The relationship between orexin levels and blood pressure changes in patients with narcolepsy

MRS study on the correlation between frontal GABA+/Glx ratio and abnormal cognitive function in medication-naive patients with narcolepsy

OBJECTIVE

To compare the GABA+/Glx (glutamate-glutamine) ratio in the prefrontal lobe under non-rapid eye movement sleep between patients with narcolepsy type 1 (NT1) and normal controls and explore the correlation between this difference and abnormal cognitive function, using synchronous electroencephalography-functional magnetic resonance spectroscopy (EEG-fMRS).

METHODS

MRS measurements of GABA+ and Glx concentrations as well as synchronous EEG data were obtained from 26 medication-naive patients with NT1 and 29 sex- and age-matched healthy community volunteers. Cognition was appraised with the Beijing version of the Montreal Cognitive Assessment, and daytime sleepiness was measured using the Epworth Sleepiness Scale. All subjects recorded a 2-week sleep log as well as an overnight polysomnography within 1 week before MR scanning to understand their sleep habits and determine sleep stages. After PSG, they also underwent multiple sleep latency trials. Patient/control group differences in the individual measurements of GABA+ and Glx and the GABA+/Glx ratio and their relationship with cognition were assessed.

RESULTS

The GABA+/Glx ratio and GABA + levels of patients with narcolepsy were higher than those of the control group (P＜0.0001 and P = 0.0008, respectively). However, there was no significant difference in Glx levels (P = 0.6360). The GABA+/Glx ratio negatively correlated with abnormal cognitive function (r = -0.6710, P = 0.0002). Moreover, GABA + levels were inversely proportional to rapid eye movement sleep latency (REML) in patients with narcolepsy (r = -0.5019, P = 0.0106).

CONCLUSION

The GABA+/Glx ratio in the prefrontal lobe was higher in NT1 patients during N2 sleep than in normal controls, mainly caused by GABA + levels; this ratio was negatively related to abnormal cognitive function. In addition, GABA + levels were inversely proportional to REML.

Sleep apnea and autonomic dysfunction in patients with dementia

Sleep apnea is common sleep disorder that is associated with an is an increase in risk of many health conditions, including systemic hypertension, stroke, atrial fibrillation, and heart failure. The predominant underlying pathophysiological mechanism for elevated risk of these conditions in patients with sleep apnea is thought to involve autonomic dysfunction in the form of sympathetic overactivity. Autonomic dysfunction is also associated with several neurodegenerative disorders and sleep apnea, in turn, has been shown to be associated with an increased risk of development of mild cognitive impairment and various types of dementia. Rapid eye movement sleep behavior disorder, which is also associated with an increased risk of alpha synucleiopathy-related dementia, is also linked with autonomic dysfunction. In this article we explore the relationship between sleep apnea, autonomic dysfunction, rapid eye movement sleep behavior disorder and dementia. This article describes the various autonomic dysfunction that are thought to occur in the context of sleep apnea. And illustrate the mechanisms by which sleep apnea, through its impact on autonomic dysfunction could potentially result in dementia. We also review the evidence examining the impact of treatment of sleep apnea on autonomic dysfunction and cognitive outcomes.

Increased very low frequency pulsations and decreased cardiorespiratory pulsations suggest altered brain clearance in narcolepsy

Background

Narcolepsy is a chronic neurological disease characterized by daytime sleep attacks, cataplexy, and fragmented sleep. The disease is hypothesized to arise from destruction or dysfunction of hypothalamic hypocretin-producing cells that innervate wake-promoting systems including the ascending arousal network (AAN), which regulates arousal via release of neurotransmitters like noradrenalin. Brain pulsations are thought to drive intracranial cerebrospinal fluid flow linked to brain metabolite transfer that sustains homeostasis. This flow increases in sleep and is suppressed by noradrenalin in the awake state. Here we tested the hypothesis that narcolepsy is associated with altered brain pulsations, and if these pulsations can differentiate narcolepsy type 1 from healthy controls.

Methods

In this case-control study, 23 patients with narcolepsy type 1 (NT1) were imaged with ultrafast fMRI (MREG) along with 23 age- and sex-matched healthy controls (HC). The physiological brain pulsations were quantified as the frequency-wise signal variance. Clinical relevance of the pulsations was investigated with correlation and receiving operating characteristic analysis.

