Hypocretins in the Control of Sleep and Wakefulness

Prescription Drugs Used in Insomnia

In insomnia, the subjective aspects of the sleep complaint are paramount in the diagnostic criteria. Epidemiologic studies increasingly point to a link between insomnia and somatic morbidity and mortality, but until now, only in the subgroup of objectively poor sleepers. Although pharmacologic treatment might offer some benefits to this subgroup of insomnia patients, to date, there is no evidence that hypnotics can ameliorate their health risks. Further unraveling of the neurobiology and genetics of sleep regulation and the pathophysiology of insomnia will help the development of drugs that not only improve subjective sleep complaints but also objective health outcomes.

The role of sleep state and time of day in modulating breathing in epilepsy: implications for sudden unexpected death in epilepsy

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of death among patients with refractory epilepsy. While the exact etiology of SUDEP is unknown, mounting evidence implicates respiratory dysfunction as a precipitating factor in cases of seizure-induced death. Dysregulation of breathing can occur in epilepsy patients during and after seizures as well as interictally, with many epilepsy patients exhibiting sleep-disordered breathing (SDB), such as obstructive sleep apnea (OSA). The majority of SUDEP cases occur during the night, with the victim found prone in or near a bed. As breathing is modulated in both a time-of-day and sleep state-dependent manner, it is relevant to examine the added burden of nocturnal seizures on respiratory function. This review explores the current state of understanding of the relationship between respiratory function, sleep state and time of day, and epilepsy. We highlight sleep as a particularly vulnerable period for individuals with epilepsy and press that this topic warrants further investigation in order to develop therapeutic interventions to mitigate the risk of SUDEP.

Effect of gastric pH and of a moderate CYP3A4 inducer on the pharmacokinetics of daridorexant, a dual orexin receptor antagonist

AIM

Daridorexant is a dual orexin receptor antagonist developed for the treatment of insomnia. The solubility of daridorexant is pH dependent and daridorexant has been shown to be a sensitive CYP3A4 substrate when co-administered with moderate CYP3A4 inhibitors. The purpose of this study was to assess the effect of an increased gastric pH on daridorexant pharmacokinetics (PK) and the extent of interaction when daridorexant is co-administered with a moderate CYP3A4 inducer.

METHODS

In this prospective, single-centre, randomized, open-label study, 24 male subjects consecutively received four treatments, i.e., daridorexant 50 mg single dose; famotidine 40 mg single dose + daridorexant 50 mg single dose; efavirenz 600 mg once a day (o.d.) during 10 days; and daridorexant 50 mg single dose + efavirenz 600 mg o.d. for 2 days. Plasma PK parameters of daridorexant were derived by noncompartmental analysis. Standard safety and tolerability evaluations were analysed descriptively.

RESULTS

When daridorexant administration was preceded by administration of famotidine, daridorexant C_max decreased by 39%, geometric means ratio (GMR) (90% confidence interval (90% CI)): 0.61 (0.50, 0.73). AUC_0-∞ remained unchanged. In the presence of steady-state efavirenz, daridorexant C_max , AUC_0-∞ , and t_½ decreased by approximately 35% (GMR (90% CI)): 0.65 (0.54, 0.78), 61% (0.39 (0.348, 0.44), and 35% (0.65 (0.58, 0.73), respectively. T_max remained unaffected. All treatments containing daridorexant were well tolerated.

CONCLUSION

Daridorexant 50 mg can be administered concomitantly with gastric pH modifiers or with moderate CYP3A4 inducers without dose adaptation based on efficacy observed at lower doses in Phase 3 studies.

Prescription Drugs Used in Insomnia

The scope of this article is to review the effects on sleep of prescription drugs that are commonly prescribed for chronic insomnia in adults. The following groups are discussed: benzodiazepines and its receptor agonists, the dual orexin receptor antagonist suvorexant, melatonin and its receptor agonists, sedating antidepressants, and antipsychotics. Together with the neurobiologic and pharmacologic properties of these drugs, clinical effects are described, including subjective and objective effects on sleep duration, continuity, and architecture. Medical prescription information is given when available. Recently published American and European guidelines for the treatment of insomnia serve as reference frame.

Adaptation and survival: hypotheses about the neural mechanisms of unihemispheric sleep

Sleep and wakefulness are opposite brain and body conditions that accomplish different but complementary functions. However, these opposing conditions have been combined in some animals by the adoption of a sleep/wake strategy that allows them to survive, while maintaining both an interaction with the environment at the same time as enabling brain and body recovery. They sleep with half of the brain while keeping the other half awake: a state known as unihemispheric sleep (US). Sleep of cetaceans is exclusively in the form of US; therefore, they experience neither bihemispheric sleep (BS) nor REM sleep. US episodes have also been recorded in eared seals and some species of birds. In those animals, US episodes are intermingled with episodes of BS and REM sleep. Studies have reported both a lateralized release of some neurotransmitters and a drop of brain temperature during US. The aims of this article are to formulate hypotheses about the neural mechanisms of unihemispheric sleep(US) based on findings regarding the neural mechanisms of the sleep/wake cycle of mammals. The neural mechanisms of the sleep/wake cycle are largely preserved across species, allowing to hypothesize about those triggering and regulating US.

