Blocking melanin-concentrating hormone MCH1 receptor affects rat sleep-wake architecture

Melanin concentrating hormone-sleep pressure loop regulates melanin degradation through both autophagic degradation and lysosomal hydrolysis in zebrafish

Melanin-concentrating hormone (MCH) is a cyclic peptide initially isolated from salmon and later found to be conserved in mammals. It plays a role in regulating melanin changes and rhythmic behaviors such as sleep and feeding, though its relationship with these processes is not fully understood. Our preliminary research revealed significant differences in melanin degradation in zebrafish under varying light conditions, suggesting a link to MCH. This study aims to explore MCH's role in lighting-induced changes in rhythmic behavior patterns and melanin of zebrafish. Using the zebrafish model, we evaluated MCH expression under different lighting conditions and analyzed the effects of arousal-promoting and sleep-inducing agents. We also investigated the impact of exogenous MCH and its inhibitors on melanin degradation, behavioral changes, and differences in MCH expression to uncover potential regulatory relationships between MCH, sleep pressure, and melanin. In-depth research using flow cytometry, acridine orange staining, LysoTracker Red staining, and quantitative real-time PCR analysis of autophagy- and apoptosis-related genes showed that melanin degradation regulation depends on MCH expression levels. Sleep pressure can intervene in MCH's effects, forming a regulatory loop to jointly regulate melanin degradation. The influence of the MCH-sleep pressure loop on melanin degradation is closely tied to autophagic and lysosomal pathways. Our findings reveal a mutually regulatory loop in zebrafish between MCH and sleep pressure, affecting melanin degradation through these pathways.

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.

Selective activation of the hypothalamic orexinergic but not melanin-concentrating hormone neurons following pilocarpine-induced seizures in rats

Introduction

Sleep disorders are common comorbidities in patients with temporal lobe epilepsy (TLE), but the underlying mechanisms remain poorly understood. Since the lateral hypothalamic (LH) and the perifornical orexinergic (ORX) and melanin-concentrating hormone (MCH) neurons are known to play opposing roles in the regulation of sleep and arousal, dysregulation of ORX and MCH neurons might contribute to the disturbance of sleep-wakefulness following epileptic seizures.

Methods

To test this hypothesis, rats were treated with lithium chloride and pilocarpine to induce status epilepticus (SE). Electroencephalogram (EEG) and electromyograph (EMG) were recorded for analysis of sleep-wake states before and 24 h after SE. Double-labeling immunohistochemistry of c-Fos and ORX or MCH was performed on brain sections from the epileptic and control rats. In addition, anterograde and retrograde tracers in combination with c-Fos immunohistochemistry were used to analyze the possible activation of the amygdala to ORX neural pathways following seizures.

Results

It was found that epileptic rats displayed prolonged wake phase and decreased non-rapid eye movement (NREM) and rapid eye movement (REM) phase compared to the control rats. Prominent neuronal activation was observed in the amygdala and the hypothalamus following seizures. Interestingly, in the LH and the perifornical nucleus, ORX but not MCH neurons were significantly activated (c-Fos+). Neural tracing showed that seizure-activated (c-Fos+) ORX neurons were closely contacted by axon terminals originating from neurons in the medial amygdala.

Discussion

These findings suggest that the spread of epileptic activity from amygdala to the hypothalamus causes selective activation of the wake-promoting ORX neurons but not sleep-promoting MCH neurons, which might contribute to the disturbance of sleep-wakefulness in TLE.

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.

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.

hERG optimization of MCHR1 antagonist benzofuro-pyridine and pyrazino-indole derivatives

Obesity is a global epidemic associated with multiple severe diseases. Several pharmacotherapies have been investigated including the antagonists of melanin concentrating hormone receptor 1 (MCHR1). The design, synthesis, and biological studies of novel MCHR1 antagonists based on benzofuro-pyridine and pyrazino-indole scaffold was performed. We confirmed that fine-tuning lipophilicity and basic pKa by modifying the benzyl-group and introducing different substituents on the aliphatic nitrogen sidechain decreases both hERG inhibition and metabolic clearance. We have succeeded to develop excellent in vitro parameters in case of compounds 17 and 23g , that can be considered as valuable tools for further pharmacological investigation.

An N-terminal fusion allele to study melanin concentrating hormone receptor 1

Cilia on neurons play critical roles in both the development and function of the central nervous system (CNS). While it remains challenging to elucidate the precise roles for neuronal cilia, it is clear that a subset of G-protein-coupled receptors (GPCRs) preferentially localize to the cilia membrane. Further, ciliary GPCR signaling has been implicated in regulating a variety of behaviors. Melanin concentrating hormone receptor 1 (MCHR1), is a GPCR expressed centrally in rodents known to be enriched in cilia. Here we have used MCHR1 as a model ciliary GPCR to develop a strategy to fluorescently tag receptors expressed from the endogenous locus in vivo. Using CRISPR/Cas9, we inserted the coding sequence of the fluorescent protein mCherry into the N-terminus of Mchr1. Analysis of the fusion protein (^mCherry MCHR1) revealed its localization to neuronal cilia in the CNS, across multiple developmental time points and in various regions of the adult brain. Our approach simultaneously produced fortuitous in/dels altering the Mchr1 start codon resulting in a new MCHR1 knockout line. Functional studies using electrophysiology show a significant alteration of synaptic strength in MCHR1 knockout mice. A reduction in strength is also detected in mice homozygous for the mCherry insertion, suggesting that while the strategy is useful for monitoring the receptor, activity could be altered. However, both lines should aid in studies of MCHR1 function and contribute to our understanding of MCHR1 signaling in the brain. Additionally, this approach could be expanded to aid in the study of other ciliary GPCRs.

The aging brain: sleep, the circadian clock and exercise

Aging is a multifactorial process likely stemming from damage accumulation and/or a decline in maintenance and repair mechanisms in the organisms that eventually determine their lifespan. In our review, we focus on the morphological and functional alterations that the aging brain undergoes affecting sleep and the circadian clock in both human and rodent models. Although both species share mammalian features, differences have been identified on several experimental levels, which we outline in this review. Additionally, we delineate some challenges on the preferred analysis and we suggest that a uniform route is followed so that findings can be smoothly compared. We conclude by discussing potential interventions and highlight the influence of physical exercise as a beneficial lifestyle intervention, and its effect on healthy aging and longevity. We emphasize that even moderate age-matched exercise is able to ameliorate several aging characteristics as far as sleep and circadian rhythms are concerned, independent of the species studied.

