Genetic inactivation of glutamate neurons in the rat sublaterodorsal tegmental nucleus recapitulates REM sleep behaviour disorder

A pontine-medullary loop crucial for REM sleep and its deficit in Parkinson's disease

Identifying the properties of the rapid eye movement (REM) sleep circuitry and its relation to diseases has been challenging due to the neuronal heterogeneity of the brainstem. Here, we show in mice that neurons in the pontine sublaterodorsal tegmentum (SubLDT) that express corticotropin-releasing hormone-binding protein (Crhbp+ neurons) and project to the medulla promote REM sleep. Within the medullary area receiving projections from Crhbp+ neurons, neurons expressing nitric oxide synthase 1 (Nos1+ neurons) project to the SubLDT and promote REM sleep, suggesting a positively interacting loop between the pons and the medulla operating as a core REM sleep circuit. Nos1+ neurons also project to areas that control wide forebrain activity. Ablating Crhbp+ neurons reduces sleep and impairs REM sleep atonia. In Parkinson's disease patients with REM sleep behavior disorders, CRHBP-immunoreactive neurons are largely reduced and contain pathologic α-synuclein, providing insight into the mechanisms underlying the sleep deficits characterizing this disease.

Major Alteration Of Motor Control During Rem Sleep In Mice Models Of Sleep Disorders

Alteration of motor control during REM sleep has been extensively described in sleep disorders, in particular in isolated REM sleep behavior disorder (iRBD) and narcolepsy type 1 (NT1). NT1 is caused by the loss of orexin/hypocretin (ORX) neurons. Unlike in iRBD, the RBD comorbid symptoms of NT1 is not associated with alpha-synucleinopathies. To determine whether the chronic absence of ORX neuropeptides is sufficient to induce RBD symptoms, we analyzed during REM sleep the EMG signal of the prepro-hypocretin knockout mice (ORX-/-), a recognized mouse model of NT1. Then, we evaluated the severity of motor alterations by comparing EMG data of ORX-/- mice to those of mice with a targeted suppression of the sublaterodorsal glutamatergic neurotransmission, a recognized rodent model of iRBD. We found a significant alteration of tonic and phasic components of EMG during REM sleep in ORX-/- mice, with more phasic events and more REM sleep episodes without atonia compared to the control wild-type mice. However, these phasic events were fewer, shorter and less complex in ORX-/- mice compared to the RBD-like ORX-/- mice. We thus show that ORX-deficiency, as seen in NT1, is sufficient to impair muscle atonia during REM sleep with a moderate severity of alteration as compared to isolated RBD mice. As described in NT1 patients, we report a major inter-individual variability in the severity and the frequency of RBD symptoms in ORX-deficient mice.

GBA-AAV mitigates sleep disruptions and motor deficits in mice with REM sleep behavior disorder

Sleep disturbances, including rapid eye movement sleep behavior disorder (RBD), excessive daytime sleepiness, and insomnia, are common non-motor manifestations of Parkinson's disease (PD). Little is known about the underlying mechanisms, partly due to the inability of current rodent models to adequately mimic the human PD sleep phenotype. Clinically, increasing studies have reported that variants of the glucocerebrosidase gene (GBA) increase the risk of PD. Here, we developed a mouse model characterized by sleep-wakefulness by injecting α-synuclein preformed fibronectin (PFF) into the sublaterodorsal tegmental nucleus (SLD) of GBA L444P mutant mice and investigated the role of the GBA L444P variant in the transition from rapid eye movement sleep behavior disorder to PD. Initially, we analyzed spectral correlates of REM and NREM sleep in GBA L444P mutant mice. Importantly, EEG power spectral analysis revealed that GBA L444P mutation mice exhibited reduced delta power during non-rapid eye movement (NREM) sleep and increased theta power (8.2-10 Hz) in active rapid eye movement (REM) sleep phases. Our study revealed that GBA L444P-mutant mice, after receiving PFF injections, exhibited increased sleep fragmentation, significant motor and cognitive dysfunctions, and loss of dopaminergic neurons in the substantia nigra. Furthermore, the over-expression of GBA-AAV partially improved these sleep disturbances and motor and cognitive impairments. In conclusion, we present the initial evidence that the GBA L444P mutant mouse serves as an essential tool in understanding the complex sleep disturbances associated with PD. This model further provides insights into potential therapeutic approaches, particularly concerning α-synuclein accumulation and its subsequent pathological consequences.

Neuronal network controlling REM sleep

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

Disrupted topological properties of structural brain networks present a glutamatergic neuropathophysiology in people with narcolepsy

STUDY OBJECTIVES

Growing evidences have documented various abnormalities of the white matter bundles in people with narcolepsy. We sought to evaluate topological properties of brain structural networks, and their association with symptoms and neuropathophysiological features in people with narcolepsy.

METHODS

Diffusion tensor imaging was conducted for people with narcolepsy (n = 30) and matched healthy controls as well as symptoms assessment. Structural connectivity for each participant was generated to analyze global and regional topological properties and their correlations with narcoleptic features. Further human brain transcriptome was extracted and spatially registered for connectivity vulnerability. Genetic functional enrichment analysis was performed and further clarified using in vivo emission computed tomography data.

RESULTS

A wide and dramatic decrease in structural connectivities was observed in people with narcolepsy, with descending network degree and global efficiency. These metrics were not only correlated with sleep latency and awakening features, but also reflected alterations of sleep macrostructure in people with narcolepsy. Network-based statistics identified a small hyperenhanced subnetwork of cingulate gyrus that was closely related to rapid eye movement sleep behavior disorder (RBD) in narcolepsy. Further imaging genetics analysis suggested glutamatergic signatures were responsible for the preferential vulnerability of connectivity alterations in people with narcolepsy, while additional PET/SPECT data verified that structural alteration was significantly correlated with metabotropic glutamate receptor 5 (mGlutR5) and N-methyl-D-aspartate receptor (NMDA).

CONCLUSIONS

People with narcolepsy endured a remarkable decrease in the structural architecture, which was not only closely related to narcolepsy symptoms but also glutamatergic signatures.

Orexin Neurons to Sublaterodorsal Tegmental Nucleus Pathway Prevents Sleep Onset REM Sleep-Like Behavior by Relieving the REM Sleep Pressure

Proper timing of vigilance states serves fundamental brain functions. Although disturbance of sleep onset rapid eye movement (SOREM) sleep is frequently reported after orexin deficiency, their causal relationship still remains elusive. Here, we further study a specific subgroup of orexin neurons with convergent projection to the REM sleep promoting sublaterodorsal tegmental nucleus (OXSLD neurons). Intriguingly, although OXSLD and other projection-labeled orexin neurons exhibit similar activity dynamics during REM sleep, only the activation level of OXSLD neurons exhibits a significant positive correlation with the post-inter-REM sleep interval duration, revealing an essential role for the orexin-sublaterodorsal tegmental nucleus (SLD) neural pathway in relieving REM sleep pressure. Monosynaptic tracing reveals that multiple inputs may help shape this REM sleep-related dynamics of OXSLD neurons. Genetic ablation further shows that the homeostatic architecture of sleep/wakefulness cycles, especially avoidance of SOREM sleep-like transition, is dependent on this activity. A positive correlation between the SOREM sleep occurrence probability and depression states of narcoleptic patients further demonstrates the possible significance of the orexin-SLD pathway on REM sleep homeostasis.

