepsy therapeutics.

Reciprocal Lateral Hypothalamic and Raphe GABAergic Projections Promote Wakefulness

The lateral hypothalamus (LH), together with multiple neuromodulatory systems of the brain, such as the dorsal raphe nucleus (DR), is implicated in arousal, yet interactions between these systems are just beginning to be explored. Using a combination of viral tracing, circuit mapping, electrophysiological recordings from identified neurons, and combinatorial optogenetics in mice, we show that GABAergic neurons in the LH selectively inhibit GABAergic neurons in the DR, resulting in increased firing of a substantial fraction of its neurons that ultimately promotes arousal. These DRGABA neurons are wake active and project to multiple brain areas involved in the control of arousal, including the LH, where their specific activation potently influences local network activity leading to arousal from sleep. Our results show how mutual inhibitory projections between the LH and the DR promote wakefulness and suggest a complex arousal control by intimate interactions between long-range connections and local circuit dynamics.SIGNIFICANCE STATEMENT: Multiple brain systems including the lateral hypothalamus and raphe serotonergic system are involved in the regulation of the sleep/wake cycle, yet the interaction between these systems have remained elusive. Here we show that mutual disinhibition mediated by long range inhibitory projections between these brain areas can promote wakefulness. The main importance of this work relies in revealing the interaction between a brain area involved in autonomic regulation and another in controlling higher brain functions including reward, patience, mood and sensory coding.

Adult hypothalamic neurogenesis and sleep-wake dysfunction in aging

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

Orexin/Hypocretin and MCH Neurons: Cognitive and Motor Roles Beyond Arousal

The lateral hypothalamus (LH) is classically implicated in sleep-wake control. It is the main source of orexin/hypocretin and melanin-concentrating hormone (MCH) neuropeptides in the brain, which have been both implicated in arousal state switching. These neuropeptides are produced by non-overlapping LH neurons, which both project widely throughout the brain, where release of orexin and MCH activates specific postsynaptic G-protein-coupled receptors. Optogenetic manipulations of orexin and MCH neurons during sleep indicate that they promote awakening and REM sleep, respectively. However, recordings from orexin and MCH neurons in awake, moving animals suggest that they also act outside sleep/wake switching. Here, we review recent studies showing that both orexin and MCH neurons can rapidly (sub-second-timescale) change their firing when awake animals experience external stimuli, or during self-paced exploration of objects and places. However, the sensory-behavioral correlates of orexin and MCH neural activation can be quite different. Orexin neurons are generally more dynamic, with about 2/3rds of them activated before and during self-initiated running, and most activated by sensory stimulation across sensory modalities. MCH neurons are activated in a more select manner, for example upon self-paced investigation of novel objects and by certain other novel stimuli. We discuss optogenetic and chemogenetic manipulations of orexin and MCH neurons, which combined with pharmacological blockade of orexin and MCH receptors, imply that these rapid LH dynamics shape fundamental cognitive and motor processes due to orexin and MCH neuropeptide actions in the awake brain. Finally, we contemplate whether the awake control of psychomotor brain functions by orexin and MCH are distinct from their “arousal” effects.

Control of wakefulness by lateral hypothalamic glutamatergic neurons in male mice

The lateral hypothalamus (LH) plays a key role in the maintenance of cortical activation and wakefulness. In the LH, the two main neuronal cell populations consist of excitatory glutamatergic neurons and inhibitory GABAergic neurons. Recent studies have shown that inhibitory LH GABAergic neurons are wake-promoting. However, the mechanism by which excitatory LH glutamatergic neurons contribute to sleep-wake regulation remains unclear. Using fiber photometry in male mice, we demonstrated that LH glutamatergic neurons exhibited high activities during both wakefulness and rapid eye movement sleep. Chemogenetic activation of LH glutamatergic neurons induced an increase in wakefulness that lasted for 6 hr, whereas suppression of LH glutamatergic neuronal activity caused a reduction in wakefulness. Brief optogenetic activation of LH glutamatergic neurons induced an immediate transition from slow-wave sleep to wakefulness, and long-lasting optogenetic stimulation of these neurons maintained wakefulness. Moreover, we found that LH-locus coeruleus/parabrachial nucleus and LH-basal forebrain projections mediated the wake-promoting effects of LH glutamatergic neurons. Taken together, our data indicate that LH glutamatergic neurons are essential for the induction and maintenance of wakefulness. The results presented here may advance our understanding of the role of LH in the control of wakefulness.

