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

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

Is paradoxical sleep setting up innate and acquired complex sensorimotor and adaptive behaviours?: A proposed function based on literature review.

We summarize here the progress in identifying the neuronal network as well as the function of paradoxical sleep and the gaps of knowledge that should be filled in priority. The core system generating paradoxical sleep localized in the brainstem is now well identified, and the next step is to clarify the role of the forebrain in particular that of the hypothalamus including the melanin-concentrating hormone neurons and of the basolateral amygdala. We discuss these two options, and also the discovery that cortical activation during paradoxical sleep is restricted to a few limbic cortices activated by the lateral supramammillary nucleus and the claustrum. Such activation nicely supports the findings recently obtained showing that neuronal reactivation occurs during paradoxical sleep in these structures, and induces both memory consolidation of important memory and forgetting of less relevant ones. The question that still remains to be answered is whether paradoxical sleep is playing more crucial roles in processing emotional and procedural than other types of memories. One attractive hypothesis is that paradoxical sleep is responsible for erasing negative emotional memories, and that this function is not properly functioning in depressed patients. On the other hand, the presence of a muscle atonia during paradoxical sleep is in favour of a role in procedural memory as new types of motor behaviours can be tried without harm during the state. In a way, it also fits with the proposed role of paradoxical sleep in setting up the sensorimotor system during development.

Rapid eye movement sleep behaviour disorder: Past, present, and future.

This manuscript presents an overview of REM sleep behaviour disorder (RBD) with a special focus on European contributions. After an introduction examining the history of the disorder, we address the pathophysiological and clinical aspects, as well as the diagnostic issues. Further, implications of RBD diagnosis and biomarkers are discussed. Contributions of European researchers to this field are highlighted.

The European Sleep Research Society - past, present and future.

It is 50 years ago, in 1972, that the founding conference of the European Sleep Research Society (ESRS) was organised in Basel. Since then the Society has had 13 presidents and a multitude of board members and has organised, among other things, another 24 congresses. At this 50th anniversary, as the 26th ESRS congress is approaching, we have summarised the history of the ESRS. In this review, we provide a background to show why the foundation of a European society was a logical step, and show how, in the course of the past 50 years, the Society changed and grew. We give special attention to some developments that occurred over the years and discuss where the ESRS stands now, and how we foresee its future.

Granule cells in the infrapyramidal blade of the dentate gyrus are activated during paradoxical (REM) sleep hypersomnia but not during wakefulness: a study using TRAP mice.

STUDY OBJECTIVES: Determine whether in the hippocampus and the supramammillary nucleus (SuM) the same neurons are reactivated when mice are exposed 1 week apart to two periods of wakefulness (W-W), paradoxical sleep rebound (PSR-PSR) or a period of W followed by a period of PSR (W-PSR). METHODS: We combined the innovative TRAP2 mice method in which neurons expressing cFos permanently express tdTomato after tamoxifen injection with cFos immunohistochemistry. RESULTS: We found out that a large number of tdTomato+ and cFos+ cells are localized in the dentate gyrus (DG) after PSR and W while CA1 and CA3 contained both types of neurons only after W. The number of cFos+ cells in the infrapyramidal but not the suprapyramidal blade of the DG was positively correlated with the amount of PS. In addition, we did not find double-labeled cells in the DG whatever the group of mice. In contrast, a high percentage of CA1 neurons were double-labeled in W-W mice. Finally, in the supramammillary nucleus, a large number of cells were double-labeled in W-W, PSR-PSR but not in W-PSR mice. CONCLUSIONS: Altogether, our results are the first to show that different neurons are activated during W and PS in the supramammillary nucleus and the hippocampus. Further, we showed for the first time that granule cells of the infrapyramidal blade of the DG are activated during PS but not during W. Further experiments are now needed to determine whether these granule cells belong to memory engrams inducing memory reactivation during PS.

Hippocampus-retrosplenial cortex interaction is increased during phasic REM and contributes to memory consolidation.