Sleep disorders cause Parkinson's disease or the reverse is true: Good GABA good night

BACKGROUND

Parkinson's disease (PD) is a progressive neurodegenerative brain disease due to degeneration of dopaminergic neurons (DNs) presented with motor and non-motor symptoms. PD symptoms are developed in response to the disturbance of diverse neurotransmitters including γ-aminobutyric acid (GABA). GABA has a neuroprotective effect against PD neuropathology by protecting DNs in the substantia nigra pars compacta (SNpc). It has been shown that the degeneration of GABAergic neurons is linked with the degeneration of DNs and the progression of motor and non-motor PD symptoms. GABA neurotransmission is a necessary pathway for normal sleep patterns, thus deregulation of GABAergic neurotransmission in PD could be the potential cause of sleep disorders in PD.

AIM

Sleep disorders affect GABA neurotransmission leading to memory and cognitive dysfunction in PD. For example, insomnia and short sleep duration are associated with a reduction of brain GABA levels. Moreover, PD-related disorders including rigidity and nocturia influence sleep patterns leading to fragmented sleep which may also affect PD neuropathology. However, the mechanistic role of GABA in PD neuropathology regarding motor and non-motor symptoms is not fully elucidated. Therefore, this narrative review aims to clarify the mechanistic role of GABA in PD neuropathology mainly in sleep disorders, and how good GABA improves PD. In addition, this review of published articles tries to elucidate how sleep disorders such as insomnia and REM sleep behavior disorder (RBD) affect PD neuropathology and severity. The present review has many limitations including the paucity of prospective studies and most findings are taken from observational and preclinical studies. GABA involvement in the pathogenesis of PD has been recently discussed by recent studies. Therefore, future prospective studies regarding the use of GABA agonists in the management of PD are suggested to observe their distinct effects on motor and non-motor symptoms.

CONCLUSION

There is a bidirectional relationship between the pathogenesis of PD and sleep disorders which might be due to GABA deregulation.

Polysomnographic features associated with clonazepam and melatonin treatment in isolated REM sleep behavior disorder: Time for new therapeutic approaches?

AIMS

Although clonazepam (CLO) and melatonin (MLT) are the most frequently used treatments for REM sleep behavior disorder, the polysomnographic features associated with their use are little known. The aim of this study was to evaluate polysomnographic and clinical parameters of patients with idiopathic/isolated REM sleep behavior disorder (iRBD) treated chronically with CLO, sustained-release MLT, alone or in combination, and in a group of drug-free iRBD patients.

METHODS

A total of 96 patients were enrolled: 43 drug-free, 21 with CLO (0.5-2 mg), 20 with sustained-release MLT (1-4 mg), and 12 taking a combination of them (same doses). Clinical variables and polysomnography were collected.

RESULTS

Although clinical improvement was reported in all groups, MLT impacted sleep architecture more than the other treatments, with significant and large increase in N3 stage, moderate reduction in N2 and REM sleep, and moderate increase in REM latency. CLO moderately increased the percentage of both REM sleep and especially N2, while reducing N1 and wakefulness. Patients treated with both CLO and MLT did not show major changes in sleep architecture.

CONCLUSION

These results suggest that the administration of MLT or CLO impacts (positively) on sleep parameters of iRBD patients. However, there is a need to better stratify patients, in order to treat them in a targeted manner, depending on the patient's individual sleep architecture and expected differential effects of these agents.

Role of the substantia nigra pars reticulata in sleep-wakefulness: A review of research progress

Sleep is a complex physiological process that includes two main stages: non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. During mammalian sleep, especially REM sleep, skeletal muscles are suppressed to varying degrees, and corresponding movements are inhibited. The synchronous occurrence of sleep and motor inhibition suggests they may share the same neural circuits. Recently, the substantia nigra pars reticulata (SNr) has attracted attention for its potential dual role in regulating sleep-wake cycles and movement. In this review, the SNr's role is surveyed by examining existing research reports regarding its involvement in sleep-wake regulation and motor control. By focusing on the SNr, the goal is to shed light on its dual role intricacies and stimulate further inquiry into potential interactions between sleep and movement regulation, thus aiming to explore sleep-wake regulatory mechanisms and offer novel directions for subsequent scientific investigation.

Brain Circuits Underlying Narcolepsy

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

Neural Control of REM Sleep and Motor Atonia: Current Perspectives

PURPOSE OF REVIEW

Since the formal discovery of rapid eye movement (REM) sleep in 1953, we have gained a vast amount of knowledge regarding the specific populations of neurons, their connections, and synaptic mechanisms regulating this stage of sleep and its accompanying features. This article discusses REM sleep circuits and their dysfunction, specifically emphasizing recent studies using conditional genetic tools.

RECENT FINDINGS

Sublaterodorsal nucleus (SLD) in the dorsolateral pons, especially the glutamatergic subpopulation in this region (SLDGlut), are shown to be indispensable for REM sleep. These neurons appear to be single REM generators in the rodent brain and may initiate and orchestrate all REM sleep events, including cortical and hippocampal activation and muscle atonia through distinct pathways. However, several cell groups in the brainstem and hypothalamus may influence SLDGlut neuron activity, thereby modulating REM sleep timing, amounts, and architecture. Damage to SLDGlut neurons or their projections involved in muscle atonia leads to REM behavior disorder, whereas the abnormal activation of this pathway during wakefulness may underlie cataplexy in narcolepsy. Despite some opposing views, it has become evident that SLDGlut neurons are the sole generators of REM sleep and its associated characteristics. Further research should prioritize a deeper understanding of their cellular, synaptic, and molecular properties, as well as the mechanisms that trigger their activation during cataplexy and make them susceptible in RBD.

The role of orexinergic system in the regulation of cataplexy

Loss of orexin/hypocretin causes serious sleep disorder; narcolepsy. Cataplexy is the most striking symptom of narcolepsy, characterized by abrupt muscle paralysis induced by emotional stimuli, and has been considered pathological activation of REM sleep atonia system. Clinical treatments for cataplexy/narcolepsy and early pharmacological studies in narcoleptic dogs tell us about the involvement of monoaminergic and cholinergic systems in the control of cataplexy/narcolepsy. Muscle atonia may be induced by activation of REM sleep-atonia generating system in the brainstem. Emotional stimuli may be processed in the limbic systems including the amygdala, nucleus accumbens, and medial prefrontal cortex. It is now considered that orexin/hypocretin prevents cataplexy by modulating the activity of different points of cataplexy-inducing circuit, including monoaminergic/cholinergic systems, muscle atonia-generating systems, and emotion-related systems. This review will describe the recent advances in understanding the neural mechanisms controlling cataplexy, with a focus on the involvement of orexin/hypocretin system, and will discuss future experimental strategies that will lead to further understanding and treatment of this disease.

Sleep disorders in Lewy body dementia: Mechanisms, clinical relevance, and unanswered questions

In Lewy body dementia (LBD), disturbances of sleep and/or arousal including insomnia, excessive daytime sleepiness, rapid eye movement (REM) sleep behavior disorder, obstructive sleep apnea, and restless leg syndrome are common. These disorders can each exert a significant negative impact on both patient and caregiver quality of life; however, their etiology is poorly understood. Little guidance is available for assessing and managing sleep disorders in LBD, and they remain under-diagnosed and under-treated. This review aims to (1) describe the specific sleep disorders which occur in LBD, considering their putative or potential mechanisms; (2) describe the history and diagnostic process for these disorders in LBD; and (3) summarize current evidence for their management in LBD and consider some of the ongoing and unanswered questions in this field and future research directions.

