CSF histamine contents in narcolepsy, idiopathic hypersomnia and obstructive sleep apnea syndrome

The Prevalence and Characteristics of Primary Headache and Dream-Enacting Behaviour in Japanese Patients with Narcolepsy or Idiopathic Hypersomnia: A Multi-Centre Cross-Sectional Study

Background

Because the prevalence and characteristics of primary headache have yet to be thoroughly studied in patients with hypersomnia disorders, including narcolepsy and idiopathic hypersomnia, we examined these parameters in the Japanese population.

Methods

In a multicentre cross-sectional survey, among 576 consecutive outpatients with sleep disorders, 68 narcolepsy patients and 35 idiopathic hypersomnia patients were included. Additionally, 61 healthy control subjects participated. Semi-structured headache questionnaires were administered to all participants.

Results

The patients with narcolepsy (52.9%) and idiopathic hypersomnia (77.1%) more frequently experienced headache than the healthy controls (24.6%; p<0.0001). The prevalence rates were 23.5%, 41.2% and 4.9% for migraine (p<0.0001) and 16.2%, 23.5% and 14.8% (p = 0.58) for tension-type headache among the narcolepsy patients, the idiopathic hypersomnia patients and the control subjects, respectively. Those who experienced migraine more frequently experienced excessive daytime sleepiness, defined as an Epworth Sleepiness Scale score of ≥10, than those who did not experience headache among the patients with narcolepsy (93.8% vs. 65.6%, p = 0.040) and idiopathic hypersomnia (86.7% vs. 37.5%, p = 0.026). Dream-enacting behaviour (DEB), as evaluated by the rapid eye movement sleep disorders questionnaire, was more frequently observed in the narcolepsy patients than in the idiopathic hypersomnia patients and the control subjects. An increased DEB frequency was observed in the narcolepsy patients with migraines compared to those without headache.

Conclusions

Migraines were frequently observed in patients with narcolepsy and idiopathic hypersomnia. DEB is a characteristic of narcolepsy patients. Further studies are required to assess the factors that contribute to migraines in narcolepsy and idiopathic hypersomnia patients.

Central Disorders of Hypersomnolence: Focus on the Narcolepsies and Idiopathic Hypersomnia

The central disorders of hypersomnolence are characterized by severe daytime sleepiness, which is present despite normal quality and timing of nocturnal sleep. Recent reclassification distinguishes three main subtypes: narcolepsy type 1, narcolepsy type 2, and idiopathic hypersomnia (IH), which are the focus of this review. Narcolepsy type 1 results from loss of hypothalamic hypocretin neurons, while the pathophysiology underlying narcolepsy type 2 and IH remains to be fully elucidated. Treatment of all three disorders focuses on the management of sleepiness, with additional treatment of cataplexy in those patients with narcolepsy type 1. Sleepiness can be treated with modafinil/armodafinil or sympathomimetic CNS stimulants, which have been shown to be beneficial in randomized controlled trials of narcolepsy and, quite recently, IH. In those patients with narcolepsy type 1, sodium oxybate is effective for the treatment of both sleepiness and cataplexy. Despite these treatments, there remains a subset of hypersomnolent patients with persistent sleepiness, in whom alternate therapies are needed. Emerging treatments for sleepiness include histamine H3 antagonists (eg, pitolisant) and possibly negative allosteric modulators of the gamma-aminobutyric acid-A receptor (eg, clarithromycin and flumazenil).

3-(1'-Cyclobutylspiro[4H-1,3-benzodioxine-2,4'-piperidine]-6-yl)-5,5-dimethyl-1,4-dihydropyridazin-6-one (CEP-32215), a new wake-promoting histamine H3 antagonist/inverse agonist

CEP-32215 is a new, potent, selective, and orally bioavailable inverse agonist of the histamine H3 receptor (H3R) with drug-like properties. High affinity in human (hH3R Ki = 2.0 ± 0.2 nM) and rat (rH3R Ki = 3.6 ± 0.7 nM) H3R radioligand binding assays was demonstrated. Potent functional antagonism (Kb = 0.3 ± 0.1 nM) and inverse agonism (EC50 = 0.6 ± 0.2 nM) were demonstrated in [(35)S]guanosine 5(')-O-(γ-thio)-triphosphate binding assays. Oral bioavailability and dose-related exposure was consistent among rat, dog, and monkey. After oral dosing, occupancy of H3R by CEP-32215 was estimated by the inhibition of ex vivo binding in rat cortical slices (ED50 = 0.1 mg/kg p.o.). Functional antagonism in brain was demonstrated by the inhibition of R-α-methylhistamine-induced drinking in the rat dipsogenia model (ED50 = 0.92 mg/kg). CEP-32215 significantly increased wake duration in the rat EEG model at 3-30 mg/kg p.o. Increased motor activity, sleep rebound or undesirable events (such as spike wave or seizure activity) was not observed following doses up to 100 mg/kg p.o., indicating an acceptable therapeutic index. CEP-32215 may have potential utility in the treatment of a variety of sleep disorders. This article is part of the Special Issue entitled 'Histamine Receptors'.