Hippocampal (HPC) theta oscillation during post-training rapid eye movement (REM) sleep supports spatial learning. Theta also modulates neuronal and oscillatory activity in the retrosplenial cortex (RSC) during REM sleep. To investigate the relevance of theta-driven interaction between these two regions to memory consolidation, we computed the Granger causality within theta range on electrophysiological data recorded in freely behaving rats during REM sleep, both before and after contextual fear conditioning. We found a training-induced modulation of causality between HPC and RSC that was correlated with memory retrieval 24 h later. Retrieval was proportional to the change in the relative influence RSC exerted upon HPC theta oscillation. Importantly, causality peaked during theta acceleration, in synchrony with phasic REM sleep. Altogether, these results support a role for phasic REM sleep in hippocampo-cortical memory consolidation and suggest that causality modulation between RSC and HPC during REM sleep plays a functional role in that phenomenon.

Is REM sleep a paradoxical state?: Different neurons are activated in the cingulate cortices and the claustrum during wakefulness and paradoxical sleep hypersomnia.

Michel Jouvet proposed in 1959 that REM sleep is a paradoxical state since it was characterized by the association of a cortical activation similar to wakefulness (W) with muscle atonia. Recently, we showed using cFos as a marker of activity that cortical activation during paradoxical sleep (PS) was limited to a few limbic cortical structures in contrast to W during which all cortices were strongly activated. However, we were not able to demonstrate whether the same neurons are activated during PS and W and to rule out that the activation observed was not linked with stress induced by the flowerpot method of PS deprivation. In the present study, we answered to these two questions by combining tdTomato and cFos immunostaining in the innovative TRAP2 transgenic mice exposed one week apart to two periods of W (W-W mice), PS rebound (PSR-PSR) or a period of W followed by a period of PSR (W-PSR mice). Using such method, we showed that different neurons are activated during W and PSR in the anterior cingulate (ACA) and rostral and caudal retrosplenial (rRSP and cRSP) cortices as well as the claustrum (CLA) previously shown to contain a large number of activated neurons after PSR. Further, the distribution of the neurons during PSR in the rRSP and cRSP was limited to the superficial layers while it was widespread across all layers during W. Our results clearly show at the cellular level that PS and W are two completely different states in term of neocortical activation.

GABA-glutamate supramammillary neurons control theta and gamma oscillations in the dentate gyrus during paradoxical (REM) sleep.

Several studies suggest that neurons from the lateral region of the SuM (SuML) innervating the dorsal dentate gyrus (DG) display a dual GABAergic and glutamatergic transmission and are specifically activated during paradoxical (REM) sleep (PS). The objective of the present study is to characterize the anatomical, neurochemical and electrophysiological properties of the SuML-DG projection neurons and to determine how they control DG oscillations and neuronal activation during PS and other vigilance states. For this purpose, we combine structural connectivity techniques using neurotropic viral vectors (rabies virus, AAV), neurochemical anatomy (immunohistochemistry, in situ hybridization) and imaging (light, electron and confocal microscopy) with in vitro (patch clamp) and in vivo (LFP, EEG) optogenetic and electrophysiological recordings performed in transgenic VGLUT2-cre male mice. At the cellular level, we show that the SuML-DG neurons co-release GABA and glutamate on dentate granule cells and increase the activity of a subset of DG granule cells. At the network level, we show that activation of the SuML-DG pathway increases theta power and frequency during PS as well as gamma power during PS and waking in the DG. At the behavioral level, we show that the activation of this pathway does not change animal behavior during PS, induces awakening during slow wave sleep and increases motor activity during waking. These results suggest that the SuML-DG pathway is capable of supporting the increase of theta and gamma power in the DG observed during PS and plays an important modulatory role of DG network activity during this state.

Targeted recombination in active populations as a new mouse genetic model to study sleep-active neuronal populations: Demonstration that Lhx6+ neurons in the ventral zona incerta are activated during paradoxical sleep hypersomnia.