Is the glymphatic system the missing link between sleep impairments and neurological disorders? Examining the implications and uncertainties

Until recently, both the purpose of the biological need for sleep and the mechanism by which the central nervous system eliminated metabolic waste products were unknown. The glymphatic system is the recently discovered macroscopic waste clearance system for the CNS, which predominantly functions during sleep states. Important implications for the glymphatic system exist for a significant proportion of neurological disorders, including traumatic brain injury, epilepsy, stroke, migraine, and Alzheimer's disease. Within the limited amount of research pertaining to this novel system there exists controversy regarding several of the key structural and functional aspects of the glymphatic system. In this review we address evidence from both standpoints regarding the prominent debates surrounding the glymphatic system, including the functional differences in wakefulness vs. sleep, the role of glial aquaporin-4 water channels, and whether it reflects a convective flow or a passive diffusion process. The answers that underlie these questions will have crucial and distinct outcomes for the future of the glymphatic system and the disorders it has been implicated in. However, this review also summarizes the potential role of the glymphatic system in the development and progression of the aforementioned neurological disorders. Furthermore, the possible contribution of the orexinergic system to this relationship between the glymphatic system, sleep, and these neurological disorders is also explored. Overall, in order to develop and utilize therapeutic interventions centred around the glymphatic system we must first dedicate further investigation to elucidating these discrepancies and unanswered questions.

The role of Orexin-A levels in epileptic seizure

BACKGROUND

The aim of this study is to determine the usefulness of Orexin-A levels in differentiating between epileptic seizures and psychogenic non-epileptic seizures in patients presenting to the emergency service with epileptic seizure-type symptoms.

METHODS

A total of 80 individuals were included in this study, including 59 who presented to the emergency service within the first four hours of having been diagnosed with generalized tonic-clonic seizures (39 with epileptic seizures (ES) and 20 with pseudoseizures (PNES) and 21 controls. Orexin-A levels were measured in venous blood samples.

RESULTS

The mean Orexin-A levels were 5.16 ng/mL in the control group, 7.17 ng/mL in the PNES group, and 11.08 ng/mL in the ES group (Table 1). The mean Orexin-A level of the ES group was significantly different from both the control group and the PNES group (Table 1, p < 0.001); the difference between the control group and the PNES group was not significant (p > 0.05).

CONCLUSIONS

Results of this study suggest that blood Orexin-A may be an effective biomarker in the differential diagnosis of epileptic seizures/psychogenic non-epileptic seizures in patients presenting to the emergency service with an epileptic seizure-type clinical picture.

Sleep disturbance in PTSD and other anxiety-related disorders: an updated review of clinical features, physiological characteristics, and psychological and neurobiological mechanisms

The current report provides an updated review of sleep disturbance in posttraumatic stress disorder and anxiety-related disorders. First, this review provides a summary description of the unique and overlapping clinical characteristics and physiological features of sleep disturbance in specific DSM anxiety-related disorders. Second, this review presents evidence of a bidirectional relationship between sleep disturbance and anxiety-related disorders, and provides a model to explain this relationship by integrating research on psychological and neurocognitive processes with a current understanding of neurobiological pathways. A heuristic neurobiological framework for understanding the bidirectional relationship between abnormalities in sleep and anxiety-related brain pathways is presented. Directions for future research are suggested.

Pharmacosynthetic Deconstruction of Sleep-Wake Circuits in the Brain

Over the past decade, basic sleep research investigating the circuitry controlling sleep and wakefulness has been boosted by pharmacosynthetic approaches, including chemogenetic techniques using designed receptors exclusively activated by designer drugs (DREADD). DREADD offers a series of tools that selectively control neuronal activity as a way to probe causal relationship between neuronal sub-populations and the regulation of the sleep-wake cycle. Following the path opened by optogenetics, DREADD tools applied to discrete neuronal sub-populations in numerous brain areas quickly made their contribution to the discovery and the expansion of our understanding of critical brain structures involved in a wide variety of behaviors and in the control of vigilance state architecture.

Parallel Arousal Pathways in the Lateral Hypothalamus

Until recently, hypocretin (Hcrt) neurons were the only known wake-promoting neuronal population in the lateral hypothalamus (LH), but subpopulations of inhibitory neurons in this area and glutamatergic neurons in the nearby supramammillary nucleus (SuM) have recently been found that also promote wakefulness. We performed chemogenetic excitation of LH neurons in mice and observed increased wakefulness that lasted more than 4 h without unusual behavior or EEG anomalies. The increased wakefulness was similar in the presence or absence of the dual orexin receptor blocker almorexant (ALM). Analysis of hM3Dq transfection and c-FOS expression in LH inhibitory neurons and in the SuM failed to confirm that the increased wakefulness was due to these wake-promoting populations, although this possibility cannot be completely excluded. To evaluate the relationship to the Hcrt system, we repeated the study in Orexin-tTA mice in the presence or absence of dietary doxycycline (DOX), which enabled us to manipulate the percentage of Hcrt neurons that expressed hM3Dq. In DOX-fed mice, 18% of Hcrt neurons as well as many other LH neurons expressed hM3Dq; these mice showed a profound increase in wake after hM3Dq activation even in the presence of ALM. In mice switched to normal chow, 62% of Hcrt neurons expressed hM3Dq along with other LH cells; chemogenetic activation produced even more sustained arousal which could be reduced to previous levels by ALM treatment. Together, these results indicate an LH neuron population that promotes wakefulness through an Hcrt-independent pathway that can act synergistically with the Hcrt system to prolong arousal.

The effect of intracerebroventricular administration of orexin receptor type 2 antagonist on pentylenetetrazol-induced kindled seizures and anxiety in rats

BACKGROUND

Current antiepileptic drugs are not able to prevent recurrent seizures in all patients. Orexins are excitatory hypothalamic neuropeptides that their receptors (Orx1R and Orx2R) are found almost in all major regions of the brain. Pentylenetetrazol (PTZ)-induced kindling is a known experimental model for epileptic seizures. The purpose of this study was to evaluate the effect of Orx2 receptor antagonist (TCS OX2 29) on seizures and anxiety of PTZ-kindled rats.

RESULTS

Our results revealed that similar to valproate, administration of 7 µg/rat of TCS OX2 29 increased the latency period and decreased the duration time of 3rd and 4th stages of epileptiform seizures. Besides, it significantly decreased mean of seizure scores. However, TCS OX2 29 did not modulate anxiety induced by repeated PTZ administration.