REM behavior disorder: When Parkinson's disease meets Morpheus

Rapid eye movement (REM) sleep behavior disorder (RBD) is a parasomnia characterized by the absence of normal muscle atonia during REM sleep, resulting in excessive motor activity while dreaming. RBD can be classified as isolated which is the strongest clinical marker of prodromal synucleinopathy, or secondary, associated with other neurological diseases, mainly Parkinson's disease (PD) and dementia with Lewy bodies. The diagnosis of RBD must be systematically documented by a video polysomnography in the case of isolated RBD. PD associated with RBD may represent a distinct phenotype compared to PD without RBD, indicating a more severe and widespread synucleinopathy. Clinically, it is associated with poorer motor and cognitive performance, more severe non-motor symptoms, and faster disease progression. Imaging studies have revealed broader brain damage and significant alterations in cerebral metabolism and neurotransmission in PD patients with RBD. The management of RBD involves safety precautions and pharmacotherapy. Safety measures aim to minimize the risk of injury during RBD episodes and include creating a safe sleeping environment and separating the patient from their bed partner if necessary. Pharmacotherapy options include clonazepam and melatonin. Clonazepam must be cautiously prescribed in older patients due to potential side effects.

Pharmacological interventions targeting α-synuclein aggregation triggered REM sleep behavior disorder and early development of Parkinson's disease

Rapid eye movement (REM) sleep behavior disorder (RBD) is a parasomnia characterized by elevated motor behaviors and dream enactments in REM sleep, often preceding the diagnosis of Parkinson's disease (PD). As RBD could serve as a biomarker for early PD developments, pharmacological interventions targeting α-synuclein aggregation triggered RBD could be applied toward early PD progression. However, robust therapeutic guidelines toward PD-induced RBD are lacking, owing in part to a historical paucity of effective treatments and trials. We reviewed the bidirectional links between α-synuclein neurodegeneration, progressive sleep disorders, and RBD. We highlighted the correlation between RBD development, α-synuclein aggregation, and neuronal apoptosis in key brainstem regions involved in REM sleep atonia maintenance. The current pharmacological intervention strategies targeting RBD and their effects on progressive PD are discussed, as well as current treatments for progressive neurodegeneration and their effects on RBD. We also evaluated emerging and potential pharmacological solutions to sleep disorders and developing synucleinopathies. This review provides insights into the mechanisms and therapeutic targets underlying RBD and PD, and explores bidirectional treatment effects for both diseases, underscoring the need for further research in this area.

A medullary hub for controlling REM sleep and pontine waves

Rapid-eye-movement (REM) sleep is a distinct behavioral state associated with vivid dreaming and memory processing. Phasic bursts of electrical activity, measurable as spike-like pontine (P)-waves, are a hallmark of REM sleep implicated in memory consolidation. However, the brainstem circuits regulating P-waves, and their interactions with circuits generating REM sleep, remain largely unknown. Here, we show that an excitatory population of dorsomedial medulla (dmM) neurons expressing corticotropin-releasing-hormone (CRH) regulates both REM sleep and P-waves in mice. Calcium imaging showed that dmM CRH neurons are selectively activated during REM sleep and recruited during P-waves, and opto- and chemogenetic experiments revealed that this population promotes REM sleep. Chemogenetic manipulation also induced prolonged changes in P-wave frequency, while brief optogenetic activation reliably triggered P-waves along with transiently accelerated theta oscillations in the electroencephalogram (EEG). Together, these findings anatomically and functionally delineate a common medullary hub for the regulation of both REM sleep and P-waves.

Awake or Sleeping? Maybe Both… A Review of Sleep-Related Dissociative States

Recent studies have begun to understand sleep not only as a whole-brain process but also as a complex local phenomenon controlled by specific neurotransmitters that act in different neural networks, which is called "local sleep". Moreover, the basic states of human consciousness-wakefulness, sleep onset (N1), light sleep (N2), deep sleep (N3), and rapid eye movement (REM) sleep-can concurrently appear, which may result in different sleep-related dissociative states. In this article, we classify these sleep-related dissociative states into physiological, pathological, and altered states of consciousness. Physiological states are daydreaming, lucid dreaming, and false awakenings. Pathological states include sleep paralysis, sleepwalking, and REM sleep behavior disorder. Altered states are hypnosis, anesthesia, and psychedelics. We review the neurophysiology and phenomenology of these sleep-related dissociative states of consciousness and update them with recent studies. We conclude that these sleep-related dissociative states have a significant basic and clinical impact since their study contributes to the understanding of consciousness and the proper treatment of neuropsychiatric diseases.

Role of pontine sub-laterodorsal tegmental nucleus (SLD) in rapid eye movement (REM) sleep, cataplexy, and emotion

Pontine sub-laterodorsal tegmental nucleus (SLD) is crucial for REM sleep. However, the necessary role of SLD for REM sleep, cataplexy that resembles REM sleep, and emotion memory by REM sleep has remained unclear. To address these questions, we focally ablated SLD neurons using adenoviral diphtheria-toxin (DTA) approach and found that SLD lesions completely eliminated REM sleep accompanied by wake increase, significantly reduced baseline cataplexy amounts by 40% and reward (sucrose) induced cataplexy amounts by 70% and altered cataplexy EEG Fast Fourier Transform (FFT) from REM sleep-like to wake-like in orexin null (OXKO) mice. We then used OXKO animals with absence of REM sleep and OXKO controls and examined elimination of REM sleep in anxiety and fear extinction. Our resulted showed that REM sleep elimination significantly increased anxiety-like behaviors in open field test (OFT), elevated plus maze test (EPM) and defensive aggression and impaired fear extinction. The data indicate that in OXKO mice the SLD is the sole generator for REM sleep; (2) the SLD selectively mediates REM sleep cataplexy (R-cataplexy) that merges with wake cataplexy (W-cataplexy); (3) REM sleep enhances positive emotion (sucrose induced cataplexy) response, reduces negative emotion state (anxiety), and promotes fear extinction.

The importance of ligand gated ion channels in sleep and sleep disorders

On average, humans spend about 26 years of their life sleeping. Increased sleep duration and quality has been linked to reduced disease risk; however, the cellular and molecular underpinnings of sleep remain open questions. It has been known for some time that pharmacological modulation of neurotransmission in the brain can promote either sleep or wakefulness thereby providing some clues about the molecular mechanisms at play. However, the field of sleep research has developed an increasingly detailed understanding of the requisite neuronal circuitry and key neurotransmitter receptor subtypes, suggesting that it may be possible to identify next generation pharmacological interventions to treat sleep disorders within this same space. The aim of this work is to examine the latest physiological and pharmacological findings highlighting the contribution of ligand gated ion channels including the inhibitory GABA_A and glycine receptors and excitatory nicotinic acetylcholine receptors and glutamate receptors in the sleep-wake cycle regulation. Overall, a better understanding of ligand gated ion channels in sleep will help determine if these highly druggable targets could facilitate a better night's sleep.

Neuroanatomical Localization of Rapid Eye Movement Sleep Behavior Disorder in Human Brain Using Lesion Network Mapping

OBJECTIVE

To localize the neuroanatomical substrate of rapid eye movement sleep behavior disorder (RBD) and to investigate the neuroanatomical locational relationship between RBD and α-synucleinopathy neurodegenerative diseases.

MATERIALS AND METHODS

Using a systematic PubMed search, we identified 19 patients with lesions in different brain regions that caused RBD. First, lesion network mapping was applied to confirm whether the lesion locations causing RBD corresponded to a common brain network. Second, the literature-based RBD lesion network map was validated using neuroimaging findings and locations of brain pathologies at post-mortem in patients with idiopathic RBD (iRBD) who were identified by independent systematic literature search using PubMed. Finally, we assessed the locational relationship between the sites of pathological alterations at the preclinical stage in α-synucleinopathy neurodegenerative diseases and the brain network for RBD.