Results

We find that variance and fractional variance in the very low frequency (MREG_vlf) band are greater in NT1 compared to HC, while cardiac (MREG_card) and respiratory band variances are lower. Interestingly, these pulsations differences are prominent in the AAN region. We further find that fractional variance in MREG_vlf shows promise as an effective bi-classification metric (AUC = 81.4%/78.5%), and that disease severity measured with narcolepsy severity score correlates with MREG_card variance (R = −0.48, p = 0.0249).

Conclusions

We suggest that our novel results reflect impaired CSF dynamics that may be linked to altered glymphatic circulation in narcolepsy type 1.

The flow of fluid surrounding and inside the human brain is thought to be caused by the movement of brain vessels, breathing and heart rate. These so called brain pulsations are linked to clearing waste from the brain. This process is increased during sleep and suppressed while we are awake. Narcolepsy is a neurological disease where the brain areas regulating being awake and asleep are affected. The diagnosis requires time-consuming hospital tests and is often delayed which has a prolonged negative impact on the patients. Here, we use brain imaging to investigate whether brain pulsations are altered in patients with narcolepsy, and if they can be utilized to differentiate patients with narcolepsy from healthy individuals. We find that narcolepsy affects all brain pulsations, and these findings show promise as an additional diagnostic tool that could help detect the disease earlier.

Järvelä et al. investigate if narcolepsy is associated with altered brain pulsations using ultrafast fMRI. They find differences in the brain pulsations between narcolepsy type 1 patients and healthy controls that may link to altered brain clearance in narcolepsy, have diagnostic potential and correlate with the severity of narcolepsy.

Awakening to sleep disorders in Europe: Survey on education, knowledge and treatment competence of European residents and neurologists

OBJECTIVES

Sleep-wake disorders are common in the general population and in most neurological disorders but are often poorly recognized. With the hypothesis that neurologists do not get sufficient training during their residency, the Young European Sleep Neurologist Association (YESNA) of the European Academy of Neurology (EAN) performed a survey on postgraduate sleep education.

METHODS

A 16-item questionnaire was developed and distributed among neurologists and residents across European countries. Questions assessed demographic, training and learning preferences in sleep disorders, as well as a self-evaluation of knowledge based on five basic multiple-choice questions (MCQs) on sleep-wake disorders.

RESULTS

The questionnaire was completed by 568 participants from 20 European countries. The mean age of participants was 31.9 years (SD 7.4 years) and was composed mostly of residents (73%). Three-quarters of the participants reported undergraduate training in sleep medicine, while fewer than 60% did not receive any training on sleep disorders during their residencies. Almost half of the participants (45%) did not feel prepared to treat neurological patients with sleep problems. Only one-third of the participants correctly answered at least three MCQs. Notably, 80% of participants favoured more education on sleep-wake disorders during the neurology residency.

CONCLUSIONS

Education and knowledge on disorders in European neurological residents is generally insufficient, despite a strong interest in the topic. The results of our study may be useful for improving the European neurology curriculum and other postgraduate educational programmes.

Cardiovascular disorders in narcolepsy: Review of associations and determinants

Narcolepsy type 1 (NT1) is a lifelong disorder of sleep-wake dysregulation defined by clinical symptoms, neurophysiological findings, and low hypocretin levels. Besides a role in sleep, hypocretins are also involved in regulation of heart rate and blood pressure. This literature review examines data on the autonomic effects of hypocretin deficiency and evidence about how narcolepsy is associated with multiple cardiovascular risk factors and comorbidities, including cardiovascular disease. An important impact in NT1 is lack of nocturnal blood pressure dipping, which has been associated with mortality in the general population. Hypertension is also prevalent in NT1. Furthermore, disrupted nighttime sleep and excessive daytime sleepiness, which are characteristic of narcolepsy, may increase cardiovascular risk. Patients with narcolepsy also often present with other comorbidities (eg, obesity, diabetes, depression, other sleep disorders) that may contribute to increased cardiovascular risk. Management of multimorbidity in patients with narcolepsy should include regular assessment of cardiovascular health (including ambulatory blood pressure monitoring), mitigation of cardiovascular risk factors (eg, cessation of smoking and other lifestyle changes, sleep hygiene, and pharmacotherapy), and prescription of a regimen of narcolepsy medications that balances symptomatic benefits with cardiovascular safety.