Intranasal Administration of Melanin-Concentrating Hormone Reduces Stress-Induced Anxiety- and Depressive-Like Behaviors in Rodents

Major depressive disorder is a complex neuropsychiatric disorder with few treatment options. Non-targeted antidepressants have low efficacy and can induce series of side effects. While a neuropeptide, melanin-concentrating hormone (MCH), is known to exhibit regulator of affective state, no study to date has assessed the anti-depressive effects of MCH in a stress-induced depression model. This study aimed to evaluate the pharmacological effects of intranasal administration of MCH on depression-related behavior in stressed rats and mice. Using a number of behavioral tests, we found that MCH treatment significantly decreased anxiety- and depressive-like behaviors induced by stress. Notably, the effects of MCH were equivalent to those of fluoxetine. MCH treatment also restored the activity of the mammalian target of rapamycin (mTOR) signaling pathway and normalized the levels of synaptic proteins, including postsynaptic density 95, glutamate receptor 1, and synapsin 1, which were all downregulated by stress. Interestingly, the protective effects of MCH were blocked by the mTOR inhibitor, rapamycin. These results suggest that MCH exhibits antidepressant properties by modulating the mTOR pathway. Altogether, this study provides an insight into the molecular mechanisms involved in the antidepressant-like effects of MCH, thereby paving the way for the future clinical application of MCH.

Sleep-Wake Control by Melanin-Concentrating Hormone (MCH) Neurons: a Review of Recent Findings

PURPOSE OF THE REVIEW

Melanin-concentrating hormone (MCH)-expressing neurons located in the lateral hypothalamus are considered as an integral component of sleep-wake circuitry. However, the precise role of MCH neurons in sleep-wake regulation has remained unclear, despite several years of research employing a wide range of techniques. We review recent data on this aspect, which are mostly inconsistent, and propose a novel role for MCH neurons in sleep regulation.

RECENT FINDINGS

While almost all studies using "gain-of-function" approaches show an increase in rapid eye movement sleep (or paradoxical sleep; PS), loss-of-function approaches have not shown reductions in PS. Similarly, the reported changes in wakefulness or non-rapid eye movement sleep (slow-wave sleep; SWS) with manipulation of the MCH system using conditional genetic methods are inconsistent. Currently available data do not support a role for MCH neurons in spontaneous sleep-wake but imply a crucial role for them in orchestrating sleep-wake responses to changes in external and internal environments.

KLF4 Exerts Sedative Effects in Pentobarbital-Treated Mice

KLF4 is a zinc-finger transcription factor that plays an essential role in many biological processes, including neuroinflammation, neuron regeneration, cell proliferation, and apoptosis. Through effects on these processes, KLF4 has likely roles in Alzheimer's disease, Parkinson's disease, and traumatic brain injury. However, little is known about the role of KLF4 in more immediate behavioral processes that similarly depend upon broad changes in brain excitability, such as the sleep process. Here, behavioral approaches, western blot, and immunohistochemical experiments were used to explore the role of KLF4 on sedation and the potential mechanisms of those effects. The results showed that overexpression of KLF4 prolonged loss of righting reflex (LORR) duration in pentobarbital-treated mice and increased c-Fos expression in the lateral hypothalamus (LH) and the ventrolateral preoptic nucleus (VLPO), while it decreased c-Fos expression in the tuberomammillary nucleus (TMN). Moreover, overexpression of KLF4 reduced the expression of p53 in the hypothalamus and increased the expression of STAT3 in the hypothalamus. Therefore, these results suggest that KLF4 exerts sedative effects through the regulation of p53 and STAT3 expression, and it indicates a role of KLF4 ligands in the treatment of sleep disorders.

The role of co-neurotransmitters in sleep and wake regulation

Sleep and wakefulness control in the mammalian brain requires the coordination of various discrete interconnected neurons. According to the most conventional sleep model, wake-promoting neurons (WPNs) and sleep-promoting neurons (SPNs) compete for network dominance, creating a systematic "switch" that results in either the sleep or awake state. WPNs and SPNs are ubiquitous in the brainstem and diencephalon, areas that together contain <1% of the neurons in the human brain. Interestingly, many of these WPNs and SPNs co-express and co-release various types of the neurotransmitters that often have opposing modulatory effects on the network. Co-transmission is often beneficial to structures with limited numbers of neurons because it provides increasing computational capability and flexibility. Moreover, co-transmission allows subcortical structures to bi-directionally control postsynaptic neurons, thus helping to orchestrate several complex physiological functions such as sleep. Here, we present an in-depth review of co-transmission in hypothalamic WPNs and SPNs and discuss its functional significance in the sleep-wake network.

Heterogeneity in the circadian and homeostatic modulation of multiunit activity in the lateral hypothalamus

The lateral hypothalamus (LH) is a relatively large hypothalamic structure containing several neurochemically different, but spatially intermingled, neuronal populations. While the role of these neurons in the homeostatic regulation of diverse physiological and behavioral functions such as sleep/wake cycle has been studied extensively, the impact of sleep history on the electrophysiology of the LH and whether this effect is homogenous across LH is unknown. By combining multiunit activity (MUA) recordings in different regions of LH with electroencephalogram recordings in freely moving rats, we unravelled a heterogeneity of neural-activity patterns within different subregions of LH. This heterogeneity was evident in both the circadian and the vigilance state-dependent modulation of MUA. Interestingly, and consistent with this heterogeneity under baseline conditions, the magnitude of MUA suppression following 6 hr of sleep deprivation (SD) was also different within different locations of LH. Unlike the cortex and in contrast to the predictions of the synaptic homeostatic hypothesis, no correlation was found between the magnitude of activity increase during SD and the percentage of suppression of MUA during recovery sleep. These data provide in vivo evidence of a functional heterogeneity in the circadian and homeostatic modulation of neuronal activity in LH.

