Rapid Eye Movement Sleep Regulation Research Articles

REM sleep and its mechanism-an updated review

Normal human sleep comprises of two states rapid eye movement (REM) and Non-REM (NREM), which alternates cyclically across a sleep episode. REM sleep was identified by its most typical behavior rapid eye movements during sleep. Electroencephalogram (EEG) of neocortex of most mammals exhibit desynchronized,low-amplitude, and high frequency fast character previously seen in waking, but behavioral sleep persists. This state of sleep called as paradoxical sleep or activated sleep or activated brain in a paralyzed state. Hippocampus has regular high voltage theta waves throughout REM sleep. Multiple neuro-scientific and physiological studies were done to understand the mechanism and genesis of REM sleep. Results of different studies analyze that REM sleep is executed by widely distributed network, rather than single REM sleep center. A number of studies have been attempted to identify pedunculopontine tegmentum (PPT) cholinergic cells present in brainstem, which when activated causes generation and modulation of REM sleep when compared with either NREM or waking. REM sleep sign generator remains in Turned-off condition when aminergic and cholinergic neurotransmitter ratio is1:1 and generator is turned-on to express REM sleep signs when the ratio is 0:0.65. REM-on cells use the neurotransmitter GABA, Ach, glutamate, and glycine, whereas REM-off cells use nor-epinephrine,serotonin, and histamine. c-AMP-PKA intracellular signaling pathway is critically involved in cholinergic cell compartment of the PPT for regulation of cholinergic tone in REM sleep-sign-generators. This review reflects the recent updates on cellular and molecular mechanisms in regulation of REM sleep.

Optogenetic activation of cholinergic neurons in the PPT or LDT induces REM sleep

Rapid eye movement (REM) sleep is an important component of the natural sleep/wake cycle, yet the mechanisms that regulate REM sleep remain incompletely understood. Cholinergic neurons in the mesopontine tegmentum have been implicated in REM sleep regulation, but lesions of this area have had varying effects on REM sleep. Therefore, this study aimed to clarify the role of cholinergic neurons in the pedunculopontine tegmentum (PPT) and laterodorsal tegmentum (LDT) in REM sleep generation. Selective optogenetic activation of cholinergic neurons in the PPT or LDT during non-REM (NREM) sleep increased the number of REM sleep episodes and did not change REM sleep episode duration. Activation of cholinergic neurons in the PPT or LDT during NREM sleep was sufficient to induce REM sleep.

Coupled flip-flop model for REM sleep regulation in the rat.

Recent experimental studies investigating the neuronal regulation of rapid eye movement (REM) sleep have identified mutually inhibitory synaptic projections among REM sleep-promoting (REM-on) and REM sleep-inhibiting (REM-off) neuronal populations that act to maintain the REM sleep state and control its onset and offset. The control mechanism of mutually inhibitory synaptic interactions mirrors the proposed flip-flop switch for sleep-wake regulation consisting of mutually inhibitory synaptic projections between wake- and sleep-promoting neuronal populations. While a number of synaptic projections have been identified between these REM-on/REM-off populations and wake/sleep-promoting populations, the specific interactions that govern behavioral state transitions have not been completely determined. Using a minimal mathematical model, we investigated behavioral state transition dynamics dictated by a system of coupled flip-flops, one to control transitions between wake and sleep states, and another to control transitions into and out of REM sleep. The model describes the neurotransmitter-mediated inhibitory interactions between a wake- and sleep-promoting population, and between a REM-on and REM-off population. We proposed interactions between the wake/sleep and REM-on/REM-off flip-flops to replicate the behavioral state statistics and probabilities of behavioral state transitions measured from experimental recordings of rat sleep under ad libitum conditions and after 24 h of REM sleep deprivation. Reliable transitions from REM sleep to wake, as dictated by the data, indicated the necessity of an excitatory projection from the REM-on population to the wake-promoting population. To replicate the increase in REM-wake-REM transitions observed after 24 h REM sleep deprivation required that this excitatory projection promote transient activation of the wake-promoting population. Obtaining the reliable wake-nonREM sleep transitions observed in the data required that activity of the wake-promoting population modulated the interaction between the REM-on and REM-off populations. This analysis suggests neuronal processes to be targeted in further experimental studies of the regulatory mechanisms of REM sleep.