RESULTS

The lesion network mapping showed lesions causing RBD to be localized to a common brain network defined by connectivity to the pons (including the locus coeruleus, dorsal raphe nucleus, central superior nucleus, and ventrolateral periaqueductal gray), regardless of the lesion location. The positive regions in the pons were replicated by the neuroimaging findings in an independent group of patients with iRBD and it coincided with the reported pathological alterations at post-mortem in patients with iRBD. Furthermore, all brain pathological sites at preclinical stages (Braak stages 1-2) in Parkinson's disease (PD) and at brainstem Lewy body disease in dementia with Lewy bodies (DLB) were involved in the brain network identified for RBD.

CONCLUSION

The brain network defined by connectivity to positive pons regions might be the regulatory network loop inducing RBD in humans. In addition, our results suggested that the underlying cause of high phenoconversion rate from iRBD to neurodegenerative α-synucleinopathy might be pathological changes in the preclinical stage of α-synucleinopathy located at the regulatory network loop of RBD.

A Narrative Review on REM Sleep Deprivation: A Promising Non-Pharmaceutical Alternative for Treating Endogenous Depression

Endogenous depression represents a severe mental health condition projected to become one of the worldwide leading causes of years lived with disability. The currently available clinical and non-clinical interventions designed to alleviate endogenous depression-associated symptoms encounter a series of inconveniences, from the lack of intervention effectiveness and medication adherence to unpleasant side effects. In addition, depressive individuals tend to be more frequent users of primary care units, which markedly affects the overall treatment costs. In parallel with the growing incidence of endogenous depression, researchers in sleep science have discovered multiple links between rapid eye movement (REM) sleep patterns and endogenous depression. Recent findings suggest that prolonged periods of REM sleep are associated with different psychiatric disorders, including endogenous depression. In addition, a growing body of experimental work confidently describes REM sleep deprivation (REM-D) as the underlying mechanism of most pharmaceutical antidepressants, proving its utility as either an independent or adjuvant approach to alleviating the symptoms of endogenous depression. In this regard, REM-D is currently being explored for its potential value as a sleep intervention-based method for improving the clinical management of endogenous depression. Therefore, this narrative review represents a comprehensive inventory of the currently available evidence supporting the potential use of REM-D as a reliable, non-pharmaceutical approach for treating endogenous depression, or as an adjuvant practice that could improve the effectiveness of currently used medication.

Clinical and neuroimaging markers of neurodegeneration in first-degree relatives of patients with REM sleep behavior disorder with and without isolated rapid eye movement sleep without atonia: A case-control clinical and dopamine PET study

OBJECTIVES

The current study aimed to examine the neurodegenerative implication of isolated REM sleep without atonia (RSWA) among first-degree relatives of patients with REM sleep behaviour disorder (RBD).

METHODS

This cross-sectional case-control study recruited three groups of subjects: First-degree relatives of RBD patients with isolated RSWA (n = 17), first-degree relatives of RBD patients without isolated RSWA (n = 18), and normal controls who did not have any RWSA and family history of RBD (n = 15). Prodromal Parkinson's Disease likelihood ratio by the updated MDS Research Criteria and striatal dopaminergic transmission function of the subjects as assessed by triple-tracer (18F-DOPA, 11C-Raclopride, and 18F-FDG) PET/CT scan were used as proxy markers of neurodegeneration.

RESULTS

In contrary to our hypothesis, the three groups did not differ in their pre- or post-striatal dopaminergic transmission function, and their Prodromal Parkinson's Disease likelihood ratio. However, they differed significantly in their frequency of a having first-degree relatives with Parkinson's disease or dementia of Lewy body (first-degree relativess with RSWA vs first degree relatives without RSWA vs normal controls = 58.8% vs 22.2% vs 0%, p = 0.001).

CONCLUSION

FDRs of RBD patients with isolated RSWA did not have increased neurodegenerative markers compared to FDRs of RBD patients without isolated RSWA and normal control, despite an paradoxical increase in frequency of Parkinson's disease or dementia of Lewy body among their family compared to FDRs of RBD patients without isolated RSWA. Further longitudinal follow-up study will be needed to ascertain their long-term prognosis.

Mechanisms of Sleep/Wake Regulation under Hypodopaminergic State: Insights from MitoPark Mouse Model of Parkinson's Disease

Sleep/wake alterations are predominant in neurological and neuropsychiatric disorders involving dopamine dysfunction. Unfortunately, specific, mechanisms-based therapies for these debilitating sleep problems are currently lacking. The pathophysiological mechanisms of sleep/wake alterations within a hypodopaminergic MitoPark mouse model of Parkinson's disease (PD) are investigated. MitoPark mice replicate most PD-related sleep alterations, including sleep fragmentation, hypersomnia, and daytime sleepiness. Surprisingly, these alterations are not accounted for by a dysfunction in the circadian or homeostatic regulatory processes of sleep, nor by acute masking effects of light or darkness. Rather, the sleep phenotype is linked with the impairment of instrumental arousal and sleep modulation by behavioral valence. These alterations correlate with changes in high-theta (8-11.5 Hz) electroencephalogram power density during motivationally-charged wakefulness. These results demonstrate that sleep/wake alterations induced by dopamine dysfunction are mediated by impaired modulation of sleep by motivational valence and provide translational insights into sleep problems associated with disorders linked to dopamine dysfunction.

To sleep or not to sleep - Effects on memory in normal aging and disease

Sleep behavior undergoes significant changes across the lifespan, and aging is associated with marked alterations in sleep amounts and quality. The primary sleep changes in healthy older adults include a shift in sleep timing, reduced slow-wave sleep, and impaired sleep maintenance. However, neurodegenerative and psychiatric disorders are more common among the elderly, which further worsen their sleep health. Irrespective of the cause, insufficient sleep adversely affects various bodily functions including energy metabolism, mood, and cognition. In this review, we will focus on the cognitive changes associated with inadequate sleep during normal aging and the underlying neural mechanisms.

Targeting Orexin Receptors for the Treatment of Insomnia: From Physiological Mechanisms to Current Clinical Evidence and Recommendations

After a detailed description of orexins and their roles in sleep and other medical disorders, we discuss here the current clinical evidence on the effects of dual (DORAs) or selective (SORAs) orexin receptor antagonists on insomnia with the aim to provide recommendations for their further assessment in a context of personalized and precision medicine. In the last decade, many trials have been conducted with orexin receptor antagonists, which represent an innovative and valid therapeutic option based on the multiple mechanisms of action of orexins on different biological circuits, both centrally and peripherally, and their role in a wide range of medical conditions which are often associated with insomnia. A very interesting aspect of this new category of drugs is that they have limited abuse liability and their discontinuation does not seem associated with significant rebound effects. Further studies on the efficacy of DORAs are required, especially on children and adolescents and in particular conditions, such as menopause. Which DORA is most suitable for each patient, based on comorbidities and/or concomitant treatments, should be the focus of further careful research. On the contrary, studies on SORAs, some of which seem to be appropriate also in insomnia in patients with psychiatric diseases, are still at an early stage and, therefore, do not allow to draw definite conclusions.

Sleep architecture and sleep-disordered breathing in fatal insomnia

STUDY OBJECTIVES

Fatal insomnia (FI) is a rare prion disease severely affecting sleep architecture. Breathing during sleep has not been systematically assessed. Our aim was to characterize the sleep architecture, respiratory patterns, and neuropathologic findings in FI.

METHODS

Eleven consecutive FI patients (ten familial, one sporadic) were examined with video-polysomnography (vPSG) between 2002 and 2017. Wake/sleep stages and respiration were evaluated using a modified scoring system. Postmortem neuropathology was assessed in seven patients.