Neuroanatomical and Neurochemical Bases of Vigilance States

In the present chapter, hypotheses on the mechanisms responsible for the genesis of the three vigilance states, namely, waking, non-rapid eye movement (non-REM) also called slow-wave sleep (SWS), and REM sleep also called paradoxical sleep (PS), are presented. A huge number of studies first indicate that waking is induced by the activation of multiple waking systems, including the serotonergic, noradrenergic, cholinergic, and hypocretin systems. At the onset of sleep, the SWS-active neurons would be activated by the circadian clock localized in the suprachiasmatic nucleus and a hypnogenic factor, adenosine, which progressively accumulates in the brain during waking. A number of studies support the hypothesis that SWS results from the activation of GABAergic neurons localized in the ventrolateral preoptic nucleus (VLPO). However, new GABAergic systems recently described localized in the parafacial, accumbens, and reticular thalamic nuclei will be also presented. In addition, we will show that a large body of data strongly suggests that the switch from SWS to PS is due to the interaction of multiple populations of glutamatergic and GABAergic neurons localized in the posterior hypothalamus and the brainstem.

Sleep-Wake Cycling and Energy Conservation: Role of Hypocretin and the Lateral Hypothalamus in Dynamic State-Dependent Resource Optimization

The hypocretin (Hcrt) system has been implicated in a wide range of physiological functions from sleep-wake regulation to cardiovascular, behavioral, metabolic, and thermoregulagtory control. These wide-ranging physiological effects have challenged the identification of a parsimonious function for Hcrt. A compelling hypothesis suggests that Hcrt plays a role in the integration of sleep-wake neurophysiology with energy metabolism. For example, Hcrt neurons promote waking and feeding, but are also sensors of energy balance. Loss of Hcrt function leads to an increase in REM sleep propensity, but a potential role for Hcrt linking energy balance with REM sleep expression has not been addressed. Here we examine a potential role for Hcrt and the lateral hypothalamus (LH) in state-dependent resource allocation as a means of optimizing resource utilization and, as a result, energy conservation. We review the energy allocation hypothesis of sleep and how state-dependent metabolic partitioning may contribute toward energy conservation, but with additional examination of how the loss of thermoregulatory function during REM sleep may impact resource optimization. Optimization of energy expenditures at the whole organism level necessitates a top-down network responsible for coordinating metabolic operations in a state-dependent manner across organ systems. In this context, we then specifically examine the potential role of the LH in regulating this output control, including the contribution from both Hcrt and melanin concentrating hormone (MCH) neurons among a diverse LH cell population. We propose that this hypothalamic integration system is responsible for global shifts in state-dependent resource allocations, ultimately promoting resource optimization and an energy conservation function of sleep-wake cycling.

Circuit mechanisms and computational models of REM sleep

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REM sleep was discovered in the 1950s.

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Many hypothalamic and brainstem areas have been found to contribute to REM sleep.

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An up-to-date picture of REM-sleep-regulating circuits is reviewed.

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A brief overview of computational models for REM sleep regulation is provided.

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Outstanding issues for future studies are discussed.

Rapid eye movement (REM) sleep or paradoxical sleep is an elusive behavioral state. Since its discovery in the 1950s, our knowledge of the neuroanatomy, neurotransmitters and neuropeptides underlying REM sleep regulation has continually evolved in parallel with the development of novel technologies. Although the pons was initially discovered to be responsible for REM sleep, it has since been revealed that many components in the hypothalamus, midbrain, pons, and medulla also contribute to REM sleep. In this review, we first provide an up-to-date overview of REM sleep-regulating circuits in the brainstem and hypothalamus by summarizing experimental evidence from neuroanatomical, neurophysiological and gain- and loss-of-function studies. Second, because quantitative approaches are essential for understanding the complexity of REM sleep-regulating circuits and because mathematical models have provided valuable insights into the dynamics underlying REM sleep genesis and maintenance, we summarize computational studies of the sleep-wake cycle, with an emphasis on REM sleep regulation. Finally, we discuss outstanding issues for future studies.

Optogenetic Investigation of Arousal Circuits

Modulation between sleep and wake states is controlled by a number of heterogeneous neuron populations. Due to the topological proximity and genetic co-localization of the neurons underlying sleep-wake state modulation optogenetic methods offer a significant improvement in the ability to benefit from both the precision of genetic targeting and millisecond temporal control. Beginning with an overview of the neuron populations mediating arousal, this review outlines the progress that has been made in the investigation of arousal circuits since the incorporation of optogenetic techniques and the first in vivo application of optogenetic stimulation in hypocretin neurons in the lateral hypothalamus. This overview is followed by a discussion of the future progress that can be made by incorporating more recent technological developments into the research of neural circuits.

The Melanin-Concentrating Hormone as an Integrative Peptide Driving Motivated Behaviors

The melanin-concentrating hormone (MCH) is an important peptide implicated in the control of motivated behaviors. History, however, made this peptide first known for its participation in the control of skin pigmentation, from which its name derives. In addition to this peripheral role, MCH is strongly implicated in motivated behaviors, such as feeding, drinking, mating and, more recently, maternal behavior. It is suggested that MCH acts as an integrative peptide, converging sensory information and contributing to a general arousal of the organism. In this review, we will discuss the various aspects of energy homeostasis to which MCH has been associated to, focusing on the different inputs that feed the MCH peptidergic system with information regarding the homeostatic status of the organism and the exogenous sensory information that drives this system, as well as the outputs that allow MCH to act over a wide range of homeostatic and behavioral controls, highlighting the available morphological and hodological aspects that underlie these integrative actions. Besides the well-described role of MCH in feeding behavior, a prime example of hypothalamic-mediated integration, we will also examine those functions in which the participation of MCH has not yet been extensively characterized, including sexual, maternal, and defensive behaviors. We also evaluated the available data on the distribution of MCH and its function in the context of animals in their natural environment. Finally, we briefly comment on the evidence for MCH acting as a coordinator between different modalities of motivated behaviors, highlighting the most pressing open questions that are open for investigations and that could provide us with important insights about hypothalamic-dependent homeostatic integration.

Understanding sleep-wake mechanisms and drug discovery

INTRODUCTION

Although not discernible at first glance, sleep is a highly active and regulated brain state. Although we spend practically one third of our lifetimes in this stage, its importance is often taken for granted. Sleep loss can lead to disease, error and economic loss. Our understanding of how sleep is achieved has greatly advanced in recent years, and with that, the management of sleep disorders has improved. There is still room for improvement and recently many new compounds have reached clinical trials with a few being approved for commercial use. Areas covered: In this review, the authors make the case of sleep disorders as a matter of public health. The mechanisms of sleep transition are discussed emphasizing the wake and sleep promoting interaction of different brain regions. Finally, advances in pharmacotherapy are examined in the context of chronic insomnia and narcolepsy. Expert opinion: The orexinergic system is an example of a breakthrough in sleep medicine that has catalyzed drug development. Nevertheless, sleep is a topic still with many unanswered questions. That being said, the melanin-concentrating hormone system is becoming increasingly relevant and we speculate it will be the next target of sleep medication.

