Ion concentrations in cerebrospinal fluid in wakefulness, sleep and sleep deprivation in healthy humans.

Sleep is controlled by a circadian rhythmicity, via a reduction of arousal-promoting neuromodulatory activity, and by accumulation of somnogenic factors in the interstitial fluid of the brain. Recent experiments in mice suggest that a reduced neuronal excitability caused by a reduced concentration of potassium in the brain, concomitant with an increased concentration of calcium and magnesium, constitutes an important mediator of sleep. In the present study, we examined whether such changes in ion concentrations could be detected in the cerebrospinal fluid of healthy humans. Each subject underwent cerebrospinal fluid collection at three occasions in a randomized order: at 15:00 hours-17:00 hours during waking, at 06:00 hours-07:00 hours immediately following 1 night of sleep, and at 06:00 hours-07:00 hours following 1 night of sleep deprivation. When compared with wakefulness, both sleep and sleep deprivation produced the same effect of a small (0.1 mm, about 3%), but robust and highly significant, reduction in potassium concentration. Calcium and magnesium concentrations were unchanged. Our results support a circadian modulation of neuronal excitability in the brain mediated via changes of the interstitial potassium concentration.

Cerebrospinal fluid egress to human parasagittal dura and the impact of sleep deprivation.

Emerging evidence suggests that the glymphatic system and meningeal lymphatic vessels are instrumental for clearance of toxic metabolites from the brain. Animal and human studies suggest that glymphatic circulation is up-regulated during sleep. Meningeal lymphatic clearance may be more efficient in the wake state, as shown in rodents. We have previously shown clearance of cerebrospinal fluid directly from the subarachnoid space to the parasagittal dura, which harbors meningeal lymphatic vessels. Hence, assessing molecular clearance from parasagittal dura provides an opportunity to decipher the role of sleep/sleep deprivation in human lymphatic clearance function. In this study, we applied magnetic resonance imaging to explore whether sleep deprivation modifies molecular clearance from human parasagittal dura, utilizing an intrathecal magnetic resonance imaging contrast agent as tracer. We hypothesized that tracer enhancement in parasagittal dura would differ after sleep deprivation. One group of individuals (n = 7) underwent one night's total sleep deprivation while a control group (n = 9) was allowed unrestricted sleep. There were no sleep restrictions after the 24-hour time point. After one night of sleep deprivation (at 24 h), we found neither evidence for altered tracer enrichment in the parasagittal dura, nor after a day of unrestricted sleep (at 48 h). The hypothesis of altered molecular egress to parasagittal dura after sleep deprivation was not supported by our data. Further studies are required to determine the role of sleep for molecular clearance from cerebrospinal fluid to meningeal lymphatic vessels in humans.

Increased Cerebrospinal Fluid Amyloid-ß During Sleep Deprivation in Healthy Middle-Aged Adults Is Not Due to Stress or Circadian Disruption.

BACKGROUND: Concentrations of soluble amyloid-ß (Aß) oscillate with the sleep-wake cycle in the interstitial fluid of mice and cerebrospinal fluid (CSF) of humans. Further, the concentration of Aß in CSF increases during sleep deprivation. Stress and disruption of the circadian clock are additional mechanisms hypothesized to increase CSF Aß levels. Cortisol is a marker for stress and has an endogenous circadian rhythm. Other factors such as glucose and lactate have been associated with changes in sleep-wake activity and/or Aß. OBJECTIVE: In this exploratory study, we used samples collected in a previous study to examine how sleep deprivation affects Aß, cortisol, lactate, and glucose in plasma and CSF from healthy middle-aged adults (N = 11). METHODS: Eleven cognitively normal participants without evidence of sleep disturbance were randomized to sleep deprivation or normal sleep control. All participants were invited to repeat the study. Cortisol, lactate, glucose, and Aß were measured in 2-h intervals over a 36-h period in both plasma and CSF. All concentrations were normalized to the mean prior to calculating mesor, amplitude, acrophase, and other parameters. RESULTS: One night of sleep deprivation increases the overnight concentration of Aß in CSF approximately 10%, but does not significantly affect cortisol, lactate, or glucose concentrations in plasma or CSF between the sleep-deprived and control conditions. CONCLUSION: These data suggest that sleep deprivation-related changes in CSF Aß are not mediated by stress or circadian disruption as measured by cortisol.

