Neuropeptidergic control of sleep and wakefulness

Chronobiological disruptions: unravelling the interplay of shift work, circadian rhythms, and vascular health in the context of stroke risk

Shift work, particularly night shifts, disrupts circadian rhythms and increases stroke risk. This manuscript explores the mechanisms connecting shift work with stroke, focusing on circadian rhythms, hypertension, and diabetes. The circadian system, controlled by different mechanisms including central and peripheral clock genes, suprachiasmatic nuclei (SCN), and pineal gland (through melatonin production), regulates body functions and responds to environmental signals. Disruptions in this system affect endothelial cells, leading to blood pressure issues. Type 2 diabetes mellitus (T2DM) is significantly associated with night shifts, with circadian disturbances affecting glucose metabolism, insulin sensitivity, and hormone regulation. The manuscript examines the relationship between melatonin, insulin, and glucose balance, highlighting pathways that link T2DM to stroke risk. Additionally, dyslipidemia, particularly reduced HDL-c levels, results from shift work and contributes to stroke development. High lipid levels cause oxidative stress, inflammation, and endothelial dysfunction, increasing cerebrovascular risks. The manuscript details the effects of dyslipidemia on brain functions, including disruptions in blood flow, blood-brain barrier integrity, and neural cell death. This comprehensive analysis emphasizes the complex interplay of circadian disruption, hypertension, diabetes, and dyslipidemia in increasing stroke risk among shift workers. Understanding these mechanisms is essential for developing targeted interventions to reduce stroke susceptibility and improve cerebrovascular health in this vulnerable population.

The relations of circulating agouti-related peptide and leptin with altered sleep architecture in patients with active Cushing's disease: a pilot study

AIM

To evaluate sleep architecture of patients with Cushing's disease (CD) and to explore whether agouti-related peptide (AgRP) and/or leptin play a permissive role in sleep alterations in patients with active CD.

METHODS

We performed polysomnography on 26 patients with active CD and age 26 age- and sex-matched control subjects. Blood samples were obtained from all participants for the analyzes of AgRP and leptin. The laboratory and sleep-related parameters were compared.

RESULTS

The groups were similar in age, gender, and body mass index. The CD group had reduced sleep efficiency (71.6 ± 12.1% vs. 78.8 ± 12.6%, p = 0.042) and increased wake after sleep onset (WASO%) (24.7 ± 13.1% vs. 17.4 ± 11.6%, p = 0.040) as compared to control group. Seventeen patients with CD (65.4%) and 18 control subjects (69.2%) had obstructive sleep apnea. Serum AgRP (13.2 ± 7.4 pg/ml vs. 9 ± 3.1, p = 0.029), leptin (59.5 mcg/l, [IQR] 32.6-94.6 vs. 25.3 mcg/l, [IQR] 12.9-57.5, p = 0.007) were higher in CD group. AgRP and leptin correlated negatively with total sleep time, sleep efficiency, stage N2 sleep (%), and positively with WASO%. In multiple regression analyses, serum cortisol (ß =  - 0.359, p = 0.042) and AgRP (ß =  - 0.481, p = 0.01) were significant predictor of sleep efficiency. AgRP was also significant predictor of WASO% (ß = 0.452 and p < 0.05).

CONCLUSIONS

Active CD carries an increased risk of impaired sleep efficiency and continuity which may worsen health-related quality of life. Elevated circulating AgRP and, to a lesser extent, leptin may be associated with decreased sleep efficiency and continuity in patients with CD. Patients with CD who have subjective sleep symptoms should be screened with polysomnography.

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

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

Identification of the functional domain of the dense core vesicle biogenesis factor HID-1

Large dense core vesicles (LDCVs) mediate the regulated release of neuropeptides and peptide hormones. HID-1 is a trans-Golgi network (TGN) localized peripheral membrane protein contributing to LDCV formation. There is no information about HID-1 structure or domain architecture, and thus it remains unknown how HID-1 binds to the TGN and performs its function. We report that the N-terminus of HID-1 mediates membrane binding through a myristoyl group with a polybasic amino acid patch but lacks specificity for the TGN. In addition, we show that the C-terminus serves as the functional domain. Indeed, this isolated domain, when tethered to the TGN, can rescue the neuroendocrine secretion and sorting defects observed in HID-1 KO cells. Finally, we report that a point mutation within that domain, identified in patients with endocrine and neurological deficits, leads to loss of function.

Does EGFR Signaling Mediate Orexin System Activity in Sleep Initiation?

Sleep-wake cycle disorders are an important symptom of many neurological diseases, including Parkinson's disease, Alzheimer's disease, and multiple sclerosis. Circadian rhythms and sleep-wake cycles play a key role in maintaining the health of organisms. To date, these processes are still poorly understood and, therefore, need more detailed elucidation. The sleep process has been extensively studied in vertebrates, such as mammals and, to a lesser extent, in invertebrates. A complex, multi-step interaction of homeostatic processes and neurotransmitters provides the sleep-wake cycle. Many other regulatory molecules are also involved in the cycle regulation, but their functions remain largely unclear. One of these signaling systems is epidermal growth factor receptor (EGFR), which regulates the activity of neurons in the modulation of the sleep-wake cycle in vertebrates. We have evaluated the possible role of the EGFR signaling pathway in the molecular regulation of sleep. Understanding the molecular mechanisms that underlie sleep-wake regulation will provide critical insight into the fundamental regulatory functions of the brain. New findings of sleep-regulatory pathways may provide new drug targets and approaches for the treatment of sleep-related diseases.