CONCLUSION

This study showed that blockade of Orx2 receptor reduced seizure-related behaviors without any significant effect on PTZ-induced anxiety.

Neuronal Mechanisms for Sleep/Wake Regulation and Modulatory Drive

Humans have been fascinated by sleep for millennia. After almost a century of scientific interrogation, significant progress has been made in understanding the neuronal regulation and functions of sleep. The application of new methods in neuroscience that enable the analysis of genetically defined neuronal circuits with unprecedented specificity and precision has been paramount in this endeavor. In this review, we first discuss electrophysiological and behavioral features of sleep/wake states and the principal neuronal populations involved in their regulation. Next, we describe the main modulatory drives of sleep and wakefulness, including homeostatic, circadian, and motivational processes. Finally, we describe a revised integrative model for sleep/wake regulation.

Orexin OX2 Receptor Antagonists as Sleep Aids

The discovery of the orexin system represents the single major progress in the sleep field of the last three to four decades. The two orexin peptides and their two receptors play a major role in arousal and sleep/wake cycles. Defects in the orexin system lead to narcolepsy with cataplexy in humans and dogs and can be experimentally reproduced in rodents. At least six orexin receptor antagonists have reached Phase II or Phase III clinical trials in insomnia, five of which are dual orexin receptor antagonists (DORAs) that target both OX1 and OX2 receptors (OX2Rs). All clinically tested DORAs induce and maintain sleep: suvorexant, recently registered in the USA and Japan for insomnia, represents the first hypnotic principle that acts in a completely different manner from the current standard medications. It is clear, however, that in the clinic, all DORAs promote sleep primarily by increasing rapid eye movement (REM) and are almost devoid of effects on slow-wave (SWS) sleep. At present, there is no consensus on whether the sole promotion of REM sleep has a negative impact in patients suffering from insomnia. However, sleep onset REM (SOREM), which has been documented with DORAs, is clearly an undesirable effect, especially for narcoleptic patients and also in fragile populations (e.g. elderly patients) where REM-associated loss of muscle tone may promote an elevated risk of falls. Debate thus remains as to the ideal orexin agent to achieve a balanced increase in REM and non-rapid eye movement (NREM) sleep. Here, we review the evidence that an OX2R antagonist should be at least equivalent, or perhaps superior, to a DORA for the treatment of insomnia. An OX2R antagonist may produce more balanced sleep than a DORA. Rodent sleep experiments show that the OX2R is the primary target of orexin receptor antagonists in sleep modulation. Furthermore, an OX2R antagonist should, in theory, have a lower narcoleptic/cataplexic potential. In the clinic, the situation remains equivocal, since OX2R antagonists are in early stages: MK-1064 has completed Phase I, and MIN202 is currently in clinical Phase II/III trials. However, data from insomnia patients have not yet been released. Promotional material suggests that balanced sleep is indeed induced by MIN-202, whereas in volunteers MK-1064 has been reported to act similarly to DORAs.

Hubs and spokes of the lateral hypothalamus: cell types, circuits and behaviour

The hypothalamus is among the most phylogenetically conserved regions in the vertebrate brain, reflecting its critical role in maintaining physiological and behavioural homeostasis. By integrating signals arising from both the brain and periphery, it governs a litany of behaviourally important functions essential for survival. In particular, the lateral hypothalamic area (LHA) is central to the orchestration of sleep-wake states, feeding, energy balance and motivated behaviour. Underlying these diverse functions is a heterogeneous assembly of cell populations typically defined by neurochemical markers, such as the well-described neuropeptides hypocretin/orexin and melanin-concentrating hormone. However, anatomical and functional evidence suggests a rich diversity of other cell populations with complex neurochemical profiles that include neuropeptides, receptors and components of fast neurotransmission. Collectively, the LHA acts as a hub for the integration of diverse central and peripheral signals and, through complex local and long-range output circuits, coordinates adaptive behavioural responses to the environment. Despite tremendous progress in our understanding of the LHA, defining the identity of functionally discrete LHA cell types, and their roles in driving complex behaviour, remain significant challenges in the field. In this review, we discuss advances in our understanding of the neurochemical and cellular heterogeneity of LHA neurons and the recent application of powerful new techniques, such as opto- and chemogenetics, in defining the role of LHA circuits in feeding, reward, arousal and stress. From pioneering work to recent developments, we review how the interrogation of LHA cells and circuits is contributing to a mechanistic understanding of how the LHA coordinates complex behaviour.

Mechanism of action of suvorexant

Suovrexant is a novel hypnotic and is the only agent clinically available that works by blocking orexin-ergic mechanisms.

Autoantibodies against ganglioside GM3 are associated with narcolepsy-cataplexy developing after Pandemrix vaccination against 2009 pandemic H1N1 type influenza virus

Following the mass vaccinations against pandemic influenza A/H1N1 virus in 2009, a sudden increase in juvenile onset narcolepsy with cataplexy (NC) was detected in several European countries where AS03-adjuvanted Pandemrix vaccine had been used. NC is a chronic neurological disorder characterized by excessive daytime sleepiness and cataplexy. In human NC, the hypocretin-producing neurons in the hypothalamus or the hypocretin signaling pathway are destroyed by an autoimmune reaction. Both genetic (e.g. HLA-DQB1*0602) and environmental risk factors (e.g. Pandemrix) contribute to the disease development, but the underlying and the mediating immunological mechanisms are largely unknown. Influenza virus hemagglutinin is known to bind gangliosides, which serve as host cell virus receptors. Anti-ganglioside antibodies have previously been linked to various neurological disorders, like the Guillain-Barré syndrome which may develop after infection or vaccination. Because of these links we screened sera of NC patients and controls for IgG anti-ganglioside antibodies against 11 human brain gangliosides (GM1, GM2, GM3, GM4, GD1a, GD1b, GD2, GD3, GT1a, GT1b, GQ1b) and a sulfatide by using a line blot assay. Samples from 173 children and adolescents were analyzed: 48 with Pandemrix-associated NC, 20 with NC without Pandemrix association, 57 Pandemrix-vaccinated and 48 unvaccinated healthy children. We found that patients with Pandemrix-associated NC had more frequently (14.6%) anti-GM3 antibodies than vaccinated healthy controls (3.5%) (P = 0.047). Anti-GM3 antibodies were significantly associated with HLA-DQB1*0602 (P = 0.016) both in vaccinated NC patients and controls. In general, anti-ganglioside antibodies were more frequent in vaccinated (18.1%) than in unvaccinated (7.3%) individuals (P = 0.035). Our data suggest that autoimmunity against GM3 is a feature of Pandemrix-associated NC and that autoantibodies against gangliosides were induced by Pandemrix vaccination.