Sleep Deprivation Affects Tau Phosphorylation in Human Cerebrospinal Fluid.

Tau hyperphosphorylation is an early step in tau-mediated neurodegeneration and is associated with intracellular aggregation of tau as neurofibrillary tangles, neuronal and synaptic loss, and eventual cognitive dysfunction in Alzheimer disease. Sleep loss increases the cerebrospinal fluid concentration of amyloid-ß and tau. Using mass spectrometry, we measured tau and phosphorylated tau concentrations in serial samples of cerebrospinal fluid collected from participants who were sleep-deprived, treated with sodium oxybate, or allowed to sleep normally. We found that sleep loss affected phosphorylated tau differently depending on the modified site. These findings suggest a mechanism for sleep loss to increase risk of Alzheimer disease. ANN NEUROL 2020;87:700-709.

Sleep-Wake Cycle in Alzheimer's Disease Is Associated with Tau Pathology and Orexin Dysregulation.

BACKGROUND: Alzheimer's disease (AD) is the most common form of dementia. It is mainly characterized by a progressive deterioration of cognition, but sleep-wake cycle disturbances frequently occur. Irregular sleep-wake cycle, insomnia, and daytime napping usually occur in patients with AD in the course of the disease. OBJECTIVE: The aim of the present study was to verify the sleep-wake cycle in mild to moderate AD patients compared to controls, and to evaluate the relationship between the sleep-wake cycle impairment and the neuropsychological testing, CSF AD biomarkers, and CSF orexin concentrations. METHODS: Mild to moderate AD patients were enrolled and underwent 14-day actigraphic recording, sleep diary, neuropsychological testing, and CSF biomarkers analysis. All patients were compared to controls. RESULTS: Eighteen AD patients were compared to ten controls. AD patients showed the alteration of the sleep-wake cycle, featured by sleep dysregulation and daytime wake fragmentation, with respect to controls. Considering the correlation analysis, we documented the correlation between tau proteins and orexin CSF levels and sleep-wake cycle dysregulation. CONCLUSION: This study confirmed the dysregulation of sleep-wake cycle in AD patients, as reflected by the daytime wake fragmentation, irregular sleep-wake rhythm, and nocturnal sleep impairment. This sleep-wake cycle disorder correlates with AD neuropathological in vivo features and brain orexin activity. Hence, we suppose that a more marked AD pathology coupled with orexinergic system dysregulation may promote sleep-wake cycle impairment in AD patients.

Repeated lumbar punctures within 3 days may affect CSF biomarker levels.

Lumbar puncture (LP) is a common way of collecting cerebrospinal fluid (CSF) both in the clinic and in research. In this extension of a study on the relationship between sleep deprivation and CSF biomarkers for Alzheimer's disease, we investigated CSF biomarker dynamics in relation to rebound sleep after sleep deprivation. Two LPs were performed within 3 days in 13 healthy volunteers. We noticed an unexpected sharp rise in biomarker concentrations in the second sample and therefore repeated the experiment, but without sleep intervention, in four additional individuals. The findings were similar in these subjects, suggesting an inherent methodological problem with repeated LPs. The result corroborates findings in studies with repeated CSF collection via indwelling lumbar catheters, and needs to be addressed in, for instance, pharmacodynamic studies employing these techniques.

Short-term sleep fragmentation enhances anxiety-related behavior: The role of hormonal alterations.

INTRODUCTION: The neuroendocrine background of acute sleep fragmentation in obstructive sleep apnea and sleep fragmentation involvement in psychiatric comorbidities, common in these patients, are still largely unknown. The aim of this study was to determine the effects of short-term experimental sleep fragmentation on anxiety -like behavior and hormonal status in rats. METHODS: Male rats were adapted to treadmill (ON and OFF mode with belt speed set on 0.02m/s and 0.00m/s) and randomized to: 1) treadmill control (TC, only OFF mode); 2) motion, activity control (AC, 10min ON and 30min OFF mode) and 3) sleep fragmentation (SF, 30s ON and 90s OFF mode) group. Six hours later, the animals were tested in the open field, elevated plus maze and light/dark test (n = 8/group). Testosterone, estradiol, progesterone and corticosterone were determined in separate animal cohort immediately upon sleep fragmentation (n = 6/group). RESULTS: SF rats showed decreased rearings number, decreased time spent in the central area and increased thigmotaxic index compared to TC and AC rats in the open field test. Similarly, increased anxiety upon sleep fragmentation was observed in the elevated plus maze and the light/dark test. Significantly lower testosterone, estradiol and progesterone levels were determined in SF in comparison to AC and TC groups, while there was no significant difference in the levels of corticosterone. CONCLUSION: Short term sleep fragmentation enhances anxiety-related behavior in rats, which could be partly mediated by the observed hormonal changes presented in the current study in form of testosterone, estradiol and progesterone depletion.

