The Brain Correlates of Laugh and Cataplexy in Childhood Narcolepsy

Recent insights into the pathophysiology of narcolepsy type 1

Narcolepsy type 1 (NT1) is a sleep-wake disorder in which people typically experience excessive daytime sleepiness, cataplexy and other sleep-wake disturbances impairing daily life activities. NT1 symptoms are due to hypocretin deficiency. The cause for the observed hypocretin deficiency remains unclear, even though the most likely hypothesis is that this is due to an auto-immune process. The search for autoantibodies and autoreactive T-cells has not yet produced conclusive evidence for or against the auto-immune hypothesis. Other mechanisms, such as reduced corticotrophin-releasing hormone production in the paraventricular nucleus have recently been suggested. There is no reversive treatment, and the therapeutic approach is symptomatic. Early diagnosis and appropriate NT1 treatment is essential, especially in children to prevent impaired cognitive, emotional and social development. Hypocretin receptor agonists have been designed to replace the attenuated hypocretin signalling. Pre-clinical and clinical trials have shown encouraging initial results. A better understanding of NT1 pathophysiology may contribute to faster diagnosis or treatments, which may cure or prevent it.

Narcolepsy and rapid eye movement sleep

Since the first description of narcolepsy at the end of the 19th Century, great progress has been made. The disease is nowadays distinguished as narcolepsy type 1 and type 2. In the 1960s, the discovery of rapid eye movement sleep at sleep onset led to improved understanding of core sleep-related disease symptoms of the disease (excessive daytime sleepiness with early occurrence of rapid eye movement sleep, sleep-related hallucinations, sleep paralysis, rapid eye movement parasomnia), as possible dysregulation of rapid eye movement sleep, and cataplexy resembling an intrusion of rapid eye movement atonia during wake. The relevance of non-sleep-related symptoms, such as obesity, precocious puberty, psychiatric and cardiovascular morbidities, has subsequently been recognized. The diagnostic tools have been improved, but sleep-onset rapid eye movement periods on polysomnography and Multiple Sleep Latency Test remain key criteria. The pathogenic mechanisms of narcolepsy type 1 have been partly elucidated after the discovery of strong HLA class II association and orexin/hypocretin deficiency, a neurotransmitter that is involved in altered rapid eye movement sleep regulation. Conversely, the causes of narcolepsy type 2, where cataplexy and orexin deficiency are absent, remain unknown. Symptomatic medications to treat patients with narcolepsy have been developed, and management has been codified with guidelines, until the recent promising orexin-receptor agonists. The present review retraces the steps of the research on narcolepsy that linked the features of the disease with rapid eye movement sleep abnormality, and those that do not appear associated with rapid eye movement sleep.

Giggle incontinence: a scoping review

Giggle incontinence (GI) is poorly described, defined, and understood. It is considered a bladder storage disorder in which laughter causes an uncontrollable episode of urinary incontinence that cannot be stopped until the bladder is completely emptied. It has been confused with stress urinary incontinence and overactive bladder. A thorough analysis of 26 articles on the subject of "giggle incontinence" and associated terms was performed, including all articles since the phrase first appeared. To date, 351 GI cases have been reported. It occurs mainly in women (69.5%) at 5 years of age, with a prevalence ranging from 8.4 to 16.2 years (average age of 12.4 years), and some cases have a family history of the disease (13-16.7%). This review discusses the historical background, current understanding, and challenges related to GI. It primarily affects females after the age of 5 years, causing complete bladder emptying during uncontrollable laughter. The exact cause is unknown, but hypotheses suggest involvement of the central nervous system. Diagnosis relies on clinical history, physical tests, and urine frequency evaluation. Management involves urotherapy techniques, biofeedback, and methylphenidate. Understanding GI will aid in developing more effective management techniques. IMPACT: Highlights limited awareness among healthcare professionals about giggle incontinence as a distinct condition, emphasizing the need for standardized diagnostic criteria and assessment tools. Addresses insufficient understanding of the underlying mechanisms and contributing factors, providing valuable insights for better diagnosis and treatment. Emphasizes the importance of patient education and support, calling for improved resources and counseling. Urges further research and evidence-based guidelines to enhance treatment strategies.

Regulation of REM sleep in mice: The role of dopamine and serotonin function in the basolateral amygdala

Animals have a sleep cycle that involves the repetitive occurrence of non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. In a previous study, we discovered that a transient increase in dopamine (DA) levels in the basolateral amygdala (BLA) during NREM sleep terminates NREM sleep and initiates REM sleep by acting on Drd2-positive neurons (Hasegawa et al., 2022). In this study, we identified the neurons activated by the transient increase of DA in the BLA and found that chemogenetic excitation of these neurons increased REM sleep. Additionally, we demonstrated that acute inhibition of serotonin (5HT) in the BLA elicited a transient increase in DA in the BLA, which triggered REM sleep.

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.

Amygdala neurocircuitry at the interface between emotional regulation and narcolepsy with cataplexy

Narcolepsy is a sleep disorder characterized by chronic and excessive daytime sleepiness, and sudden intrusion of sleep during wakefulness that can fall into two categories: type 1 and type 2. Type 1 narcolepsy in humans is widely believed to be caused as a result of loss of neurons in the brain that contain the key arousal neuropeptide Orexin (Orx; also known as Hypocretin). Patients with type 1 narcolepsy often also present with cataplexy, the sudden paralysis of voluntary muscles which is triggered by strong emotions (e.g., laughter in humans, social play in dogs, and chocolate in rodents). The amygdala is a crucial emotion-processing center of the brain; however, little is known about the role of the amygdala in sleep/wake and narcolepsy with cataplexy. A collection of reports across human functional neuroimaging analyses and rodent behavioral paradigms points toward the amygdala as a critical node linking emotional regulation to cataplexy. Here, we review the existing evidence suggesting a functional role for the amygdala network in narcolepsy, and build upon a framework that describes relevant contributions from the central nucleus of the amygdala (CeA), basolateral amygdala (BLA), and the extended amygdala, including the bed nucleus of stria terminalis (BNST). We propose that detailed examinations of amygdala neurocircuitry controlling transitions between emotional arousal states may substantially advance progress in understanding the etiology of narcolepsy with cataplexy, leading to enhanced treatment opportunities.

Activation of the rostral nucleus accumbens shell by optogenetics induces cataplexy-like behavior in orexin neuron-ablated mice

Cataplexy is one of the symptoms of type 1 narcolepsy, characterized by a sudden loss of muscle tone. It can be seen as a behavioral index of salience, predominantly positive emotion, since it is triggered by laughter in humans and palatable foods in mice. In our previous study using chemogenetic techniques in narcoleptic mice (orexin neuron-ablated mice), we found that the rostral nucleus accumbens (NAc) shell is needed for chocolate-induced cataplexy. In this study, we investigated whether a short-lasting stimulation/inhibition of the NAc by optogenetics led to a similar result. Photo-illumination to the NAc in the channel rhodopsin-expressing mice showed a higher incidence (34.9 ± 5.1%) of cataplexy-like behavior than the control mice (17.8 ± 3.1%, P = 0.0056). Meanwhile, inactivation with archaerhodopsin did not affect incidence. The episode duration of cataplexy-like behavior was not affected by activation or inactivation. Immunohistochemical analysis revealed that photo-illumination activated channel rhodopsin-expressing NAc shell neurons. Thus, activation of the NAc, whether transient (light stimulation) or longer-lasting (chemical stimulation in our previous study), facilitates cataplexy-like behaviors and contributes to the induction but not maintenance in them. On the other hand, our study's result from optogenetic inhibition of the NAc (no effect) was different from chemogenetic inhibition (reduction of cataplexy-like behavior) in our previous study. We propose that the initiation of cataplexy-like behavior is facilitated by activation of the NAc, while NAc-independent mechanisms determine the termination of the behavior.