Type 1 narcolepsy: a CD8(+) T cell-mediated disease?

Type 1 narcolepsy is a sleep disorder characterized by excessive daytime sleepiness with unintentional sleep attacks and cataplexy. The disorder is caused by a loss of hypocretinergic neurons in the brain. The specific loss of these neurons in narcolepsy is thought to result from an autoimmune attack, and this is supported by evidence of both environmental and genetic factors pointing toward an involvement of the immune system. However, definitive proof of an autoimmune etiology is still missing. Several different immune-mediated disorders targeting neurons are known, and many of these are believed to be caused by autoreactive CD8(+) T cells. In this paper, we review the current knowledge on CD8(+) T cell-mediated neuronal damage on the basis of our understanding of other autoimmune disorders and experimental studies. We identify major histocompatibility complex class I presentation of autoantigens on neurons as a possible mechanism in the development of the disease, and propose T cell-mediated pathogenesis, with cytotoxic CD8(+) T cells targeting the hypocretinergic neurons, as a central element.

Des-acyl ghrelin attenuates pilocarpine-induced limbic seizures via the ghrelin receptor and not the orexin pathway

Des-acyl ghrelin, widely accepted to work independently of the ghrelin receptor, is increasingly being implicated in a number of biological functions. The involvement of des-acyl ghrelin in epilepsy has only been recently reported. In this study, apart from unravelling the effect of des-acyl ghrelin on seizure thresholds and seizure severity in two models of pilocarpine-induced seizures, we mainly attempted to unravel its anticonvulsant mechanism of action. Since it was found that des-acyl ghrelin administration affected food intake via the orexin pathway, we first determined whether this pathway was responsible for des-acyl ghrelin's seizure-attenuating properties using the dual orexin receptor antagonist almorexant. We noted that, while des-acyl ghrelin showed dose-dependent anticonvulsant effects against focal pilocarpine-evoked seizures in rats, almorexant did not affect seizure severity and did not reverse des-acyl ghrelin's anticonvulsant effect. Subsequently, to investigate whether the ghrelin receptor was implicated in des-acyl ghrelin's anticonvulsant properties, we tested this peptide in ghrelin receptor deficient mice and wild type mice, all infused with pilocarpine intravenously. Unexpectedly, we found that des-acyl ghrelin significantly elevated seizure thresholds in C57Bl/6 and wild type mice but not in ghrelin receptor knock-out mice. Taken together, our results indicate the involvement of the ghrelin receptor in the anticonvulsant effects of des-acyl ghrelin on pilocarpine-induced seizures. We also show for the first time that dual antagonism of hippocampal orexin receptors does not affect seizure severity.

Evolutionarily conserved regulation of hypocretin neuron specification by Lhx9

Loss of neurons that express the neuropeptide hypocretin (Hcrt) has been implicated in narcolepsy, a debilitating disorder characterized by excessive daytime sleepiness and cataplexy. Cell replacement therapy, using Hcrt-expressing neurons generated in vitro, is a potentially useful therapeutic approach, but factors sufficient to specify Hcrt neurons are unknown. Using zebrafish as a high-throughput system to screen for factors that can specify Hcrt neurons in vivo, we identified the LIM homeobox transcription factor Lhx9 as necessary and sufficient to specify Hcrt neurons. We found that Lhx9 can directly induce hcrt expression and we identified two potential Lhx9 binding sites in the zebrafish hcrt promoter. Akin to its function in zebrafish, we found that Lhx9 is sufficient to specify Hcrt-expressing neurons in the developing mouse hypothalamus. Our results elucidate an evolutionarily conserved role for Lhx9 in Hcrt neuron specification that improves our understanding of Hcrt neuron development.

A Framework for Quantitative Modeling of Neural Circuits Involved in Sleep-to-Wake Transition

Identifying the neuronal circuits and dynamics of sleep-to-wake transition is essential to understanding brain regulation of behavioral states, including sleep–wake cycles, arousal, and hyperarousal. Recent work by different laboratories has used optogenetics to determine the role of individual neuromodulators in state transitions. The optogenetically driven data do not yet provide a multi-dimensional schematic of the mechanisms underlying changes in vigilance states. This work presents a modeling framework to interpret, assist, and drive research on the sleep-regulatory network. We identify feedback, redundancy, and gating hierarchy as three fundamental aspects of this model. The presented model is expected to expand as additional data on the contribution of each transmitter to a vigilance state becomes available. Incorporation of conductance-based models of neuronal ensembles into this model and existing models of cortical excitability will provide more comprehensive insight into sleep dynamics as well as sleep and arousal-related disorders.