The sleep-wake cycle regulates brain interstitial fluid tau in mice and CSF tau in humans.

The sleep-wake cycle regulates interstitial fluid (ISF) and cerebrospinal fluid (CSF) levels of ß-amyloid (Aß) that accumulates in Alzheimer's disease (AD). Furthermore, chronic sleep deprivation (SD) increases Aß plaques. However, tau, not Aß, accumulation appears to drive AD neurodegeneration. We tested whether ISF/CSF tau and tau seeding and spreading were influenced by the sleep-wake cycle and SD. Mouse ISF tau was increased ~90% during normal wakefulness versus sleep and ~100% during SD. Human CSF tau also increased more than 50% during SD. In a tau seeding-and-spreading model, chronic SD increased tau pathology spreading. Chemogenetically driven wakefulness in mice also significantly increased both ISF Aß and tau. Thus, the sleep-wake cycle regulates ISF tau, and SD increases ISF and CSF tau as well as tau pathology spreading.

Obstructive sleep apnea treatment, slow wave activity, and amyloid-ß.

Obstructive sleep apnea (OSA) increases risk of dementia, a relationship that may be mediated by amyloid-ß (Aß) and downstream Alzheimer disease pathology. We previously showed that OSA may impair Aß clearance and affect the relationship between slow wave activity (SWA) and Aß. In this study, SWA and CSF Aß were measured in participants with OSA before and 1 to 4 months after treatment. OSA treatment increased SWA, and SWA was significantly correlated with lower Aß after treatment. Greater improvement in OSA was associated with greater decreases in Aß. We propose a model whereby OSA treatment may affect both Aß release and clearance. Ann Neurol 2018 ANN NEUROL 2019;85:291-295.

Sleep deprivation and cerebrospinal fluid biomarkers for Alzheimer's disease.

Study Objectives: To investigate the cumulative effect of five consecutive nights of partial sleep deprivation (PSD) on a panel of cerebrospinal fluid (CSF) biomarkers in healthy adults. Methods: A randomized, cross-over study conducted at the University of Gothenburg. The participants (N = 13) were healthy adults (20-40 years of age) with a normal sleeping pattern. The participants underwent a baseline sleep period consisting of five nights with 8 hr spent in bed. A subsequent period with PSD consisted of five nights of maximum 4 hr of sleep per night. Four participants were also subjected to a prolonged period of PSD consisting of eight nights with 4 hr of sleep per night. Sleep was monitored by means of observation, actigraphy, and continuous polysomnographic recordings. CSF samples were collected by routine lumbar puncture after each period. CSF biomarkers included the 38, 40, and 42 amino acid-long Aß isoforms, total-τ, phospho-τ, orexin, monoamine metabolites (3-methoxy-4-hydroxyphenylglycol, homovanillinic acid, and 5-hydroxyindoleacetic acid), neuron-derived biomarkers (neurofilament light, neuron-specific enolase, and fatty acid-binding protein), and astro- and microglia-derived biomarkers (glial fibrillary acidic protein, S-100B, and YKL-40). Results: PSD was associated with a 27 per cent increase in CSF orexin concentrations (p = 0.001). No PSD-related changes in CSF biomarkers for amyloid build-up in the brain, Alzheimer's disease (AD)-type neurodegeneration, or astroglial activation were observed. PSD led to a shortening of time spent in all sleep stages except slow-wave sleep (SWS). Conclusion: Five to eight consecutive nights of PSD, with preserved SWS, increased CSF orexin but had no effect on CSF biomarkers for amyloid deposition, neuronal injury, and astroglial activation.

Slow wave sleep disruption increases cerebrospinal fluid amyloid-ß levels.