Sleep and cargo reorganization: A hypothesis

Several molecules that act in the nervous system to regulate sleep and wake were first identified based on their transport effects in pigmented cells. I compiled a list of such molecules like melatonin, melanin-concentrating hormone, and pigment dispersing factor, etc. Molecules that induce pigment aggregation promote sleep whereas molecules that induce pigment dispersal promote wake. I call these Sleep and PIgment Regulating Factors SPIRFs. SPIRFs regulate organelle trafficking in both pigmentary models and neurons. I propose that cargo transport fulfills necessary sleep functions such as remodeling synapses and restoring homeostasis in the distribution of cell components. I put forth the hypothesis that sleep-promoting SPIRFs induce states of increased cargo movement towards the cell body, and propose that this function is a critical neuron maintenance task for which animals must sleep.

Neuropeptide glutamic acid-isoleucine (NEI)-induced paradoxical sleep in rats

Neuropeptideglutamic acid-isoleucine (NEI) as well as melanin concentrating hormone (MCH) is cleaved from the 165 amino acid protein, prepro-melanin concentrating hormone (prepro-MCH). Among many physiological roles of MCH, we demonstrated that intracerebroventricular (icv) injection of MCH induced increases in REM sleep episodes as well as in non REM sleep episodes. However, there are no studies on the effect of NEI on the sleep-wake cycle. As for the sites of action of MCH for induction of REM sleep, the ventrolateral periaqueductal gray (vlPAG) has been reported to be one of its site of action. Although MCH neurons contain NEI, GABA, MCH, and other neuropeptides, we do not know which transmitter(s) might induce REM sleep by acting on the vlPAG. Thus, we first examined the effect of icv injection of NEI on the sleep-wake cycle, and investigated how microinjection of either NEI, MCH, or GABA into the vlPAG affected REM sleep in rats. Icv injection of NEI (0.61μg/5μl: n=7) significantly increased the time spent in REM episodes compared to control (saline: 5μl; n=6). Microinjection of either NEI (61ng/0.2μl: n=7), MCH (100ng/0.2μl: n=6) or GABA (250mM/0.2μl: n=7) into the vlPAG significantly increased the time spent in REM episodes and the AUC. Precise hourly analysis of REM sleep also revealed that after those microinjections, NEI and MCH increased REM episodes at the latter phase, compared to GABA which increased REM episodes at the earlier phase. This result suggests that NEI and MCH may induce sustained REM sleep, while GABA may initiate REM sleep. In conclusion, our findings demonstrate that NEI, a cleaved peptide from the same precursor, prepro-MCH, as MCH, induce REM sleep at least in part through acting on the vlPAG.

Pharmaco-EEG Studies in Animals: A History-Based Introduction to Contemporary Translational Applications

Current research on the effects of pharmacological agents on human neurophysiology finds its roots in animal research, which is also reflected in contemporary animal pharmaco-electroencephalography (p-EEG) applications. The contributions, present value and translational appreciation of animal p-EEG-based applications are strongly interlinked with progress in recording and neuroscience analysis methodology. After the pioneering years in the late 19th and early 20th century, animal p-EEG research flourished in the pharmaceutical industry in the early 1980s. However, around the turn of the millennium the emergence of structurally and functionally revealing imaging techniques and the increasing application of molecular biology caused a temporary reduction in the use of EEG as a window into the brain for the prediction of drug efficacy. Today, animal p-EEG is applied again for its biomarker potential - extensive databases of p-EEG and polysomnography studies in rats and mice hold EEG signatures of a broad collection of psychoactive reference and test compounds. A multitude of functional EEG measures has been investigated, ranging from simple spectral power and sleep-wake parameters to advanced neuronal connectivity and plasticity parameters. Compared to clinical p-EEG studies, where the level of vigilance can be well controlled, changes in sleep-waking behaviour are generally a prominent confounding variable in animal p-EEG studies and need to be dealt with. Contributions of rodent pharmaco-sleep EEG research are outlined to illustrate the value and limitations of such preclinical p-EEG data for pharmacodynamic and chronopharmacological drug profiling. Contemporary applications of p-EEG and pharmaco-sleep EEG recordings in animals provide a common and relatively inexpensive window into the functional brain early in the preclinical and clinical development of psychoactive drugs in comparison to other brain imaging techniques. They provide information on the impact of drugs on arousal and sleep architecture, assessing their neuropharmacological characteristics in vivo, including central exposure and information on kinetics. In view of the clear disadvantages as well as advantages of animal p-EEG as compared to clinical p-EEG, general statements about the usefulness of EEG as a biomarker to demonstrate the translatability of p-EEG effects should be made with caution, however, because they depend on the particular EEG or sleep parameter that is being studied. The contribution of animal p-EEG studies to the translational characterisation of centrally active drugs can be furthered by adherence to guidelines for methodological standardisation, which are presently under construction by the International Pharmaco-EEG Society (IPEG).

Optogenetic activation of melanin-concentrating hormone neurons increases non-rapid eye movement and rapid eye movement sleep during the night in rats

Neurons containing melanin-concentrating hormone (MCH) are located in the hypothalamus. In mice, optogenetic activation of the MCH neurons induces both non-rapid eye movement (NREM) and rapid eye movement (REM) sleep at night, the normal wake-active period for nocturnal rodents [R. R. Konadhode et al. (2013) J. Neurosci., 33, 10257-10263]. Here we selectively activate these neurons in rats to test the validity of the sleep network hypothesis in another species. Channelrhodopsin-2 (ChR2) driven by the MCH promoter was selectively expressed by MCH neurons after injection of rAAV-MCHp-ChR2-EYFP into the hypothalamus of Long-Evans rats. An in vitro study confirmed that the optogenetic activation of MCH neurons faithfully triggered action potentials. In the second study, in Long-Evans rats, rAAV-MCH-ChR2, or the control vector, rAAV-MCH-EYFP, were delivered into the hypothalamus. Three weeks later, baseline sleep was recorded for 48 h without optogenetic stimulation (0 Hz). Subsequently, at the start of the lights-off cycle, the MCH neurons were stimulated at 5, 10, or 30 Hz (1 mW at tip; 1 min on - 4 min off) for 24 h. Sleep was recorded during the 24-h stimulation period. Optogenetic activation of MCH neurons increased both REM and NREM sleep at night, whereas during the day cycle, only REM sleep was increased. Delta power, an indicator of sleep intensity, was also increased. In control rats without ChR2, optogenetic stimulation did not increase sleep or delta power. These results lend further support to the view that sleep-active MCH neurons contribute to drive sleep in mammals.