Narcolepsy and emotions: Is there a place for a theory of mind approach?

Narcolepsy type 1 is a central disorder of hypersomnolence characterized by excessive daytime sleepiness, rapid eye movement sleep-related manifestations, and cataplexy. In the current literature there is general agreement regarding neural correlates of Narcolepsy type 1 that appear to be related to anatomical and functional abnormalities in the hypothalamic region. In the last two decades, researchers shed light on the neurological bases of cataplexy by focusing on the neurobiological correlates of emotions. Although the results of these studies differ, they all point to an impairment in the amygdala and hypothalamus functions that are known to be involved in emotional processing, suggesting an impairment in this domain in narcoleptic patients. Indeed, despite heterogeneous results, several studies showed that narcoleptic patients differed from healthy controls in processing emotional stimuli. From a behavioral point of view, these findings suggest that alterations in emotional processing may be driven, at least in part, by compensatory strategies to avoid or reduce the frequency of cataplexy attacks. Surprisingly, the only study exploring in NT1 the behavioural performances in emotional facial recognition found no differences between NT1 adults and controls. We hypothesize that narcoleptic patients may present an alteration in a more complex socio-cognitive ability that is related to emotional processing, namely Theory of Mind. This review aims to investigate the literature supporting this hypothesis and to propose possible future developments on this topic.

Approach to a sleepy child: Diagnosis and treatment of excessive daytime sleepiness in children and adolescents

The aim of this review is to give updated information to pediatric neurologists on the correct diagnostic approach and treatment of excessive daytime sleepiness (EDS) in children and adolescents. Due to the change in the society habits, EDS is becoming an emerging problem for the health system. At the present there are few articles specifically devoted to the evaluation of EDS. EDS is often reported in several manuscripts as a side effect of other sleep disorders (obstructive sleep apnea, circadian disorders, etc.) or of the use of drugs or of the substance abuse or as a consequence of bad sleep habits and poor sleep hygiene. EDS, especially in children, may manifest with paradoxical symptoms like hyperactivity, inattention, and impulsiveness. However, common sign of EDS in children are the propensity to sleep longer than usual, the difficulty waking up in the morning, and falling asleep frequently during the day in monotonous situation. The diagnosis should include subjective (sleep diaries, questionnaires) and objective (polysomnography, multiple sleep latency test, etc.) instruments to avoid misdiagnosis. Narcolepsy is the most studied central disorder of hypersomnolence, and it is a predominantly pediatric disease with a peak age of onset in prepuberty but the diagnosis is often delayed especially in mild forms. The early and correct treatment of narcolepsy and of other form of EDS is extremely important since late and inappropriate treatments can affect the psychosocial development of the children and adolescents.

Abnormal Regional Spontaneous Neural Activity and Functional Connectivity in Unmedicated Patients with Narcolepsy Type 1: A Resting-State fMRI Study

BACKGROUND

Previous Resting-state functional magnetic resonance imaging (fMRI) studies have mainly focused on cerebral functional alteration in processing different emotional stimuli in patients with narcolepsy type 1 (NT1), but were short of exploration of characteristic brain activity and its remote interaction patterns. This study aimed to investigate the spontaneous blood oxygen fluctuations at rest and to elucidate the neural mechanisms underlying neuropsychiatric behavior.

METHOD

A total of 18 unmedicated patients with NT1 and matched healthy individuals were recruited in a resting-state fMRI study. Magnetic resonance imaging (MRI) data were first analyzed using fractional low-frequency amplitude of low-frequency fluctuation (fALFF) to detect changes in local neural activity, and regions with group differences were taken as regions of interest (ROIs). Secondly, functional connectivity (FC) analysis was used to explore altered connectivity between ROIs and other areas. Lastly, the relationship between functional brain activity and neuropsychiatric behaviors was analyzed with correlation analysis.

RESULTS

fALFF analysis revealed enhanced neural activity in bilateral fusiform gyrus (FFG), right precentral gyrus, and left postcentral gyrus (PoCG) in the NT1 group. The patients indicated reduced activity in the bilateral temporal pole middle temporal gyrus (TPOmid), left caudate nucleus (CAU), left parahippocampus, left precuneus (PCUN), right amygdala, and right anterior cingulate and paracingulate gyri. ESS score was negatively correlated with fALFF in the right FFG. The NT1 group revealed decreased connectivity between left TPOmid and right PoCG, the bilateral middle frontal gyrus, left superior frontal gyrus, medial, and right supramarginal gyrus. Epworth Sleepiness Scale (ESS) was negatively correlated with FC of the left TPOmid with left putamen (PUT) in NT1. Compared with healthy controls (HCs), enhanced FC of the left CAU with right FFG was positively associated with MSLT-SOREMPs in patients. Furthermore, increased FC of the left PCUN with right PoCG was positively correlated with SDS score.

CONCLUSIONS

We found that multiple functional activities related to the processing of emotional regulation and sensory information processing were abnormal, and some were related to clinical characteristics. fALFF in the left postcentral or right precentral gyrus may be used as a biomarker of narcolepsy, whereas fALFF in the right fusiform and the FC strength of the left temporal pole middle temporal gyrus with the putamen may be clinical indicators to assess the drowsiness severity of narcolepsy.

When laughter arrests speech: fMRI-based evidence

Who has not experienced that sensation of losing the power of speech owing to an involuntary bout of laughter? An investigation of this phenomenon affords an insight into the neuronal processes that underlie laughter. In our functional magnetic resonance imaging study, participants were made to laugh by tickling in a first condition; in a second one they were requested to produce vocal utterances under the provocation of laughter by tickling. This investigation reveals increased neuronal activity in the sensorimotor cortex, the anterior cingulate gyrus, the insula, the nucleus accumbens, the hypothalamus and the periaqueductal grey for both conditions, thereby replicating the results of previous studies on ticklish laughter. However, further analysis indicates the activity in the emotion-associated regions to be lower when tickling is accompanied by voluntary vocalization. Here, a typical pattern of activation is identified, including the primary sensory cortex, a ventral area of the anterior insula and the ventral tegmental field, to which belongs to the nucleus ambiguus, namely, the common effector organ for voluntary and involuntary vocalizations. During the conflictual voluntary-vocalization versus laughter experience, the laughter-triggering network appears to rely heavily on a sensory and a deep interoceptive analysis, as well as on motor effectors in the brainstem. This article is part of the theme issue 'Cracking the laugh code: laughter through the lens of biology, psychology and neuroscience'.

50th anniversary of the ESRS in 2022-JSR special issue

This article addresses the clinical presentation, diagnosis, pathophysiology and management of narcolepsy type 1 and 2, with a focus on recent findings. A low level of hypocretin-1/orexin-A in the cerebrospinal fluid is sufficient to diagnose narcolepsy type 1, being a highly specific and sensitive biomarker, and the irreversible loss of hypocretin neurons is responsible for the main symptoms of the disease: sleepiness, cataplexy, sleep-related hallucinations and paralysis, and disrupted nocturnal sleep. The process responsible for the destruction of hypocretin neurons is highly suspected to be autoimmune, or dysimmune. Over the last two decades, remarkable progress has been made for the understanding of these mechanisms that were made possible with the development of new techniques. Conversely, narcolepsy type 2 is a less well-defined disorder, with a variable phenotype and evolution, and few reliable biomarkers discovered so far. There is a dearth of knowledge about this disorder, and its aetiology remains unclear and needs to be further explored. Treatment of narcolepsy is still nowadays only symptomatic, targeting sleepiness, cataplexy and disrupted nocturnal sleep. However, new psychostimulants have been recently developed, and the upcoming arrival of non-peptide hypocretin receptor-2 agonists should be a revolution in the management of this rare sleep disease, and maybe also for disorders beyond narcolepsy.