Serum Levels of Neuropeptides in Epileptic Encephalopathy With Spike-and-Wave Activation in Sleep

BACKGROUND

Epileptic encephalopathy with spike-and-wave activation in sleep (EE-SWAS) is a syndrome of childhood, characterized by diffuse or generalized spike-wave activity in electroencephalography during non-rapid eye movement sleep. Neuropeptides have been demonstrated in several studies to function in the sleep-wake cycle and display convulsant and anticonvulsant features. In this study, we aimed to investigate the relationship between EE-SWAS and neuropeptides such as dynorphin, galanin, ghrelin, leptin, melatonin, and orexin.

METHODS

This multicenter study was conducted from July 2019 to January 2021. There were three groups: Group 1 contained patients with EE-SWAS. Group 2 consisted of patients with self-limited focal epilepsy of childhood (SeLFE), and group 3 was the control group. Levels of neuropeptides were compared in the sera of these three groups.

RESULTS

There were 59 children aged between four and 15 years. Group 1 contained 14 children, group 2 contained 24 children, and group 3 contained 21 children. The level of leptin is higher and the level of melatonin is lower in group 1 than in group 3 (P = 0.01 and P = 0.005, respectively). In group 3, the level of orexin was lower than in both groups 2 and 3 (P = 0.01 and P = 0.01).

CONCLUSIONS

These data show that the level of leptin was higher and the level of melatonin was lower in patients with EE-SWAS than in the control group. Furthermore, patients with EE-SWAS had lower orexin levels than both the control group and patients with SeLFE. Further research is required to understand the potential role of these neuropeptides in the pathophysiology of EE-SWAS.

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.

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.

Sleep Disturbance and Alzheimer's Disease: The Glial Connection

Poor quality and quantity of sleep are very common in elderly people throughout the world. Growing evidence has suggested that sleep disturbances could accelerate the process of neurodegeneration. Recent reports have shown a positive correlation between sleep deprivation and amyloid-β (Aβ)/tau aggregation in the brain of Alzheimer's patients. Glial cells have long been implicated in the progression of Alzheimer's disease (AD) and recent findings have also suggested their role in regulating sleep homeostasis. However, how glial cells control the sleep-wake balance and exactly how disturbed sleep may act as a trigger for Alzheimer's or other neurological disorders have recently gotten attention. In an attempt to connect the dots, the present review has highlighted the role of glia-derived sleep regulatory molecules in AD pathogenesis. Role of glia in sleep disturbance and Alzheimer's progression.

Arousal Fluctuations Govern Oscillatory Transitions Between Dominant γ and α Occipital Activity During Eyes Open/Closed Conditions

Arousal results in widespread activation of brain areas to increase their response in task and behavior relevant ways. Mediated by the Ascending Reticular Arousal System (ARAS), arousal-dependent inputs interact with neural circuitry to shape their dynamics. In the occipital cortex, such inputs may trigger shifts between dominant oscillations, whereα activity is replaced byγ activity, or vice versa. A salient example of this are spectral power alternations observed while eyes are opened and/or closed. These transitions closely follow fluctuations in arousal, suggesting a common origin. To better understand the mechanisms at play, we developed and analyzed a computational model composed of two modules: a thalamocortical feedback circuit coupled with a superficial cortical network. Upon activation by noise-like inputs originating from the ARAS, our model is able to demonstrate that noise-driven non-linear interactions mediate transitions in dominant peak frequency, resulting in the simultaneous suppression ofα limit cycle activity and the emergence ofγ oscillations through coherence resonance. Reduction in input provoked the reverse effect - leading to anticorrelated transitions betweenα andγ power. Taken together, these results shed a new light on how arousal shapes oscillatory brain activity.

Gene family evolution underlies cell-type diversification in the hypothalamus of teleosts

Hundreds of cell types form the vertebrate brain but it is largely unknown how similar cellular repertoires are between or within species or how cell-type diversity evolves. To examine cell-type diversity across and within species, we performed single-cell RNA sequencing of ~130,000 hypothalamic cells from zebrafish (Danio rerio) and surface and cave morphs of Mexican tetra (Astyanax mexicanus). We found that over 75% of cell types were shared between zebrafish and Mexican tetra, which diverged from a common ancestor over 150 million years ago. Shared cell types displayed shifts in paralogue expression that were generated by subfunctionalization after genome duplication. Expression of terminal effector genes, such as neuropeptides, was more conserved than the expression of their associated transcriptional regulators. Species-specific cell types were enriched for the expression of species-specific genes and characterized by the neofunctionalization of expression patterns of members of recently expanded or contracted gene families. Comparisons between surface and cave morphs revealed differences in immune repertoires and transcriptional changes in neuropeptidergic cell types associated with genomic differences. The single-cell atlases presented here are a powerful resource to explore hypothalamic cell types and reveal how gene family evolution and shifts in paralogue expression contribute to cellular diversity.

Transcriptome Profiling of Dysregulated GPCRs Reveals Overlapping Patterns across Psychiatric Disorders and Age-Disease Interactions