Interactions of the histamine and hypocretin systems in CNS disorders

Histamine and hypocretin neurons are localized to the hypothalamus, a brain area critical to autonomic function and sleep. Narcolepsy type 1, also known as narcolepsy with cataplexy, is a neurological disorder characterized by excessive daytime sleepiness, impaired night-time sleep, cataplexy, sleep paralysis and short latency to rapid eye movement (REM) sleep after sleep onset. In narcolepsy, 90% of hypocretin neurons are lost; in addition, two groups reported in 2014 that the number of histamine neurons is increased by 64% or more in human patients with narcolepsy, suggesting involvement of histamine in the aetiology of this disorder. Here, we review the role of the histamine and hypocretin systems in sleep-wake modulation. Furthermore, we summarize the neuropathological changes to these two systems in narcolepsy and discuss the possibility that narcolepsy-associated histamine abnormalities could mediate or result from the same processes that cause the hypocretin cell loss. We also review the changes in the hypocretin and histamine systems, and the associated sleep disruptions, in Parkinson disease, Alzheimer disease, Huntington disease and Tourette syndrome. Finally, we discuss novel therapeutic approaches for manipulation of the histamine system.

Hypersomnia subtypes, sleep and relapse in bipolar disorder

BACKGROUND

Though poorly defined, hypersomnia is associated with negative health outcomes and new-onset and recurrence of psychiatric illness. Lack of definition impedes generalizability across studies. The present research clarifies hypersomnia diagnoses in bipolar disorder by exploring possible subgroups and their relationship to prospective sleep data and relapse into mood episodes.

METHOD

A community sample of 159 adults (aged 18-70 years) with bipolar spectrum diagnoses, euthymic at study entry, was included. Self-report inventories and clinician-administered interviews determined features of hypersomnia. Participants completed sleep diaries and wore wrist actigraphs at home to obtain prospective sleep data. Approximately 7 months later, psychiatric status was reassessed. Factor analysis and latent profile analysis explored empirical groupings within hypersomnia diagnoses.

RESULTS

Factor analyses confirmed two separate subtypes of hypersomnia ('long sleep' and 'excessive sleepiness') that were uncorrelated. Latent profile analyses suggested a four-class solution, with 'long sleep' and 'excessive sleepiness' again representing two separate classes. Prospective sleep data suggested that the sleep of 'long sleepers' is characterized by a long time in bed, not long sleep duration. Longitudinal assessment suggested that 'excessive sleepiness' at baseline predicted mania/hypomania relapse.

CONCLUSIONS

This study is the largest of hypersomnia to include objective sleep measurement, and refines our understanding of classification, characterization and associated morbidity. Hypersomnia appears to be comprised of two separate subgroups: long sleep and excessive sleepiness. Long sleep is characterized primarily by long bedrest duration. Excessive sleepiness is not associated with longer sleep or bedrest, but predicts relapse to mania/hypomania. Understanding these entities has important research and treatment implications.

Interactions of the orexin/hypocretin neurones and the histaminergic system

Histaminergic and orexin/hypocretin systems are components in the brain wake-promoting system. Both are affected in the sleep disorder narcolepsy, but the role of histamine in narcolepsy is unclear. The histaminergic neurones are activated by the orexin/hypocretin system in rodents, and the development of the orexin/hypocretin neurones is bidirectionally regulated by the histaminergic system in zebrafish. This review summarizes the current knowledge of the interactions of these two systems in normal and pathological conditions in humans and different animal models.

The human histaminergic system in neuropsychiatric disorders

Histaminergic neurons are exclusively located in the hypothalamic tuberomamillary nucleus, from where they project to many brain areas. The histaminergic system is involved in basic physiological functions, such as the sleep-wake cycle, energy and endocrine homeostasis, sensory and motor functions, cognition, and attention, which are all severely affected in neuropsychiatric disorders. Here, we present recent postmortem findings on the alterations in this system in neuropsychiatric disorders, including Parkinson's disease (PD), Alzheimer's disease (AD), Huntington's disease (HD), depression, and narcolepsy. In addition, we highlight the need to validate animal models for these diseases and also for Tourette's syndrome (TS) in relation to alterations in the histaminergic system. Moreover, we discuss the potential for, and concerns over, the use of novel histamine 3 receptor (H3R) antagonists/inverse agonists as treatment for such disorders.

MiRNA profiles in cerebrospinal fluid from patients with central hypersomnias

MicroRNAs (miRNAs) are involved in the pathogenesis of many human diseases, including some neurological disorders. Recently, we have reported dysregulated miRNAs in plasma from patients with central hypersomnias including type 1 and type 2 narcolepsy, and idiopathic hypersomnia. This study addressed whether miRNA levels are altered in the cerebrospinal fluid (CSF) of patients with central hypersomnias. We conducted high-throughput analyses of miRNAs in CSF from patients using quantitative real-time polymerase chain reaction panels. We identified 13, 9, and 11 miRNAs with a more than two-fold change in concentration in CSF from patients with type 1 and type 2 narcolepsy and idiopathic hypersomnia, respectively, compared with matched healthy controls. Most miRNAs differed in more than one of the sleep disorders. However, all miRNAs were detected at low levels in CSF and varied between individuals. None of them showed significant differences in concentrations between groups after correcting for multiple testing, and none could be validated in an independent cohort. Nevertheless, approximately 60% of the most abundant miRNAs in the profile reported here have previously been identified in the CSF of healthy individuals, showing consistency with previous miRNA profiles found in CSF. In conclusion, we were not able to demonstrate distinct levels or patterns of miRNAs in CSF from central hypersomnia patients.