Pharmacological management of narcolepsy and cataplexy in pediatric patients

Narcolepsy is a neurological disorder frequently occurring from childhood and persisting through adolescence and adulthood. Individuals suffering from narcolepsy exhibit excessive daytime somnolence, sleep attacks, cataplexy, dysomnia, metabolic perturbations including weight gain, and problems in social interaction and academic performance. The prevalence of narcolepsy in childhood is not known but can be estimated from adult studies to be greater than 20-60 per 100,000 in Western countries. The 2009 (A) H1N1 vaccination campaign led to an increase of narcoleptic cases both in children and in adults, supporting the autoimmune hypothesis of the disease. This article focuses on the epidemiology, etiology, and particularities of treatment in pediatric narcolepsy and details the effects of the drugs used to treat this condition, including recent trends in the field. Future therapeutic directions are also discussed. At present, medications used to treat children or adolescents have shown efficacy mostly based on clinical experience, given the lack of level 1 evidence-based studies in the pediatric population. Therefore, most compounds used in adult narcolepsy to target clinical symptoms such as wake-promoting or anticataplectic agents are prescribed off-label in pediatric patients. Published research shows the benefit of drug therapy for narcoleptic children, but these must be dispensed with caution in the absence of well conducted clinical trials.

Formulation development for the orexin receptor antagonist almorexant: assessment in two clinical studies

Almorexant, a dual orexin receptor antagonist, was investigated for the treatment of insomnia. The following observations initiated further formulation development: the active pharmaceutical ingredient (API) was sticking to the apparatus used during tablet compression; almorexant has an absolute bioavailability of 11.2%; and almorexant modestly decreased the latency to persistent sleep by 10.4 minutes in patients. Two randomized crossover studies were performed to investigate the pharmacokinetics of several new formulations in healthy subjects. In study I, the old "sticky" tablet was compared to two new formulations developed to prevent sticking: a qualitatively similar tablet but with a larger API crystal size and a tablet with 30% more excipients as well as a larger API crystal size. This latter formulation was available in two strengths. The geometric mean ratios and 90% confidence interval of the area under the curve (AUC) were within the bioequivalence range of 0.80-1.25 for the different comparisons between formulations. In study II, 100 mg of the reference tablet was compared to 25 and 50 mg of a liquid-filled hard gelatin capsule developed to increase the bioavailability of almorexant. The geometric mean ratios of the maximum concentration and AUC comparing the new 25 and 50 mg capsule formulations to the reference tablet did not exceed 0.25 and 0.50, respectively, indicating that the new capsule formulation did not increase the maximum concentration of or the total exposure to almorexant. In conclusion, a new tablet was developed but formulation development aimed at increasing the bioavailability of almorexant failed.

Pharmacokinetic interactions between the orexin receptor antagonist almorexant and the CYP3A4 inhibitors ketoconazole and diltiazem

Almorexant, a tetrahydroisoquinoline orexin receptor antagonist and first representative of a new class of compounds for the treatment of insomnia, is a substrate of the cytochrome P450 3A4 isoenzyme (CYP3A4). Two randomized two-way crossover studies were performed in healthy subjects investigating the pharmacokinetic interaction between almorexant and the CYP3A4 inhibitors ketoconazole and diltiazem. When administered as a single dose of 100 mg almorexant during steady state of ketoconazole (400 mg once daily for 14 days) or diltiazem treatment (300 mg once daily for 11 days), the exposure to almorexant was 10.5- and 3.5-fold, respectively, greater when compared with almorexant alone. Exposure to the phenol metabolites M3 and M8 increased in the presence of the CYP3A4 inhibitors, whereas that to M6 (dealkylated metabolite) decreased. Concomitant ketoconazole decreased formation of the dehydrogenated metabolite M5 and diltiazem increased concentrations of this metabolite. Higher almorexant exposure was associated with an increased incidence of typical almorexant-related adverse events such as fatigue (both studies) and somnolence (ketoconazole study only). The present results indicate that dose adaptation must be considered when almorexant would be coadministered with inhibitors of CYP3A4.

Orexin as an input of circadian system in goldfish: Effects on clock gene expression and locomotor activity rhythms

Orexins are neuropeptides mainly known for regulating feeding behavior and sleep-wakefulness cycle in vertebrates. Daily variations of orexin-A expression have been reported in fish, with the highest levels preceding feeding time. However, it is unknown if such variations could be related with daily rhythms of clock genes, which form the molecular core of circadian oscillators. The aim of the present study was to identify the possible role of orexin as an input element of the goldfish circadian system. It was investigated the effects of orexin-A (10ng/gbw) intracerebroventricular injections on the expression of clock genes, NPY and ghrelin, as well as on daily locomotor activity rhythms. Goldfish held under 12L:12D photoperiod and injected at midday with orexin or saline, were sacrificed at 1 and 3h post-injection. The analysis of genes expression by qReal Time PCR showed an increment of Per genes in hypothalamus and foregut at 3h post-injection, but not in hindgut and liver. The gBmal1a expression remained unaltered in all the studied tissues. Orexin induced NPY in the hypothalamus and ghrelin in the foregut. Locomotor activity was studied in fish daily injected with orexin for several consecutive days under different experimental conditions. Orexin synchronized locomotor activity in goldfish maintained in 24L and fasting conditions. Present results support a cross-talking between orexin-A and other feeding regulators at central and peripheral level, and suggest, for the first time, a role of this peptide as an input of the circadian system in fish.

Narcolepsy as an immune-mediated disease

Narcolepsy is a neurological disorder characterized by excessive daytime sleepiness, cataplexy, hypnagonic hallucinations, sleep paralysis, and disturbed nocturnal sleep patterns. This disease is secondary to the specific loss of hypothalamic hypocretin (orexin)-producing neurons in the lateral hypothalamus. An autoimmune basis for the disease has long been suspected based on its strong association with the genetic marker DQB1∗06:02, and current studies greatly support this hypothesis. Narcolepsy with hypocretin deficiency is associated with human leukocyte antigen (HLA) and T cell receptor (TCR) polymorphisms, suggesting that an autoimmune process targets a peptide unique to hypocretin-producing neurons via specific HLA-peptide-TCR interactions. This concept has gained a lot of notoriety after the increase of childhood narcolepsy in 2010 following the 2009 H1N1 pandemic (pH1N1) in China and vaccination with Pandemrix, an adjuvanted H1N1 vaccine that was used in Scandinavia. The surge of narcolepsy cases subsequent to influenza A H1N1 infection and H1N1 vaccination suggests that processes such as molecular mimicry or bystander activation might be crucial for disease development.