Dopamine inhibits neurons from the rat dorsal subcoeruleus nucleus through the activation of α2-adrenergic receptors

Previous studies have revealed that the central dopaminergic system may participate in regulating sleep/wakefulness. In particular, rapid eye movement (REM) sleep behavior disorder (RBD) occurs in patients with Parkinson's disease (PD), highlighting the possible connection between dopamine and REM sleep-related neural structures. The dorsal subcoeruleus nucleus (SubCD) is a critical structure for the generation and maintenance of REM sleep. Thus, the present study investigated the modulatory effects of dopamine on SubCD neurons. Using whole-cell patch clamp recordings, we first observed that dopamine induced a hyperpolarization of the membrane potentials in SubCD neurons and thus inhibited their firing. We determined that a dose-dependent and tetrodotoxin-resistant postsynaptic outward current underpinned this inhibitory effect on SubCD neurons induced by dopamine. Finally, using pharmacological agents, we revealed that the dopamine-elicited outward current in SubCD neurons was mediated by α2-adrenergic receptors, but not by the dopamine receptors, including D1-like and D2-like receptors. These results suggest that the central dopaminergic system may play a role in the regulation of REM sleep through the effect of dopamine on SubCD neurons. The relationship between the loss of this effect and the RBD in PD is discussed.

Essential Roles of GABA Transporter-1 in Controlling Rapid Eye Movement Sleep and in Increased Slow Wave Activity after Sleep Deprivation

GABA is the major inhibitory neurotransmitter in the mammalian central nervous system that has been strongly implicated in the regulation of sleep. GABA transporter subtype 1 (GAT1) constructs high affinity reuptake sites for GABA and regulates GABAergic transmission in the brain. However, the role of GAT1 in sleep-wake regulation remains elusive. In the current study, we characterized the spontaneous sleep-wake cycle and responses to sleep deprivation in GAT1 knock-out (KO) mice. GAT1 KO mice exhibited dominant theta-activity and a remarkable reduction of EEG power in low frequencies across all vigilance stages. Under baseline conditions, spontaneous rapid eye movement (REM) sleep of KO mice was elevated both during the light and dark periods, and non-REM (NREM) sleep was reduced during the light period only. KO mice also showed more state transitions from NREM to REM sleep and from REM sleep to wakefulness, as well as more number of REM and NREM sleep bouts than WT mice. During the dark period, KO mice exhibited more REM sleep bouts only. Six hours of sleep deprivation induced rebound increases in NREM and REM sleep in both genotypes. However, slow wave activity, the intensity component of NREM sleep was briefly elevated in WT mice but remained completely unchanged in KO mice, compared with their respective baselines. These results indicate that GAT1 plays a critical role in the regulation of REM sleep and homeostasis of NREM sleep.