Acid-sensing hypothalamic neurons controlling arousal

Breathing and vigilance are regulated by pH and CO2 levels in the central nervous system. The hypocretin/orexin (Hcrt/Orx)- and histamine (HA)-containing hypothalamic neurons synergistically control different aspects of the waking state. Acidification inhibits firing of most neurons but these two groups in the caudal hypothalamus are excited by hypercapnia and protons, similar to the chemosensory neurons in the brain stem. Activation of hypothalamic wake-on neurons in response to hypercapnia, seen with the c-Fos assay, is supported by patch-clamp recordings in rodent brain slices: Hcrt/Orx and HA neurons are excited by acidification in the physiological range (pH from 7.4 to 7.0). Multiple molecular mechanisms mediate wake-promoting effects of protons in HA neurons in the tuberomamillary nucleus (TMN): among them are acid-sensing ion channels, Na(+),K(+)-ATPase, group I metabotropic glutamate receptors (mGluRI). HA neurons are remarkably sensitive to the mGluRI agonist DHPG (threshold concentration 0.5 µM) and mGluRI antagonists abolish proton-induced excitation of HA neurons. Hcrt/Orx neurons are excited through block of a potassium conductance and release glutamate with their peptides in TMN. The two hypothalamic nuclei and the serotonergic dorsal raphe cooperate toward CO2/acid-induced arousal. Their interactions and molecular mechanisms of H(+)/CO2-induced activation are relevant for the understanding and treatment of respiratory and metabolic disorders related to sleep-waking such as obstructive sleep apnea and sudden infant death syndrome.

Current and emerging options for the drug treatment of narcolepsy

Narcolepsy/hypocretin deficiency (now called type 1 narcolepsy) is a lifelong neurologic disorder with well-established diagnostic criteria and etiology. Narcolepsy is a chronic sleep disorder characterized by excessive daytime sleepiness (EDS) and symptoms of dissociated rapid eye movement sleep such as cataplexy (sudden loss of muscle tone), hypnagogic hallucinations (sensory events that occur at the transition from wakefulness to sleep), sleep paralysis (inability to perform movements upon wakening or sleep onset), and nocturnal sleep disruption. As these symptoms are often disabling, most patients need life-long treatment. The treatment of narcolepsy is well defined, and, traditionally, amphetamine-like stimulants (i.e., dopaminergic release enhancers) have been used for clinical management to improve EDS and sleep attacks, whereas tricyclic antidepressants have been used as anticataplectics. However, treatments have evolved to better-tolerated compounds such as modafinil or armodafinil (for EDS) and adrenergic/serotonergic selective reuptake inhibitors (as anticataplectics). In addition, night-time administration of a short-acting sedative, c-hydroxybutyrate (sodium oxybate), has been used for the treatment for EDS and cataplexy. These therapies are almost always needed in combination with non-pharmacologic treatments (i.e., behavioral modification). A series of new drugs is currently being tested in animal models and in humans. These include a wide variety of hypocretin agonists, melanin- concentrating hormone receptor antagonists, antigenspecific immunopharmacology, and histamine H3 receptor antagonists/inverse agonists (e.g., pitolisant), which have been proposed for specific therapeutic applications, including the treatment of Alzheimer's disease, attention-deficit hyperactivity disorder, epilepsy, and more recently, narcolepsy. Even though current treatment is strictly symptomatic, based on the present state of knowledge of the pathophysiology of narcolepsy, we expect that more pathophysiology-based treatments will be available in the near future.

New insights into the role of histamine in subventricular zone-olfactory bulb neurogenesis

The subventricular zone (SVZ) contains neural stem cells (NSCs) that generate new neurons throughout life. Many brain diseases stimulate NSCs proliferation, neuronal differentiation and homing of these newborns cells into damaged regions. However, complete cell replacement has never been fully achieved. Hence, the identification of proneurogenic factors crucial for stem cell-based therapies will have an impact in brain repair. Histamine, a neurotransmitter and immune mediator, has been recently described to modulate proliferation and commitment of NSCs. Histamine levels are increased in the brain parenchyma and at the cerebrospinal fluid (CSF) upon inflammation and brain injury, thus being able to modulate neurogenesis. Herein, we add new data showing that in vivo administration of histamine in the lateral ventricles has a potent proneurogenic effect, increasing the production of new neuroblasts in the SVZ that ultimately reach the olfactory bulb (OB). This report emphasizes the multidimensional effects of histamine in the modulation of NSCs dynamics and sheds light into the promising therapeutic role of histamine for brain regenerative medicine.