Schizophrenia: the role of sleep and circadian rhythms in regulating dopamine and psychosis

Schizophrenia has long been associated with abnormalities in circadian rhythms and sleep. Up until now, there have been no thorough reviews of the potential mechanisms behind the myriad of circadian and sleep abnormalities observed in schizophrenia and psychosis. We present evidence of sleep playing an important role in psychosis predominantly mediated by dopaminergic pathways. A synthesis of both human and animal experimental work suggests that the interplay between sleep and dopamine is important in the generation and maintenance of psychosis. In particular, both animal and human data point to sleep disruption increasing dopamine release and sensitivity. Furthermore, elevated dopamine levels disrupt sleep and circadian rhythms. The synthesis of knowledge suggests that circadian rhythms, dopamine dysregulation, and psychosis are intricately linked. This suggests that treatment of circadian disturbance may be a useful target in improving the lives and symptoms of patients with schizophrenia.

Melanin-concentrating hormone neurons specifically promote rapid eye movement sleep in mice

Currently available evidence indicates that neurons containing melanin-concentrating hormone (MCH) in the lateral hypothalamus are critical modulators of sleep-wakefulness, but their precise role in this function is not clear. Studies employing optogenetic stimulation of MCH neurons have yielded inconsistent results, presumably due to differences in the optogenetic stimulation protocols, which do not approximate normal patterns of cell firing. In order to resolve this discrepancy, we (1) selectively activated the MCH neurons using a chemogenetic approach (Cre-dependent hM3Dq expression) and (2) selectively destroyed MCH neurons using a genetically targeted diphtheria toxin deletion method, and studied the changes in sleep-wake in mice. Our results indicate that selective activation of MCH neurons causes specific increases in rapid eye movement (REM) sleep without altering wake or non-REM (NREM) sleep. On the other hand, selective deletions of MCH neurons altered the diurnal rhythm of wake and REM sleep without altering their total amounts. These results indicate that activation of MCH neurons primarily drives REM sleep and their presence may be necessary for normal expression of diurnal variation of REM sleep and wake.

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.

MCH levels in the CSF, brain preproMCH and MCHR1 gene expression during paradoxical sleep deprivation, sleep rebound and chronic sleep restriction

Neurons that utilize melanin-concentrating hormone (MCH) as neuromodulator are located in the lateral hypothalamus and incerto-hypothalamic area. These neurons project throughout the central nervous system and play a role in sleep regulation. With the hypothesis that the MCHergic system function would be modified by the time of the day as well as by disruptions of the sleep-wake cycle, we quantified in rats the concentration of MCH in the cerebrospinal fluid (CSF), the expression of the MCH precursor (Pmch) gene in the hypothalamus, and the expression of the MCH receptor 1 (Mchr1) gene in the frontal cortex and hippocampus. These analyses were performed during paradoxical sleep deprivation (by a modified multiple platform technique), paradoxical sleep rebound and chronic sleep restriction, both at the end of the active (dark) phase (lights were turned on at Zeitgeber time zero, ZT0) and during the inactive (light) phase (ZT8). We observed that in control condition (waking and sleep ad libitum), Mchr1 gene expression was larger at ZT8 (when sleep predominates) than at ZT0, both in frontal cortex and hippocampus. In addition, compared to control, disturbances of the sleep-wake cycle produced the following effects: paradoxical sleep deprivation for 96 and 120 h reduced the expression of Mchr1 gene in frontal cortex at ZT0. Sleep rebound that followed 96 h of paradoxical sleep deprivation increased the MCH concentration in the CSF also at ZT0. Twenty-one days of sleep restriction produced a significant increment in MCH CSF levels at ZT8. Finally, sleep disruptions unveiled day/night differences in MCH CSF levels and in Pmch gene expression that were not observed in control (undisturbed) conditions. In conclusion, the time of the day and sleep disruptions produced subtle modifications in the physiology of the MCHergic system.

Sleep architecture and homeostasis in mice with partial ablation of melanin-concentrating hormone neurons

Recent reports support a key role of tuberal hypothalamic neurons secreting melanin concentrating-hormone (MCH) in the promotion of Paradoxical Sleep (PS). Controversies remain concerning their concomitant involvement in Slow-Wave Sleep (SWS). We studied the effects of their selective loss achieved by an Ataxin 3-mediated ablation strategy to decipher the contribution of MCH neurons to SWS and/or PS. Polysomnographic recordings were performed on male adult transgenic mice expressing Ataxin-3 transgene within MCH neurons (MCH(Atax)) and their wild-type littermates (MCH(WT)) bred on two genetic backgrounds (FVB/N and C57BL/6). Compared to MCH(WT) mice, MCH(Atax) mice were characterized by a significant drop in MCH mRNAs (-70%), a partial loss of MCH-immunoreactive neurons (-30%) and a marked reduction in brain density of MCH-immunoreactive fibers. Under basal condition, such MCH(Atax) mice exhibited higher PS amounts during the light period and a pronounced SWS fragmentation without any modification of SWS quantities. Moreover, SWS and PS rebounds following 4-h total sleep deprivation were quantitatively similar in MCH(Atax)vs. MCH(WT) mice. Additionally, MCH(Atax) mice were unable to consolidate SWS and increase slow-wave activity (SWA) in response to this homeostatic challenge as observed in MCH(WT) littermates. Here, we show that the partial loss of MCH neurons is sufficient to disturb the fine-tuning of sleep. Our data provided new insights into their contribution to subtle process managing SWS quality and its efficiency rather than SWS quantities, as evidenced by the deleterious impact on two powerful markers of sleep depth, i.e., SWS consolidation/fragmentation and SWA intensity under basal condition and under high sleep pressure.