Novel Neuroimaging Biomarker for Sleep Quality in Insomnia Disorder: A Hypothalamus Resting State Study

Despite striking progress in the understanding of the neurobiology of insomnia disorder (ID), about 40% of ID patients do not reach sustained remission with the primary treatments. It is necessary to reveal novel neuroimaging biomarkers for sleep quality in ID. The hypothalamus has a central role in sleep-wake regulation by communicating with different brain regions. However, the functional implications of hypothalamus circuitry with other brain areas remains largely unknown in ID. It may be speculated that dysfunctional circuitry in the hypothalamus is involved in the pathogenesis of ID. Thus, we investigated the different network organizations of the bilateral hypothalamus during the resting-state between 26 ID patients and 28 healthy controls (HC). Correlation analysis has been carried out to link the neuroimaging findings and Pittsburgh sleep quality index (PSQI) scores. Group comparisons reveal that the resting-state functional connectivity (RSFC) between the left hypothalamic region and a few other brain regions, including the medial prefrontal cortex (mPFC) and pallidum, are significantly higher in ID compared with HC. The right inferior temporal cortex showed reduced RSFC with the left hypothalamus. No significantly different RSFC between ID and HC was detected for the right hypothalamus. Positive correlations with PSQI scores were observed for RSFC strength between the left hypothalamus and bilateral mPFC (left: r = 0.2985, p = 0.0393; right: r = 0.3723, p = 0.0056). Similarly, the RSFC strength between the right hypothalamus and bilateral mPFC (left: r = 0.3980, p = 0.0029; right: r = 0.2972, p = 0.0291) also showed significant positive correlations with PSQI scores. In conclusion, we reveal a novel neuroimaging biomarker for sleep quality, i.e., the RSFC strength of the hypothalamus-mPFC pathway. Consistent with the hyperarousal model of ID, our results shed new insights into the implications of the hyper-connection within hypothalamus circuits in the pathology of the ID.

Optogenetic sleep enhancement improves fear-associated memory processing following trauma exposure in rats

Sleep disturbances are commonly found in trauma-exposed populations. Additionally, trauma exposure results in fear-associated memory impairments. Given the interactions of sleep with learning and memory, we hypothesized that increasing sleep duration following trauma exposure would restore overall function and improve trauma-induced fear-associated memory dysfunction. Here, we utilized single prolonged stress, a validated rodent model of post-traumatic stress disorder, in combination with optogenetic activation of hypothalamic melanin-concentrating hormone containing cells to increase sleep duration. The goal of this work was to ascertain if post-trauma sleep increases are sufficient to improve fear-associated memory function. In our laboratory, optogenetic stimulation after trauma exposure was sufficient to increase REM sleep duration during both the Light and Dark Phase, whereas NREM sleep duration was only increased during the Dark Phase of the circadian day. Interestingly though, animals that received optogenetic stimulation showed significantly improved fear-associated memory processing compared to non-stimulated controls. These results suggest that sleep therapeutics immediately following trauma exposure may be beneficial and that post-trauma sleep needs to be further examined in the context of the development of post-traumatic stress disorder.

Ultra-sparse Connectivity within the Lateral Hypothalamus

The lateral hypothalamic area (LH) is a vital controller of arousal, feeding, and metabolism [1, 2], which integrates external and internal sensory information. Whereas sensory and whole-body output properties of LH cell populations have received much interest, their intrinsic synaptic organization has remained largely unstudied. Local inhibitory and excitatory connections could help integrate and filter sensory information and mutually inhibitory connections [3] could allow coordinating activity between LH cell types, some of which have mutually exclusive behavioral effects, such as LH VGLUT2 and VGAT neurons [4-7] and orexin- (ORX) and melanin-concentrating hormone (MCH) neurons [8-10]. However, classical Golgi staining studies did not find interneurons with locally ramifying axons in the LH [11, 12], and nearby subthalamic and thalamic areas lack local synaptic connectivity [13, 14]. Studies with optogenetic circuit mapping within the LH have demonstrated only a minority of connections when a large pool of presynaptic neurons was activated [15-19]. Because multiple patch clamp has not been used to study LH connectivity, aside from a limited dataset of MCH neurons where no connections were discovered [15], we used quadruple whole-cell recordings to screen connectivity within the LH with standard methodology we previously used in the neocortex [20-22]. Finding a lack of local connectivity, we used optogenetic circuit mapping to study the strength of LH optogenetic responses and network oscillations, which were consistent with ultra-sparse intrinsic connectivity within the LH. These results suggest that input from other brain structures is decisive for selecting active populations in the LH.