See Mander et al. (doi:10.1093/awx174) for a scientific commentary on this article.Sleep deprivation increases amyloid-ß, suggesting that chronically disrupted sleep may promote amyloid plaques and other downstream Alzheimer's disease pathologies including tauopathy or inflammation. To date, studies have not examined which aspect of sleep modulates amyloid-ß or other Alzheimer's disease biomarkers. Seventeen healthy adults (age 35-65 years) without sleep disorders underwent 5-14 days of actigraphy, followed by slow wave activity disruption during polysomnogram, and cerebrospinal fluid collection the following morning for measurement of amyloid-ß, tau, total protein, YKL-40, and hypocretin. Data were compared to an identical protocol, with a sham condition during polysomnogram. Specific disruption of slow wave activity correlated with an increase in amyloid-ß40 (r = 0.610, P = 0.009). This effect was specific for slow wave activity, and not for sleep duration or efficiency. This effect was also specific to amyloid-ß, and not total protein, tau, YKL-40, or hypocretin. Additionally, worse home sleep quality, as measured by sleep efficiency by actigraphy in the six nights preceding lumbar punctures, was associated with higher tau (r = 0.543, P = 0.045). Slow wave activity disruption increases amyloid-ß levels acutely, and poorer sleep quality over several days increases tau. These effects are specific to neuronally-derived proteins, which suggests they are likely driven by changes in neuronal activity during disrupted sleep.

Continuous theta burst stimulation facilitates the clearance efficiency of the glymphatic pathway in a mouse model of sleep deprivation.

Sleep deprivation (SD) is a common condition associated with a variety of nervous system diseases, and has a negative impact on emotional and cognitive function. Continuous theta burst stimulation (cTBS) is known to improve cognition and emotion function in normal situations as well as in various types of dysfunction, but the mechanism remains unknown. We used two-photon in vivo imaging to explore the effect of cTBS on glymphatic pathway clearance in normal and SD C57BL/6J mice. Aquaporin-4 (AQP4) polarization was detected by immunofluorescence. Anxiety-like behaviors was measured using open field tests. We found that SD reduced influx efficiency along the peri-vascular space (PVS), disturbed AQP4 polarization and induced anxiety-like behaviors. CTBS significantly attenuated the decrease in efficiency of solute clearance usually incurred with SD, restored the loss of AQP4 polarization and improved anxiety-like behavior in SD animals. Our results implied that cTBS had the potential to protect against neuronal dysfunction induced by sleep disorders.

Glymphatic distribution of CSF-derived apoE into brain is isoform specific and suppressed during sleep deprivation.

BACKGROUND: Apolipoprotein E (apoE) is a major carrier of cholesterol and essential for synaptic plasticity. In brain, it's expressed by many cells but highly expressed by the choroid plexus and the predominant apolipoprotein in cerebrospinal fluid (CSF). The role of apoE in the CSF is unclear. Recently, the glymphatic system was described as a clearance system whereby CSF and ISF (interstitial fluid) is exchanged via the peri-arterial space and convective flow of ISF clearance is mediated by aquaporin 4 (AQP4), a water channel. We reasoned that this system also serves to distribute essential molecules in CSF into brain. The aim was to establish whether apoE in CSF, secreted by the choroid plexus, is distributed into brain, and whether this distribution pattern was altered by sleep deprivation. METHODS: We used fluorescently labeled lipidated apoE isoforms, lenti-apoE3 delivered to the choroid plexus, immunohistochemistry to map apoE brain distribution, immunolabeled cells and proteins in brain, Western blot analysis and ELISA to determine apoE levels and radiolabeled molecules to quantify CSF inflow into brain and brain clearance in mice. Data were statistically analyzed using ANOVA or Student's t- test. RESULTS: We show that the glymphatic fluid transporting system contributes to the delivery of choroid plexus/CSF-derived human apoE to neurons. CSF-delivered human apoE entered brain via the perivascular space of penetrating arteries and flows radially around arteries, but not veins, in an isoform specific manner (apoE2 > apoE3 > apoE4). Flow of apoE around arteries was facilitated by AQP4, a characteristic feature of the glymphatic system. ApoE3, delivered by lentivirus to the choroid plexus and ependymal layer but not to the parenchymal cells, was present in the CSF, penetrating arteries and neurons. The inflow of CSF, which contains apoE, into brain and its clearance from the interstitium were severely suppressed by sleep deprivation compared to the sleep state. CONCLUSIONS: Thus, choroid plexus/CSF provides an additional source of apoE and the glymphatic fluid transporting system delivers it to brain via the periarterial space. By implication, failure in this essential physiological role of the glymphatic fluid flow and ISF clearance may also contribute to apoE isoform-specific disorders in the long term.