RESULTS

Median age at onset was 48 years and survival after vPSG was 1 year. All patients had different combinations of breathing disturbances including increased respiratory rate variability (RRV; n = 7), stridor (n = 9), central sleep apnea (CSA) (n = 5), hiccup (n = 6), catathrenia (n = 7), and other expiratory sounds (n = 10). RRV in NREM sleep correlated with ambiguous and solitary nuclei degeneration (r = 0.9, p = 0.008) and reduced survival (r = -0.7, p = 0.037). Two new stages, Subwake1 and Subwake2, present in all patients, were characterized. NREM sleep (conventional or undifferentiated) was identifiable in ten patients but reduced in duration in eight. REM sleep occurred in short segments in nine patients, and their reduced duration correlated with medullary raphe nuclei degeneration (r = -0.9, p = 0.005). Seven patients had REM without atonia. Three vPSG patterns were identified: agitated, with aperiodic, manipulative, and finalistic movements (n = 4); quiet-apneic, with CSA (n = 4); and quiet-non-apneic (n = 3).

CONCLUSIONS

FI patients show frequent breathing alterations, associated with respiratory nuclei damage, and, in addition to NREM sleep distortion, have severe impairment of REM sleep, related with raphe nuclei degeneration. Brainstem impairment is crucial in FI.

A cluster of mesopontine GABAergic neurons suppresses REM sleep and curbs cataplexy

Physiological rapid eye movement (REM) sleep termination is vital for initiating non-REM (NREM) sleep or arousal, whereas the suppression of excessive REM sleep is promising in treating narcolepsy. However, the neuronal mechanisms controlling REM sleep termination and keeping sleep continuation remain largely unknown. Here, we reveal a key brainstem region of GABAergic neurons in the control of both physiological REM sleep and cataplexy. Using fiber photometry and optic tetrode recording, we characterized the dorsal part of the deep mesencephalic nucleus (dDpMe) GABAergic neurons as REM relatively inactive and two different firing patterns under spontaneous sleep–wake cycles. Next, we investigated the roles of dDpMe GABAergic neuronal circuits in brain state regulation using optogenetics, RNA interference technology, and celltype-specific lesion. Physiologically, dDpMe GABAergic neurons causally suppressed REM sleep and promoted NREM sleep through the sublaterodorsal nucleus and lateral hypothalamus. In-depth studies of neural circuits revealed that sublaterodorsal nucleus glutamatergic neurons were essential for REM sleep termination by dDpMe GABAergic neurons. In addition, dDpMe GABAergic neurons efficiently suppressed cataplexy in a rodent model. Our results demonstrated that dDpMe GABAergic neurons controlled REM sleep termination along with REM/NREM transitions and represented a novel potential target to treat narcolepsy.

Research progress on neuromolecular imaging of REM sleep behavior disorder

Idiopathic rapid eye movement sleep behavior disorder (iRBD) is an important non-motor complication of Parkinson's disease. At the same time, iRBD is considered to be the prodromal stage of α-synucleinopathy. This high risk of conversion suggests that iRBD becomes a nerve It is a window for early research on degenerative diseases and is the best candidate for neuroprotection trials. A wide range of neuroimaging techniques has improved our understanding of iRBD as a prodromal stage of the disease. In addition, neuroimaging of abnormal iRBD is expected to be a potential biomarker for predicting clinical phenotypic transformation. This article reviews the research progress of neuromolecular imaging in patients with iRBD from the perspective of iRBD transforming synucleinopathies.

REM sleep behavior and olfactory dysfunction: improving the utility and translation of animal models in the search for neuroprotective therapies for Parkinson's disease

Parkinson's disease (PD) is a heterogeneous neurodegenerative disease that belongs to the family of synucleiopathies, varying in age, symptoms and progression. Hallmark of the disease is the accumulation of misfolded α-synuclein protein (α-Syn) in neuronal and non-neuronal brain cells. In past decades, diagnosis and treatment of PD has focused on motor deficits, which for the clinical endpoint, have contributed to the prevalence of deficits in the nigrostriatal dopaminergic system and animal models related to motor behavior to study disease. However, clinical trials have failed to translate results from animal models into effective treatments. PD as a multisystem disorder therefore requires additional assessment of motor and non-motor symptoms. Braak's staging revealed early α-Syn pathology in pontine brainstem and olfactory circuits controlling rapid eye movement sleep behavior disorder (RBD) and olfaction, respectively. Recent converging evidence from multicenter clinical studies supports that RBD is the most important risk factor for prodromal PD and the conduct of neuroprotective therapeutic trials in RBD-enriched cohorts has been recommended. Animal models of RBD and olfaction dysfunction can aid to fill the gap in translational research.

REM sleep behavior disorder as a complex condition with heterogeneous underlying disorders: clinical management and prognostic implications [Commentary]

PURPOSE

To review how REM sleep behavior disorder (RBD) is a complex condition with heterogeneous underlying disorders; and to review clinical management issues and prognostic implications.

METHODS

PubMed literature search and contents from the first textbook of RBD (2018).

RESULTS

RBD, with its core objective diagnostic feature of REM-without-atonia (RWA) documented by video-polysomnography, can emerge during the entire lifespan, and can initially present as an idiopathic (isolated) condition (iRBD), or can be associated with a broad spectrum of disorders including narcolepsy, alpha-synuclein neurodegenerative disorders (esp. Parkinson's disease [PD] and dementia with Lewy bodies [DLB]), paraneoplastic neurological syndromes and autoimmune disorders, CNS lesions (e.g., tumors, stroke), other neurological disorders, psychiatric disorders (PTSD, mood disorders), can be triggered by antidepressant/other medications, and can emerge acutely with drug withdrawal states, toxic-metabolic states, etc. Important clinical issues include the evolution of iRBD to PD/DLB in most middle-aged and older patients over a period of years to several decades, with compelling prognostic implications, along with the hope of enrolling these patients in future clinical trials to test promising disease-modifying therapies. Also, the strong link of RBD with narcolepsy needs further investigation. Parasomnia overlap disorder involves RBD and NREM parasomnias that can be idiopathic or linked with a broad range of clinical disorders. RBD usually responds to therapy consisting mainly of melatonin and/or clonazepam at bedtime. The complex associations of RBD with OSA are being increasingly investigated. RBD mimics with dream-enactment need to be recognized for diagnostic and management purposes, including severe OSA, NREM parasomnias, PLMD, nocturnal seizures, and other conditions.

CONCLUSIONS

The clinical and research RBD fields span across the disciplines of neurology, pulmonary, psychiatry, psychology, and pediatric sleep medicine, along with physical medicine and rehabilitation medicine, other allied disciplines, and the basic and clinical neurosciences.

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.

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.

Reduced Intracortical Facilitation to TMS in Both Isolated REM Sleep Behavior Disorder (RBD) and Early Parkinson's Disease with RBD

BACKGROUND

a reduced intracortical facilitation (ICF), a transcranial magnetic stimulation (TMS) measure largely mediated by glutamatergic neurotransmission, was observed in subjects affected by isolated REM sleep behavior disorder (iRBD). However, direct comparison between iRBD and Parkinson's disease (PD) with RBD is currently lacking.

METHODS

resting motor threshold, contralateral cortical silent period, amplitude and latency of motor evoked potentials, short-interval intracortical inhibition, and intracortical facilitation (ICF) were recorded from 15 drug-naïve iRBD patients, 15 drug-naïve PD with RBD patients, and 15 healthy participants from the right First Dorsal Interosseous muscle. REM sleep atonia index (RAI), Mini Mental State Examination (MMSE), Geriatric Depression Scale (GDS), and Epworth Sleepiness Scale (ESS) were assessed.

RESULTS

Groups were similar for sex, age, education, and patients for RBD duration and RAI. Neurological examination, MMSE, ESS, and GDS were normal in iRBD patients and controls; ESS scored worse in PD patients, but with no difference between groups at post hoc analysis. Compared to controls, both patient groups exhibited a significantly decreased ICF, without difference between them.