Rapid eye movement sleep is initiated by basolateral amygdala dopamine signaling in mice

The sleep cycle is characterized by alternating non-rapid eye movement (NREM) and rapid eye movement (REM) sleeps. The mechanisms by which this cycle is generated are incompletely understood. We found that a transient increase of dopamine (DA) in the basolateral amygdala (BLA) during NREM sleep terminates NREM sleep and initiates REM sleep. DA acts on dopamine receptor D2 (Drd2)-expressing neurons in the BLA to induce the NREM-to-REM transition. This mechanism also plays a role in cataplectic attacks-a pathological intrusion of REM sleep into wakefulness-in narcoleptics. These results show a critical role of DA signaling in the BLA in initiating REM sleep and provide a neuronal basis for sleep cycle generation.

Hypothalamus and amygdala functional connectivity at rest in narcolepsy type 1

INTRODUCTION

functional and structural MRI studies suggest that the orexin (hypocretin) deficiency in the dorso-lateral hypothalamus of narcoleptic patients would influence both brain metabolism and perfusion and would cause reduction in cortical grey matter. Previous fMRI studies have mainly focused on cerebral functioning during emotional processing. The aim of the present study was to explore the hemodynamic behaviour of spontaneous BOLD fluctuation at rest in patients with Narcolepsy type 1 (NT1) close to disease onset.

METHODS

Fifteen drug naïve children/adolescents with NT1 (9 males; mean age 11.7 ± 3 years) and fifteen healthy children/adolescents (9 males; mean age 12.4 ± 2.8 years) participated in an EEG-fMRI study in order to investigate the resting-state functional connectivity of hypothalamus and amygdala. Functional images were acquired on a 3 T system. Seed-based functional connectivity analyses were performed using SPM12. Regions of Interest were the lateral hypothalamus and the amygdala.

RESULTS

compared to controls, NT1 patients showed decreased functional connectivity between the lateral hypothalamus and the left superior parietal lobule, the hippocampus and the parahippocampal gyrus. Decreased functional connectivity was detected between the amygdala and the post-central gyrus and several occipital regions, whereas it was increased between the amygdala and the inferior frontal gyrus, claustrum, insula, and putamen.

CONCLUSION

in NT1 patients the abnormal connectivity between the hypothalamus and brain regions involved in memory consolidation during sleep, such as the hippocampus, may be linked to the loss of orexin containing neurons in the dorsolateral hypothalamus. Moreover, also functional connectivity of the amygdala seems to be influenced by the loss of orexin-containing neurons. Therefore, we can hypothesize that dysfunctional interactions between regions subserving the maintenance of arousal, memory and emotional processing may contribute to the main symptom of narcolepsy.

Dream Activity in Narcoleptic Patients During the COVID-19 Lockdown in Italy

Some studies highlighted that patients with narcolepsy type-1 (NT1) experience high lucid dream frequency, and this phenomenon has been associated with a creative personality. Starting from the well-known “pandemic effect” on sleep and dreaming, we presented a picture of dream activity in pharmacologically treated NT1 patients during the Italian lockdown. Forty-three NT1 patients completed a web-survey during Spring 2021 and were compared with 86 matched-controls. Statistical comparisons revealed that: (a) NT1 patients showed greater sleepiness than controls; (b) controls showed higher sleep disturbances than NT1 patients, and this result disappeared when the medication effect in NT1 was controlled; (c) NT1 patients reported higher lucid dream frequency than controls. Focusing on dreaming in NT1 patients, we found that (a) nightmare frequency was correlated with female gender, longer sleep duration, higher intrasleep wakefulness; (b) dream recall, nightmare and lucid dream frequency were positively correlated with sleepiness. Comparisons between low and high NT1 lucid dreamers showed that patients more frequently experiencing lucid dreams reported a greater influence of dreaming during wakefulness, especially concerning problem-solving and creativity. Overall, our results are consistent with previous studies on pandemic dreaming carried out on healthy subjects. Moreover, we confirmed a link between lucidity and creativity in NT1 patients. Considering the small sample size and the cross-sectional design, our findings cannot provide a causal relationship between lucid dreams and the COVID-19 lockdown. Nevertheless, they represent a first contribution to address future studies on this issue, suggesting that some stable characteristics could interact with changes provoked by the pandemic.

Induction of narcolepsy-like symptoms by orexin receptor antagonists in mice

Orexins/hypocretins are hypothalamic neuropeptides that promote and stabilize wakefulness by binding to the orexin receptor type-1 (OX1R) and type-2 (OX2R). Disruption of orexinergic signaling results in the sleep disorder narcolepsy in mice, rats, dogs, and humans. The orexin receptor antagonist suvorexant promotes sleep by blocking both OX1R and OX2R. Whereas suvorexant has been clinically approved for the treatment of insomnia because it is well tolerated in experimental animals as well as in human patients, a logical question remains as to why orexin receptor antagonists do not induce overt narcolepsy-like symptoms. Here we show that acute and chronic suvorexant promotes both rapid eye movement (REM) and non-REM (NREM) sleep without inducing cataplexy in mice. Interestingly, chronic suvorexant increases OX2R mRNA and decreases orexin mRNA and peptide levels, which remain low long after termination of suvorexant administration. When mice are chronically treated with suvorexant and then re-challenged with the antagonist after a 1-week washout, however, cataplexy and sleep-onset REM (SOREM) are observed, which are exacerbated by chocolate administration. Heterozygous orexin knockout mice, with lower brain orexin levels, show cataplexy and SOREM after acute suvorexant administration. Furthermore, we find that acute suvorexant can induce cataplexy and SOREM in wild-type mice when co-administered with chocolate under stress-free (temporally anesthetized) conditions. Taken together, these results suggest that suvorexant can inhibit orexin synthesis resulting in susceptibility to narcolepsy-like symptoms in mice under certain conditions.

Abnormal Brain Network Topology During Non-rapid Eye Movement Sleep and Its Correlation With Cognitive Behavioral Abnormalities in Narcolepsy Type 1

Objective: Simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) were applied to investigate the abnormalities in the topological characteristics of functional brain networks during non-rapid eye movement(NREM)sleep. And we investigated its relationship with cognitive abnormalities in patients with narcolepsy type 1 (NT1) disorder in the current study. Methods: The Beijing version of the Montreal Cognitive Assessment (MoCA-BJ) and EEG-fMRI were applied in 25 patients with NT1 and 25 age-matched healthy controls. All subjects participated in a nocturnal video polysomnography(PSG)study, and total sleep time (TST), percentage of TST (%TST) for each sleep stage and arousal index were calculated. The Epworth Sleepiness Score (ESS) was used to measure the degree of daytime sleepiness. The EEG-fMRI study was performed simultaneously using a 3T MRI system and a 32-channel MRI-compatible EEG system during sleep. Visual scoring of EEG data was used for sleep staging. Cognitive function was assessed for all subjects using the MoCA-BJ. The fMRI data were applied to establish a whole-brain functional connectivity network for all subjects, and the topological characteristics of the whole-brain functional network were analyzed using a graph-theoretic approach. The topological parameters were compared between groups. Lastly, the correlation between topological parameters and the assessment scale using Montreal Cognition was analyzed. Results: The MoCA-BJ scores were lower in patients with NT1 than in normal controls. Whole-brain global efficiency during stage N2 sleep in patients with NT1 displayed significantly lower small-world properties than in normal controls. Whole-brain functional network global efficiency in patients with NT1 was significantly correlated with MoCA-BJ scores. Conclusion: The global efficiency of the functional brain network during stage N2 sleep in patients with NT1 and the correspondingly reduced small-world attributes were associated with cognitive impairment.