Health, social and economic consequences of hypersomnia: a controlled national study from a national registry evaluating the societal effect on patients and their partners

Hypersomnia causes significant socioeconomic burden, but there is insufficient information about the time course and the effect on the partner. The aim of this study was to estimate the factual direct and productivity costs of hypersomnia in a controlled study including all national patients and their partners. Using records from the Danish National Patient Registry (1997-2009), we identified all patients with a diagnosis of hypersomnia and compared these patients and their partners with randomly chosen controls matched for age, gender, geographic area and marital status. Direct and productivity costs, including frequencies of primary and sector contacts and procedures, medication, labour supply and social transfer payments were extracted from the national databases. A total of 2,855 national patients was compared to 11,382 controls. About 70 % of patients and controls were married or cohabiting. Patients with hypersomnia had significantly higher rates of health-related contact, medication use and socioeconomic cost. Furthermore, they had slightly lower employment rates, and those in employment had a lower income level than control subjects. The annual mean excess health-related cost including social transfers was <euro>3,498 for patients with hypersomnia and <euro>3,851 for their partners. The social and health-related consequences could be identified up to 11 years before the first diagnosis among both the patients and their partners and became more pronounced as the disease advanced. The health effects were present in all age groups and in both genders. On the basis of this retrospective controlled study in the Danish population, symptoms and findings of hypersomnia are associated with major socioeconomic consequences for patients, their partners and society.

Histaminergic system in brain disorders: lessons from the translational approach and future perspectives

Histamine and its receptors were first described as part of immune and gastrointestinal systems, but their presence in the central nervous system and importance in behavior are gaining more attention. The histaminergic system modulates different processes including wakefulness, feeding, and learning and memory consolidation. Histamine receptors (H1R, H2R, H3R, and H4R) belong to the rhodopsin-like family of G protein-coupled receptors, present constitutive activity, and are subjected to inverse agonist action. The involvement of the histaminergic system in brain disorders, such as Alzheimer's disease, schizophrenia, sleep disorders, drug dependence, and Parkinson's disease, is largely studied. Data obtained from preclinical studies point antagonists of histamine receptors as promising alternatives to treat brain disorders. Thus, clinical trials are currently ongoing to assess the effects of these drugs on humans. This review summarizes the role of histaminergic system in brain disorders, as well as the effects of different histamine antagonists on animal models and humans.

Test-retest reliability of the multiple sleep latency test in narcolepsy without cataplexy and idiopathic hypersomnia

STUDY OBJECTIVES

Differentiation of narcolepsy without cataplexy from idiopathic hypersomnia relies entirely upon the multiple sleep latency test (MSLT). However, the test-retest reliability for these central nervous system hypersomnias has never been determined.

METHODS

Patients with narcolepsy without cataplexy, idiopathic hypersomnia, and physiologic hypersomnia who underwent two diagnostic multiple sleep latency tests were identified retrospectively. Correlations between the mean sleep latencies on the two studies were evaluated, and we probed for demographic and clinical features associated with reproducibility versus change in diagnosis.

RESULTS

Thirty-six patients (58% women, mean age 34 years) were included. Inter -test interval was 4.2 ± 3.8 years (range 2.5 months to 16.9 years). Mean sleep latencies on the first and second tests were 5.5 (± 3.7 SD) and 7.3 (± 3.9) minutes, respectively, with no significant correlation (r = 0.17, p = 0.31). A change in diagnosis occurred in 53% of patients, and was accounted for by a difference in the mean sleep latency (N = 15, 42%) or the number of sleep onset REM periods (N = 11, 31%). The only feature predictive of a diagnosis change was a history of hypnagogic or hypnopompic hallucinations.

CONCLUSIONS

The multiple sleep latency test demonstrates poor test-retest reliability in a clinical population of patients with central nervous system hypersomnia evaluated in a tertiary referral center. Alternative diagnostic tools are needed.

Modulation of vigilance in the primary hypersomnias by endogenous enhancement of GABAA receptors

The biology underlying excessive daytime sleepiness (hypersomnolence) is incompletely understood. After excluding known causes of sleepiness in 32 hypersomnolent patients, we showed that, in the presence of 10 μM γ-aminobutyric acid (GABA), cerebrospinal fluid (CSF) from these subjects stimulated GABA(A) receptor function in vitro by 84.0 ± 40.7% (SD) relative to the 35.8 ± 7.5% (SD) stimulation obtained with CSF from control subjects (Student's t test, t = 6.47, P < 0.0001); CSF alone had no effect on GABA(A) signaling. The bioactive CSF component had a mass of 500 to 3000 daltons and was neutralized by trypsin. Enhancement was greater for α2 subunit- versus α1 subunit-containing GABA(A) receptors and negligible for α4 subunit-containing ones. CSF samples from hypersomnolent patients also modestly enhanced benzodiazepine (BZD)-insensitive GABA(A) receptors and did not competitively displace BZDs from human brain tissue. Flumazenil--a drug that is generally believed to antagonize the sedative-hypnotic actions of BZDs only at the classical BZD-binding domain in GABA(A) receptors and to lack intrinsic activity--nevertheless reversed enhancement of GABA(A) signaling by hypersomnolent CSF in vitro. Furthermore, flumazenil normalized vigilance in seven hypersomnolent patients. We conclude that a naturally occurring substance in CSF augments inhibitory GABA signaling, thus revealing a new pathophysiology associated with excessive daytime sleepiness.