REM Sleep Problems Predict Parkinson's, Lewy Body Dementia

SAN DIEGO – Rapid eye movement (REM) sleep behavior disorder (RBD) is the earliest indication that elderly patients are destined to develop Parkinson's disease, Lewy body dementia, or another synucleinopathy, and it precedes the onset of motor and cognitive problems by years, according to a growing body of research. Its presence also distinguishes synucleinopathies from Alzheimer's disease and other problems that can have similar early presentations. RBD “equals synucleinopathy,” said Dr. Ronald Postuma of the department of neurology at McGill University in Montreal. “The way I explain RBD to patients is that normally, when most people dream, they are paralyzed, but you are not. Therefore, you are capable of acting out the content of your dreams.” Dr. Postuma made his comments at the annual meeting of the American Academy of Neurology. Also there, researchers from the Mayo Clinic in Rochester, Minn., presented an autopsy study, now published in Sleep Medicine. The Mayo team analyzed neuropathologic findings from 172 patients diagnosed with RBD before death. They found that 160 (94%) were synucleinopathies. Among them were 136 patients with Lewy bodies and 19 with multiple-system atrophy. The remaining few had findings consistent with Alzheimer's disease or other nonsynucleinopathies. RBD was diagnosed at a mean age of 62 years. It preceded the diagnosis of Parkinsonism in 151 patients by a mean of 6 years. The diagnosis of RBD preceded death by a mean of 13 years. “Lewy body disease was by far the most common underlying neurologic disorder. … We've been looking for [cases of] Alzheimer's associated with RBD for well over 10 years, and they are just hard to find,” said lead investigator Dr. Bradley Boeve, chair of the division of behavioral neurology at Mayo. The findings “argue that the selective vulnerability involves … REM sleep circuitry.” At autopsy, 98% of polysomnography (PSG)-confirmed cases had a synucleinopathy, Dr. Boeve noted. The take-home message is that “if you have a pretty good history of RBD but don't have a PSG to confirm it, there's a 94% chance that you have a synucleinopathy. If you do have PSG, there's a 98% chance of having a synucleinopathy,” Dr. Postuma said. “Asking about REM sleep behavior disorder in your clinics tomorrow will help you diagnose disease.” Investigators from Barcelona, Spain, came to similar conclusions in a paper published recently in Lancet Neurology (Lancet Neurol. 2013;12[5]:443-53). For most, RBD “represents the prodromal phase of a Lewy body disorder … such as Parkinson's disease (PD) or dementia with Lewy bodies. … [RBD] is a candidate for the study of early events and progression of this prodromal phase, and to test disease-modifying strategies to slow or stop the neurodegenerative process,” they concluded. The Spanish team followed 44 RBD cases diagnosed between 1991 and 2003. By 2012, 82% had developed a synucleinopathy: 16 with Parkinson's disease, 14 with Lewy body dementia, and 1 with multiple system atrophy. “The rates of neurological-disease-free survival from time of [RBD] diagnosis were 65.2% at 5 years, 26.6% at 10 years, and 7.5% at 14 years,” they reported. Most RBD patients “developed a Lewy body disorder with time. Patients who remained disease-free at follow-up showed markers of increased short-term risk for developing PD,” including lesions “in the brainstem nuclei that regulate REM sleep atonia,” the Spanish researchers found. Asked to comment on the Spanish study, Dr. Postuma said that the findings “emphatically confirm the incredible risk that patients with RBD have for developing neurodegenerative disease.” The ability to identify a neurodegenerative disease 10 years before it can be diagnosed “provides profound opportunities to study early stages of disease.” Dr. Boeve's research has been supported by Cephalon, Allon Therapeutics, and GE Healthcare. Dr. Postuma disclosed personal support from Teva and Novartis.

Perspectives on the rapid eye movement sleep switch in rapid eye movement sleep behavior disorder

Rapid eye movement (REM) sleep in mammals is associated with wakelike cortical and hippocampal activation and concurrent postural muscle atonia. Research during the past 5 decades has revealed the details of the neural circuitry regulating REM sleep and muscle atonia during this state. REM-active glutamatergic neurons in the sublaterodorsal nucleus (SLD) of the dorsal pons are critical for generation for REM sleep atonia. Descending projections from SLD glutamatergic neurons activate inhibitory premotor neurons in the ventromedial medulla (VMM) and in the spinal cord to antagonize the glutamatergic supraspinal inputs on the motor neurons during REM sleep. REM sleep behavior disorder (RBD) consists of simple behaviors (i.e., twitching, jerking) and complex behaviors (i.e., defensive behavior, talking). Animal research has lead to the hypothesis that complex behaviors in RBD are due to SLD pathology, while simple behaviors of RBD may be due to less severe SLD pathology or dysfunction of the VMM, ventral pons, or spinal cord.

2-AG into the lateral hypothalamus increases REM sleep and cFos expression in melanin concentrating hormone neurons in rats

Orexins/hypocretins (OX) and melanin-concentrating hormone (MCH) neurons located in the lateral hypothalamus seem to modulate different stages of the sleep–wake cycle. OX are necessary for wakefulness and MCH appears to regulate rapid eye movement sleep (REMS). Likewise, endocannabinoids, the endogenous ligands for cannabinoid receptors 1 and 2 (CB1R, CB2R), also modulate REMS in rats. Moreover, it has been shown that the activation of the CB1R in the lateral hypothalamus of rats excites MCH neurons while inhibiting OX neurons in in vitro preparations. Hence, we assessed the effects of 2-arachidonoylglicerol (2-AG, an endocannabinoid) in the lateral hypothalamus on the sleep–wake cycle of rats. We also utilized the CB1R inverse agonist AM251 to further support the involvement of this receptor, and we performed double immunofluorescence experiments to detect c-Fos, as a marker of neural activation, in OX and in MCH neurons to determine which neurons were activated. Our results indicate that 2-AG increases REMS through CB1R activation, and increases c-Fos expression in MCH neurons. These results suggest that endocannabinoid activation of the CB1R in the lateral hypothalamus, which activates MCH neurons, is one mechanism by which REMS is triggered.