The cFos immunostaining allowed the identification of multiple populations of neurons involved in the generation of paradoxical sleep. We adopted the transgenic (targeted recombination in active populations) mouse model, which following injection of tamoxifen, allows expression of Cre-dependent reporter constructs (i.e., mCherry) in neurons expressing cFos during waking or paradoxical sleep hypersomnia following automatic paradoxical sleep deprivation. Three groups of mice were subjected to two periods of waking, one period of waking and one of paradoxical sleep hypersomnia, or two periods of paradoxical sleep hypersomnia. A high percentage of double-labelled neurons was observed in the lateral hypothalamic area and zona incerta of two periods of waking and two periods of paradoxical sleep hypersomnia in mice, but not in those of one period of waking and one of paradoxical sleep hypersomnia in animals. Melanin-concentrating hormone neurons in the lateral hypothalamic area and Lhx6+ cells in the zona incerta constituted 5.7 ± 1.5% and 8.8 ± 2.3% of all mCherry+ cells and 20.6 ± 4.8% and 24.6 ± 5.9% of all cFos+ neurons in two periods of paradoxical sleep hypersomnia in animals. In addition, melanin-concentrating hormone cells as well as Lhx6+ neurons rarely expressed mCherry (or cFos) in the waking condition, in contrast to orexin neurons, which constituted approximately 30% of mCherry+ and cFos+ neurons. Our results validate the TRAP methodology and open the way to use it for identifying the neurons activated during waking and paradoxical sleep hypersomnia. Furthermore, they indicate for the first time that Lhx6+ neurons in the zona incerta, like melanin-concentrating hormone cells in the lateral hypothalamic area, are activated during paradoxical sleep hypersomnia but not during waking. These results indicate that Lhx6+ neurons might play a role in the control of paradoxical sleep, like the melanin-concentrating hormone cells.

Insights into paradoxical (REM) sleep homeostatic regulation in mice using an innovative automated sleep deprivation method.

Identifying the precise neuronal networks activated during paradoxical sleep (PS, also called REM sleep) has been a challenge since its discovery. Similarly, our understanding of the homeostatic mechanisms regulating PS, whether through external modulation by circadian and ultradian drives or via intrinsic homeostatic regulation, is still limited, largely due to interfering factors rendering the investigation difficult. Indeed, none of the studies published so far were able to manipulate PS without significantly altering slow-wave sleep and/or stress level, thus introducing a potential bias in the analyses. With the aim of achieving a better understanding of PS homeostasis, we developed a new method based on automated scoring of vigilance states-using electroencephalogram and electromyogram features-and which involves closed-loop PS deprivation through the induction of cage floor movements when PS is detected. Vigilance states were analyzed during 6 and 48 h of PS deprivation as well as their following recovery periods. Using this new automated methodology, we were able to deprive mice of PS with high efficiency and specificity, for short or longer periods of time, observing no sign of stress (as evaluated by plasma corticosterone level and sleep latency) and requiring no human intervention or environmental changes. We show here that PS can be homeostatically modulated and regulated while no significant changes are induced on slow-wave sleep and wakefulness, with a PS rebound duration depending on the amount of prior PS deficit. We also show that PS interval duration is not correlated with prior PS episode duration in the context of recovery from PS deprivation.

[Michel Jouvet, from the discovery of paradoxical sleep and muscle atonia to the role of neuropeptides]. / Michel Jouvet, de la découverte du sommeil paradoxal et de l'atonie musculaire au rôle des neuropeptides.

This article focuses on the contributions made by Michel Jouvet about the neurons responsible for generating the muscle atonia of paradoxical sleep (REM sleep). He was the first to describe the neurons responsible for muscle atonia during paradoxical sleep using "pontine" cats (in which the forebrain has been removed down to the pons) and localized pontine lesions. Also discussed is the research going on in the 1980s, when Michel Jouvet was hunting for the hypnogenic factor. At that time, he thought that it was secreted by the hypophysis; but this factor finally turned out to be controlled by the hypocretin/orexin and melanin concentrating hormone neurones located in the lateral hypothalamus. Several unforgettable moments with Michel Jouvet are described which occurred between 1983 and his last moments with us.

TITLE: Michel Jouvet, de la découverte du sommeil paradoxal et de l'atonie musculaire au rôle des neuropeptides. ABSTRACT: Cet article porte sur les contributions que Michel Jouvet a apportées à la connaissance des systèmes responsables de l'atonie musculaire du sommeil paradoxal. Michel Jouvet a été le premier à décrire les structures du tronc cérébral responsables de l'atonie musculaire pendant le sommeil paradoxal à l'aide de chats dits « pontiques ¼ (dont le cerveau, après ablation, est réduit à sa partie postérieure à partir du pont de Varole) ou porteurs de lésions localisées au niveau du pont. Les recherches en cours dans les années 1980, alors que Michel Jouvet était à la recherche du facteur hypnogénique, sont également abordées. À cette époque, Jouvet pensait que ce facteur était sécrété par l'hypophyse mais il s'est finalement avéré que deux types de populations de neurones antagonistes, les neurones à hypocrétine/orexine et ceux à hormone de mélanoconcentration situés dans l'hypothalamus latéral, étaient impliqués. Plusieurs moments inoubliables avec Michel Jouvet sont décrits, qui se sont déroulés entre 1983 et ses derniers moments.