G-protein-coupled receptors (GPCRs) play an integral role in the neurobiology of psychiatric disorders. Almost all neurotransmitters involved in psychiatric disorders act through GPCRs, and GPCRs are the most common targets of therapeutic drugs currently used in the treatment of psychiatric disorders. However, the roles of GPCRs in the etiology and pathophysiology of psychiatric disorders are not fully understood. Using publically available datasets, we performed a comprehensive analysis of the transcriptomic signatures of G-protein-linked signaling across the major psychiatric disorders: autism spectrum disorder (ASD), schizophrenia (SCZ), bipolar disorder (BP), and major depressive disorder (MDD). We also used the BrainSpan transcriptomic dataset of the developing human brain to examine whether GPCRs that exhibit chronological age-associated expressions have a higher tendency to be dysregulated in psychiatric disorders than age-independent GPCRs. We found that most GPCR genes were differentially expressed in the four disorders and that the GPCR superfamily as a gene cluster was overrepresented in the four disorders. We also identified a greater amplitude of gene expression changes in GPCRs than other gene families in the four psychiatric disorders. Further, dysregulated GPCRs overlapped across the four psychiatric disorders, with SCZ exhibiting the highest overlap with the three other disorders. Finally, the results revealed a greater tendency of age-associated GPCRs to be dysregulated in ASD than random GPCRs. Our results substantiate the central role of GPCR signaling pathways in the etiology and pathophysiology of psychiatric disorders. Furthermore, our study suggests that common GPCRs' signaling may mediate distinct phenotypic presentations across psychiatric disorders. Consequently, targeting these GPCRs could serve as a common therapeutic strategy to treat specific clinical symptoms across psychiatric disorders.

Astroglial Calcium Signaling Encodes Sleep Need in Drosophila

Sleep is under homeostatic control, whereby increasing wakefulness generates sleep need and triggers sleep drive. However, the molecular and cellular pathways by which sleep need is encoded are poorly understood. In addition, the mechanisms underlying both how and when sleep need is transformed to sleep drive are unknown. Here, using ex vivo and in vivo imaging, we show in Drosophila that astroglial Ca²⁺ signaling increases with sleep need. We demonstrate that this signaling is dependent on a specific L-type Ca²⁺ channel and is necessary for homeostatic sleep rebound. Thermogenetically increasing Ca²⁺ in astrocytes induces persistent sleep behavior, and we exploit this phenotype to conduct a genetic screen for genes required for the homeostatic regulation of sleep. From this large-scale screen, we identify TyrRII, a monoaminergic receptor required in astrocytes for sleep homeostasis. TyrRII levels rise following sleep deprivation in a Ca²⁺-dependent manner, promoting further increases in astrocytic Ca²⁺ and resulting in a positive-feedback loop. Moreover, our findings suggest that astrocytes then transmit this sleep need to a sleep drive circuit by upregulating and releasing the interleukin-1 analog Spätzle, which then acts on Toll receptors on R5 neurons. These findings define astroglial Ca²⁺ signaling mechanisms encoding sleep need and reveal dynamic properties of the sleep homeostatic control system.

RPamide neuropeptides NLP-22 and NLP-2 act through GnRH-like receptors to promote sleep and wakefulness in C. elegans

Sleep and wakefulness are fundamental behavioral states of which the underlying molecular principles are becoming slowly elucidated. Transitions between these states require the coordination of multiple neurochemical and modulatory systems. In Caenorhabditis elegans sleep occurs during a larval transition stage called lethargus and is induced by somnogenic neuropeptides. Here, we identify two opposing neuropeptide/receptor signaling pathways: NLP-22 promotes behavioral quiescence, whereas NLP-2 promotes movement during lethargus, by signaling through gonadotropin-releasing hormone (GnRH) related receptors. Both NLP-2 and NLP-22 belong to the RPamide neuropeptide family and share sequence similarities with neuropeptides of the bilaterian GnRH, adipokinetic hormone (AKH) and corazonin family. RPamide neuropeptides dose-dependently activate the GnRH/AKH-like receptors GNRR-3 and GNRR-6 in a cellular receptor activation assay. In addition, nlp-22-induced locomotion quiescence requires the receptor gnrr-6. By contrast, wakefulness induced by nlp-2 overexpression is diminished by deletion of either gnrr-3 or gnrr-6. nlp-2 is expressed in a pair of olfactory AWA neurons and cycles with larval periodicity, as reported for nlp-22, which is expressed in RIA. Our data suggest that the somnogenic NLP-22 neuropeptide signals through GNRR-6, and that both GNRR-3 and GNRR-6 are required for the wake-promoting action of NLP-2 neuropeptides.

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

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

Early Life Trauma Has Lifelong Consequences for Sleep And Behavior

Sleep quality varies widely across individuals, especially during normal aging, with impaired sleep contributing to deficits in cognition and emotional regulation. Sleep can also be impacted by a variety of adverse events, including childhood adversity. Here we examined how early life adverse events impacted later life sleep structure and physiology using an animal model to test the relationship between early life adversity and sleep quality across the life span. Rat pups were exposed to an Adversity-Scarcity model from postnatal day 8–12, where insufficient bedding for nest building induces maternal maltreatment of pups. Polysomnography and sleep physiology were assessed in weaning, early adult and older adults. Early life adversity induced age-dependent disruptions in sleep and behavior, including lifelong spindle decreases and later life NREM sleep fragmentation. Given the importance of sleep in cognitive and emotional functions, these results highlight an important factor driving variation in sleep, cognition and emotion throughout the lifespan that suggest age-appropriate and trauma informed treatment of sleep problems.