Sleep disturbances among soldiers with combat-related traumatic brain injury

BACKGROUND

Sleep complaints are common among patients with traumatic brain injury. Evaluation of this population is confounded by polypharmacy and comorbid disease, with few studies addressing combat-related injuries. The aim of this study was to assess the prevalence of sleep disorders among soldiers who sustained combat-related traumatic brain injury.

METHODS

The study design was a retrospective review of soldiers returning from combat with mild to moderate traumatic brain injury. All underwent comprehensive sleep evaluations. We determined the prevalence of sleep complaints and disorders in this population and assessed demographics, mechanism of injury, medication use, comorbid psychiatric disease, and polysomnographic findings to identify variables that correlated with the development of specific sleep disorders.

RESULTS

Of 116 consecutive patients, 96.6% were men (mean age, 31.1 ± 9.8 years; mean BMI, 27.8 ± 4.1 kg/m²), and 29.5% and 70.5% sustained blunt and blast injuries, respectively. Nearly all (97.4%) reported sleep complaints. Hypersomnia and sleep fragmentation were reported in 85.2% and 54.3%, respectively. Obstructive sleep apnea syndrome (OSAS) was found in 34.5%, and 55.2% had insomnia. Patients with blast injuries developed more anxiety (50.6% vs 20.0%, P = .002) and insomnia (63% vs 40%, P = .02), whereas patients with blunt trauma had significantly more OSAS (54.3% vs 25.9%, P = .003). In multivariate analysis, blunt trauma was a significant predictor of OSAS (OR, 3.09; 95% CI, 1.02-9.38; P = .047).

CONCLUSIONS

Sleep disruption is common following traumatic brain injury, and the majority of patients develop a chronic sleep disorder. It appears that sleep disturbances may be influenced by the mechanism of injury in those with combat-related traumatic brain injury, with blunt injury potentially predicting the development of OSAS.

Normal cerebrospinal fluid histamine and tele-methylhistamine levels in hypersomnia conditions

STUDY OBJECTIVES

To determine the activity of cerebral histaminergic system evaluated by CSF levels of histamine (HA) and tele-methylhistamine (t-MHA), its major metabolite, and their relationships with hypocretin-1 levels in a large population of patients with hypersomnia and neurological conditions.

DESIGN

sensitive liquid chromatographic-electrospray/tandem mass spectrometric assay was developed for the simultaneous quantification of CSF HA and t-MHA.

SETTING

ata were collected and CSF hypocretin-1 levels were measured using radioimmunoassay at the Sleep Disorders Center, Montpellier, France. CSF HA and t-MHA were measured in Bioprojet-Biotech, France

PARTICIPANTS

One hundred fourteen unrelated patients with a suspicion of central hypersomnia underwent one night of polysomnography followed by the multiple sleep latency test. Sleep disorders were diagnosed clinically and using sleep studies: narcolepsy-cataplexy NC (n = 56), narcolepsy without cataplexy NwC (n = 27), idiopathic hypersomnia IH (n = 11), secondary narcolepsy (n = 3), and unspecified hypersomnia Uns EDS (n = 17). Fifty neurological patients without daytime sleepiness were included as controls.

MEASUREMENTS AND RESULTS

No between-hypersomnia group differences were found for CSF HA levels (median 708.62 pM extreme range [55.92-3335.50] in NC; 781.34 [174.08-4391.50] in NwC; 489.42 [177.45-906.70] in IH, and 1155.40 [134.80-2736.59] in Uns EDS) or for t-MHA levels. No association was found between CSF HA, t-MHA, or HA + t-MHA, sleepiness, treatment intake, and frequency of cataplexy. A slight negative correlation was found between age and HA levels. Further adjustment for the age revealed no significant HA levels difference between hypersomnia patients and controls.

CONCLUSION

CSF histamine and tele-methylhistamine did not significantly differ between patients with narcolepsy-cataplexy and other etiologies of non-hypocretin-1 deficient central hypersomnias; these measurements, therefore, are not useful in assessing the etiology or severity of centrally mediated hypersomnia.

Control of sleep and wakefulness

This review summarizes the brain mechanisms controlling sleep and wakefulness. Wakefulness promoting systems cause low-voltage, fast activity in the electroencephalogram (EEG). Multiple interacting neurotransmitter systems in the brain stem, hypothalamus, and basal forebrain converge onto common effector systems in the thalamus and cortex. Sleep results from the inhibition of wake-promoting systems by homeostatic sleep factors such as adenosine and nitric oxide and GABAergic neurons in the preoptic area of the hypothalamus, resulting in large-amplitude, slow EEG oscillations. Local, activity-dependent factors modulate the amplitude and frequency of cortical slow oscillations. Non-rapid-eye-movement (NREM) sleep results in conservation of brain energy and facilitates memory consolidation through the modulation of synaptic weights. Rapid-eye-movement (REM) sleep results from the interaction of brain stem cholinergic, aminergic, and GABAergic neurons which control the activity of glutamatergic reticular formation neurons leading to REM sleep phenomena such as muscle atonia, REMs, dreaming, and cortical activation. Strong activation of limbic regions during REM sleep suggests a role in regulation of emotion. Genetic studies suggest that brain mechanisms controlling waking and NREM sleep are strongly conserved throughout evolution, underscoring their enormous importance for brain function. Sleep disruption interferes with the normal restorative functions of NREM and REM sleep, resulting in disruptions of breathing and cardiovascular function, changes in emotional reactivity, and cognitive impairments in attention, memory, and decision making.