Neurodegenerative disease status and post-mortem pathology in idiopathic rapid-eye-movement sleep behaviour disorder: an observational cohort study

We postulated that idiopathic rapid-eye-movement (REM) sleep behaviour disorder (IRBD) represents the prodromal phase of a Lewy body disorder and that, with sufficient follow-up, most cases would eventually be diagnosed with a clinical defined Lewy body disorder, such as Parkinson's disease (PD) or dementia with Lewy bodies (DLB). Patients from an IRBD cohort recruited between 1991 and 2003, and previously assessed in 2005, were followed up during an additional period of 7 years. In this original cohort, we sought to identify the nature and frequency of emerging defined neurodegenerative syndromes diagnosed by standard clinical criteria. We estimated rates of survival free from defined neurodegenerative disease by means of the Kaplan-Meier method. We further characterised individuals who remained diagnosed as having only IRBD, through dopamine transporter (DAT) imaging, transcranial sonography (TCS), and olfactory testing. We did a neuropathological assessment in three patients who died during follow-up and who had the antemortem diagnosis of PD or DLB. Of the 44 participants from the original cohort, 36 (82%) had developed a defined neurodegenerative syndrome by the 2012 assessment (16 patients were diagnosed with PD, 14 with DLB, one with multiple system atrophy, and five with mild cognitive impairment). The rates of neurological-disease-free survival from time of IRBD diagnosis were 65·2% (95% CI 50·9 to 79·5) at 5 years, 26·6% (12·7 to 40·5) at 10 years, and 7·5% (-1·9 to 16·9) at 14 years. Of the four remaining neurological-disease-free individuals who underwent neuroimaging and olfactory tests, all four had decreased striatal DAT uptake, one had substantia nigra hyperechogenicity on TCS, and two had impaired olfaction. In three patients, the antemortem diagnoses of PD and DLB were confirmed by neuropathological examination showing widespread Lewy bodies in the brain, and α-synuclein aggregates in the peripheral autonomic nervous system in one case. In these three patients, neuronal loss and Lewy pathology (α-synuclein-containing Lewy bodies and Lewy neurites) were found in the brainstem nuclei that regulate REM sleep atonia. Most IRBD individuals from our cohort developed a Lewy body disorder with time. Patients who remained disease-free at follow-up showed markers of increased short-term risk for developing PD and DLB in IRBD, such as decreased striatal DAT binding. Our findings indicate that in most patients diagnosed with IRBD this parasomnia represents the prodromal phase of a Lewy body disorder. IRBD is a candidate for the study of early events and progression of this prodromal phase, and to test disease-modifying strategies to slow or stop the neurodegenerative process. None.

Characteristics of rapid eye movement sleep behavior disorder in narcolepsy

Rapid eye movement (REM) sleep behavior disorder (RBD) is characterized by dreamenacting behavior and impaired motor inhibition during REM sleep (REM sleep without atonia, RSWA). RBD is commonly associated with Parkinsonian disorders, but is also reported in narcolepsy. Most patients with narcolepsy with cataplexy lack the hypocretin neurons in the lateral hypothalamus. In contrast, RBD, RSWA, and hypocretin deficiency are rare in narcolepsy without cataplexy. Phasic motor activity in REM and non-REM (NREM) and dreamenacting behavior (RBD) coexist with cataplexy in narcolepsy because of hypocretin deficiency. Thus, hypocretin deficiency is linked to the two major disturbances of REM sleep motor regulation in narcolepsy: RBD and cataplexy. Moreover, it is likely that hypocretin deficiency independently predicts periodic limb movements in REM and NREM sleep, probably via involvement of the dopaminergic system. This supports the hypothesis that an impaired hypocretin system causes general instability of motor regulation during wakefulness, REM and NREM sleep in human narcolepsy. We propose that hypocretin neurons are centrally involved in motor tone control during wakefulness and sleep in humans and that hypocretin deficiency causes a functional defect in the motor control involved in the development of cataplexy during wakefulness and RBD/RSWA/ phasic motor activity during REM sleep.