CONCLUSIONS

iRBD and PD with RBD shared a reduced ICF, thus suggesting the involvement of glutamatergic transmission both in subjects at risk for degeneration and in those with an overt α-synucleinopathy.

Clinical and imaging evidence of brain-first and body-first Parkinson's disease

Braak's hypothesis has been extremely influential over the last two decades. However, neuropathological and clinical evidence suggest that the model does not conform to all patients with Parkinson's disease (PD). To resolve this controversy, a new model was recently proposed; in brain-first PD, the initial α-synuclein pathology arise inside the central nervous system, likely rostral to the substantia nigra pars compacta, and spread via interconnected structures - eventually affecting the autonomic nervous system; in body-first PD, the initial pathological α-synuclein originates in the enteric nervous system with subsequent caudo-rostral propagation to the autonomic and central nervous system. By using REM-sleep behavior disorder (RBD) as a clinical identifier to distinguish between body-first PD (RBD-positive at motor symptom onset) and brain-first PD (RBD-negative at motor symptom onset), we explored the literature to evaluate clinical and imaging differences between these proposed subtypes. Body-first PD patients display: 1) a larger burden of autonomic symptoms - in particular orthostatic hypotension and constipation, 2) more frequent pathological α-synuclein in peripheral tissues, 3) more brainstem and autonomic nervous system involvement in imaging studies, 4) more symmetric striatal dopaminergic loss and motor symptoms, and 5) slightly more olfactory dysfunction. In contrast, only minor cortical metabolic alterations emerge before motor symptoms in body-first. Brain-first PD is characterized by the opposite clinical and imaging patterns. Patients with pathological LRRK2 genetic variants mostly resemble a brain-first PD profile whereas patients with GBA variants typically conform to a body-first profile. SNCA-variant carriers are equally distributed between both subtypes. Overall, the literature indicates that body-first and brain-first PD might be two distinguishable entities on some clinical and imaging markers.

Generalized EEG Slowing Across Phasic REM Sleep, Not Subjective RBD Severity, Predicts Neurodegeneration in Idiopathic RBD

PURPOSE

Idiopathic rapid eye movement sleep behavior disorder (iRBD) is the prodromal marker of α-synuclein degeneration with markedly high predictive value. We aim to evaluate the value of electroencephalography (EEG) data during rapid eye movement (REM) sleep and subjective RBD severity in predicting the conversion to neurodegenerative diseases in iRBD patients.

METHODS

At the baseline, iRBD patients underwent clinical assessment and video-polysomnography (PSG). Relative spectral power for nine frequency bands during phasic and tonic REM sleep in three regions of interest, slow-to-fast ratios, clinical and PSG variables were estimated and compared between iRBD patients who converted to neurodegenerative diseases (iRBD-C) and iRBD patients who remained disease-free (iRBD-NC). Receiver operating characteristic (ROC) curves evaluated the predictive performance of slow-to-fast ratios, and subjective RBD severity as assessed with RBD Questionnaire-Hong Kong.

RESULTS

Twenty-two (33.8%) patients eventually developed neurodegenerative diseases. The iRBD-C group showed shorter total sleep time (p < 0.001), lower stage 2 sleep percentage (p = 0.044), more periodic leg-movement-related arousal index (p = 0.004), increased tonic chin electromyelographic activity (p = 0.040) and higher REM density in the third REM episode (p = 0.034) than the iRBD-NC group. EEG spectral power analyses revealed that iRBD phenoconverters showed significantly higher delta and lower alpha power, especially in central and occipital regions during the phasic REM state compared to the iRBD-NC group. Significantly higher slow-to-fast ratios were observed in a more generalized way during the phasic state in the iRBD-C group compared to the iRBD-NC group. ROC analyses of the slowing ratio in occipital areas during phasic REM sleep yielded an area under the curve of 0.749 (p = 0.001), while no significant predictive value of subjective RBD severity was observed.

CONCLUSION

Our study shows that EEG slowing, especially in a more generalized manner during the phasic period, may be a promising marker in predicting phenoconversion in iRBD, rather than subjective RBD severity.

Neurophysiological Aspects of REM Sleep Behavior Disorder (RBD): A Narrative Review

REM sleep without atonia (RSWA) is the polysomnographic (PSG) hallmark of rapid eye movement (REM) sleep behavior disorder (RBD), a feature essential for the diagnosis of this condition. Several additional neurophysiological aspects of this complex disorder have also recently been investigated in depth, which constitute the focus of this narrative review, together with RSWA. First, we describe the complex neural network underlying REM sleep and its muscle atonia, focusing on the disordered mechanisms leading to RSWA. RSWA is then described in terms of its polysomnographic features, and the methods (visual and automatic) currently available for its scoring and quantification are exposed and discussed. Subsequently, more recent and advanced neurophysiological features of RBD are described, such as electroencephalography during wakefulness and sleep, transcranial magnetic stimulation, and vestibular evoked myogenic potentials. The role of the assessment of neurophysiological features in the study of RBD is then carefully discussed, highlighting their usefulness and sensitivity in detecting neurodegeneration in the early or prodromal stages of RBD, as well as their relationship with other proposed biomarkers for the diagnosis, prognosis, and monitoring of this condition. Finally, a future research agenda is proposed to help clarify the many still unclear aspects of RBD.

Neurophysiological Aspects of REM Sleep Behavior Disorder (RBD): A Narrative Review

REM sleep without atonia (RSWA) is the polysomnographic (PSG) hallmark of rapid eye movement (REM) sleep behavior disorder (RBD), a feature essential for the diagnosis of this condition. Several additional neurophysiological aspects of this complex disorder have also recently been investigated in depth, which constitute the focus of this narrative review, together with RSWA. First, we describe the complex neural network underlying REM sleep and its muscle atonia, focusing on the disordered mechanisms leading to RSWA. RSWA is then described in terms of its polysomnographic features, and the methods (visual and automatic) currently available for its scoring and quantification are exposed and discussed. Subsequently, more recent and advanced neurophysiological features of RBD are described, such as electroencephalography during wakefulness and sleep, transcranial magnetic stimulation, and vestibular evoked myogenic potentials. The role of the assessment of neurophysiological features in the study of RBD is then carefully discussed, highlighting their usefulness and sensitivity in detecting neurodegeneration in the early or prodromal stages of RBD, as well as their relationship with other proposed biomarkers for the diagnosis, prognosis, and monitoring of this condition. Finally, a future research agenda is proposed to help clarify the many still unclear aspects of RBD.

Neurochemical Features of Rem Sleep Behaviour Disorder

Dopaminergic deficiency, shown by many studies using functional neuroimaging with Single Photon Emission Computerized Tomography (SPECT) and Positron Emission Tomography (PET), is the most consistent neurochemical feature of rapid eye movement (REM) sleep behaviour disorder (RBD) and, together with transcranial ultrasonography, and determination of alpha-synuclein in certain tissues, should be considered as a reliable marker for the phenoconversion of idiopathic RBD (iRBD) to a synucleopathy (Parkinson’s disease –PD- or Lewy body dementia -LBD). The possible role in the pathogenesis of RBD of other neurotransmitters such as noradrenaline, acetylcholine, and excitatory and inhibitory neurotransmitters; hormones such as melatonin, and proinflammatory factors have also been suggested by recent reports. In general, brain perfusion and brain glucose metabolism studies have shown patterns resembling partially those of PD and LBD. Finally, the results of structural and functional MRI suggest the presence of structural changes in deep gray matter nuclei, cortical gray matter atrophy, and alterations in the functional connectivity within the basal ganglia, the cortico-striatal, and the cortico-cortical networks, but they should be considered as preliminary.