Diurnal fluctuation in histidine decarboxylase expression, the rate limiting enzyme for histamine production, and its disorder in neurodegenerative diseases

STUDY OBJECTIVES

Neuronal histamine shows diurnal rhythms in rodents and plays a major role in the maintenance of vigilance. No data are available on its diurnal fluctuation in humans, either in health or in neurodegenerative disorders such as Parkinson disease (PD), Alzheimer disease (AD), or Huntington disease (HD), all of which are characterized by sleep-wake disturbances.

DESIGN

Quantitative in situ hybridization was used to study the mRNA expression of histidine decarboxylase (HDC), the key enzyme of histamine production in the tuberomammillary nucleus (TMN) in postmortem human hypothalamic tissue, obtained from 33 controls and 31 patients with a neurodegenerative disease-PD (n = 15), AD (n = 9), and HD (n = 8)-and covering the full 24-h cycle with respect to clock time of death.

RESULTS

HDC-mRNA levels in controls were found to be significantly higher during the daytime than at night (e.g., 08:01-20:00 versus 20:01-08:00, P = 0.004). This day-night fluctuation was markedly different in patients with neurodegenerative diseases.

CONCLUSION

The diurnal fluctuation of HDC-mRNA expression in human TMN supports a role for neuronal histamine in regulating day-night rhythms. Future studies should investigate histamine rhythm abnormalities in neurodegenerative disorders.

CITATION

Shan L; Hofman MA; van Wamelen DJ; Van Someren EJW; Bao AM; Swaab DF. Diurnal fluctuation in histidine decarboxylase expression, the rate limiting enzyme for histamine production, and its disorder in neurodegenerative diseases.

Histamine stimulates neurogenesis in the rodent subventricular zone

Neural stem/progenitor cells present in the subventricular zone (SVZ) are a potential source of repairing cells after injury. Therefore, the identification of novel players that modulate neural stem cells differentiation can have a huge impact in stem cell-based therapies. Herein, we describe a unique role of histamine in inducing functional neuronal differentiation from cultured mouse SVZ stem/progenitor cells. This proneurogenic effect depends on histamine 1 receptor activation and involves epigenetic modifications and increased expression of Mash1, Dlx2, and Ngn1 genes. Biocompatible poly (lactic-co-glycolic acid) microparticles, engineered to release histamine in a controlled and prolonged manner, also triggered robust neuronal differentiation in vitro. Preconditioning with histamine-loaded microparticles facilitated neuronal differentiation of SVZ-GFP cells grafted in hippocampal slices and in in vivo rodent brain. We propose that neuronal commitment triggered by histamine per se or released from biomaterial-derived vehicles may represent a new tool for brain repair strategies.

The histaminergic system regulates wakefulness and orexin/hypocretin neuron development via histamine receptor H1 in zebrafish

The histaminergic and hypocretin/orexin (hcrt) neurotransmitter systems play crucial roles in alertness/wakefulness in rodents. We elucidated the role of histamine in wakefulness and the interaction of the histamine and hcrt systems in larval zebrafish. Translation inhibition of histidine decarboxylase (hdc) with morpholino oligonucleotides (MOs) led to a behaviorally measurable decline in light-associated activity, which was partially rescued by hdc mRNA injections and mimicked by histamine receptor H1 (Hrh1) antagonist pyrilamine treatment. Histamine-immunoreactive fibers targeted the dorsal telencephalon, an area that expresses histamine receptors hrh1 and hrh3 and contains predominantly glutamatergic neurons. Tract tracing with DiI revealed that projections from dorsal telencephalon innervate the hcrt and histaminergic neurons. Translation inhibition of hdc decreased the number of hcrt neurons in a Hrh1-dependent manner. The reduction was rescued by overexpression of hdc mRNA. hdc mRNA injection alone led to an up-regulation of hcrt neuron numbers. These results suggest that histamine is essential for the development of a functional and intact hcrt system and that histamine has a bidirectional effect on the development of the hcrt neurons. In summary, our findings provide evidence that these two systems are linked both functionally and developmentally, which may have important implications in sleep disorders and narcolepsy. development via histamine receptor H1 in zebrafish.

Sleep neurobiology from a clinical perspective

Many neurochemical systems interact to generate wakefulness and sleep. Wakefulness is promoted by neurons in the pons, midbrain, and posterior hypothalamus that produce acetylcholine, norepinephrine, dopamine, serotonin, histamine, and orexin/hypocretin. Most of these ascending arousal systems diffusely activate the cortex and other forebrain targets. NREM sleep is mainly driven by neurons in the preoptic area that inhibit the ascending arousal systems, while REM sleep is regulated primarily by neurons in the pons, with additional influence arising in the hypothalamus. Mutual inhibition between these wake- and sleep-regulating regions likely helps generate full wakefulness and sleep with rapid transitions between states. This up-to-date review of these systems should allow clinicians and researchers to better understand the effects of drugs, lesions, and neurologic disease on sleep and wakefulness.