Hyperactivation of the habenula as a link between depression and sleep disturbance

Depression occurs frequently with sleep disturbance such as insomnia. Sleep in depression is associated with disinhibition of the rapid eye movement (REM) sleep. Despite the coincidence of the depression and sleep disturbance, neural substrate for depressive behaviors and sleep regulation remains unknown. Habenula is an epithalamic structure regulating the activities of monoaminergic neurons in the brain stem. Since the imaging studies showed blood flow increase in the habenula of depressive patients, hyperactivation of the habenula has been implicated in the pathophysiology of the depression. Recent electrophysiological studies reported a novel role of the habenular structure in regulation of REM sleep. In this article, we propose possible cellular mechanisms which could elicit the hyperactivation of the habenular neurons and a hypothesis that dysfunction in the habenular circuit causes the behavioral and sleep disturbance in depression. Analysis of the animals with hyperactivated habenula would open the door to understand roles of the habenula in the heterogeneous symptoms such as reduced motor behavior and altered REM sleep in depression.

The Pathophysiology and Clinical Relevance of Rapid Eye Movement Sleep Behavior Disorder

In this issue of Internal Medicine, Chen et al. (1) documented the case of a 30-year-old man who presented with an 11-month history of abnormal nocturnal behavior related to vivid dreams. Brain magnetic resonance images revealed lesions involving the pontomesencephalic junction and the upper pons, and polysomnography (PSG) findings confirmed a diagnosis of rapid eye movement (REM) sleep behavior disorder (RBD). A brainstem biopsy revealed diffuse large B-cell lymphoma. Notably, chemotherapy for lymphoma resulted in the disappearance of the lesions and reduced the frequency of RBD symptoms in the patient. RBD is a parasomnia characterized by dream-enacting behaviors and a loss of normal muscle atonia during REM sleep. The estimated prevalence of this disorder was reported to be 0.5% in a survey of approximately 4,900 subjects between the ages of 15 and 100 years (2). The dreams of patients with RBD usually include unpleasant and aggressive content, and the patient’s abnormal behavior is typically aggressive and violent, often resulting in serious injury to the patient or their bed partner (3). Based on the International Classification of Sleep Disorders, second edition (4), the use of PSG is essential for diagnosing RBD. The following criteria should be met: A, the presence of REM sleep without atonia, including excessive amounts of sustained or intermittent elevations of submental electromyographic (EMG) tone or excessive phasic submental or limb EMG twitching; B, abnormal REM sleep behavior based on the patient’s history and/or PSG findings; C, the absence of electroencephalogram (EEG) epileptiform activity during REM sleep; and D, the sleep disturbance is not better explained by medication use or another sleep, medical, neurological, mental or substance use disorder. In almost 90% of patients with RBD, the administration of clonazepam (0.5 to 1.5 mg) at bedtime is effective. Additionally, melatonin, pramipexole and Yi-Gan San alone or in conjunction with clonazepam may effectively treat RBD. The anatomic substrate for REM sleep control in humans includes a “REM-off” region, which consists of the ventrolateral part of the periaqueductal gray matter and lateral pontine tegmentum, and a “REM-on” region, which consists of the precoeruleus, sublaterodorsal nucleus, extended portion of the ventrolateral preoptic nucleus, locus coeruleus, laterodorsal tegmental nucleus, pedunculopontine nucleus and raphe nucleus (5). Motor behaviors in patients with RBD may reflect brainstem impairment, while the frightening dreams of RBD may reflect amygdala dysfunction (6). In humans, RBD can be caused secondarily by brain lesions including the brainstem nuclei, which regulate REM sleep, and the supratentorial structures, including the posterior hypothalamus, anterior thalamus and limbic system, which connect with the brainstem nuclei. Brain tumors, demyelinating plaque, strokes and limbic encephalitis have been reported to cause RBD (6), and narcolepsy is associated with RBD. Several medications can cause RBD, including antidepressants such as tricyclics, selective serotonin reuptake inhibitors and serotonin-norepinephrine reuptake inhibitors (3). In 1996, Schenck et al. (7) first reported the delayed emergence of Parkinsonian disorders in 38% of 29 older men initially diagnosed with idiopathic RBD, with a mean interval of 3.7 years after RBD diagnosis and a mean interval of 12.7 years after RBD onset. After an additional 7year follow-up, the conversion rate from idiopathic RBD to neurodegenerative diseases increased to 65%. Additionally, Iranzo et al. (8) reported that 45% of 44 patients with idiopathic RBD developed neurodegenerative diseases (n=9, Parkinson’s disease (PD); n=6, dementia with Lewy bodies (DLB); n=4, mild cognitive impairment; n=1, multiple system atrophy) at a mean follow-up of 5.1 years and a mean of 11.5 years after RBD onset. Postuma et al. (9) reported that 28% of 93 patients with idiopathic RBD developed neurodegenerative diseases (n=14, PD; n=7, DLB; n=4, Al-

REM Sleep Regulating Mechanisms in the Cholinergic Cell Compartment of the Brainstem.