Rapid eye movement sleep disruption and sleep fragmentation are associated with increased orexin-A cerebrospinal-fluid levels in mild cognitive impairment due to Alzheimer's disease.

The orexin system has been investigated in patients affected by mild cognitive impairment (MCI) due to Alzheimer's disease (AD) by measuring orexin-A concentrations in the cerebrospinal fluid (CSF), and correlated to subjective and objective sleep parameters, quantified by questionnaires and polysomnography, respectively. Twenty drug-naïve patients with MCI due to AD were studied and compared with a population of 26 age and/or sex matched controls, divided into subgroups on the basis of the Pittsburgh Sleep Quality Index (PSQI) score. Increased CSF-orexin levels were detected in patients with MCI due to AD in comparison with controls (p < 0.05). In particular, CSF-orexin concentrations were higher in MCI patients suffering from sleep complaints (PSQI ≥5, n = 10) compared with MCI patients with a regular sleep-wake cycle (PSQI <5, n = 10, p < 0.001) and compared with both control groups (with sleep complaints, PSQI ≥5, n = 11, p < 0.001; without sleep complaints, PSQI <5, n = 15, p < 0.001). Moreover, REM sleep was reduced in MCI patients compared with controls (p < 0.01), and had a negative correlation coupled with a reciprocal influence at the multiple regression analysis with CSF-orexin levels (R = -0.65; ß = -8.90). REM sleep disruption and sleep fragmentation are related to higher CSF-orexin levels in patients with MCI due to AD, thus suggesting that the orexin system may be involved even in the earliest stages of AD, resulting in prolonged sleep latency, reduced sleep efficiency, and REM sleep impairment.

Hypocretin-1 Levels Associate with Fragmented Sleep in Patients with Narcolepsy Type 1.

STUDY OBJECTIVES: We aimed to analyze nocturnal sleep characteristics of patients with narcolepsy type 1 (narcolepsy with cataplexy) measured by actigraphy in respect to cerebrospinal fluid hypocretin-1 levels of the same patients. METHODS: Actigraphy recording of 1-2 w and hypocretin-1 concentration analysis were done to thirty-six unmedicated patients, aged 7 to 63 y, 50% female. Twenty-six of them had hypocretin-1 levels under 30 pg/mL and the rest had levels of 31-79 pg/mL. RESULTS: According to actigraphy, patients with very low hypocretin levels had statistically significantly longer sleep latency (P = 0.033) and more fragmented sleep, indicated by both the number of immobile phases of 1 min (P = 0.020) and movement + fragmentation index (P = 0.049). There were no statistically significant differences in the actual sleep time or circadian rhythm parameters measured by actigraphy. CONCLUSIONS: Actigraphy gives additional information about the stabilization of sleep in patients with narcolepsy type 1. Very low hypocretin levels associate with more wake intruding into sleep.

Biomarkers of traumatic injury are transported from brain to blood via the glymphatic system.

The nonspecific and variable presentation of traumatic brain injury (TBI) has motivated an intense search for blood-based biomarkers that can objectively predict the severity of injury. However, it is not known how cytosolic proteins released from traumatized brain tissue reach the peripheral blood. Here we show in a murine TBI model that CSF movement through the recently characterized glymphatic pathway transports biomarkers to blood via the cervical lymphatics. Clinically relevant manipulation of glymphatic activity, including sleep deprivation and cisternotomy, suppressed or eliminated TBI-induced increases in serum S100ß, GFAP, and neuron specific enolase. We conclude that routine TBI patient management may limit the clinical utility of blood-based biomarkers because their brain-to-blood transport depends on glymphatic activity.

Effect of 1 night of total sleep deprivation on cerebrospinal fluid ß-amyloid 42 in healthy middle-aged men: a randomized clinical trial.