The wake-promoting transmitter histamine preferentially enhances α-4 subunit-containing GABAA receptors

Histamine is an important wake-promoting neurotransmitter that activates seven-transmembrane G-protein coupled histamine receptors. However, histamine demonstrates target promiscuity, including direct interaction with the structurally unrelated glutamate (NMDA) and GABA(A) receptor channels. Previous work showed that histamine enhances the activity of recombinant GABA(A) receptor isoforms typically found in synaptic locations, although co-release of histamine and GABA is not known to occur in vivo. Here we used patch clamp recordings of various recombinant GABA(A) receptor isoforms (α1-6, β1-3, γ1-3, δ) to test the hypothesis that histamine might show subunit preference under low GABA concentration (extrasynaptic) conditions. We found that histamine potentiated the whole-cell responses to GABA for all tested subunit combinations. However, the magnitude of enhancement was largest (∼400% of EC(10) GABA-evoked currents) with α4β3 and α4β3X isoforms, where X could be γ or δ. In contrast, histamine (1 mM) had small effects on prolonging deactivation of α4β3γ2 receptors following brief (5 ms) pulses of 1 mM GABA. These findings suggest GABA-histamine cross-talk may occur preferentially at low GABA concentrations, which could theoretically be inhibitory (via enhancing tonic inhibition), directly excitatory (via enhancing presynaptic GABAergic signaling), or indirectly excitatory (via inhibiting GABAergic interneurons).

Sleep disorders in patients with traumatic brain injury: a review

Traumatic brain injury (TBI) is a global problem and causes long-term disability in millions of individuals. This is a major problem for both military- and civilian-related populations. The prevalence of sleep disorders in individuals with TBI is very high, yet mostly unrecognized. Approximately 46% of all chronic TBI patients have sleep disorders, which require nocturnal polysomnography and the Multiple Sleep Latency Test for diagnosis. These disorders include sleep apnoea (23% of all TBI patients), post-traumatic hypersomnia (11%), narcolepsy (6%) and periodic limb movements (7%). Over half of all TBI patients will have insomnia complaints, most often with less severe injury and after personal assault, and half of these may be related to a circadian rhythm disorder. Hypothalamic injury with decreased levels of wake-promoting neurotransmitters such as hypocretin (orexin) and histamine may be involved in the pathophysiology of excessive sleepiness associated with TBI. These sleep disorders result in additional neurocognitive deficits and functional impairment, which might be attributed to the original brain injury itself and thus be left without specific treatment. Most standard treatment regimens of sleep disorders appear to be effective in these patients, including continuous positive airway pressure for sleep apnoea, pramipexole for periodic limb movements and cognitive behavioural therapy for insomnia. The role of wake-promoting agents and CNS stimulants for TBI-associated narcolepsy, post-traumatic hypersomnia and excessive daytime sleepiness requires further study with larger numbers of patients to determine effectiveness and benefit in this population. Future research with multiple collaborating centres should attempt to delineate the pathophysiology of TBI-associated sleep disorders, including CNS-derived hypersomnia and circadian rhythm disturbances, and determine definitive, effective treatment for associated sleep disorders.

Histamine H3 receptors and sleep-wake regulation

The histaminergic system fulfills a major role in the maintenance of waking. Histaminergic neurons are located exclusively in the posterior hypothalamus from where they project to most areas of the central nervous system. The histamine H(3) receptors are autoreceptors damping histamine synthesis, the firing frequency of histamine neurons, and the release of histamine from axonal varicosities. It is noteworthy that this action also extends to heteroreceptors on the axons of most other neurotransmitter systems, allowing a powerful control over multiple homeostatic functions. The particular properties and locations of histamine H(3) receptors provide quite favorable attributes to make this a most promising target for pharmacological interventions of sleep and waking disorders associated with narcolepsy, Parkinson's disease, and other neuropsychiatric indications.

Histamine in the regulation of wakefulness

The histaminergic system is exclusively localized within the posterior hypothalamus with projection to almost all the major regions of the central nervous system. Strong and consistent evidence exist to suggest that histamine, acting via H₁ and/or H₃ receptor has a pivotal role in the regulation of sleep-wakefulness. Administration of histamine or H₁ receptor agonists induces wakefulness, whereas administration of H₁ receptor antagonists promotes sleep. The H₃ receptor functions as an auto-receptor and regulates the synthesis and release of histamine. Activation of H₃ receptor reduces histamine release and promotes sleep. Conversely, blockade of H₃ receptor promotes wakefulness. Histamine release in the hypothalamus and other target regions is highest during wakefulness. The histaminergic neurons display maximal activity during the state of high vigilance, and cease their activity during non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. The cerebrospinal levels of histamine are reduced in diseased states where hypersomnolence is a major symptom. The histamine deficient L-histidine decarboxylase knockout (HDC KO) mice display sleep fragmentation and increased REM sleep during the light period along with profound wakefulness deficit at dark onset, and in novel environment. Similar results have been obtained when histamine neurons are lesioned. These studies strongly implicate the histaminergic neurons of the TMN to play a critical role in the maintenance of high vigilance state during wakefulness.