Rapid eye movement (REM) sleep is a highly evolved yet paradoxical behavioral state (highly activated brain in a paralyzed body) in mammalian species. Since the discovery of REM sleep and its physiological distinction from other sleep states1, a vast number of studies in neurosciences have been dedicated toward understanding the mechanisms and functions of this behavioral state. Collectively, studies have shown that each of the physiological events that characterize the behavioral state of REM sleep is executed by distinct cell groups located in the brainstem. These cell groups are discrete components of a widely distributed network, rather than a single REM sleep center. The final activity within each of these executive cell groups is controlled by the ratio of cholinergic neurotransmission emanating from the pedunculopontine tegmentum (PPT) to aminergic neurotransmission emanating from the locus coeruleus (LC) and raphe nucleus (RN). In this review, we summarize the most recent findings on the cellular and molecular mechanisms in the PPT cholinergic cell compartment that underlie the regulation of REM sleep. This up-to-date review should allow clinicians and researchers to better understand the effects of drugs and neurologic disease on REM sleep.

Contrasting Existence and Robustness of REM/Non-REM Cycling in Physiologically Based Models of REM Sleep Regulatory Networks

Typical human sleep throughout the night consists of alternating periods of rapid eye movement (REM) sleep and non-REM (NREM) sleep. This ultradian rhythm of NREM/REM cycling is thought to be produced by the state-dependent activity of “REM-on” and “REM-off” brainstem and hypothalamic neuronal populations that, respectively, promote or suppress REM sleep. Synaptic interactions among these populations define REM sleep regulatory networks; however, the identity of the key neuronal populations in these networks and the dynamics of interactions among them are disputed and cannot be addressed comprehensively with current experimental techniques. The purpose of this study is to use physiologically based mathematical models to explore the dynamic implications associated with competing hypotheses for network-based REM sleep regulation. Generally, putative REM sleep regulatory networks fall into two categories: a reciprocal interaction network consisting of an excitatory REM-on population interacting with an inhibitory REM-off population, and a mutual inhibition network where both REM-on and REM-off populations are inhibitory. We focus on the generation of regular periodic cycling solutions, which would generate the NREM/REM ultradian rhythm, in these networks. By applying our understanding of network mechanisms, we develop efficient numerical criteria for the existence of stable cycling solutions in each network structure. To investigate the robustness of cycling, we systematically analyze the response of model dynamics to manipulation of the components governing network interactions. By establishing the implications of network structure for the mechanisms and dynamics of NREM/REM state transitions, this comparative analysis identifies key targets for future experimental work to distinguish the structure of the proposed physiological REM sleep regulatory network.

A Fast-Slow Analysis of the Dynamics of REM Sleep

Waking and sleep states are regulated by the coordinated activity of a number of neuronal populations in the brainstem and hypothalamus whose synaptic interactions compose a sleep-wake regulatory network. Physiologically based mathematical models of the sleep-wake regulatory network contain mechanisms operating on multiple time scales including relatively fast synaptic-based interactions between neuronal populations, and much slower homeostatic and circadian processes that modulate sleep-wake temporal patterning. In this study, we exploit the naturally arising slow time scale of the homeostatic sleep drive in a reduced sleep-wake regulatory network model to utilize fast-slow analysis to investigate the dynamics of rapid eye movement (REM) sleep regulation. The network model consists of a reduced number of wake-, non-REM (NREM) sleep-, and REM sleep-promoting neuronal populations with synaptic interactions reflecting the mutually inhibitory flip-flop conceptual model for sleep-wake regulation and the reciprocal interaction model for REM sleep regulation. Network dynamics regularly alternate between wake and sleep states as governed by the slow homeostatic sleep drive. By varying a parameter associated with the activation of the REM-promoting population, we cause REM dynamics during sleep episodes to vary from suppression to single activations to regular REM-NREM cycling, corresponding to changes in REM patterning induced by circadian modulation and observed in different mammalian species. We also utilize fast-slow analysis to explain complex effects on sleep-wake patterning of simulated experiments in which agonists and antagonists of different neurotransmitters are microinjected into specific neuronal populations participating in the sleep-wake regulatory network.