Hypothalamic Neurons that Regulate Feeding Can Influence Sleep/Wake States Based on Homeostatic Need

Eating and sleeping represent two mutually exclusive behaviors that satisfy distinct homeostatic needs. Because an animal cannot eat and sleep at the same time, brain systems that regulate energy homeostasis are likely to influence sleep/wake behavior. Indeed, previous studies indicate that animals adjust sleep cycles around periods of food need and availability. Furthermore, hormones that affect energy homeostasis also affect sleep/wake states: the orexigenic hormone ghrelin promotes wakefulness, and the anorexigenic hormones leptin and insulin increase the duration of slow-wave sleep. However, whether neural populations that regulate feeding can influence sleep/wake states is unknown. The hypothalamic arcuate nucleus contains two neuronal populations that exert opposing effects on energy homeostasis: agouti-related protein (AgRP)-expressing neurons detect caloric need and orchestrate food-seeking behavior, whereas activity in pro-opiomelanocortin (POMC)-expressing neurons induces satiety. We tested the hypotheses that AgRP neurons affect sleep homeostasis by promoting states of wakefulness, whereas POMC neurons promote states of sleep. Indeed, optogenetic or chemogenetic stimulation of AgRP neurons in mice promoted wakefulness while decreasing the quantity and integrity of sleep. Inhibition of AgRP neurons rescued sleep integrity in food-deprived mice, highlighting the physiological importance of AgRP neuron activity for the suppression of sleep by hunger. Conversely, stimulation of POMC neurons promoted sleep states and decreased sleep fragmentation in food-deprived mice. Interestingly, we also found that sleep deprivation attenuated the effects of AgRP neuron activity on food intake and wakefulness. These results indicate that homeostatic feeding neurons can hierarchically affect behavioral outcomes, depending on homeostatic need.

Hypothalamic Dysfunction in Obesity and Metabolic Disorders

The hypothalamus is the brain region responsible for the maintenance of energetic homeostasis. The regulation of this process arises from the ability of the hypothalamus to orchestrate complex physiological responses such as food intake and energy expenditure, circadian rhythm, stress response, and fertility. Metabolic alterations such as obesity can compromise these hypothalamic regulatory functions. Alterations in circadian rhythm, stress response, and fertility further contribute to aggravate the metabolic dysfunction of obesity and contribute to the development of chronic disorders such as depression and infertility.At cellular level, obesity caused by overnutrition can damage the hypothalamus promoting inflammation and impairing hypothalamic neurogenesis. Furthermore, hypothalamic neurons suffer apoptosis and impairment in synaptic plasticity that can compromise the proper functioning of the hypothalamus. Several factors contribute to these phenomena such as ER stress, oxidative stress, and impairments in autophagy. All these observations occur at the same time and it is still difficult to discern whether inflammatory processes are the main drivers of these cellular dysfunctions or if the hypothalamic hormone resistance (insulin, leptin, and ghrelin) can be pinpointed as the source of several of these events.Understanding the mechanisms that underlie the pathophysiology of obesity in the hypothalamus is crucial for the development of strategies that can prevent or attenuate the deleterious effects of obesity.

Sleep-Wake Neurochemistry

The regulated alternations between wakefulness and sleep states reflect complex behavioral processes, orchestrated by distinct neurochemical changes in brain parenchyma. No single neurotransmitter or neuromodulator controls the sleep-wake states in isolation. Rather, fine-tuned interactions within organized neuronal circuits regulate waking and sleep states and drive their transitions. Structural or functional dysregulation and medications interfering with these ensembles can lead to sleep-wake disorders and exert wanted or unwanted pharmacological actions on sleep-wake states. Knowledge of the neurochemical bases of sleep-wake states, which will be discussed in this article, provides the conceptual framework for understanding pharmacological effects on sleep and wake.

Genetic dissection of neuropeptide cell biology at high and low activity in a defined sensory neuron

Neuropeptides are ubiquitous modulators of behavior and physiology. They are packaged in specialized secretory organelles called dense core vesicles (DCVs) that are released upon neural stimulation. Whereas local recycling of synaptic vesicles has been investigated intensively, there are few studies on recycling of DCV proteins. We set up a paradigm to study DCVs in a neuron whose activity we can control. We validate our model by confirming many previous observations on DCV cell biology. We identify a set of genes involved in recycling of DCV proteins. We also find evidence that different mechanisms of DCV priming and exocytosis may operate at high and low neural activity.

Neuropeptides are ubiquitous modulators of behavior and physiology. They are packaged in specialized secretory organelles called dense core vesicles (DCVs) that are released upon neural stimulation. Unlike synaptic vesicles, which can be recycled and refilled close to release sites, DCVs must be replenished by de novo synthesis in the cell body. Here, we dissect DCV cell biology in vivo in a Caenorhabditis elegans sensory neuron whose tonic activity we can control using a natural stimulus. We express fluorescently tagged neuropeptides in the neuron and define parameters that describe their subcellular distribution. We measure these parameters at high and low neural activity in 187 mutants defective in proteins implicated in membrane traffic, neuroendocrine secretion, and neuronal or synaptic activity. Using unsupervised hierarchical clustering methods, we analyze these data and identify 62 groups of genes with similar mutant phenotypes. We explore the function of a subset of these groups. We recapitulate many previous findings, validating our paradigm. We uncover a large battery of proteins involved in recycling DCV membrane proteins, something hitherto poorly explored. We show that the unfolded protein response promotes DCV production, which may contribute to intertissue communication of stress. We also find evidence that different mechanisms of priming and exocytosis may operate at high and low neural activity. Our work provides a defined framework to study DCV biology at different neural activity levels.

ER Lipid Defects in Neuropeptidergic Neurons Impair Sleep Patterns in Parkinson's Disease

Parkinson's disease patients report disturbed sleep patterns long before motor dysfunction. Here, in parkin and pink1 models, we identify circadian rhythm and sleep pattern defects and map these to specific neuropeptidergic neurons in fly models and in hypothalamic neurons differentiated from patient induced pluripotent stem cells (iPSCs). Parkin and Pink1 control the clearance of mitochondria by protein ubiquitination. Although we do not observe major defects in mitochondria of mutant neuropeptidergic neurons, we do find an excess of endoplasmic reticulum-mitochondrial contacts. These excessive contact sites cause abnormal lipid trafficking that depletes phosphatidylserine from the endoplasmic reticulum (ER) and disrupts the production of neuropeptide-containing vesicles. Feeding mutant animals phosphatidylserine rescues neuropeptidergic vesicle production and acutely restores normal sleep patterns in mutant animals. Hence, sleep patterns and circadian disturbances in Parkinson's disease models are explained by excessive ER-mitochondrial contacts, and blocking their formation or increasing phosphatidylserine levels rescues the defects in vivo.