Effects of safinamide on REM sleep behavior disorder in Parkinson disease: A randomized, longitudinal, cross-over pilot study

BACKGROUND

Rapid Eye Movement sleep behavior disorder (RBD) is characterized by dream enactment and loss of muscle atonia during REM-sleep. RBD as a premotor feature occurred souvent in patients who develop Parkinson's disease. The glutamatergic, glycinergic, and GABA-ergic systems appear to play a crucial role in the pathogenesis of RBD.

METHODS

The present exploratory longitudinal cross-over study aimed to observe the effect of safinamide on RBD symptoms. Thirty patients with PD and RBD were randomized into two groups (15 subjects each), those that received for a period of 3-months safinamide (50 mg/die) in addition (Group A + ) or in absence (Group B - ) to the usual antiparkinsonian therapy. Patients exploring the clinical and video-polysomnographic changes occurred during this pharmacological therapy.

RESULTS

Twenty-two of 30 patients reported clear improvement in symptoms during safinamide treatment, and 16 were absolutely free from clinical RBD-symptoms at the end of the treatment. Eight patients reported slight improvement in RBD-symptoms. In 6/30 patients no substantial improvement was recorded about clinical RBD-symptoms had frightening dreams or from the bed after 1-week of treatment. In addition, after safinamide, the mean UPDRS-II and III scores decreased, while PDSS-2 score indicating an improvement in both motor symptoms and nocturnal sleep features. A significant reduction of sleep behavior disorder by questionnaire-Hong Kong-score (RBDQ-HS), mainly for two individual RBDQ-HK-items (dream related movements and failing out of bed) was registered.

CONCLUSIONS

This pilot study indicated that safinamide is well tolerated and improves RBD-symptom in parkinsonian.

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 one 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.

A Questionnaire-Based Study on Clinical REM Sleep Behavior Disorder and Subtypes in Multiple System Atrophy

OBJECTIVES

Studies documenting the association between rapid eye movement sleep behavior disorder (RBD) and subtypes of multiple system atrophy (MSA) are rare. In this study, we investigated the presence of clinical RBD in MSA patients and compared the prevalence and severity of RBD in patients with MSA-P and MSA-C subtypes.

METHODS

We evaluated 54 consecutive patients presenting with MSA and hospitalized in the neurology ward of Beijing Hospital from February 2012 to June 2020. The healthy control (HC) group consisted of 100 healthy individuals who came to our hospital for physical examination. The clinical diagnosis of RBD was based on the minimal diagnostic criteria of International Classification of Sleep Disorders, revised. The severity of clinical RBD was rated on a digital scale from 0 to 3. The patients were divided into 2 subgroups: MSA-P and MSA-C. The MSA and HC groups were compared in terms of frequency of clinical RBD. The MSA-P and MSA-C subgroups were compared with each other for age, sex, onset age, disease duration, and features of clinical RBD. The correlation between severity of clinical RBD and clinical characteristics of MSA was analyzed in the patient groups.

RESULTS

The frequency of clinical RBD in MSA and HC groups was 70.4% (38/54) and 5% (5/100), respectively. The difference between 2 groups was significant (χ2 = 74.453, p = 0.000). Among the patients, 57.4% (31/54) had the MSA-P subtype. There were no significant differences between MSA-P and MSA-C subtypes in the prevalence (χ2 = 1.734, p = 0.188) and severity (χ2 = 1.776, p = 0.412) of clinical RBD. The onset of clinical RBD during the premotor period was not different between the subtypes of MSA, either in patients' number of preceding the onset of motor symptoms (χ2 = 0.581, p = 0.446) or the preceding time (Z = -0.550, p = 0.582). For the MSA-C patients, there was a negative correlation between the score of severity of the RBD scale and RBD preceding motor symptoms (r = -0.482, p = 0.020).

CONCLUSION

In our study, the prevalence of clinical RBD is unrelated to the subtypes of MSA. The onset of clinical RBD during the premotor period was not different between subtypes of MSA. However, we found that the severity of RBD occurring before the motor symptoms was more than that occurring after the motor symptoms in MSA-C patients. Our results showed that MSA-P and MSA-C patients may have a probable indicator for the similar pathologic mechanism of the disease and its sleep problems.

Neural circuitry underlying REM sleep: A review of the literature and current concepts

As one of the fundamental sleep states, rapid eye movement (REM) sleep is believed to be associated with dreaming and is characterized by low-voltage, fast electroencephalographic activity and loss of muscle tone. However, the mechanisms of REM sleep generation have remained unclear despite decades of research. Several models of REM sleep have been established, including a reciprocal interaction model, limit-cycle model, flip-flop model, and a model involving γ-aminobutyric acid, glutamate, and aminergic/orexin/melanin-concentrating hormone neurons. In the present review, we discuss these models and summarize two typical disorders related to REM sleep, namely REM sleep behavior disorder and narcolepsy. REM sleep behavior disorder is a sleep muscle-tone-related disorder and can be treated with clonazepam and melatonin. Narcolepsy, with core symptoms of excessive daytime sleepiness and cataplexy, is strongly connected with orexin in early adulthood.

α-Synuclein Responses in the Laterodorsal Tegmentum, the Pedunculopontine Tegmentum, and the Substantia Nigra: Implications for Early Appearance of Sleep Disorders in Parkinson's Disease

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative disorder associated with insoluble pathological aggregates of the protein α-synuclein. While PD is diagnosed by motor symptoms putatively due to aggregated α-synuclein-mediated damage to substantia nigra (SN) neurons, up to a decade before motor symptom appearance, patients exhibit sleep disorders (SDs). Therefore, we hypothesized that α-synuclein, which can be present in monomeric, fibril, and other forms, has deleterious cellular actions on sleep-control nuclei.

OBJECTIVE

We investigated whether native monomer and fibril forms of α-synuclein have effects on neuronal function, calcium dynamics, and cell-death-induction in two sleep-controlling nuclei: the laterodorsal tegmentum (LDT), and the pedunculopontine tegmentum (PPT), as well as the motor-controlling SN.

METHODS

Size exclusion chromatography, Thioflavin T emission, and circular dichroism spectroscopy were used to isolate structurally defined forms of recombinant, human α-synuclein. Neuronal and viability effects of characterized monomeric and fibril forms of α-synuclein were determined on LDT, PPT, and SN neurons using electrophysiology, calcium imaging, and neurotoxicity assays.

RESULTS

In LDT and PPT, both forms of α-synuclein induced excitation and increased calcium, and the monomeric form heightened putatively excitotoxic neuronal death, whereas, in the SN we saw inhibition, decreased intracellular calcium, and monomeric α-synuclein was not associated with heightened cell death.

CONCLUSION

Nucleus-specific differential effects suggest mechanistic underpinnings of SDs' prodromal appearance in PD. While speculative, we hypothesize that the monomeric form of α-synuclein compromises functionality of sleep-control neurons, leading to the presence of SDs decades prior to motor dysfunction.

Rapid Eye Movement Sleep Behavior Disorder and Other Rapid Eye Movement Parasomnias

PURPOSE OF REVIEW

The discovery of rapid eye movement (REM) sleep and, in particular, REM sleep behavior disorder (RBD) have brought elusive nightmarish experiences to scientific scrutiny. This article summarizes a century of sleep research to examine the maladies of dreaming, their pathophysiologic significance, and management.