Emerging treatments for narcolepsy and its related disorders

IMPORTANCE OF THE FIELD

Narcolepsy is a chronic sleep disorder, characterized by excessive daytime sleepiness (EDS), cataplexy, hypnagogic hallucinations, sleep paralysis and nocturnal sleep disruption. Non-pharmacological treatments (i.e., behavioral modification) are often helpful for the clinical management of narcoleptic patients. As these symptoms are often disabling, most patients need life-long treatments. Over 90% of diagnosed narcoleptic patients are currently prescribed medications to control their symptoms; however, available treatments are merely symptomatic.

AREAS COVERED IN THIS REVIEW

This review presents a description of the clinical symptoms of narcolepsy, followed by a discussion of the state-of-the-art knowledge regarding the disorder and related emerging treatments. In preparing this review, an extensive literature search was conducted using Pubmed. Only selected references from 1970 to 2008 are cited.

WHAT THE READER WILL GAIN

This review focuses on emerging treatments for human narcolepsy, and the reader will gain significant knowledge of current and future treatment for this and related disorders. Traditionally, amphetamine-like stimulants (i.e., dopaminergic release enhancers) have been used for clinical management to improve EDS, and tricyclic antidepressants have been used as anticataplectics. However, treatments have recently evolved which utilize better tolerated compounds, such as modafinil (for EDS) and adrenergic/serotonergic selective reuptake inhibitors (as anticataplectics). In addition, night time administration of a short-acting sedative, gamma-hydroxybutyrate, has been used for the treatment for EDS and cataplexy. As a large majority of human narcolepsy is hypocretin peptide deficient, hypocretin replacement therapy may also be a new therapeutic option; yet, this option is still unavailable. In addition to the hypocretin-based therapy, a series of new treatments are currently being tested in animal and/or humans models. These potential options include novel stimulant and anticataplectic drugs as well as immunotherapy, based on current knowledge of the pathophysiology of narcolepsy with cataplexy.

TAKE HOME MESSAGE

We expect that more pathophysiology-based treatments, capable of curing and/or preventing narcolepsy and related diseases, will be available in near future. As cases of EDS, associated with other neurological conditions (i.e., symptomatic narcolepsy or narcolepsy due to medical conditions), are often linked with hypocretin deficiency, these novel therapeutic options may also be applied to treatment of these disabling conditions.

Animal models of narcolepsy

Narcolepsy is a debilitating sleep disorder with excessive daytime sleepiness and cataplexy as its two major symptoms. Although this disease was first described about one century ago, an animal model was not available until the 1970s. With the establishment of the Stanford canine narcolepsy colony, researchers were able to conduct multiple neurochemical studies to explore the pathophysiology of this disease. It was concluded that there was an imbalance between monoaminergic and cholinergic systems in canine narcolepsy. In 1999, two independent studies revealed that orexin neurotransmission deficiency was pivotal to the development of narcolepsy with cataplexy. This scientific leap fueled the generation of several genetically engineered mouse and rat models of narcolepsy. To facilitate further research, it is imperative that researchers reach a consensus concerning the evaluation of narcoleptic behavioral and EEG phenomenology in these models.

Narcolepsy with long sleep time: a specific entity?

BACKGROUND

The classical narcolepsy patient reports intense feelings of sleepiness (with/out cataplexy), normal or disrupted nighttime sleep, and takes short and restorative naps. However, with long-term monitoring, we identified some narcoleptics resembling patients with idiopathic hypersomnia.

OBJECTIVE

To isolate and describe a new subtype of narcolepsy with long sleep time).

SETTING

University Hospital

DESIGN

Controlled, prospective cohort

PARTICIPANTS

Out of 160 narcoleptics newly diagnosed within the past 3 years, 29 (18%) had a long sleep time (more than 11 h/24 h). We compared narcoleptics with (n = 23) and without (n = 29) long sleep time to 25 hypersomniacs with long sleep time and 20 healthy subjects.

INTERVENTION

Patients and controls underwent face-to face interviews, questionnaires, human leukocyte antigen (HLA) genotype, an overnight polysomnography, multiple sleep latency tests, and 24-h ad libitum sleep monitoring.

RESULTS

Narcoleptics with long sleep time had a similar disease course and similar frequencies of cataplexy, sleep paralysis, hallucinations, multiple sleep onset in REM periods, short mean sleep latencies, and HLA DQB1*0602 positivity as narcoleptics with normal sleep time did. However, they had longer sleep time during 24 h, and higher sleep efficiency, lower Epworth Sleepiness Scale scores, and reported their naps were more often unrefreshing. Only 3/23 had core narcolepsy (HLA and cataplexy positive).

CONCLUSIONS

The subgroup of narcoleptics with a long sleep time comprises 18% of narcoleptics. Their symptoms combine the disabilities of both narcolepsy (severe sleepiness) and idiopathic hypersomnia (long sleep time and unrefreshing naps). Thus, they may constitute a group with multiple arousal system dysfunctions.