Brainstem and Spinal Cord Circuitry Regulating REM Sleep and Muscle Atonia

BackgroundPrevious work has suggested, but not demonstrated directly, a critical role for both glutamatergic and GABAergic neurons of the pontine tegmentum in the regulation of rapid eye movement (REM) sleep.Methodology/Principal FindingsTo determine the in vivo roles of these fast-acting neurotransmitters in putative REM pontine circuits, we injected an adeno-associated viral vector expressing Cre recombinase (AAV-Cre) into mice harboring lox-P modified alleles of either the vesicular glutamate transporter 2 (VGLUT2) or vesicular GABA-glycine transporter (VGAT) genes. Our results show that glutamatergic neurons of the sublaterodorsal nucleus (SLD) and glycinergic/GABAergic interneurons of the spinal ventral horn contribute to REM atonia, whereas a separate population of glutamatergic neurons in the caudal laterodorsal tegmental nucleus (cLDT) and SLD are important for REM sleep generation. Our results further suggest that presynaptic GABA release in the cLDT-SLD, ventrolateral periaqueductal gray matter (vlPAG) and lateral pontine tegmentum (LPT) are not critically involved in REM sleep control.Conclusions/SignificanceThese findings reveal the critical and divergent in vivo role of pontine glutamate and spinal cord GABA/glycine in the regulation of REM sleep and atonia and suggest a possible etiological basis for REM sleep behavior disorder (RBD).

Association between the activation of MCH and orexin immunorective neurons and REM sleep architecture during REM rebound after a three day long REM deprivation

Rapid eye movement (REM) sleep rebound following REM deprivation using the platform-on-water method is characterized by increased time spent in REM sleep and activation of melanin-concentrating hormone (MCH) expressing neurons. Orexinergic neurons discharge reciprocally to MCH-ergic neurons across the sleep-wake cycle. However, the relation between REM architecture and the aforementioned neuropeptides remained unclear. MCH-ergic neurons can be divided into two subpopulations regarding their cocaine- and amphetamine-regulated transcript (CART) immunoreactivity, and among them the activation of CART-immunoreactive subpopulation is higher during the REM rebound. However, the possible role of stress in this association has not been elucidated.Our aims were to analyze the relationship between the architecture of REM rebound and the activation of hypothalamic MCH-ergic and orexinergic neurons. We also intended to separate the effect of stress and REM deprivation on the subsequent activation of subpopulations of MCH-ergic neurons. In order to detect neuronal activity, we performed MCH/cFos and orexin/cFos double immunohistochemistry on home cage, sleep deprived and sleep-rebound rats using the platform-on-water method with small and large (stress control) platforms. Furthermore, REM architecture was analyzed and a triple MCH/CART/cFos immunohistochemistry was also performed on the rebound groups in the same animals.We found that the activity of MCH- and orexin-immunoreactive neurons during REM rebound was positively and negatively correlated with the number of REM bouts, respectively. A negative reciprocal correlation was also found between the activation of MCH- and orexin-immunoreactive neurons during REM rebound. Furthermore, difference between the activation of CART-immunoreactive (CART-IR) and non-CART-immunoreactive MCH-ergic neuron subpopulations was found only after selective REM deprivation, it was absent in the large platform (stress control) rebound group.These results support the role of CART-IR subpopulation of MCH-ergic neurons and the inverse relationship of MCH and orexin in the regulation of REM sleep after REM sleep deprivation.