Two Neural Networks for Laughter: A Tractography Study

Laughter is a complex motor behavior occurring in both emotional and nonemotional contexts. Here, we investigated whether the different functions of laughter are mediated by distinct networks and, if this is the case, which are the white matter tracts sustaining them. We performed a multifiber tractography investigation placing seeds in regions involved in laughter production, as identified by previous intracerebral electrical stimulation studies in humans: the pregenual anterior cingulate (pACC), ventral temporal pole (TPv), frontal operculum (FO), presupplementary motor cortex, and ventral striatum/nucleus accumbens (VS/NAcc). The primary motor cortex (M1) and two subcortical territories were also studied to trace the descending projections. Results provided evidence for the existence of two relatively distinct networks. A first network, including pACC, TPv, and VS/NAcc, is interconnected through the anterior cingulate bundle, the accumbofrontal tract, and the uncinate fasciculus, reaching the brainstem throughout the mamillo-tegmental tract. This network is likely involved in the production of emotional laughter. A second network, anchored to FO and M1, projects to the brainstem motor nuclei through the internal capsule. It is most likely the neural basis of nonemotional and conversational laughter. The two networks interact throughout the pre-SMA that is connected to both pACC and FO.

Sleep-Wake Disorders in Childhood

PURPOSE OF REVIEW

The presentation of sleep issues in childhood differs from the presentation in adulthood and may be more subtle. Sleep issues may affect children differently than adults, and distinct treatment approaches are often used in children.

RECENT FINDINGS

Sodium oxybate was approved by the US Food and Drug Administration (FDA) in October 2018 for an expanded indication of treatment of sleepiness or cataplexy in patients with narcolepsy type 1 or narcolepsy type 2 aged 7 years or older, with side effect and safety profiles similar to those seen in adults. Restless sleep disorder is a recently proposed entity in which restless sleep, daytime sleepiness, and often iron deficiency are observed, but children do not meet the criteria for restless legs syndrome or periodic limb movement disorder.

SUMMARY

Children's sleep is discussed in this article, including normal sleep patterns and effects of insufficient sleep. Sleep disorders of childhood are reviewed, including insomnia, obstructive sleep apnea, restless legs syndrome, parasomnias, narcolepsy, and Kleine-Levin syndrome. Children with neurologic issues or neurodevelopmental disorders frequently have sleep disorders arising from an interaction of heterogeneous factors. Further attention to sleep may often be warranted through a polysomnogram or referral to a pediatric sleep specialist. Sleep disorders may cause indelible effects on children's cognitive functioning, general health, and well-being, and awareness of sleep disorders is imperative for neurologists who treat children.

Giving a voice to cataplectic experience: recollections from patients with narcolepsy type 1

STUDY OBJECTIVES

The objective of this study was to assess the narratives from the recalled accounts of cataplexy attacks of patients with narcolepsy type 1 (NT1).

METHODS

Twenty-two drug-naive adult patients meeting the International Classification of Sleep Disorders criteria for the diagnosis of NT1 referring to the Narcolepsy Center of the University of Bologna in the year 2017 underwent a semistructured interview focusing on their personal experiences during the cataplectic attacks. Verbatim transcripts were analyzed by thematic analysis of elementary contexts using T-LAB software.

RESULTS

The thematic analysis performed on the entire body text showed 3 clusters that explained 36.2%, 34.1%, and 29.7% of the variance, respectively: a cluster related to situations that trigger attacks of cataplexy, a cluster to bodily sensations, and another control strategies during episodes. The thematic content highlighted a tendency to disregard emotional experiences, thus affecting the ability to name, recognize, and regulate critical emotions.

CONCLUSIONS

The study showed that patients with NT1 spoke of their cataplectic attacks in terms of self-reported bodily experiences, trigger situations, and their management. Therefore, patients may have developed strategies of symptom management focused on emotion avoidance and/or inhibition.

Therapy for Cataplexy

Purpose of the review

Cataplexy, an involuntary loss of muscle activity triggered by strong emotions is the most impressive symptom in narcolepsy. This review gives an overview of the current understanding of cataplexy and its available treatment options.

Recent findings

With the discovery of hypocretin/orexin, the understanding of the pathophysiology of cataplexy advanced in the past decades. In the recent years, with the development of new anticataplectic agents (e.g., Pitolisant) symptomatic treatment of cataplexy has further improved. Abrupt cessation of anticataplectic medication especially antidepressants increase the risk of status cataplecticus, a virtually continuous series of long-lasting cataplectic attacks.

Summary

Cataplexies still remain an under-recognized phenomenon due to missing diagnostic measures. Treatment for cataplexy still remains symptomatic but new agents with better tolerability and usability are continuously developed. New therapeutic actions either targeting the autoimmune mechanisms underlying orexin cell death or substituting orexin action are promising treatments for the near future.

Neuroimaging of Narcolepsy and Primary Hypersomnias

Advances in neuroimaging open up the possibility for new powerful tools to be developed that potentially can be applied to clinical populations to improve the diagnosis of neurological disorders, including sleep disorders. At present, the diagnosis of narcolepsy and primary hypersomnias is largely limited to subjective assessments and objective measurements of behavior and sleep physiology. In this review, we focus on recent neuroimaging findings that provide insight into the neural basis of narcolepsy and the primary hypersomnias Kleine-Levin syndrome and idiopathic hypersomnia. We describe the role of neuroimaging in confirming previous genetic, neurochemical, and neurophysiological findings and highlight studies that permit a greater understanding of the symptoms of these sleep disorders. We conclude by considering some of the remaining challenges to overcome, the existing knowledge gaps, and the potential role for neuroimaging in understanding the pathogenesis and clinical features of narcolepsy and primary hypersomnias.

Autism Spectrum Disorder and Narcolepsy: A Possible Connection That Deserves to Be Investigated

Narcolepsy in childhood-adolescence is characterized by a high occurrence of psychiatric comorbidities. The most frequent psychiatric disorders reported in these patients are attention deficit/hyperactivity disorder, depression, anxiety disorder, and schizophrenia. However, narcolepsy can be associated also with introversion, sorrowfulness, feelings of inferiority, impaired affectivity modulation, emotional lability, irritability, aggressiveness, and poor attention, that have been pooled by some authors under a definition of "narcoleptic personality." Some aspects of this "narcoleptic personality," and in particular introversion, impaired affectivity modulation, irritability, and poor attention, partially overlap with the clinical features of the individuals with autism spectrum disorder, considering also those that are not regarded as core autism symptoms. Till now, in literature the number of cases affected by both narcolepsy and autism spectrum disorder (seven patients) has been clearly too small to demonstrate the presence of a pathogenetic link between these two conditions, but this possible connection has not yet been adequately investigated, despite the presence of several points in common. The finding of a connection between narcolepsy and autism spectrum disorder could boost the study of possible etiopathogenetic mechanisms shared between these two apparently so distant disorders. Basing on the literature data summarized in this paper, in the diagnostic work-up of a child with narcolepsy it is essential to evaluate also the social-communicative behavior using standardized tools in order to detect the real recurrence of clinical features suggesting an autism spectrum disorder. At the same time, it appears necessary to screen in the individuals with autism spectrum disorder for the possible presence of evoking symptoms of narcolepsy.

Motor and Limbic System Contribution to Emotional Laughter across the Lifespan

Laughter is a universal human behavior generated by the cooperation of different systems toward the construction of an expressive vocal pattern. Given the sensitivity of neuroimaging techniques to movements, the neural mechanisms underlying laughter expression remain unclear. Herein, we characterized the neural correlates of emotional laughter using the onsets and the duration of laughter bursts to inform functional magnetic resonance imaging. Laughter-related blood oxygen level-dependent (BOLD) increases involved both the motor (motor cortex, supplementary motor area, frontal operculum) and the emotional/limbic (anterior cingulate cortex, amygdala, n. accumbens, hippocampus) systems, as well as modulatory circuitries encompassing the basal ganglia, thalamus, and cerebellum. BOLD changes related to the 2 s preceding the laughter outbreak were selectively observed at the temporo-occipital junction and the periaqueductal gray matter, supporting the role of the former in the detection of incongruity and the gating role of the latter in the initiation of spontaneous laughter. Moreover, developmental changes were identified in laughter processing, consisting in a greater engagement of the reward circuitry in younger subjects; conversely, the default mode network appears more activated in older participants. Our findings contribute valuable information about the processing of real-life humorous materials and suggest a close link between laughter-related motor, affective, and cognitive elements, confirming its complex and multi-faceted nature.