Neuropeptidome of the Hypothalamus and Pituitary Gland of Indicine × Taurine Heifers: Evidence of Differential Neuropeptide Processing in the Pituitary Gland before and after Puberty

Puberty in cattle is regulated by an endocrine axis, which includes a complex milieu of neuropeptides in the hypothalamus and pituitary gland. The neuropeptidome of hypothalamic-pituitary gland tissue of pre- (PRE) and postpubertal (POST) Bos indicus-influenced heifers was characterized, followed by quantitative analysis of 51 fertility-related neuropeptides in these tissues. Comparison of peptide abundances with gene expression levels allowed assessment of post-transcriptional peptide processing. On the basis of classical cleavage, 124 mature neuropeptides from 35 precursor proteins were detected in hypothalamus and pituitary gland tissues of three PRE and three POST Brangus heifers. An additional 19 peptides (cerebellins, PEN peptides) previously reported as neuropeptides that did not follow classical cleavage were also identified. In the pre-pubertal hypothalamus, a greater diversity of neuropeptides (25.8%) was identified relative to post-pubertal heifers, while in the pituitary gland, 38.6% more neuropeptides were detected in the post-pubertal heifers. Neuro-tissues of PRE and POST heifers revealed abundance differences ( p < 0.05) in peptides from protein precursors involved in packaging and processing (e.g., the granin family and ProSAAS) or neuron stimulation (PENK, CART, POMC, cerebellins). On their own, the transcriptome data of the precursor genes could not predict the neuropeptide profile in the exact same tissues in several cases. This provides further evidence of the importance of differential processing of the neuropeptide precursors in the pituitary before and after puberty.

Layer- and Cell Type-Specific Modulation of Excitatory Neuronal Activity in the Neocortex

From an anatomical point of view the neocortex is subdivided into up to six layers depending on the cortical area. This subdivision has been described already by Meynert and Brodmann in the late 19/early 20. century and is mainly based on cytoarchitectonic features such as the size and location of the pyramidal cell bodies. Hence, cortical lamination is originally an anatomical concept based on the distribution of excitatory neuron. However, it has become apparent in recent years that apart from the layer-specific differences in morphological features, many functional properties of neurons are also dependent on cortical layer or cell type. Such functional differences include changes in neuronal excitability and synaptic activity by neuromodulatory transmitters. Many of these neuromodulators are released from axonal afferents from subcortical brain regions while others are released intrinsically. In this review we aim to describe layer- and cell-type specific differences in the effects of neuromodulator receptors in excitatory neurons in layers 2–6 of different cortical areas. We will focus on the neuromodulator systems using adenosine, acetylcholine, dopamine, and orexin/hypocretin as examples because these neuromodulator systems show important differences in receptor type and distribution, mode of release and functional mechanisms and effects. We try to summarize how layer- and cell type-specific neuromodulation may affect synaptic signaling in cortical microcircuits.

The effects of diurnal intermittent fasting on the wake-promoting neurotransmitter orexin-A

BACKGROUND:

Food restriction has been demonstrated to increase the alertness in different species and to increase the levels of the wake-promoting neurotransmitter orexin. We hypothesized that diurnal intermittent fasting (DIF) increases orexin-A levels during fasting. Therefore, we conducted this study to assess the effects of DIF, during the month of Ramadan, on orexin, while controlling for lifestyle changes that may accompany Ramadan such as sleep duration, bedtime and wake time, energy expenditure, light exposure, and food.

METHODS:

Eight young healthy volunteers (mean age, 25.4 ± 3.5 years) reported to the laboratory on three occasions: (1) 4 weeks before Ramadan while performing DIF for 1 week outside the month of Ramadan (fasting outside Ramadan); (2) 1 week before Ramadan (nonfasting baseline) (BL); and (3) during the 2^nd week of Ramadan while performing DIF (Ramadan). Plasma levels of orexin-A were measured using an enzyme immunoassay five times at 22:00, 02:00, 04:00, 06:00, and 11:00. Caloric intake, light exposure, and sleep schedule were maintained during the participants’ stays in the laboratory in the three study periods.

RESULTS:

Orexin-A levels increased in the daytime during fasting and decreased at night compared to BL. The differences in orexin-A levels between DIF and BL were significant at 06:00, 11:00, 22:00, and 02:00.

CONCLUSIONS:

DIF increases orexin-A levels in the plasma during fasting hours. This finding supports findings from animal studies showing that fasting increases alertness.

Neuropeptide Y Regulates Sleep by Modulating Noradrenergic Signaling

Sleep is an essential and evolutionarily conserved behavioral state whose regulation remains poorly understood. To identify genes that regulate vertebrate sleep, we recently performed a genetic screen in zebrafish, and here we report the identification of neuropeptide Y (NPY) as both necessary for normal daytime sleep duration and sufficient to promote sleep. We show that overexpression of NPY increases sleep, whereas mutation of npy or ablation of npy-expressing neurons decreases sleep. By analyzing sleep architecture, we show that NPY regulates sleep primarily by modulating the length of wake bouts. To determine how NPY regulates sleep, we tested for interactions with several systems known to regulate sleep, and provide anatomical, molecular, genetic, and pharmacological evidence that NPY promotes sleep by inhibiting noradrenergic signaling. These data establish NPY as an important vertebrate sleep/wake regulator and link NPY signaling to an established arousal-promoting system.