Melanin concentrating hormone in central hypersomnia

Narcolepsy with cataplexy (NC) is a disabling disorder characterized by excessive daytime sleepiness and abnormal rapid eye movement (REM) sleep manifestations, due to a deficient hypocretin/orexin neurotransmission. Melanin concentrating hormone (MCH) neurons involved in the homeostatic regulation of REM sleep are intact. We hypothesized that an increased release of MCH in NC would be partly responsible for the abnormal REM sleep manifestations. Twenty-two untreated patients affected with central hypersomnia were included: 14 NC, six idiopathic hypersomnia with long sleep time, and two post-traumatic hypersomnia. Fourteen neurological patients without any sleep disorders were included as controls. Using radioimmunoassays, we measured hypocretin-1 and MCH levels in cerebrospinal fluid (CSF). The MCH level was slightly but significantly lower in patients with hypersomnia (98 ± 32 pg/ml) compared to controls (118 ± 20 pg/ml). After exclusion of patients affected with post-traumatic hypersomnia the difference became non-significant. We also failed to find any association between MCH level and hypocretin level, the severity of daytime sleepiness, the number of SOREMPs, the frequency of cataplexy, and the presence of hypnagogic hallucinations or sleep paralysis. This study reports the first measurement of MCH in CSF using radioimmunoassay technology. It appears to be a non-informative tool to differentiate etiologies of central hypersomnia with or without REM sleep dysregulation.

Ca2+ modulation in dorsal raphe plays an important role in NREM and REM sleep regulation during pentobarbital hypnosis

Our previous studies indicated that L-type calcium channel blocker diltiazem could potentiate pentobarbital-induced hypnosis through serotonergic system. In view of the important role of dorsal raphe nucleus (DRN) on the sleep regulation and the pharmacological actions of calcium channel blocker, we presumed that Ca2+ in the DRN may play an important role in sleep regulation in pentobarbital treated rats. Therefore, we investigated whether the Ca2+ modulation in DRN by the microinjection of L-type Ca2+ channel antagonist diltiazem, agonist BAY-K-8644, Ca2+ chelator EGTA and CaCl2 would alter the sleep parameters in pentobarbital treated rats. Results showed that perfusion of the agents attenuating Ca2+ function, such as diltiazem (5 or 20nmol) or EGTA (3 or 6pmol) into DRN significantly increased pentobarbital (35mg/kg, i.p.)-induced total sleep (TS), non-rapid eye movement (NREM) sleep and the slow wave sleep (SWS) ratio in NREM sleep. On the contrary, the DRN injection of the agents improving Ca2+ function, such as BAY-K-8644 (10nmol) or CaCl2 (50 or 100nmol) significantly reduced pentobarbital (35mg/kg, i.p.)-induced TS, NREM sleep, rapid eye movement (REM) sleep and REM sleep ratio in TS without influence on SWS. These results suggested that the suppression of Ca2+ function in DRN could increase NREM sleep including SWS, and the elevation of Ca2+ function could reduce both NREM and REM sleep in pentobarbital treated rats.

Differential roles of orexin receptor-1 and -2 in the regulation of non-REM and REM sleep.

Orexin-A and orexin-B are hypothalamic neuropeptides that play critical roles in the maintenance of wakefulness. Intracerebroventricular (ICV) administration of orexin-A has been shown to promote wakefulness and suppress both rapid eye movement (REM) sleep and non-REM (NREM) sleep through the orexin receptor-1 (OX(1)R) and orexin receptor-2 (OX(2)R). Here, we elucidated the differential roles of orexin receptors in the regulation of sleep and wakefulness by comparing the effects of ICV orexin-A administration in wild-type, OX(1)R(-/-), and OX(2)R(-/-) mice. The effects of orexin-A on wakefulness and NREM sleep were significantly attenuated in both knock-out mice as compared with wild-type mice, with substantially larger attenuation in OX(2)R(-/-) mice than in OX(1)R(-/-) mice. These results suggest that although the OX(2)R-mediated pathway has a pivotal role in the promotion of wakefulness, OX(1)R also plays additional roles in promoting arousal. In contrast, suppression of REM sleep by orexin-A administration was slightly and similarly attenuated in both OX(1)R(-/-) and OX(2)R(-/-) mice, suggesting a comparable contribution of the two receptors to REM sleep suppression. Histological studies demonstrated differential distributions of each receptor subtype in distinct neuronal populations with specific neurotransmitter identities in brainstem cholinergic/monoaminergic neurons. In the laterodorsal tegmental and pedunculopontine tegmental nuclei especially, cholinergic neurons exclusively expressed OX(1)R mRNA, but OX(2)R mRNA was expressed mainly in GABAergic putative interneurons. Thus, each orexin receptor subtype plays differential roles in gating NREM and REM sleep through distinct neuronal pathways.