The clinical characteristics of cataplectic attack in narcolepsy type 1

OBJECTIVE

Cataplexy is a pathognomonic symptom of narcolepsy type 1. This study was conducted to clarify the clinical characteristics of cataplexy by staging, and to further analyse the correlations of clinical features and cataplectic stages in patients with narcolepsy type 1 (NT1).

METHODS

We experimentally triggered patients with NT1 into cataplexy while under video-polysomnography (v-PSG) monitoring in the sleep lab. The most serious cataplectic attack from each patient was analysed. Each cataplectic episode was segmented into four stages according to the v-PSG. Correlations were analysed between cataplectic stages in pairs, and between cataplectic stages and other clinical features.

RESULTS

We observed 81 cataplectic episodes in 21 patients with diverse triggers, including humorous or exciting videos, tickling, recalling horrible memories and exercising. Nine patients (43%) went through complete cataplectic attacks while the others experienced partial attacks. Four cataplectic stages (ie, triggering, resisting, atonic, and recovering) were identified according to clinical and electromyograms characteristics. Resisting stage is predominant (56.4%) in cataplexy, while atonic stage is most related with the total duration of cataplexy. The Epworth Sleepiness Scale score (ESS) has a positive correlation with the total duration of cataplexy. Both duration of cataplexy and ESS score are negatively correlated with disease course. However, medication history seems have no influence on either cataplexy duration or ESS score.

CONCLUSION

Four-stage segmentation shows the dynamic process of the cataplectic attack, which is different from the traditional classification of complete or partial cataplexy. Resisting stage is necessary for every cataplexy and might reflect the compensation mechanism, while atonic stage may be omitted in some patients. The severity of narcolepsy reduces with the extension of natural course regardless of medication history.

Hypocretin-deficient narcolepsy patients have abnormal brain activation during humor processing

Study Objectives

To assess brain activation patterns in response to fun-rated and neutral-rated movies we performed functional magnetic resonance imaging (fMRI) during a humor-paradigm in narcolepsy type 1 (NT1) patients with cataplexy (muscle atonia triggered by emotions) and controls.

Methods

The fMRI-humor-paradigm consisted of short movies (25/30 with a humorous punchline; 5/30 without a humorous punchline [but with similar build-up/anticipation]) rated by participants based on their humor experience. We included 41 NT1 patients and 44 controls. Group-level inferences were made using permutation testing.

Results

Permutation testing revealed no group differences in average movie ratings. fMRI analysis found no group differences in brain activations to fun-rated movies. Patients showed significantly higher activations compared to controls during neutral-rated movies; including bilaterally in the thalamus, pallidum, putamen, amygdala, hippocampus, middle temporal gyrus, cerebellum, brainstem and in the left precuneus, supramarginal gyrus, and caudate. We found no brain overactivation for patients during movies without a humorous punchline (89.0% neutral-rated). Group analyses revealed significantly stronger differentiation between fun-rated and neutral-rated movies in controls compared with patients (patients showed no significant differentiation), including bilaterally in the inferior frontal gyrus, thalamus, putamen, precentral gyrus, lingual gyrus, supramarginal gyrus, occipital areas, temporal areas, cerebellum and in the right hippocampus, postcentral gyrus, pallidum, and insula.

Conclusion

Patients showed significantly higher activations in several cortical and subcortical regions during neutral-rated movies, with no differentiation from activations during fun-rated movies. This lower threshold for activating the humor response (even during neutral-rated movies), might represent insight into the mechanisms associated with cataplexy.

The Functional Role of Dreaming in Emotional Processes

Dream experience (DE) represents a fascinating condition linked to emotional processes and the human inner world. Although the overlap between REM sleep and dreaming has been overcome, several studies point out that emotional and perceptually vivid contents are more frequent when reported upon awakenings from this sleep stage. Actually, it is well-known that REM sleep plays a pivotal role in the processing of salient and emotional waking-life experiences, strongly contributing to the emotional memory consolidation. In this vein, we highlighted that, to some extent, neuroimaging studies showed that the processes that regulate dreaming and emotional salience in sleep mentation share similar neural substrates of those controlling emotions during wakefulness. Furthermore, the research on EEG correlates of the presence/absence of DE and the results on EEG pattern related to the incorporated memories converged to assign a crucial role of REM theta oscillations in emotional re-processing. In particular, the theta activity is involved in memory processes during REM sleep as well as during the waking state, in line with the continuity hypothesis. Also, the gamma activity seems to be related to emotional processes and dream recall as well as to lucid dreams. Interestingly, similar EEG correlates of DE have been found in clinical samples when nightmares or dreams occur. Research on clinical samples revealed that promoting the rehearsal of frightening contents aimed to change them is a promising method to treat nightmares, and that lucid dreams are associated with an attenuation of nightmares. In this view, DE can defuse emotional traumatic memories when the emotional regulation and the fear extinction mechanisms are compromised by traumatic and frightening events. Finally, dreams could represent a sort of simulation of reality, providing the possibility to create a new scenario with emotional mastery elements to cope with dysphoric items included in nightmares. In addition, it could be hypothesized that the insertion of bizarre items besides traumatic memories might be functional to "impoverish" the negative charge of the experiences.

Fluctuation of primary motor cortex excitability during cataplexy in narcolepsy

Objective

Cataplexy is a complicated and dynamic process in narcolepsy type 1 (NT1) patients. This study aimed to clarify the distinct stages during a cataplectic attack and identify the changes of the primary motor cortex (PMC) excitability during these stages.

Methods

Thirty-five patients with NT1 and 29 healthy controls were recruited to this study. Cataplectic stages were distinguished from a cataplectic attack by video-polysomnogram monitoring. Transcranial magnetic stimulation motor-evoked potential (TMS-MEP) was performed to measure the excitability of PMC during quiet wakefulness, laughter without cataplexy, and each cataplectic stage.

Results

Based on the video and electromyogram observations, a typical cataplectic attack (CA) process is divided into four stages: triggering (CA1), resisting (CA2), atonic (CA3), and recovering stages (CA4). Compared with healthy controls, NT1 patients showed significantly decreased intracortical facilitation during quiet wakefulness. During the laughter stage, both patients and controls showed increased MEP amplitude compared with quiet wakefulness. The MEP amplitude significantly increased even higher in CA1 and 2, and then dramatically decreased in CA3 accompanied with prolonged MEP latency compared with the laughter stage and quiet wakefulness. The MEP amplitude and latency gradually recovered during CA4.

Interpretation

This study identifies four stages during cataplectic attack and reveals the existence of a resisting stage that might change the process of cataplexy. The fluctuation of MEP amplitude and MEP latency shows a potential participation of PMC and motor control pathway during cataplexy, and the increased MEP amplitude during CA1 and 2 strongly implies a compensatory mechanism in motor control that may resist or avoid cataplectic attack.

The neuronal network of laughing in young patients with untreated narcolepsy

OBJECTIVE

To investigate the neuronal correlates of spontaneous laughter in drug-naive pediatric patients with narcolepsy type I (NT1) compared to healthy controls by means of blood oxygen level-dependent (BOLD) MRI.

METHODS

Twenty-one children/adolescents with recent onset of NT1 and 21 age- and sex-matched healthy controls were studied with fMRI while viewing funny videos using a naturalistic paradigm. Whole-brain hemodynamic correlates of spontaneous laughter were investigated in each group and compared by use of appropriate second-level general linear model analyses. If recorded, cataplexy events were treated as the effect of no interest at the single-participant level. Correlations analyses between these contrasts and behavioral findings were performed.