RECENT FINDINGS

Under healthy physiologic conditions, REM sleep is characterized by vivid mentation combined with skeletal muscle paralysis. The loss of REM sleep atonia in RBD results in vivid, potentially injurious dream enactment to patients and bed partners. RBD is common, affecting at least 1% of the population and is primarily caused by α-synuclein pathology of REM sleep-related brainstem neurons. The majority of patients with RBD ultimately develop a neurodegenerative syndrome such as Parkinson disease, dementia with Lewy bodies, or multiple system atrophy. Among patients with Parkinson disease, RBD predicts an aggressive disease course with rapid cognitive, motor, and autonomic decline. RBD is diagnosed by the presence of dream enactment episodes (either recorded or clinically recalled) and physiologic evidence of REM sleep without atonia demonstrated on polysomnography. Bedroom safety is of paramount importance in the management of RBD while pharmacokinetic options include melatonin or clonazepam.

SUMMARY

The injurious dream enactment of RBD is common and treatable. It is a syndrome of α-synuclein pathology with most patients ultimately developing Parkinson disease, dementia with Lewy bodies, or a related disorder.

A circuit perspective on narcolepsy

The sleep disorder narcolepsy is associated with symptoms related to either boundary state control that include excessive daytime sleepiness and sleep fragmentation, or rapid eye movement (REM) sleep features including cataplexy, sleep paralysis, hallucinations, and sleep-onset REM sleep events (SOREMs). Although the loss of Hypocretin/Orexin (Hcrt/Ox) peptides or their receptors have been associated with the disease, here we propose a circuit perspective of the pathophysiological mechanisms of these narcolepsy symptoms that encompasses brain regions, neuronal circuits, cell types, and transmitters beyond the Hcrt/Ox system. We further discuss future experimental strategies to investigate brain-wide mechanisms of narcolepsy that will be essential for a better understanding and treatment of the disease.

Propagated α-synucleinopathy recapitulates REM sleep behaviour disorder followed by parkinsonian phenotypes in mice

Idiopathic rapid eye movement sleep behaviour disorder (RBD) is now recognized as an early manifestation of α-synucleinopathies. Increasing experimental studies demonstrate that manipulative lesion or inactivation of the neurons within the sublaterodorsal tegmental nucleus (also known as the subcoeruleus nucleus in humans) can induce RBD-like behaviours in animals. As current RBD animal models are not established on the basis of α-synucleinopathy, they do not represent the pathological substrate of idiopathic RBD and thus cannot model the phenoconversion to Parkinson's disease. The purpose of this study was therefore to establish an α-synucleinopathy-based RBD animal model with the potential to convert to parkinsonian disorder. To this end, we first determined the functional neuroanatomical location of the sublaterodorsal tegmental nucleus in wild-type C57BL/6J mice and then validated its function by recapitulating RBD-like behaviours based on this determined nucleus. Next, we injected preformed α-synuclein fibrils into the sublaterodorsal tegmental nucleus and performed regular polysomnographic recordings and parkinsonian behavioural and histopathological studies in these mice. As a result, we recapitulated RBD-like behaviours in the mice and further showed that the α-synucleinopathy and neuron degeneration identified within the sublaterodorsal tegmental nucleus acted as the neuropathological substrates. Subsequent parkinsonian behavioural studies indicated that the α-synucleinopathy-based RBD mouse model were not stationary, but could further progress to display parkinsonian locomotor dysfunction, depression-like disorder, olfactory dysfunction and gastrointestinal dysmotility. Corresponding to that, we determined α-synuclein pathology in the substantia nigra pars compacta, olfactory bulb, enteral neuroplexus and dorsal motor nucleus of vagus nerve, which could underlie the parkinsonian manifestations in mice. In conclusion, we established a novel α-synucleinopathy-based RBD mouse model and further demonstrated the phenoconversion of RBD to Parkinson's disease in this animal model.

A high-density electroencephalography study reveals abnormal sleep homeostasis in patients with rapid eye movement sleep behavior disorder

Rapid eye movement (REM) sleep behavior disorder (RBD) is characterized by disrupting motor enactments during REM sleep, but also cognitive impairments across several domains. In addition to REM sleep abnormalities, we hypothesized that RBD patients may also display EEG abnormalities during NREM sleep. We collected all-night recordings with 256-channel high-density EEG in nine RBD patients, predominantly early-onset medicated individuals, nine sex- and age- matched healthy controls, and nine additional controls with matched medications and comorbidities. Power spectra in delta to gamma frequency bands were compared during both REM and NREM sleep, between phasic and tonic REM sleep, and between the first versus last cycle of NREM sleep. Controls, but not RBD patients, displayed a decrease in beta power during phasic compared to tonic REM sleep. Compared to controls, RBD patients displayed a reduced decline in SWA from early to late NREM sleep. Overnight changes in the distribution of the amplitude of slow waves were also reduced in RBD patients. Without suppression of beta rhythms during phasic REM sleep, RBD patients might demonstrate heightened cortical arousal, favoring the emergence of behavioral episodes. A blunted difference between REM sleep sub-stages may constitute a sensitive biomarker for RBD. Moreover, reduced overnight decline in SWA suggests a reduced capacity for synaptic plasticity in RBD patients, which may favor progression towards neurodegenerative diseases.

A Discrete Glycinergic Neuronal Population in the Ventromedial Medulla That Induces Muscle Atonia during REM Sleep and Cataplexy in Mice

During rapid eye movement (REM) sleep, anti-gravity muscle tone and bodily movements are mostly absent, because somatic motoneurons are inhibited by descending inhibitory pathways. Recent studies showed that glycine/GABA neurons in the ventromedial medulla (VMM; Gly^VMM neurons) play an important role in generating muscle atonia during REM sleep (REM-atonia). However, how these REM-atonia-inducing neurons interconnect with other neuronal populations has been unknown. In the present study, we first identified a specific subpopulation of Gly^VMM neurons that play an important role in induction of REM-atonia by virus vector-mediated tracing in male mice in which glycinergic neurons expressed Cre recombinase. We found these neurons receive direct synaptic input from neurons in several brain stem regions, including glutamatergic neurons in the sublaterodorsal tegmental nucleus (SLD; Glu^SLD neurons). Silencing this circuit by specifically expressing tetanus toxin light chain (TeTNLC) resulted in REM sleep without atonia. This manipulation also caused a marked decrease in time spent in cataplexy-like episodes (CLEs) when applied to narcoleptic orexin-ataxin-3 mice. We also showed that Gly^VMM neurons play an important role in maintenance of sleep. This present study identified a population of glycinergic neurons in the VMM that are commonly involved in REM-atonia and cataplexy.SIGNIFICANCE STATEMENT We identified a population of glycinergic neurons in the ventral medulla that plays an important role in inducing muscle atonia during rapid eye movement (REM) sleep. It sends axonal projections almost exclusively to motoneurons in the spinal cord and brain stem except to those that innervate extraocular muscles, while other glycinergic neurons in the same region also send projections to other regions including monoaminergic nuclei. Furthermore, these neurons receive direct inputs from several brainstem regions including glutamatergic neurons in the sublaterodorsal tegmental nucleus (SLD). Genetic silencing of this pathway resulted in REM sleep without atonia and a decrease of cataplexy when applied to narcoleptic mice. This work identified a neural population involved in generating muscle atonia during REM sleep and cataplexy.

Sleep Disorders in dogs: A Pathophysiological and Clinical Review

Sleep is a fundamental process in mammals, including domestic dogs. Disturbances in sleep affect physiological functions like cognitive and physical performance, immune response, pain sensation and increase the risk of diseases. In dogs, sleep can be affected by several conditions, with narcolepsy, REM sleep behavior disorder and sleep breathing disorders being the most frequent causes. Furthermore, sleep disturbances can be a symptom of other primary diseases where they can contribute to the worsening of clinical signs. This review describes reciprocally interacting sleep and wakefulness promoting systems and how their dysfunction can explain the pathophysiological mechanisms of sleep disorders. Additionally, this work discusses the clinical characteristics, diagnostic tools and available treatments for these disorders while highlighting areas in where further studies are needed so as to improve their treatment and prevention.