A coordinated cross-disciplinary research initiative to address an increased incidence of narcolepsy following the 2009-2010 Pandemrix vaccination programme in Sweden

In response to the 2009-2010 influenza A(H1N1)pdm09 pandemic, a mass vaccination programme with the AS03-adjuvanted influenza A(H1N1) vaccine Pandemrix was initiated in Sweden. Unexpectedly, there were a number of narcolepsy cases amongst vaccinated children and adolescents reported. In this review, we summarize the results of a joint cross-disciplinary national research effort to investigate the adverse reaction signal from the spontaneous reporting system and to better understand possible causative mechanisms. A three- to fourfold increased risk of narcolepsy in vaccinated children and adolescents was verified by epidemiological studies. Of importance, no risk increase was observed for the other neurological and autoimmune diseases studied. Genetic studies confirmed the association with the allele HLA-DQB1*06:02, which is known to be related to sporadic narcolepsy. Furthermore, a number of studies using cellular and molecular experimental models investigated possible links between influenza vaccination and narcolepsy. Serum analysis, using a peptide microarray platform, showed that individuals who received Pandemrix exhibited a different epitope reactivity pattern to neuraminidase and haemagglutinin, as compared to individuals who were infected with H1N1. Patients with narcolepsy were also found to have increased levels of interferon-gamma production in response to streptococcus-associated antigens. The chain of patient-related events and the study results emerging over time were subjected to intense nationwide media attention. The importance of transparent communication and collaboration with patient representatives to maintain public trust in vaccination programmes is also discussed in the review. Organizational challenges due to this unexpected event delayed the initiation of some of the research projects, still the main objectives of this joint, cross-disciplinary research effort were reached, and important insights were acquired for future, similar situations in which a fast and effective task force may be required to evaluate vaccination-related adverse events.

To ingest or rest? Specialized roles of lateral hypothalamic area neurons in coordinating energy balance

Survival depends on an organism’s ability to sense nutrient status and accordingly regulate intake and energy expenditure behaviors. Uncoupling of energy sensing and behavior, however, underlies energy balance disorders such as anorexia or obesity. The hypothalamus regulates energy balance, and in particular the lateral hypothalamic area (LHA) is poised to coordinate peripheral cues of energy status and behaviors that impact weight, such as drinking, locomotor behavior, arousal/sleep and autonomic output. There are several populations of LHA neurons that are defined by their neuropeptide content and contribute to energy balance. LHA neurons that express the neuropeptides melanin-concentrating hormone (MCH) or orexins/hypocretins (OX) are best characterized and these neurons play important roles in regulating ingestion, arousal, locomotor behavior and autonomic function via distinct neuronal circuits. Recently, another population of LHA neurons containing the neuropeptide Neurotensin (Nts) has been implicated in coordinating anorectic stimuli and behavior to regulate hydration and energy balance. Understanding the specific roles of MCH, OX and Nts neurons in harmonizing energy sensing and behavior thus has the potential to inform pharmacological strategies to modify behaviors and treat energy balance disorders.

Narcolepsy patients have antibodies that stain distinct cell populations in rat brain and influence sleep patterns

Narcolepsy is a chronic sleep disorder, likely with an autoimmune component. During 2009 and 2010, a link between A(H1N1)pdm09 Pandemrix vaccination and onset of narcolepsy was suggested in Scandinavia. In this study, we searched for autoantibodies related to narcolepsy using a neuroanatomical array: rat brain sections were processed for immunohistochemistry/double labeling using patient sera/cerebrospinal fluid as primary antibodies. Sera from 89 narcoleptic patients, 52 patients with other sleep-related disorders (OSRDs), and 137 healthy controls were examined. Three distinct patterns of immunoreactivity were of particular interest: pattern A, hypothalamic melanin-concentrating hormone and proopiomelanocortin but not hypocretin/orexin neurons; pattern B, GABAergic cortical interneurons; and pattern C, mainly globus pallidus neurons. Altogether, 24 of 89 (27%) narcoleptics exhibited pattern A or B or C. None of the patterns were exclusive for narcolepsy but were also detected in the OSRD group at significantly lower numbers. Also, some healthy controls exhibited these patterns. The antigen of pattern A autoantibodies was identified as the common C-terminal epitope of neuropeptide glutamic acid-isoleucine/α-melanocyte-stimulating hormone (NEI/αMSH) peptides. Passive transfer experiments on rat showed significant effects of pattern A human IgGs on rapid eye movement and slow-wave sleep time parameters in the inactive phase and EEG θ-power in the active phase. We suggest that NEI/αMSH autoantibodies may interfere with the fine regulation of sleep, contributing to the complex pathogenesis of narcolepsy and OSRDs. Also, patterns B and C are potentially interesting, because recent data suggest a relevance of those brain regions/neuron populations in the regulation of sleep/arousal.

Optogenetic manipulation of activity and temporally controlled cell-specific ablation reveal a role for MCH neurons in sleep/wake regulation

Melanin-concentrating hormone (MCH) is a neuropeptide produced in neurons sparsely distributed in the lateral hypothalamic area. Recent studies have reported that MCH neurons are active during rapid eye movement (REM) sleep, but their physiological role in the regulation of sleep/wakefulness is not fully understood. To determine the physiological role of MCH neurons, newly developed transgenic mouse strains that enable manipulation of the activity and fate of MCH neurons in vivo were generated using the recently developed knockin-mediated enhanced gene expression by improved tetracycline-controlled gene induction system. The activity of these cells was controlled by optogenetics by expressing channelrhodopsin2 (E123T/T159C) or archaerhodopsin-T in MCH neurons. Acute optogenetic activation of MCH neurons at 10 Hz induced transitions from non-REM (NREM) to REM sleep and increased REM sleep time in conjunction with decreased NREM sleep. Activation of MCH neurons while mice were in NREM sleep induced REM sleep, but activation during wakefulness was ineffective. Acute optogenetic silencing of MCH neurons using archaerhodopsin-T had no effect on any vigilance states. Temporally controlled ablation of MCH neurons by cell-specific expression of diphtheria toxin A increased wakefulness and decreased NREM sleep duration without affecting REM sleep. Together, these results indicate that acute activation of MCH neurons is sufficient, but not necessary, to trigger the transition from NREM to REM sleep and that MCH neurons also play a role in the initiation and maintenance of NREM sleep.