Orexin A and B in vitro modify orexins receptors expression and gonadotropins secretion of anterior pituitary cells of proestrous rats

AIM

Orexin A and orexin B (hypocretins) are neuropeptides synthesized mainly by neurons located in the lateral hypothalamus and projections throughout the brain. They are agonists at both the orexin 1 and orexin 2G protein-coupled receptors. They have been related to arousal, sleep and feeding, autonomic and neuroendocrine functions. Their role in the brain control of gonadotropins secretion was postulated in rodents and humans. Previously, we demonstrated the participation of the orexinergic system in attaining successful reproduction in in vivo studies.

METHODS

We studied in vitro the effects of both neuropeptides, in the presence or absence of selective antagonists, on the mRNA expression of orexin 1 and orexin 2 receptors in anterior pituitary cells of proestrous rats, as well as the direct effects on FSH and LH secretion.

RESULTS

Both orexin A and orexin B increased FSH and LH secretion; these effects were suppressed by the orexin 1 receptor blocking agent SB-334867 and the orexin 2 receptor antagonists JNJ-10397049. Orexin A and orexin B decreased OX1 receptor mRNA expression and this effect was modified only when both blocking agents were present. Neither orexin A nor the blocking drugs by themselves modified OX2 receptor mRNA expression. Orexin B treatment increased the mRNA expression of OX2 receptor. The effect was abolished only by the OX2 receptor antagonist.

CONCLUSION

In an in vitro model, we demonstrated a direct effect of orexins on gonadotropins release and orexins receptors expression, underlining the hypothesis that orexins participate in the brain control of pituitary functions.

Role of synaptic activity in the regulation of amyloid beta levels in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia. Accumulation of amyloid-beta (Aβ) peptides is regarded as the critical component associated with AD pathogenesis, which is derived from the amyloid precursor protein (APP) cleavage. Recent studies suggest that synaptic activity is one of the most important factors that regulate Aβ levels. It has been found that synaptic activity facilitates APP internalization and influences APP cleavage. Glutamatergic, cholinergic, serotonergic, leptin, adrenergic, orexin, and gamma-amino butyric acid receptors, as well as the activity-regulated cytoskeleton-associated protein (Arc) are all involved in these processes. The present review summarizes the evidence for synaptic activity-modulated Aβ levels and the mechanisms underlying this regulation. Interestingly, the immediate early gene product Arc may also be the downstream signaling molecule of several receptors in the synaptic activity-modulated Aβ levels. Elucidating how Aβ levels are regulated by synaptic activity may provide new insights in both the understanding of the pathogenesis of AD and in the development of therapies to slow down the progression of AD.

The effects of amphetamine injections on feeding behavior and the brain expression of orexin, CART, tyrosine hydroxylase (TH) and thyrotropin releasing hormone (TRH) in goldfish (Carassius auratus)

In this study, the effects of peripheral (intraperitoneal) injections of D-amphetamine on feeding behavior were assessed in goldfish. Compared with the saline-injected group, amphetamine injections decreased food intake at doses ranging from 1 to 75 μg/g, but not 0.5 μg/g, but increased locomotor behavior, as indicated by the increased number of total feeding and non-feeding acts, at doses ranging from 2.5 to 25 μg/g. Amphetamine at high doses inhibited both food intake (at 25, 50 and 75 μg/g) and feeding behavior (at 75 μg/g). In the hypothalamus, the expression of orexin was down-regulated, and both CART 1 and CART 2 expressions were up-regulated in amphetamine-treated fish (50 μg/g) as compared to saline-injected fish, but amphetamine treatment had no effect on either hypothalamic TH or TRH expression. In the telencephalon, amphetamine treatment (50 μg/g) up-regulated CART 1, CART 2 and TH mRNA expressions but had no effect on either orexin or TRH. Our results suggest that, as in mammals, the orexin, CART and TH systems might be involved in amphetamine-induced feeding/locomotor responses in goldfish.

The autoimmune basis of narcolepsy

Narcolepsy is a neurological disorder characterized by excessive daytime sleepiness, cataplexy, hypnagonic hallucinations, sleep paralysis, and disturbed nocturnal sleep patterns. Narcolepsy is caused by the loss of hypocretin (orexin)-producing neurons in the lateral hypothalamus. Evidence, such as a strong association with HLA DQB1*06:02, strongly suggests an autoimmune basis targeting hypocretin neurons. Genome-wide association studies have strengthened the association between narcolepsy and immune system gene polymorphisms, including the identification of polymorphisms in the T cell receptor alpha locus, TNFSF4 (also called OX40L), Cathepsin H (CTSH) the purinergic receptor P2RY11, and the DNA methyltransferase DNMT1. Recently, attention has been raised regarding a spike in cases of childhood narcolepsy in 2010 following the 2009 H1N1 pandemic (pH1N1) in China and vaccination with Pandemrix, an adjuvanted H1N1 vaccine that was used in Europe. How the immune system may be involved in disease initiation and/or progression remains a challenge to researchers. Potential immunological pathways that could lead to the specific elimination of hypocretin producing neurons include molecular mimicry or bystander activation, and are likely a combination of genetic and environmental factors, such as upper airway infections.