RESULTS

Emotion-induced laughter occurred in 16 patients (294 events) and 21 controls (357 events). In controls, laughter-related BOLD increases involved a widespread cortical and subcortical network including the bilateral motor and premotor areas, cingulated cortex, insula, and amygdala. In NT1, laughter induced BOLD signal increments in the motor cortex, right thalamus, and left subthalamic nucleus/zona incerta (STN/ZI). STN/ZI and thalamic changes were significantly higher during fMRI sessions with laughter without cataplexy compared to sessions in which laughter was associated with cataplexy.

CONCLUSION

Laughter expression in individuals with NT1 involves different brain circuits compared to controls by means of overactivation of cortical and subcortical regions belonging to the volitional control of laughter. The activation of the STN/ZI region observed predominantly in patients with NT1 during laugh episodes without cataplexy suggests that the ZI could act to prevent cataplexy.

Narcolepsy and emotional experience: a review of the literature

Narcolepsy is a chronic sleep disorder characterized by excessive daytime sleepiness, cataplexy, hypnagogic hallucinations, and sleep paralysis. This disease affects significantly the overall patient functioning, interfering with social, work, and affective life. Some symptoms of narcolepsy depend on emotional stimuli; for instance, cataplectic attacks can be triggered by emotional inputs such as laughing, joking, a pleasant surprise, and also anger. Neurophysiological and neurochemical findings suggest the involvement of emotional brain circuits in the physiopathology of cataplexy, which seems to depending on the dysfunctional interplay between the hypothalamus and the amygdala associated with an alteration of hypocretin levels. Furthermore, behavioral studies suggest an impairment of emotions processing in narcolepsy-cataplexy (NC), like a probable coping strategy to avoid or reduce the frequency of cataplexy attacks. Consistently, NC patients seem to use coping strategies even during their sleep, avoiding unpleasant mental sleep activity through lucid dreaming. Interestingly, NC patients, even during sleep, have a different emotional experience than healthy subjects, with more vivid, bizarre, and frightening dreams. Notwithstanding this evidence, the relationship between emotion and narcolepsy is poorly investigated. This review aims to provide a synthesis of behavioral, neurophysiological, and neurochemical evidence to discuss the complex relationship between NC and emotional experience and to direct future research.

Automatic detection of cataplexy

OBJECTIVE

Although being the most specific symptom of narcolepsy type 1 (NT1), cataplexy is currently investigated by clinical interview only, with potential diagnostic pitfalls. Our study aimed at testing the accuracy of an automatic video detection of cataplexy in NT1 patients vs. non-cataplectic subjects undergoing a standardized test with emotional stimulation.

METHODS

Fifteen drug-naive NT1 patients and 15 age- and sex-balanced non-cataplectic subjects underwent a standardized video recording procedure including emotional stimulation causing laughter. Video recordings were visually inspected by human scorers to detect three typical cataplexy facial motor patterns (ptosis, mouth opening and head drop), and then analysed by SHIATSU (Semantic-based HIearchical Automatic Tagging of videos by Segmentation using cUts). Expert-based and automatic attack detection was compared in NT1 patients and non-cataplectic subjects.

RESULTS

All NT1 patients and none of the non-cataplectic subjects displayed cataplexy during emotional stimulation. Automatic detection correlated well with experts' assessments in NT1 with an overall accuracy of 81%. In non-cataplectic subjects, automatic detection falsely identified cataplexy in two out of 15 (13.3%) subjects who showed active eyes closure during intense laughter as a confounder with ptosis.

CONCLUSIONS

Automatic cataplexy detection by applying SHIATSU to a standardized test for video documentation of cataplexy is feasible, with an overall accuracy of 81% compared to human examiners. Further studies are warranted to enlarge the range of elementary motor patterns detected, analyse their temporal/spatial relations and quantify cataplexy for diagnostic purposes.

Magnetic resonance imaging of the human locus coeruleus: A systematic review

The locus coeruleus (LC), the major origin of noradrenergic modulation of the central nervous system, innervates extensive areas throughout the brain and is implicated in a variety of autonomic and cognitive functions. Alterations in the LC-noradrenergic system have been associated with healthy ageing and neuropsychiatric disorders including Parkinson's disease, Alzheimer's disease and depression. The last decade has seen advances in imaging the structure and function of the LC, and this paper systematically reviews the methodology and outcomes of sixty-nine structural and functional MRI studies of the LC in humans. Structural MRI studies consistently showed lower LC signal intensity and volume in clinical groups compared to healthy controls. Within functional studies, the LC was activated by a variety of tasks/stimuli and had functional connectivity to a range of brain regions. However, reported functional LC location coordinates were widely distributed compared to previously published neuroanatomical locations. Methodological and demographic factors potentially contributing to these differences are discussed, together with recommendations to optimize the reliability and validity of future LC imaging studies.

The Integration of Emotional Expression and Experience: A Pragmatist Review of Recent Evidence From Brain Stimulation

A common view in affective neuroscience considers emotions as a multifaceted phenomenon constituted by independent affective and motor components. Such dualistic connotation, obtained by rephrasing the classic Darwin and James’s theories of emotion, leads to the assumption that emotional expression is controlled by motor centers in the anterior cingulate, frontal operculum, and supplementary motor area, whereas emotional experience depends on interoceptive centers in the insula. Recent stimulation studies provide a different perspective. I will outline two sets of findings. First, affective experiences can be elicited also following the stimulation of motor centers. Second, emotional expressions can be elicited by stimulating interoceptive regions. Echoing the original pragmatist theories of emotion, I will make a case for the notion that emotional experience emerges from the integration of sensory and motor signals, encoded in the same functional network.

Cataplexy and Its Mimics: Clinical Recognition and Management

OPINION STATEMENT

This review describes the diagnosis and management of cataplexy: attacks of bilateral loss of muscle tone, triggered by emotions and with preserved consciousness. Although cataplexy is rare, its recognition is important as in most cases, it leads to a diagnosis of narcolepsy, a disorder that still takes a median of 9 years to be diagnosed. The expression of cataplexy varies widely, from partial episodes affecting only the neck muscles to generalized attacks leading to falls. Moreover, childhood cataplexy differs from the presentation in adults, with a prominent facial involvement, already evident without clear emotional triggers ('cataplectic facies') and 'active' motor phenomena especially of the tongue and perioral muscles. Next to narcolepsy, cataplexy can sometimes be caused by other diseases, such as Niemann-Pick type C, Prader Willi Syndrome, or lesions in the hypothalamic or pontomedullary region. Cataplexy mimics include syncope, epilepsy, hyperekplexia, drop attacks and pseudocataplexy. They can be differentiated from cataplexy using thorough history taking, supplemented with (home)video recordings whenever possible. Childhood narcolepsy, with its profound facial hypotonia, can be confused with neuromuscular disorders, and the active motor phenomenona resemble those found in childhood movement disorders such as Sydenham's chorea. Currently, the diagnosis of cataplexy is made almost solely on clinical grounds, based on history taking and (home) videos. Cataplexy shows remarkable differences in childhood compared to adults, with profound facial hypotonia and complex active motor phenomena. Over time, these severe symptoms evolve to the milder adult phenotype, and this pattern is crucial to recognize when assessing the outcome of uncontrolled case series with potential treatments such as immunomodulation. Symptomatic treatment is possible with antidepressants and sodium oxybate. Importantly, management also needs to involve sleep hygiene advice, safety measures whenever applicable and guidance with regard to the social sequelae of cataplexy.