Why are seizures rare in rapid eye movement sleep? Review of the frequency of seizures in different sleep stages

Since the formal characterization of sleep stages, there have been reports that seizures may preferentially occur in certain phases of sleep. Through ascending cholinergic connections from the brainstem, rapid eye movement (REM) sleep is physiologically characterized by low voltage fast activity on the electroencephalogram, REMs, and muscle atonia. Multiple independent studies confirm that, in REM sleep, there is a strikingly low proportion of seizures (~1% or less). We review a total of 42 distinct conventional and intracranial studies in the literature which comprised a net of 1458 patients. Indexed to duration, we found that REM sleep was the most protective stage of sleep against focal seizures, generalized seizures, focal interictal discharges, and two particular epilepsy syndromes. REM sleep had an additional protective effect compared to wakefulness with an average 7.83 times fewer focal seizures, 3.25 times fewer generalized seizures, and 1.11 times fewer focal interictal discharges. In further studies REM sleep has also demonstrated utility in localizing epileptogenic foci with potential translation into postsurgical seizure freedom. Based on emerging connectivity data in sleep, we hypothesize that the influence of REM sleep on seizures is due to a desynchronized EEG pattern which reflects important connectivity differences unique to this sleep stage.

Nesfatin-1/NUCB2 as a potential new element of sleep regulation in rats

Study Objectives

Millions suffer from sleep disorders that often accompany severe illnesses such as major depression; a leading psychiatric disorder characterized by appetite and rapid eye movement sleep (REMS) abnormalities. Melanin-concentrating hormone (MCH) and nesfatin-1/NUCB2 (nesfatin) are strongly co - expressed in the hypothalamus and are involved both in food intake regulation and depression. Since MCH was recognized earlier as a hypnogenic factor, we analyzed the potential role of nesfatin on vigilance.

Design

We subjected rats to a 72 h-long REMS deprivation using the classic flower pot method, followed by a 3 h-long ‘rebound sleep’. Nesfatin mRNA and protein expressions as well as neuronal activity (Fos) were measured by quantitative in situ hybridization technique, ELISA and immunohistochemistry, respectively, in ‘deprived’ and ‘rebound’ groups, relative to controls sacrificed at the same time. We also analyzed electroencephalogram of rats treated by intracerebroventricularly administered nesfatin-1, or saline.

Results

REMS deprivation downregulated the expression of nesfatin (mRNA and protein), however, enhanced REMS during ‘rebound’ reversed this to control levels. Additionally, increased transcriptional activity (Fos) was demonstrated in nesfatin neurons during ‘rebound’. Centrally administered nesfatin-1 at light on reduced REMS and intermediate stage of sleep, while increased passive wake for several hours and also caused a short-term increase in light slow wave sleep.

Conclusions

The data designate nesfatin as a potential new factor in sleep regulation, which fact can also be relevant in the better understanding of the role of nesfatin in the pathomechanism of depression.

Microinjection of melanin concentrating hormone into the lateral preoptic area promotes non-REM sleep in the rat

The ventrolateral preoptic area (VLPO) has been recognized as one of the key structures responsible for the generation of non-REM (NREM) sleep. The melanin-concentrating hormone (MCH)-containing neurons, which are located in the lateral hypothalamus and incerto-hypothalamic area, project widely throughout the central nervous system and include projections to the VLPO. The MCH has been associated with the central regulation of feeding and energy homeostasis. In addition, recent findings strongly suggest that the MCHergic system promotes sleep. The aim of the present study was to determine if MCH generates sleep by regulating VLPO neuronal activity. To this purpose, we characterized the effect of unilateral and bilateral microinjections of MCH into the VLPO on sleep and wakefulness in the rat. Unilateral administration of MCH into the VLPO and adjacent dorsal preoptic area did not modify sleep. On the contrary, bilateral microinjections of MCH (100 ng) into these areas significantly increased light sleep (LS, 39.2±4.8 vs. 21.6±2.5 min, P<0.05) and total NREM sleep (142.4±23.2 vs. 86.5±10.5 min, P<0.05) compared to control (saline) microinjections. No effect was observed on REM sleep. We conclude that MCH administration into the VLPO and adjacent dorsal lateral preoptic area promotes the generation of NREM sleep.

Tuberal hypothalamic neurons secreting the satiety molecule Nesfatin-1 are critically involved in paradoxical (REM) sleep homeostasis

The recently discovered Nesfatin-1 plays a role in appetite regulation as a satiety factor through hypothalamic leptin-independent mechanisms. Nesfatin-1 is co-expressed with Melanin-Concentrating Hormone (MCH) in neurons from the tuberal hypothalamic area (THA) which are recruited during sleep states, especially paradoxical sleep (PS). To help decipher the contribution of this contingent of THA neurons to sleep regulatory mechanisms, we thus investigated in rats whether the co-factor Nesfatin-1 is also endowed with sleep-modulating properties. Here, we found that the disruption of the brain Nesfatin-1 signaling achieved by icv administration of Nesfatin-1 antiserum or antisense against the nucleobindin2 (NUCB2) prohormone suppressed PS with little, if any alteration of slow wave sleep (SWS). Further, the infusion of Nesfatin-1 antiserum after a selective PS deprivation, designed for elevating PS needs, severely prevented the ensuing expected PS recovery. Strengthening these pharmacological data, we finally demonstrated by using c-Fos as an index of neuronal activation that the recruitment of Nesfatin-1-immunoreactive neurons within THA is positively correlated to PS but not to SWS amounts experienced by rats prior to sacrifice. In conclusion, this work supports a functional contribution of the Nesfatin-1 signaling, operated by THA neurons, to PS regulatory mechanisms. We propose that these neurons, likely releasing MCH as a synergistic factor, constitute an appropriate lever by which the hypothalamus may integrate endogenous signals to adapt the ultradian rhythm and maintenance of PS in a manner dictated by homeostatic needs. This could be done through the inhibition of downstream targets comprised primarily of the local hypothalamic wake-active orexin- and histamine-containing neurons.