Genetic and neuronal regulation of sleep by neuropeptide VF

Sleep is an essential and phylogenetically conserved behavioral state, but it remains unclear to what extent genes identified in invertebrates also regulate vertebrate sleep. RFamide-related neuropeptides have been shown to promote invertebrate sleep, and here we report that the vertebrate hypothalamic RFamide neuropeptide VF (NPVF) regulates sleep in the zebrafish, a diurnal vertebrate. We found that NPVF signaling and npvf-expressing neurons are both necessary and sufficient to promote sleep, that mature peptides derived from the NPVF preproprotein promote sleep in a synergistic manner, and that stimulation of npvf-expressing neurons induces neuronal activity levels consistent with normal sleep. These results identify NPVF signaling and npvf-expressing neurons as a novel vertebrate sleep-promoting system and suggest that RFamide neuropeptides participate in an ancient and central aspect of sleep control.

Ancestral Circuits for the Coordinated Modulation of Brain State

Internal states of the brain profoundly influence behavior. Fluctuating states such as alertness can be governed by neuromodulation, but the underlying mechanisms and cell types involved are not fully understood. We developed a method to globally screen for cell types involved in behavior by integrating brain-wide activity imaging with high-content molecular phenotyping and volume registration at cellular resolution. We used this method (MultiMAP) to record from 22 neuromodulatory cell types in behaving zebrafish during a reaction-time task that reports alertness. We identified multiple monoaminergic, cholinergic, and peptidergic cell types linked to alertness and found that activity in these cell types was mutually correlated during heightened alertness. We next recorded from and controlled homologous neuromodulatory cells in mice; alertness-related cell-type dynamics exhibited striking evolutionary conservation and modulated behavior similarly. These experiments establish a method for unbiased discovery of cellular elements underlying behavior and reveal an evolutionarily conserved set of diverse neuromodulatory systems that collectively govern internal state.

HID-1 controls formation of large dense core vesicles by influencing cargo sorting and trans-Golgi network acidification

The peripheral membrane protein HID-1 localizes to the trans-Golgi network, where it contributes to the formation of large dense core vesicles of neuroendocrine cells by influencing cargo sorting and trans-Golgi network acidification.

Large dense core vesicles (LDCVs) mediate the regulated release of neuropeptides and peptide hormones. They form at the trans-Golgi network (TGN), where their soluble content aggregates to form a dense core, but the mechanisms controlling biogenesis are still not completely understood. Recent studies have implicated the peripheral membrane protein HID-1 in neuropeptide sorting and insulin secretion. Using CRISPR/Cas9, we generated HID-1 KO rat neuroendocrine cells, and we show that the absence of HID-1 results in specific defects in peptide hormone and monoamine storage and regulated secretion. Loss of HID-1 causes a reduction in the number of LDCVs and affects their morphology and biochemical properties, due to impaired cargo sorting and dense core formation. HID-1 KO cells also exhibit defects in TGN acidification together with mislocalization of the Golgi-enriched vacuolar H⁺-ATPase subunit isoform a2. We propose that HID-1 influences early steps in LDCV formation by controlling dense core formation at the TGN.

Neuronal substrates for initiation, maintenance, and structural organization of sleep/wake states

Animals continuously alternate between sleep and wake states throughout their life. The daily organization of sleep and wakefulness is orchestrated by circadian, homeostatic, and motivational processes. Over the last decades, much progress has been made toward determining the neuronal populations involved in sleep/wake regulation. Here, we will discuss how the application of advanced in vivo tools for cell type–specific manipulations now permits the functional interrogation of different features of sleep/wake state regulation: initiation, maintenance, and structural organization. We will specifically focus on recent studies examining the roles of wake-promoting neuronal populations.

Analysis of the NK2 homeobox gene ceh-24 reveals sublateral motor neuron control of left-right turning during sleep

Sleep is a behavior that is found in all animals that have a nervous system and that have been studied carefully. In Caenorhabditis elegans larvae, sleep is associated with a turning behavior, called flipping, in which animals rotate 180° about their longitudinal axis. However, the molecular and neural substrates of this enigmatic behavior are not known. Here, we identified the conserved NK-2 homeobox gene ceh-24 to be crucially required for flipping. ceh-24 is required for the formation of processes and for cholinergic function of sublateral motor neurons, which separately innervate the four body muscle quadrants. Knockdown of cholinergic function in a subset of these sublateral neurons, the SIAs, abolishes flipping. The SIAs depolarize during flipping and their optogenetic activation induces flipping in a fraction of events. Thus, we identified the sublateral SIA neurons to control the three-dimensional movements of flipping. These neurons may also control other types of motion.

DOI:http://dx.doi.org/10.7554/eLife.24846.001

Although sleeping individuals do not move voluntarily, they are not completely immobile. Both people and animals regularly change position in their sleep, but it is not known why these movements occur or what regulates them.

One of the simplest animals known to require sleep is the nematode worm Caenorhabditis elegans, which is often used by researchers to study the molecular basis of behavior. In common with more complex animals, worms go to sleep lying on either their left or right side and then switch periodically between the two. This “flipping” behavior is typically not seen outside of sleep.

By screening worms with mutations in different genes, Schwarz and Bringmann identified one mutant that does not flip during sleep. The mutant lacked a gene called ceh-24, which is normally active in a set of four neurons known as SIAs. These are a type of motor neuron; that is, neurons that control the contraction of muscles.

The body wall muscles of C. elegans run along the length of its body and are organized into “quadrants” that each cover a quarter of the worm. Schwarz and Bringmann show that unlike other C. elegans motor neurons, SIA neurons control each quadrant separately. By activating specific SIA neurons the worms can contract the muscles on each side of the body independently, and thereby flip from one side to the other.