Sleep-wake physiology.

This chapter presents hypotheses on the mechanisms responsible for the succession of the three vigilance states, namely waking, nonrapid eye movement (non-REM) (slow-wave sleep-SWS), and REM sleep (paradoxical sleep-PS). It can be proposed that waking is induced by the activity of multiple waking systems, including the serotonergic, noradrenergic, cholinergic, and hypocretin systems. At the onset of sleep, the SWS-active neurons are 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. However, additional GABAergic systems have been described, localized in the parafacial, accumbens, and reticular thalamic nuclei, and these are also presented. In addition, the chapter discusses the fact 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.

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.

ONEIROS, a new miniature standalone device for recording sleep electrophysiology, physiology, temperatures and behavior in the lab and field.

BACKGROUND: Sleep is an inactive state of reduced environmental awareness shared by all animals. When compared to wakefulness, sleep behavior is associated with changes in physiology and brain activity. The nature of these changes varies considerably across species, and therefore is a rich resource for gaining insight into the evolution and functions of sleep. A major obstacle to capitalizing on this resource is the lack of a small device capable of recording multiple biological parameters for extended periods of time both in the laboratory and the field. NEW METHOD: ONEIROS is a new tool designed for conducting sleep research on small, freely moving animals. The miniature, standalone system is capable of recording up to 26 electrophysiological signals (electroencephalogram, electromyogram, electrooculogram, electrocardiogram), metabolic (3 temperature channels) and behavior via an accelerometer for several days. In addition, the device is equipped with a vibrating motor which can be used to assess arousal thresholds and to disrupt sleep. The system is available in telemetric or data-logger configuration useable in the field. RESULTS: To demonstrate the efficacy of this tool, we simultaneously recorded for the first time, electroencephalogram, hippocampal local field potential, electromyogram, electrooculogram, brain, body and ambient temperature, and 3D accelerometry. We also deprived rats of paradoxical sleep by triggering the vibrating motor after online recognition of the state. Finally, by successfully recording a pigeon in an 8 m3 aviary in a social context with the device in the logger configuration, we demonstrate the feasibility of using the device in the field.

A Particular Medullary-Spinal Inhibitory Pathway is Recruited for the Expression of Muscle Atonia During REM Sleep.

Muscle atonia is a major pathognomonic sign of paradoxical sleep (PS; coined REM Sleep), during which dreams mainly occur. In the 1980s, an idiopathic syndrome called REM sleep behavior disorder (RBD) was described in patients endowed with loss of PS paralysis concomitant to abnormal movements, suggesting a dysfunction of PS networks. Another major clinical RBD feature is its prevalent phenoconversion into synucleinopathies as Parkinson's disease in a delay of 10-15 years after diagnosis. Thus, we undertook experiments in rats to disentangle brainstem networks involved in PS, including atonia. We first identified a contingent of pontine glutamate neurons recruited during PS with inputs to the ventromedial medulla (vmM) where they contact γ-aminobutyric acid (GABA)/glycine inhibitory neurons also activated during PS. Here, we further show that these vmM inhibitory neurons send efferents to somatic spinal motoneurons until lumbar levels. As reported for the pontine generator, the genetic inactivation of the vmM inhibitory neurons abolishes atonia during PS without effects on waking locomotion and is sufficient to recapitulate major RBD symptoms. These original data suggest that RBD may reflect a severe dysfunction and/or degeneration linked to a developing synucleinopathic attack targeting specifically neurons that generate PS-specific atonia.

Partial homologies between sleep states in lizards, mammals, and birds suggest a complex evolution of sleep states in amniotes.