Immunohistochemical evidence for synaptic release of GABA from melanin-concentrating hormone containing varicosities in the locus coeruleus

Melanin-concentrating hormone (MCH) is synthesized by neurons located in the hypothalamus and projecting to widespread regions of the brain, including the locus coeruleus (LC), through which MCH could modulate sleep-wake states. Yet MCH does not appear to exert direct postsynaptic effects on target neurons, including the noradrenergic LC neurons. Previous studies using in situ hybridization showed that MCH neurons synthesize glutamic acid decarboxylase (GAD) and could thus utilize GABA as a neurotransmitter. To determine whether MCH varicosities can release GABA, we examined by fluorescent microscopy in the LC, whether their terminals also contain the vesicular transporter for GABA (VGAT). In dual-immunostained sections, we found that approximately 6% of MCH varicosities was immunopositive for VGAT and a similar proportion for synaptophysin, the presynaptic marker for small synaptic vesicles, whereas <1% was positive for the vesicular glutamate transporter (VGluT2). Moreover, of the MCH varicosities, ∼5% abutted puncta that were immunostained for gephyrin, the postsynaptic marker for GABAergic synapses. In triple-immunostained sections viewed with confocal laser scanning microscopy, we established that MCH varicosities that also contained VGAT or abutted upon gephyrin puncta contacted the tyrosine hydroxylase-immunostained neurons of the LC. Our results suggest that although MCH neurons can influence noradrenergic LC neurons through paracrine release and indirect effects of their peptide, they can also do so through synaptic release and direct postsynaptic effects of GABA and thus serve to inhibit the LC neurons during sleep, when they are silent, and the MCH neurons discharge.

Control of sleep and wakefulness

This review summarizes the brain mechanisms controlling sleep and wakefulness. Wakefulness promoting systems cause low-voltage, fast activity in the electroencephalogram (EEG). Multiple interacting neurotransmitter systems in the brain stem, hypothalamus, and basal forebrain converge onto common effector systems in the thalamus and cortex. Sleep results from the inhibition of wake-promoting systems by homeostatic sleep factors such as adenosine and nitric oxide and GABAergic neurons in the preoptic area of the hypothalamus, resulting in large-amplitude, slow EEG oscillations. Local, activity-dependent factors modulate the amplitude and frequency of cortical slow oscillations. Non-rapid-eye-movement (NREM) sleep results in conservation of brain energy and facilitates memory consolidation through the modulation of synaptic weights. Rapid-eye-movement (REM) sleep results from the interaction of brain stem cholinergic, aminergic, and GABAergic neurons which control the activity of glutamatergic reticular formation neurons leading to REM sleep phenomena such as muscle atonia, REMs, dreaming, and cortical activation. Strong activation of limbic regions during REM sleep suggests a role in regulation of emotion. Genetic studies suggest that brain mechanisms controlling waking and NREM sleep are strongly conserved throughout evolution, underscoring their enormous importance for brain function. Sleep disruption interferes with the normal restorative functions of NREM and REM sleep, resulting in disruptions of breathing and cardiovascular function, changes in emotional reactivity, and cognitive impairments in attention, memory, and decision making.

Microinjection of the melanin-concentrating hormone into the lateral basal forebrain increases REM sleep and reduces wakefulness in the rat

AIMS

To examine the effects of bilateral microinjection of melanin-concentrating hormone (MCH) 50 and 100 ng into the horizontal limb of the diagonal band of Broca (HDB) on sleep variables during the light phase of the light-dark cycle of the rat.

MAIN METHODS

Male Wistar rats were implanted for chronic sleep recordings. In addition, a guide cannula was implanted above the right and left HDB. Following the microinjection of MCH or control solution the electroencephalogram and the electromyogram were recorded for 6 h. Data was collected and classified as either wakefulness (W), light sleep, slow wave sleep (SWS) or REM sleep (REMS). Latencies for SWS and REMS, as well as the number of REM periods and the mean duration of REM episodes were also determined.

KEY FINDINGS

MCH 50 and 100 ng significantly decreased W during the first 2-h of recording. Moreover, MCH 100 ng significantly reduced REMS latency and increased REMS time during the first 2-h block of the recording, due to an increase in the number of REM periods.

SIGNIFICANCE

Our findings tend to suggest that the basal forebrain participates in the effects of MCH on W and REMS through the deactivation of cholinergic, glutamatergic and γ-aminobutyric acid (GABA)-ergic cells.

Thyrotropin-releasing hormone (TRH) inhibits melanin-concentrating hormone neurons: implications for TRH-mediated anorexic and arousal actions

Thyrotropin-releasing hormone (TRH) increases activity and decreases food intake, body weight, and sleep, in part through hypothalamic actions. The mechanism of this action is unknown. Melanin-concentrating hormone (MCH) and hypocretin/orexin neurons in the lateral hypothalamus (LH) together with neuropeptide Y (NPY) and proopiomelanocortin (POMC) neurons in the arcuate nucleus play central roles in energy homeostasis. Here, we provide electrophysiological evidence from GFP-reporter transgenic mouse brain slices that shows TRH modulates the activity of MCH neurons. Using whole-cell current-clamp recording, we unexpectedly found that TRH and its agonist, montrelin, dose-dependently inhibited MCH neurons. Consistent with previous reports, TRH excited hypocretin/orexin neurons. No effect was observed on arcuate nucleus POMC or NPY neurons. The TRH inhibition of MCH neurons was eliminated by bicuculline and tetrodotoxin, suggesting that the effect was mediated indirectly through synaptic mechanisms. TRH increased spontaneous IPSC frequency without affecting amplitude and had no effect on miniature IPSCs or EPSCs. Immunocytochemistry revealed little interaction between TRH axons and MCH neurons, but showed TRH axons terminating on or near GABA neurons. TRH inhibition of MCH neurons was attenuated by Na(+)-Ca(2+) exchanger (NCX) inhibitors, TRPC channel blockers and the phospholipase C inhibitor U-73122. TRH excited LH GABA neurons, and this was also reduced by NCX inhibitors. Finally, TRH attenuated the excitation of MCH neurons by hypocretin. Together, our data suggest that TRH inhibits MCH neurons by increasing synaptic inhibition from local GABA neurons. Inhibition of MCH neurons may contribute to the TRH-mediated reduction in food intake and sleep.

Sleep neurobiology from a clinical perspective

Many neurochemical systems interact to generate wakefulness and sleep. Wakefulness is promoted by neurons in the pons, midbrain, and posterior hypothalamus that produce acetylcholine, norepinephrine, dopamine, serotonin, histamine, and orexin/hypocretin. Most of these ascending arousal systems diffusely activate the cortex and other forebrain targets. NREM sleep is mainly driven by neurons in the preoptic area that inhibit the ascending arousal systems, while REM sleep is regulated primarily by neurons in the pons, with additional influence arising in the hypothalamus. Mutual inhibition between these wake- and sleep-regulating regions likely helps generate full wakefulness and sleep with rapid transitions between states. This up-to-date review of these systems should allow clinicians and researchers to better understand the effects of drugs, lesions, and neurologic disease on sleep and wakefulness.