Further investigation revealed that the SIA motor neurons can also control other types of complex movement. Additional experiments are now needed to determine how the neurons support these behaviors. Another challenge will be to work out the purpose of posture changes during sleep for C. elegans and other animals.

DOI:http://dx.doi.org/10.7554/eLife.24846.002

Assessment of Wakefulness and Brain Arousal Regulation in Psychiatric Research

During the last few decades, much knowledge has been gained about sleep being a heterogeneous condition with several distinct sleep stages that represent fundamentally different physiological states. The same applies for the wake state which also comprises distinct global functional states (called vigilance stages). However, various terms and concepts have been introduced describing different aspects of wakefulness, and accordingly several methods of assessment exist, e.g. sleep laboratory assessments (Multiple Sleep Latency Test, Maintenance of Wakefulness Test), questionnaires (Epworth Sleepiness Scale, Karolinska Sleepiness Scale), behavioural tasks (Psychomotor Vigilance Test) or electroencephalography (EEG)-based assessments (Alpha Attenuation Test, Karolinska Drowsiness Test). Furthermore, several theoretical concepts about the regulation of sleep and wakefulness have been put forward, and physiological correlates have been identified. Most relevant for healthy functioning is the regulation of brain arousal and the adaption of wakefulness to the environmental and situational needs so that the optimal balance between energy conservation and responsiveness can be obtained. Since one approach to the assessment of brain arousal regulation is the classification of EEG vigilance stages, a computer-based algorithm (Vigilance Algorithm Leipzig) has been introduced, allowing classification of EEG vigilance stages in EEG recordings under resting conditions. The time course of EEG vigilance stages in EEGs of 15-20 min duration allows estimation of the individual arousal regulation (hyperstable, adaptive, or unstable vigilance pattern). The vigilance model of affective disorders and attention-deficit/hyperactivity disorder links a disturbed arousal regulation to the pathogenesis of psychiatric disorders and accordingly helps to explain and possibly also predict treatment effects of pharmacological and non-pharmacological interventions for these conditions.

Cilia-based flow network in the brain ventricles

Cerebrospinal fluid conveys many physiologically important signaling factors through the ventricular cavities of the brain. We investigated the transport of cerebrospinal fluid in the third ventricle of the mouse brain and discovered a highly organized pattern of cilia modules, which collectively give rise to a network of fluid flows that allows for precise transport within this ventricle. We also discovered a cilia-based switch that reliably and periodically alters the flow pattern so as to create a dynamic subdivision that may control substance distribution in the third ventricle. Complex flow patterns were also present in the third ventricles of rats and pigs. Our work suggests that ciliated epithelia can generate and maintain complex, spatiotemporally regulated flow networks.

Allatostatin A Signalling in Drosophila Regulates Feeding and Sleep and Is Modulated by PDF

Feeding and sleep are fundamental behaviours with significant interconnections and cross-modulations. The circadian system and peptidergic signals are important components of this modulation, but still little is known about the mechanisms and networks by which they interact to regulate feeding and sleep. We show that specific thermogenetic activation of peptidergic Allatostatin A (AstA)-expressing PLP neurons and enteroendocrine cells reduces feeding and promotes sleep in the fruit fly Drosophila. The effects of AstA cell activation are mediated by AstA peptides with receptors homolog to galanin receptors subserving similar and apparently conserved functions in vertebrates. We further identify the PLP neurons as a downstream target of the neuropeptide pigment-dispersing factor (PDF), an output factor of the circadian clock. PLP neurons are contacted by PDF-expressing clock neurons, and express a functional PDF receptor demonstrated by cAMP imaging. Silencing of AstA signalling and continuous input to AstA cells by tethered PDF changes the sleep/activity ratio in opposite directions but does not affect rhythmicity. Taken together, our results suggest that pleiotropic AstA signalling by a distinct neuronal and enteroendocrine AstA cell subset adapts the fly to a digestive energy-saving state which can be modulated by PDF.

Molecular regulation of hypothalamic development and physiological functions

The hypothalamus is composed of many heterogeneous nuclei that control distinct physiological functions. Investigating molecular mechanisms that regulate the specification of these nuclei and specific neuronal subtypes, and their contribution to diverse hypothalamic functions, is an exciting research focus. Here, we begin by summarizing the hypothalamic functions of feeding regulation, sleep-wake cycles, stress responses, and circadian rhythm, and describing their anatomical bases. Next, we review the molecular regulation of formation of hypothalamic territories, specification of nuclei and subnuclei, and generation of specific neurons. Finally, we highlight physiological and behavioral consequences of altered hypothalamic development. Identifying molecules that regulate hypothalamic development and function will increase our understanding of hypothalamus-related disorders, such as obesity and diabetes, and aid in the development of therapies aimed specifically at their etiologies.

C. elegans Stress-Induced Sleep Emerges from the Collective Action of Multiple Neuropeptides

The genetic basis of sleep regulation remains poorly understood. In C. elegans, cellular stress induces sleep through epidermal growth factor (EGF)-dependent activation of the EGF receptor in the ALA neuron. The downstream mechanism by which this neuron promotes sleep is unknown. Single-cell RNA sequencing of ALA reveals that the most highly expressed, ALA-enriched genes encode neuropeptides. Here we have systematically investigated the four most highly enriched neuropeptides: flp-7, nlp-8, flp-24, and flp-13. When individually removed by null mutation, these peptides had little or no effect on stress-induced sleep. However, stress-induced sleep was abolished in nlp-8; flp-24; flp-13 triple-mutant animals, indicating that these neuropeptides work collectively in controlling stress-induced sleep. We tested the effect of overexpression of these neuropeptide genes on five behaviors modulated during sleep-pharyngeal pumping, defecation, locomotion, head movement, and avoidance response to an aversive stimulus-and we found that, if individually overexpressed, each of three neuropeptides (nlp-8, flp-24, or flp-13) induced a different suite of sleep-associated behaviors. These overexpression results raise the possibility that individual components of sleep might be specified by individual neuropeptides or combinations of neuropeptides.