Activating autoantibodies against G protein-coupled receptors in narcolepsy type 1

STUDY OBJECTIVES

Narcolepsy type 1 is a rare hypersomnia of central origin, which is caused by loss of hypothalamic neurons that produce the neuropeptides hypocretin-1 and -2. Hypocretin-containing nerve terminals are found in areas known to play a central role in autonomic control and in pain signaling. Cholinergic M2 receptors are found in brain areas involved with the occurrence of hallucinations and cataplexy. In addition to classical symptoms of narcolepsy, the patients suffer frequently from autonomic dysfunction, chronic pain, and hypnagogic/hypnopompic hallucinations. We aimed to test whether narcolepsy type 1 patients have autoantibodies against autonomic β2 adrenergic receptor, M2 muscarinic receptors, or nociception receptors.

METHODS

We tested the serum of ten narcolepsy type 1 patients (five female) for activating β2 adrenergic receptor autoantibodies, M2 muscarinic receptor autoantibodies, and nociception receptor autoantibodies.

RESULTS

Ten of ten patients were positive for muscarinic M2 receptor autoantibodies (P < 0.001), 9/10 were positive for autoantibodies against nociception receptors (P < 0.001), and 5/10 were positive for β2 adrenergic receptor autoantibodies (P < 0.001).

CONCLUSIONS

Narcolepsy type 1 patients harbored activating autoantibodies against M2 muscarinic receptors, nociception receptors, and β2 adrenergic receptors. M2 receptor autoantibodies may be related to the occurrence of cataplexy and, moreover, hallucinations in narcolepsy since they are found in the same brain areas that are involved with these symptoms. The occurrence of nociception receptor autoantibodies strengthens the association between narcolepsy type 1 and pain. The connection between narcolepsy type 1, autonomic complaints, and the presumed cardiovascular morbidity might be associated with the occurrence of β2 adrenergic receptor autoantibodies. On the other hand, the presence of the autoantibodies may be secondary to the destruction of the hypocretin pathways.

Associations of plasma hypocretin-1 with metabolic and reproductive health: Two systematic reviews of clinical studies

The hypocretin system consists of two peptides hypocretin-1 and hypocretin-2 (HCRT1 and HCRT2). Hypocretin-containing neurons are located in the posterior and lateral hypothalamus, and have widespread projections throughout the brain and spinal cord. In addition to its presence in the cerebrospinal fluid (CSF), peripheral HCRT1 has been detected in plasma. Robust experimental evidence demonstrates functions of hypothalamic-originated HCRT1 in regulation of multiple biological systems related to sleep-wake states, energy homeostasis and endocrine function. In contrast, HCRT1 studies with human participants are limited by the necessarily invasive assessment of CSF HCRT1 to patients with underlying morbidity. Regulation by HCRT1 of energy homeostasis and reproduction in animals suggests similar regulation in humans and prompts these two systematic reviews. These reviews translate prior experimental findings from animal studies to humans and examine associations between HCRT1 and: 1) metabolic risk factors; 2) reproductive function in men, women and children. A total of 21 studies and six studies met the inclusion criteria for the two searches, respectively. Research question, study design, study population, assessments of HCRT1, reproductive, cardiometabolic data and main findings were extracted. Associations between HCRT1, metabolic and reproductive function are inconsistent. Limitations of studies and future research directions are outlined.