Serotonin neurons in the dorsal raphe mediate the anticataplectic action of orexin neurons by reducing amygdala activity

Narcolepsy is a sleep disorder caused by the loss of orexin (hypocretin)-producing neurons and marked by excessive daytime sleepiness and a sudden weakening of muscle tone, or cataplexy, often triggered by strong emotions. In a mouse model for narcolepsy, we previously demonstrated that serotonin neurons of the dorsal raphe nucleus (DRN) mediate the suppression of cataplexy-like episodes (CLEs) by orexin neurons. Using an optogenetic tool, in this paper we show that the acute activation of DRN serotonin neuron terminals in the amygdala, but not in nuclei involved in regulating rapid eye-movement sleep and atonia, suppressed CLEs. Not only did stimulating serotonin nerve terminals reduce amygdala activity, but the chemogenetic inhibition of the amygdala using designer receptors exclusively activated by designer drugs also drastically decreased CLEs, whereas chemogenetic activation increased them. Moreover, the optogenetic inhibition of serotonin nerve terminals in the amygdala blocked the anticataplectic effects of orexin signaling in DRN serotonin neurons. Taken together, the results suggest that DRN serotonin neurons, as a downstream target of orexin neurons, inhibit cataplexy by reducing the activity of amygdala as a center for emotional processing.

GABAergic Neurons of the Central Amygdala Promote Cataplexy

Narcolepsy is characterized by chronic sleepiness and cataplexy-sudden muscle paralysis triggered by strong, positive emotions. This condition is caused by a lack of orexin (hypocretin) signaling, but little is known about the neural mechanisms that mediate cataplexy. The amygdala regulates responses to rewarding stimuli and contains neurons active during cataplexy. In addition, lesions of the amygdala reduce cataplexy. Because GABAergic neurons of the central nucleus of the amygdala (CeA) target brainstem regions known to regulate muscle tone, we hypothesized that these cells promote emotion-triggered cataplexy. We injected adeno-associated viral vectors coding for Cre-dependent DREADDs or a control vector into the CeA of orexin knock-out mice crossed with vGAT-Cre mice, resulting in selective expression of the excitatory hM3 receptor or the inhibitory hM4 receptor in GABAergic neurons of the CeA. We measured sleep/wake behavior and cataplexy after injection of saline or the hM3/hM4 ligand clozapine-N-oxide (CNO) under baseline conditions and under conditions that should elicit positive emotions. In mice expressing hM3, CNO approximately doubled the amount of cataplexy in the first 3 h after dosing under baseline conditions. Rewarding stimuli (chocolate or running wheels) also increased cataplexy, but CNO produced no further increase. In mice expressing hM4, CNO reduced cataplexy in the presence of chocolate or running wheels. These results demonstrate that GABAergic neurons of the CeA are sufficient and necessary for the production of cataplexy in mice, and they likely are a key part of the mechanism through which positive emotions trigger cataplexy.SIGNIFICANCE STATEMENT Cataplexy is one of the major symptoms of narcolepsy, but little is known about how strong, positive emotions trigger these episodes of muscle paralysis. Prior research shows that amygdala neurons are active during cataplexy and cataplexy is reduced by lesions of the amygdala. We found that cataplexy is substantially increased by selective activation of GABAergic neurons in the central nucleus of the amygdala (CeA). We also demonstrate that inhibition of these neurons reduces reward-promoted cataplexy. These results build upon prior work to establish the CeA as a crucial element in the neural mechanisms of cataplexy. These results demonstrate the importance of the CeA in regulating responses to rewarding stimuli, shedding light on the broader neurobiology of emotions and motor control.

GABA Cells in the Central Nucleus of the Amygdala Promote Cataplexy

Cataplexy is a hallmark of narcolepsy characterized by the sudden uncontrollable onset of muscle weakness or paralysis during wakefulness. It can occur spontaneously, but is typically triggered by positive emotions such as laughter. Although cataplexy was identified >130 years ago, its neural mechanism remains unclear. Here, we show that a newly identified GABA circuit within the central nucleus of the amygdala (CeA) promotes cataplexy. We used behavioral, electrophysiological, immunohistochemical, and chemogenetic strategies to target and manipulate CeA activity selectively in narcoleptic (orexin^-/-) mice to determine its functional role in controlling cataplexy. First, we show that chemogenetic activation of the entire CeA produces a marked increase in cataplexy attacks. Then, we show that GABA cells within the CeA are responsible for mediating this effect. To manipulate GABA cells specifically, we developed a new mouse line that enables genetic targeting of GABA cells in orexin^-/- mice. We found that chemogenetic activation of GABA CeA cells triggered a 253% increase in the number of cataplexy attacks without affecting their duration, suggesting that GABA cells play a functional role in initiating but not maintaining cataplexy. We show that GABA cell activation only promotes cataplexy attacks associated with emotionally rewarding stimuli, not those occurring spontaneously. However, we found that chemogenetic inhibition of GABA CeA cells does not prevent cataplexy, suggesting these cells are not required for initiating cataplexy attacks. Our results indicate that the CeA promotes cataplexy onset and that emotionally rewarding stimuli may trigger cataplexy by activating GABA cells in the CeA.SIGNIFICANCE STATEMENT Although cataplexy has been closely linked to positive emotions for >130 years, the neural circuitry that underlies this relationship is poorly understood. Recent work suggests that the amygdala, a brain area important for processing emotion, may be part of this circuit. This study provides the first functional evidence to implicate GABA cells in the amygdala as regulators of cataplexy triggered by positive emotions and identifies the amygdala as the brain region important more for gating the entrance into rather than the exit from cataplexy. We also generated a new mouse model for studying GABA neurons in narcoleptic mice, which could serve as a useful tool for studying the neurobiological underpinnings of narcolepsy.

Narcolepsy

Narcolepsy is a chronic sleep disorder that has a typical onset in adolescence and is characterized by excessive daytime sleepiness, which can have severe consequences for the patient. Problems faced by patients with narcolepsy include social stigma associated with this disease, difficulties in obtaining an education and keeping a job, a reduced quality of life and socioeconomic consequences. Two subtypes of narcolepsy have been described (narcolepsy type 1 and narcolepsy type 2), both of which have similar clinical profiles, except for the presence of cataplexy, which occurs only in patients with narcolepsy type 1. The pathogenesis of narcolepsy type 1 is hypothesized to be the autoimmune destruction of the hypocretin-producing neurons in the hypothalamus; this hypothesis is supported by immune-related genetic and environmental factors associated with the disease. However, direct evidence in support of the autoimmune hypothesis is currently unavailable. Diagnosis of narcolepsy encompasses clinical, electrophysiological and biological evaluations, but simpler and faster procedures are needed. Several medications are available for the symptomatic treatment of narcolepsy, all of which have quite good efficacy and safety profiles. However, to date, no treatment hinders or slows disease development. Improved diagnostic tools and increased understanding of the pathogenesis of narcolepsy type 1 are needed and might lead to therapeutic or even preventative interventions.

Safety and efficacy of pitolisant on cataplexy in patients with narcolepsy: a randomised, double-blind, placebo-controlled trial

BACKGROUND

Histaminergic neurons are crucial to maintain wakefulness, but their role in cataplexy is unknown. We assessed the safety and efficacy of pitolisant, a histamine H3 receptor inverse agonist, for treatment of cataplexy in patients with narcolepsy.

METHODS

For this randomised, double-blind, placebo-controlled trial we recruited patients with narcolepsy from 16 sleep centres in nine countries (Bulgaria, Czech Republic, Hungary, Macedonia, Poland, Russia, Serbia, Turkey, and Ukraine). Patients were eligible if they were aged 18 years or older, diagnosed with narcolepsy with cataplexy according to version two of the International Classification of Sleep Disorders criteria, experienced at least three cataplexies per week, and had excessive daytime sleepiness (defined as an Epworth Sleepiness Scale score ≥12). We used a computer-generated sequence via an interactive web response system to randomly assign patients to receive either pitolisant or placebo once per day (1:1 ratio). Randomisation was done in blocks of four. Participants and investigators were masked to treatment allocation. Treatment lasted for 7 weeks: 3 weeks of flexible dosing decided by investigators according to efficacy and tolerance (5 mg, 10 mg, or 20 mg oral pitolisant), followed by 4 weeks of stable dosing (5 mg, 10 mg, 20 mg, or 40 mg). The primary endpoint was the change in the average number of cataplexy attacks per week as recorded in patient diaries (weekly cataplexy rate [WCR]) between the 2 weeks of baseline and the 4 weeks of stable dosing period. Analysis was by intention to treat. This trial is registered with ClinicalTrials.gov, number NCT01800045.