REM sleep dysregulation in depression: state of the art

Disturbances of sleep are typical for most depressed patients and belong to the core symptoms of the disorder. Since the 1960s polysomnographic sleep research has demonstrated that besides disturbances of sleep continuity, depression is associated with altered sleep architecture, i.e., a decrease in slow wave sleep (SWS) production and disturbed rapid eye movement (REM) sleep regulation. Shortened REM latency (i.e., the interval between sleep onset and the occurrence of the first REM period), increased REM sleep duration and increased REM density (i.e., the frequency of rapid eye movements per REM period) have been considered as biological markers of depression which might predict relapse and recurrence. High risk studies including healthy relatives of patients with depression demonstrate that REM sleep alterations may precede the clinical expression of depression and may thus be useful in identifying subjects at high risk for the illness. Several models have been developed to explain REM sleep abnormalities in depression, like the cholinergic-aminergic imbalance model or chronobiologically inspired theories, which are reviewed in this overview. Moreover, REM sleep alterations have been recently considered not only as biological "scars" but as true endophenotypes of depression. This review discusses the genetic, neurochemical and neurobiological factors that have been implicated to play a role in the complex relationships between REM sleep and depression. We hypothesize on the one hand that REM sleep dysregulation in depression may be linked to a genetic predisposition/vulnerability to develop the illness; on the other hand it is conceivable that REM sleep disinhibition in itself is a part of a maladaptive stress reaction with increased allostatic load. We also discuss whether the REM sleep changes in depression may contribute themselves to the development of central symptoms of depression such as cognitive distortions including negative self-esteem and the overnight consolidation of negatively toned emotional memories.

Reciprocal interactions between sleep, circadian rhythms and Alzheimer's disease: focus on the role of hypocretin and melatonin

AD, sleep and circadian rhythm physiology display an intricate relationship. On the one hand, AD pathology leads to sleep and circadian disturbances, with a clear negative influence on quality of life. On the other hand, there is increasing evidence that both sleep and circadian regulating systems exert an influence on AD pathology. In this review we describe the impairments of both sleep regulating systems and circadian rhythms in AD and their link to clinical symptoms, as this may increase knowledge on appropriate diagnosis and adequate treatment of sleep problems in AD. Furthermore we discuss how sleep regulating systems, and especially neurotransmitters such as melatonin and hypocretin, may affect AD pathophysiology, as this may provide a role for lack of sleep and circadian rhythm deterioration in the onset of AD.

Molecules affecting hypothalamic control of core body temperature in response to calorie intake

Core body temperature (CBT) and calorie intake are main components of energy homeostasis and two important regulators of health, longevity, and aging. In homeotherms, CBT can be influenced by calorie intake as food deprivation or calorie restriction (CR) lowers CBT whereas feeding has hyperthermic effects. The finding that in mice CBT prolonged lifespan independently of CR, suggested that the mechanisms modulating CBT may represent important regulators of aging. Here we summarize the current knowledge on the signaling molecules and their receptors that participate in the regulation of CBT responses to calorie intake. These include hypothalamic neuropeptides regulating feeding but also energy expenditure via modulation of thermogenesis. We also report studies indicating that nutrient signals can contribute to regulation of CBT by direct action on hypothalamic preoptic warm-sensitive neurons that in turn regulate adaptive thermogenesis and hence CBT. Finally, we show the role played by two orphans G protein-coupled receptor: GPR50 and GPR83, that were recently demonstrated to regulate temperature-dependent energy expenditure.

Genetic ablation of hypocretin neurons alters behavioral state transitions in zebrafish

Sleep is an essential biological need of all animals studied to date. The sleep disorder narcolepsy is characterized by excessive daytime sleepiness, fragmentation of nighttime sleep, and cataplexy. Narcolepsy is caused by selective degeneration of hypothalamic hypocretin/orexin (HCRT) neurons. In mammals, HCRT neurons primarily regulate the sleep/wake cycle, feeding, reward-seeking, and addiction. The role of HCRT neurons in zebrafish is implicated in both sleep and wake regulation. We established a transgenic zebrafish model enabling inducible ablation of HCRT neurons and used these animals to understand the function of HCRT neurons and narcolepsy. Loss of HCRT neurons increased the expression of the HCRT receptor (hcrtr). Behavioral assays revealed that HCRT neuron-ablated larvae had normal locomotor activity, but demonstrated an increase in sleep time during the day and an increased number of sleep/wake transitions during both day and night. Mild sleep disturbance reduced sleep and increased c-fos expression in HCRT neuron-ablated larvae. Furthermore, ablation of HCRT neurons altered the behavioral response to external stimuli. Exposure to light during the night decreased locomotor activity of wild-type siblings, but induced an opposite response in HCRT neuron-ablated larvae. Sound stimulus during the day reduced the locomotor activity of wild-type sibling larvae, while HCRT neuron-ablated larvae demonstrated a hyposensitive response. This study establishes zebrafish as a model for narcolepsy, and indicating a role of HCRT neurons in regulation of sleep/wake transitions during both day and night. Our results further suggest a key role of HCRT neurons in mediating behavioral state transitions in response to external stimuli.

Role of dopamine tone in the pursuit of brain stimulation reward

Dopaminergic neurons contribute to intracranial self-stimulation (ICSS) and other reward-seeking behaviors, but it is not yet known where dopaminergic neurons intervene in the neural circuitry underlying reward pursuit or which psychological processes are involved. In rats working for electrical stimulation of the medial forebrain bundle, we assessed the effect of GBR-12909 (1-[2-[bis(4-fluorophenyl)-methoxy]ethyl]-4-[3- phenylpropyl]piperazine), a specific blocker of the dopamine transporter. Operant performance was measured as a function of the strength and cost of electrical stimulation. GBR-12909 increased the opportunity cost most subjects were willing to pay for a reward of a given intensity. However, this effect was smaller than that produced by a regimen of cocaine administration that drove similar increases in nucleus accumbens (NAc) dopamine levels in unstimulated rats. Delivery of rewarding stimulation to drug-treated rats caused an additional increase in dopamine concentration in the NAc shell in cocaine-treated, but not GBR-12909-treated, rats. These behavioral and neurochemical differences may reflect blockade of the norepinephrine transporter by cocaine but not by GBR-12909. Whereas the effect of psychomotor stimulants on ICSS has long been attributed to dopaminergic action at early stages of the reward pathway, the results reported here imply that increased dopamine tone boosts reward pursuit by acting at or beyond the output of the circuitry that temporally and spatially summates the output of the directly stimulated neurons underlying ICSS. The observed enhancement of reward seeking could be attributable to a decrease in the value of competing behaviors, a decrease in subjective effort costs, or an increase in reward-system gain.