It is crucial to determine whether rapid eye movement (REM) sleep and slow-wave sleep (SWS) (or non-REM sleep), identified in most mammals and birds, also exist in lizards, as they share a common ancestor with these groups. Recently, a study in the bearded dragon (P. vitticeps) reported states analogous to REM and SWS alternating in a surprisingly regular 80-s period, suggesting a common origin of the two sleep states across amniotes. We first confirmed these results in the bearded dragon with deep brain recordings and electro-oculogram (EOG) recordings. Then, to confirm a common origin and more finely characterize sleep in lizards, we developed a multiparametric approach in the tegu lizard, a species never recorded to date. We recorded EOG, electromyogram (EMG), heart rate, and local field potentials (LFPs) and included data on arousal thresholds, sleep deprivation, and pharmacological treatments with fluoxetine, a serotonin reuptake blocker that suppresses REM sleep in mammals. As in the bearded dragon, we demonstrate the existence of two sleep states in tegu lizards. However, no clear periodicity is apparent. The first sleep state (S1 sleep) showed high-amplitude isolated sharp waves, and the second sleep state (S2 sleep) displayed 15-Hz oscillations, isolated ocular movements, and a decrease in heart rate variability and muscle tone compared to S1. Fluoxetine treatment induced a significant decrease in S2 quantities and in the number of sharp waves in S1. Because S2 sleep is characterized by the presence of ocular movements and is inhibited by a serotonin reuptake inhibitor, as is REM sleep in birds and mammals, it might be analogous to this state. However, S2 displays a type of oscillation never previously reported and does not display a desynchronized electroencephalogram (EEG) as is observed in the bearded dragons, mammals, and birds. This suggests that the phenotype of sleep states and possibly their role can differ even between closely related species. Finally, our results suggest a common origin of two sleep states in amniotes. Yet, they also highlight a diversity of sleep phenotypes across lizards, demonstrating that the evolution of sleep states is more complex than previously thought.

REM sleep behaviour disorder.

Rapid eye movement (REM) sleep behaviour disorder (RBD) is a parasomnia that is characterized by loss of muscle atonia during REM sleep (known as REM sleep without atonia, or RSWA) and abnormal behaviours occurring during REM sleep, often as dream enactments that can cause injury. RBD is categorized as either idiopathic RBD or symptomatic (also known as secondary) RBD; the latter is associated with antidepressant use or with neurological diseases, especially α-synucleinopathies (such as Parkinson disease, dementia with Lewy bodies and multiple system atrophy) but also narcolepsy type 1. A clinical history of dream enactment or complex motor behaviours together with the presence of muscle activity during REM sleep confirmed by video polysomnography are mandatory for a definite RBD diagnosis. Management involves clonazepam and/or melatonin and counselling and aims to suppress unpleasant dreams and behaviours and improve bedpartner quality of life. RSWA and RBD are now recognized as manifestations of an α-synucleinopathy; most older adults with idiopathic RBD will eventually develop an overt neurodegenerative syndrome. In the future, studies will likely evaluate neuroprotective therapies in patients with idiopathic RBD to prevent or delay α-synucleinopathy-related motor and cognitive decline.

Jouvet's animal model of RBD, clinical RBD, and their relationships to REM sleep mechanisms.

This article focuses on the contributions made by Michel Jouvet concerning the systems responsible for the muscle atonia of paradoxical sleep (REM sleep). He was the first to describe the brainstem system mechanisms responsible for muscle atonia during paradoxical sleep using pontine cats and localized pontine lesions. Also discussed is the research going on in the eighties, when Michel Jouvet was hunting for the hypnogenetic factor. At that time, he thought that it was secreted by the hypophysis; but it finally turned out to be controlled by the hypocretin/orexin and melanin concentrating hormone neurones located in the lateral hypothalamus. Several unforgettable moments with Michel Jouvet are described which occurred between 1983 as well as his last moments with us.

Sub-regions of the dorsal raphé nucleus receive different inputs from the brainstem.

The dorsal raphe nucleus (DRN) through its extensive efferent projections has been implicated in a great variety of physiological and behavioral functions including the regulation of the sleep-wake cycle. This nucleus is composed of five sub-regions defined according to the distribution of its serotonergic (5-HT) neurons. In addition to its heterogeneity in neuronal populations, the DRN contains a great diversity of 5-HT neuronal subtypes identified based on their electrophysiological characteristics, morphology and sub-regional distribution. This suggests that the DRN sub-regions may play different functional roles. Recent studies reported long-range inputs specific to the 5-HT neurons of the DRN; but they did not differentiate whether some inputs were specific to a DRN sub-region, or another region. To fulfill this gap, we have previously described the forebrain afferents to the different sub-regions of the DRN using cholera toxin b subunit and Phaseolus vulgaris-leucoagglutinin, as retrograde and anterograde tracers respectively. In the present work, we provide a detailed map of the brainstem projections to these different sub-regions. We show that if some brainstem structures project homogeneously to all sub-regions, most of the brainstem long-range inputs project in a topographically organized manner onto the DRN and, moreover, that a rich interconnected network is present within the DRN.