FINDINGS

The trial was done between April 19, 2013, and Jan 28, 2015. We screened 117 patients, 106 of whom were randomly assigned to treatment (54 to pitolisant and 52 to placebo) and, after dropout, 54 patients from the pitolisant group and 51 from the placebo group were included in the intention-to-treat analysis. The WCR during the stable dosing period compared with baseline was decreased by 75% (WCR_final=2·27; WCR_baseline=9·15; WCR_{final/baseline}=0·25) in patients who received pitolisant and 38% (WCR_final=4·52; WCR_baseline=7·31; WCR_{final/baseline}=0·62) in patients who received placebo (rate ratio 0·512; 95% CI 0·43-0·60, p<0·0001). Treatment-related adverse events were significantly more common in the pitolisant group than in the placebo group (15 [28%] of 54 vs 6 [12%] of 51; p=0·048). There were no serious adverse events, but one case of severe nausea in the pitolisant group. The most frequent adverse events in the pitolisant group (headache, irritability, anxiety, and nausea) were mild or moderate except one case of severe nausea. No withdrawal syndrome was detected following pitolisant treatment; one case was detected in the placebo group.

INTERPRETATION

Pitolisant was well tolerated and efficacious in reducing cataplexy. If confirmed in long-term studies, pitolisant might constitute a useful first-line therapy for cataplexy in patients with narcolepsy, for whom there are currently few therapeutic options.

FUNDING

Bioprojet, France.

Orexin/Hypocretin and Organizing Principles for a Diversity of Wake-Promoting Neurons in the Brain

An enigmatic feature of behavioural state control is the rich diversity of wake-promoting neural systems. This diversity has been rationalized as 'robustness via redundancy', wherein wakefulness control is not critically dependent on one type of neuron or molecule. Studies of the brain orexin/hypocretin system challenge this view by demonstrating that wakefulness control fails upon loss of this neurotransmitter system. Since orexin neurons signal arousal need, and excite other wake-promoting neurons, their actions illuminate nonredundant principles of arousal control. Here, we suggest such principles by reviewing the orexin system from a collective viewpoint of biology, physics and engineering. Orexin peptides excite other arousal-promoting neurons (noradrenaline, histamine, serotonin, acetylcholine neurons), either by activating mixed-cation conductances or by inhibiting potassium conductances. Ohm's law predicts that these opposite conductance changes will produce opposite effects on sensitivity of neuronal excitability to current inputs, thus enabling orexin to differentially control input-output gain of its target networks. Orexin neurons also produce other transmitters, including glutamate. When orexin cells fire, glutamate-mediated downstream excitation displays temporal decay, but orexin-mediated excitation escalates, as if orexin transmission enabled arousal controllers to compute a time integral of arousal need. Since the anatomical and functional architecture of the orexin system contains negative feedback loops (e.g. orexin ➔ histamine ➔ noradrenaline/serotonin-orexin), such computations may stabilize wakefulness via integral feedback, a basic engineering strategy for set point control in uncertain environments. Such dynamic behavioural control requires several distinct wake-promoting modules, which perform nonredundant transformations of arousal signals and are connected in feedback loops.

Treatment cost of narcolepsy with cataplexy in Central Europe

Background

Narcolepsy is a lifelong, rare neurological sleep disorder characterized by chronic, excessive attacks of daytime sleepiness. This disease is often extremely incapacitating, interfering with every aspect of life, in work and social settings.

Objective

The purpose of this study is to specify the treatment costs of patients in Central Europe (Czech Republic), while the attention is mainly paid to the drugs that were fully or partially covered by public health insurance. Furthermore, concomitant therapy is also evaluated, since it incurs a certain financial burden for patients and their family members. On the basis of the calculated costs, impact on the public budget is evaluated.

Patients and methods

This study monitors the direct costs of the drugs for 13 patients, who represent ~1.3% of the total number of diagnosed patients in the Czech Republic, and evaluates the costs associated with their treatment during the period from January 9, 2011 to April 23, 2013.

Results

Most of the treatment costs (~80%) were covered by publicly available sources. This finding is also true for the concomitant therapy of comorbidities. Additional payments for the drugs constitute about 20% of the total costs.

Psychosocial Profile and Quality of Life in Children With Type 1 Narcolepsy: A Case-Control Study

STUDY OBJECTIVES

To investigate behavioral aspects and quality of life in children and adolescents with type 1 narcolepsy (NT1).

METHODS

We performed a case-control study comparing 29 patients with NT1 versus sex- and age-matched patients with idiopathic epilepsy (n = 39) and healthy controls (n = 39). Behavior and quality of life were evaluated by self-administered questionnaires (Child Behavior Checklist, Pediatric Quality of Life Inventory). Patient groups were contrasted and scale results were correlated with clinical and polysomnographic parameters, and cerebrospinal fluid hypocretin-1 levels.

RESULTS

Young patients with NT1 showed increased internalizing problems associated with aggressive behavior. Emotional profile in patients with NT1 positively correlated with age at onset, diagnostic delay, and subjective sleepiness, whereas treatment and disease duration were associated with fewer behavioral problems (attention problems, aggressive behavior, and attention deficit/hyperactivity disorder). Psychosocial health domains of pediatric NT1 were worse than in healthy controls, whereas the physical health domains were comparable.

CONCLUSIONS

Young NT1 patients show a discrete pattern of altered behavioral, thought, and mood profile in comparison with healthy controls and with idiopathic epilepsy patients thus suggesting a direct link with sleepiness. Further studies investigating behavior in patients with idiopathic hypersomnia or type 2 narcolepsy are needed to disentangle the role of REM sleep dysfunction and hypocretin deficiency in psychiatric disorders. Symptoms of withdrawal, depression, somatic complaints, thought problems, and aggressiveness were common, NT1 children perceived lower school competencies than healthy children, and their parents also reported worse psychosocial health. Our data suggest that early effective treatment and disease self-awareness should be promoted in NT1 children for their positive effect on behavior and psychosocial health.

Progress in elucidating the pathophysiological basis of nonrapid eye movement parasomnias: not yet informing therapeutic strategies

Nonrapid eye movement (NREM) or arousal parasomnias are prevalent conditions in children and young adults, apparently provoked by any medical, physical, mental, or pharmacologic/toxic agent disturbing normal biorhythm and causing sleep fragmentation or abundant amount of slow wave sleep. The nadir and the ascending slope of the first sleep cycle of night sleep are the typical periods when NREM parasomnias, especially sleepwalking may occur on sleep-microstructural level; microarousals are the typical moments allowing NREM parasomnias. While sleep-disturbing factors have a clear precipitating effect, a genetic predisposition appears necessary in most cases. A candidate gene for sleepwalking has been identified on chromosome 20q12-q13.12 in one sleepwalking family. NREM parasomnias have a genetic and clinical link with nocturnal-frontal lobe epilepsies; possibly through an abnormality of the acetylcholine-related sleep-control system. The association of NREM parasomnias with the human leukocyte antigen system might be the sign of an autoimmune background to be further clarified. In the treatment of arousal parasomnias, the main tools are adequate sleep hygiene and the management of underlying conditions. Their pharmacotherapy has remained unresolved; the best options are clonazepam and some of the antidepressants, while a psychotherapy approach is also justified.