A common neuronal mechanism of hypertension and sleep disturbances in spontaneously hypertensive rats: Role of orexinergic neurons

Epidemiologic studies have shown that sleep disorders are associated with the development of hypertension. The present study investigated dynamic changes in sleep patterns during the development of hypertension across the lifespan in spontaneously hypertensive rats (SHRs) and the neural mechanism that underlies these comorbidities, with a focus on the orexinergic system. Blood pressure in rats was measured using a noninvasive blood pressure tail cuff. Sleep was monitored by electroencephalographic and electromyographic recordings. Immunohistochemistry was used to detect the density and activity of orexinergic neurons in the perifornical nucleus. Hcrt2-SAP (400 or 800 ng) was microinjected in the lateral hypothalamus to lesion orexinergic neurons. Compared with Wistar-Kyoto rats, SHRs exhibited various patterns of sleep disturbances. In SHRs, dynamic changes in hypersomnia in the rats' active phase was not synchronized with the development of hypertension, but hyperarousal in the inactive phase and difficulties in falling asleep were observed concurrently with the development of hypertension. Furthermore, the density and activity of orexinergic neurons in the perifornical nucleus were significantly higher in SHRs than in age-matched Wistar-Kyoto rats. The reduction of orexinergic neurons in the lateral hypothalamus partially ameliorated the development of hypertension and prevented difficulties in falling asleep in SHRs. These results indicate that although the correlation between sleep disturbances and hypertension is very complex, common mechanisms may underlie these comorbidities in SHRs. Overactivity of the orexin system may be one such common mechanism.

Neurological Sleep Disorders and Blood Pressure: Current Evidence

Hypertension is a major determinant of cardiovascular morbidity and mortality and is highly prevalent in the general population. While the relationship between sleep apnea and increased blood pressure has been well documented, less recognized is emerging evidence linking sleep-related movement disorders such as restless legs syndrome/periodic limb movements of sleep and sleep-related bruxism with blood pressure (BP) dysregulation and hypertension. There is also recent literature linking narcolepsy-cataplexy with elevated BP and altered pressor responses, and there are data suggesting abnormal BP control in rapid eye movement sleep behavior disorder. It is thought that neural circulatory mechanisms, sympathetic activation in particular, comprise the predominant mediator underlying elevated BP in these neurological sleep disorders. There is very limited evidence that treating these sleep disorders may be beneficial in lowering BP primarily because this question has received very little attention. In this review, we discuss the potential pathophysiologic mechanisms underlying elevated BP in restless legs syndrome/periodic limb movements of sleep, sleep-related bruxism, narcolepsy-cataplexy, and rapid eye movement sleep behavior disorder. We also examine the relationship between these sleep disorders and elevated BP and the impact of treatment of these conditions on BP control. Last, we discuss gaps in the literature evaluating the associations between these sleep disorders and elevated BP and identify areas for further research.

Autonomic regulation during sleep and wakefulness: a review with implications for defining the pathophysiology of neurological disorders

Cardiovascular and respiratory parameters change during sleep and wakefulness. This observation underscores an important, albeit incompletely understood, role for the central nervous system in the differential regulation of autonomic functions. Understanding sleep/wake-dependent sympathetic modulations provides insights into diseases involving autonomic dysfunction. The purpose of this review was to define the central nervous system nuclei regulating sleep and cardiovascular function and to identify reciprocal networks that may underlie autonomic symptoms of disorders such as insomnia, sleep apnea, restless leg syndrome, rapid eye movement sleep behavior disorder, and narcolepsy/cataplexy. In this review, we examine the functional and anatomical significance of hypothalamic, pontine, and medullary networks on sleep, cardiovascular function, and breathing.

Orexins, Sleep, and Blood Pressure

Purpose of Review

The aim of this review was to summarize collected data on the role of orexin and orexin neurons in the control of sleep and blood pressure.

Recent Findings

Although orexins (hypocretins) have been known for only 20 years, an impressive amount of data is now available regarding their physiological role. Hypothalamic orexin neurons are responsible for the control of food intake and energy expenditure, motivation, circadian rhythm of sleep and wake, memory, cognitive functions, and the cardiovascular system. Multiple studies show that orexinergic stimulation results in increased blood pressure and heart rate and that this effect may be efficiently attenuated by orexinergic antagonism. Increased activity of orexinergic neurons is also observed in animal models of hypertension.

Summary

Pharmacological intervention in the orexinergic system is now one of the therapeutic possibilities in insomnia. Although the role of orexin in the control of blood pressure is well described, we are still lacking clinical evidence that this is a possibility for a new approach in the treatment of cardiovascular diseases.