IMPORTANCE: Increasing evidence suggests a relationship between poor sleep and the risk of developing Alzheimer disease. A previous study found an effect of sleep on ß-amyloid (Aß), which is a key protein in Alzheimer disease pathology. OBJECTIVE: To determine the effect of 1 night of total sleep deprivation on cerebrospinal fluid Aß42 protein levels in healthy middle-aged men. DESIGN, SETTING, AND PARTICIPANTS: The Alzheimer, Wakefulness, and Amyloid Kinetics (AWAKE) study at the Radboud Alzheimer Center, a randomized clinical trial that took place between June 1, 2012, and October 1, 2012. Participants were cognitively normal middle-aged men (40-60 years of age) with normal sleep (n = 26) recruited from the local population. INTERVENTIONS: Participants were randomized to 1 night with unrestricted sleep (n = 13) or 1 night of total sleep deprivation (24 hours of wakefulness) (n = 13). MAIN OUTCOMES AND MEASURES: Sleep was monitored using continuous polysomnographic recording from 3 pm until 10 am. Cerebrospinal fluid samples were collected using an intrathecal catheter at defined times to compare cerebral Aß42 concentrations between evening and morning. RESULTS: A night of unrestricted sleep led to a 6% decrease in Aß42 levels of 25.3 pg/mL (95% CI [0.94, 49.6], P = .04), whereas sleep deprivation counteracted this decrease. When accounting for the individual trajectories of Aß42 over time, a difference of 75.8 pg/mL of Aß42 was shown between the unrestricted sleep and sleep deprivation group (95% CI [3.4, 148.4], P = .04). The individual trajectories of evening and morning Aß42 concentrations differed between the unrestricted sleep and sleep deprivation groups (P = .04) in contrast to stable Aß40, tau, and total protein levels. CONCLUSIONS AND RELEVANCE: Sleep deprivation, or prolonged wakefulness, interferes with a physiological morning decrease in Aß42. We hypothesize that chronic sleep deprivation increases cerebral Aß42 levels, which elevates the risk of Alzheimer disease. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT01194713.

Melanin concentrating hormone in central hypersomnia.

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

Relationship between clinical characteristics of narcolepsy and CSF orexin-A levels.

Although an abnormally low cerebrospinal fluid (CSF)-orexin level is well known to be a specific finding in narcoleptic patients, the relationships between the severity of the core symptoms of narcolepsy [i.e. daytime sleepiness and increased rapid eye movement (REM) propensity], as well as levels of obesity, and CSF-orexin levels have not been well elucidated. The aim of this study was to examine the relationship between these characteristic symptoms of narcolepsy and CSF-orexin level. Fifty-three patients with narcolepsy with cataplexy (NA/CA) and 17 without cataplexy (NA w/o CA) were enrolled. Sleep latency and sleep onset REM latency were measured using the multiple sleep latency test (MSLT). Multiple linear regression analysis was used to determine factors associated with both mean sleep latency and mean sleep onset REM latency on MSLT, with %body mass index (BMI), gender, onset age, length of excessive daytime sleepiness (EDS) morbidity, diagnostic subgroup and CSF-orexin levels being used as independent variables. The NA/CA group included a significantly higher number of patients with undetectable CSF-orexin levels and shorter sleep onset and rapid eye movement (SOREM) latency, as well as a higher %BMI, versus NA w/o CA. Multiple linear regression analysis revealed that sleep latency was associated significantly with CSF-orexin levels and gender. With regard to sleep onset REM latency and %BMI, only CSF-orexin levels appeared to be a significantly associated factor. In narcoleptic patients, the severity of both excessive daytime sleepiness and increased REM propensity, as well as the level of obesity, could be associated with CSF-orexin deficiency, rather than with subcategories of the disorder.

Sleep deprivation increases oleoylethanolamide in human cerebrospinal fluid.

This study investigated the role of two fatty acid ethanolamides, the endogenous cannabinoid anandamide and its structural analog oleoylethanolamide in sleep deprivation of human volunteers. Serum and cerebrospinal fluid (CSF) samples were obtained from 20 healthy volunteers before and after a night of sleep deprivation with an interval of about 12 months. We found increased levels of oleoylethanolamide in CSF (P = 0.011) but not in serum (P = 0.068) after 24 h of sleep deprivation. Oleoylethanolamide is an endogenous lipid messenger that is released after neural injury and activates peroxisome proliferator-activated receptor-alpha (PPAR-alpha) with nanomolar potency. Exogenous PPAR-alpha agonists, such as hypolipidemic fibrates and oleoylethanolamide, exert both neuroprotective and neurotrophic effects. Thus, our results suggest that oleoylethanolamide release may represent an endogenous neuroprotective signal during sleep deprivation.