Modulation of primary cilia length by melanin-concentrating hormone receptor 1

Melanin-concentrating hormone (MCH) receptor 1 (MCHR1) is a class A G-protein-coupled receptor (GPCR). The MCH-MCHR1 system has been implicated in the regulation of feeding, emotional processing, and sleep in rodents. Recent work revealed that MCHR1 is selectively expressed in neuronal primary cilia of the central nervous system. Cilia have various chemosensory functions in many types of cell, and ciliary dysfunction is associated with ciliopathies such as polycystic kidney disease and obesity. Although dynamic modulation of neuronal cilia length is observed in obese mice, the functional interaction of neuronal ciliary GPCR and its endogenous ligand has not yet been elucidated. We report here that MCH treatment significantly reduced cilia length in hTERT-RPE1 cells (hRPE1 cells) transfected with MCHR1. Quantitative analyses indicated that MCH-induced cilia shortening progressed in a dose-dependent manner with an EC50 lower than 1nM when cells were treated for 6h. Although the assembly and disassembly of primary cilia are tightly coupled to the cell cycle, cell cycle reentry was not a determinant of MCH-induced cilia shortening. We confirmed that MCH elicited receptor internalization, Ca(2+) mobilization, ERK and Akt phosphorylation, and inhibition of cyclic AMP accumulation in MCHR1-expressing hRPE1 cells. Among these diverse pathways, we revealed that Gi/o-dependent Akt phosphorylation was an important component in the initial stage of MCH-induced cilia length shortening. Furthermore, induction of fewer cilia by Kif3A siRNA treatment significantly decreased the MCH-mediated phosphorylation of Akt, indicating the functional importance of the MCHR1-Akt pathway in primary cilia. Taken together, the present data suggest that the MCH-MCHR1 axis may modulate the sensitivity of cells to external environments by controlling the cilia length. Therefore, further characterization of MCHR1 as a ciliary GPCR will provide a potential molecular mechanism to link cilia length control with obesity.

Astrogliosis: An integral player in the pathogenesis of Alzheimer's disease

Alzheimer's disease is the main cause of dementia in the elderly and begins with a subtle decline in episodic memory followed by a more general decline in overall cognitive abilities. Though the exact trigger for this cascade of events remains unknown the presence of the misfolded amyloid-beta protein triggers reactive gliosis, a prominent neuropathological feature in the brains of Alzheimer's patients. The cytoskeletal and morphological changes of astrogliosis are its evident features, while changes in oxidative stress defense, cholesterol metabolism, and gene transcription programs are less manifest. However, these latter molecular changes may underlie a disruption in homeostatic regulation that keeps the brain environment balanced. Astrocytes in Alzheimer's disease show changes in glutamate and GABA signaling and recycling, potassium buffering, and in cholinergic, purinergic, and calcium signaling. Ultimately the dysregulation of homeostasis maintained by astrocytes can have grave consequences for the stability of microcircuits within key brain regions. Specifically, altered inhibition influenced by astrocytes can lead to local circuit imbalance with farther reaching consequences for the functioning of larger neuronal networks. Healthy astrocytes have a role in maintaining and modulating normal neuronal communication, synaptic physiology and energy metabolism, astrogliosis interferes with these functions. This review considers the molecular and functional changes occurring during astrogliosis in Alzheimer's disease, and proposes that astrocytes are key players in the development of dementia.

Melanin-Concentrating Hormone (MCH): Role in REM Sleep and Depression

The melanin-concentrating hormone (MCH) is a peptidergic neuromodulator synthesized by neurons of the lateral sector of the posterior hypothalamus and zona incerta. MCHergic neurons project throughout the central nervous system, including areas such as the dorsal (DR) and median (MR) raphe nuclei, which are involved in the control of sleep and mood. Major Depression (MD) is a prevalent psychiatric disease diagnosed on the basis of symptomatic criteria such as sadness or melancholia, guilt, irritability, and anhedonia. A short REM sleep latency (i.e., the interval between sleep onset and the first REM sleep period), as well as an increase in the duration of REM sleep and the density of rapid-eye movements during this state, are considered important biological markers of depression. The fact that the greatest firing rate of MCHergic neurons occurs during REM sleep and that optogenetic stimulation of these neurons induces sleep, tends to indicate that MCH plays a critical role in the generation and maintenance of sleep, especially REM sleep. In addition, the acute microinjection of MCH into the DR promotes REM sleep, while immunoneutralization of this peptide within the DR decreases the time spent in this state. Moreover, microinjections of MCH into either the DR or MR promote a depressive-like behavior. In the DR, this effect is prevented by the systemic administration of antidepressant drugs (either fluoxetine or nortriptyline) and blocked by the intra-DR microinjection of a specific MCH receptor antagonist. Using electrophysiological and microdialysis techniques we demonstrated also that MCH decreases the activity of serotonergic DR neurons. Therefore, there are substantive experimental data suggesting that the MCHergic system plays a role in the control of REM sleep and, in addition, in the pathophysiology of depression. Consequently, in the present report, we summarize and evaluate the current data and hypotheses related to the role of MCH in REM sleep and MD.