Inter-tissue networks between the basal forebrain, hippocampus, and prefrontal cortex in a model for depression caused by disturbed sleep

Disturbances in sleep are encountered in the majority of patients with depressive disorder. To elucidate the molecular mechanisms behind this relationship, we examined gene expression changes in a rodent model for disturbed sleep and depression. The animals were treated with daily injections of clomipramine to affect their sleep during early infancy. This early interference with sleep is known to induce depression-like behavior in adult animals. After 2 weeks of treatment, the change in gene expression was examined using the Affymetrix Rat 230.2 chip. We studied the gene expression in the basal forebrain, hippocampus, and frontal cortex and combined the results to reveal the otherwise indissectible networks between and around the tissues. The major disrupted pathways between the three brain areas were related to synaptic transmission, regulation of translation, and ubiquitinylation. The involved pathways were within the cellular components of the axons, growth cones, melanosomes, and pigment granules. A network analysis allowing for additional interactors, in the form of chemicals or gene products, revealed a disturbed communicational network between the different brain areas. This disturbed network is centered around serotonin, Mn(II), and Rhoa. The findings elucidate inter-tissue pathways and networks in the brain that are involved in sleep and mood regulation. The findings are of uttermost interest, some are quite predictable and obvious, but some are novel or have only been proposed by rare theoretical speculations (such as the melanosome and Mn(II) involvement). Equally important as the findings are the methods described in this article. In this study, we present two novel simple ways to perform system biological analysis based on gene expression array data. We used two already existing tools in a new way, and by careful planning of the input data, managed to extrapolate intricate hidden inter-tissue networks to build a molecular picture of disease.

OX2R activation induces PKC-mediated ERK and CREB phosphorylation

Deficiencies in brain orexins and components of mitogen activated protein kinase (MAPK) signaling pathway have been reported in either human depression or animal model of depression. Brain administration of orexins affects behaviors toward improvement of depressive symptoms. However, the documentation of endogenous linkage between orexin receptor activation and MAPK signaling pathway remains to be insufficient. In this study, we report the effects of orexin 2 receptor (OX2R) activation on cell signaling in CHO cells over-expressing OX2R and in mouse hypothalamus cell line CLU172. Short-term extracellular signal-regulated kinase (ERK) phosphorylation and long-term cyclic adenosine monophosphate (cAMP) response element binding protein (CREB) phosphorylation were subsequently observed in CHO cells that over-express OX2R while 20 min of ERK phosphorylation was significantly detected in mouse adult hypothalamus neuron cell line CLU172. Orexin A, which can also activate OX2R, mediated ERK phosphorylation was as the same as orexin B in CHO cells. A MAPK inhibitor eliminated ERK phosphorylation but not CREB phosphorylation in CHO cells. Also, ERK and CREB phosphorylation was not mediated by protein kinase A (PKA) or calmodulin kinase (CaMK). However, inhibition of protein kinase C (PKC) by GF 109203X eliminated the phosphorylation of ERK and CREB in CHO cells. A significant decrease in ERK and CREB phosphorylation was observed with 1 μM GF 109203X pre-treatment indicating that the conventional and novel isoforms of PKC are responsible for CREB phosphorylation after OX2R activation. In contrast, ERK phosphorylation induced by orexin B in CLU172 cells cannot be inhibited by 1 μM of protein kinase C inhibitor. From above observation we conclude that OX2R activation by orexin B induces ERK and CREB phosphorylation and orexin A played the same role as orexin B. Several isoforms of PKC may be involved in prolonged CREB phosphorylation. Orexin B induced ERK phosphorylation in mouse hypothalamus neuron cells differs from CHO cell line and cannot be inhibited by PKC inhibitor GF 109203X. And hypothalamus neuron cells may use different downsteam pathway for orexin B induced ERK phosphorylation. This result supports findings that orexins might have anti-depressive roles.

Active coping with stress suppresses glucose metabolism in the rat hypothalamus

We used 18F-fluorodeoxyglucose small-animal positron-emission tomography to determine whether different styles of coping with stress are associated with different patterns of neuronal activity in the hypothalamus. Adult rats were subjected to immobilization (IMO)-stress or to a non-immobilized condition for 30 min, in random order on separate days, each of which was followed by brain-scanning. Some rats in the immobilized condition were allowed to actively cope with the stress by chewing a wooden stick during IMO, while the other immobilized rats were given nothing to chew on. Voxel-based statistical analysis of the brain imaging data shows that chewing counteracted the stress-induced increased glucose uptake in the hypothalamus to the level of the non-immobilized condition. Region-of-interest analysis of the glucose uptake values further showed that chewing significantly suppressed stress-induced increased glucose uptake in the paraventricular hypothalamic nucleus and the anterior hypothalamic area but not in the lateral hypothalamus. Together with the finding that the mean plasma corticosterone concentration at the termination of the IMO was also significantly suppressed when rats had an opportunity to chew a wooden stick, our results showed that active coping by chewing inhibited the activation of the hypothalamic-pituitary-adrenal axis to reduce the endocrine stress response.

Hypocretin/orexin signaling in the hypothalamic paraventricular nucleus is essential for the expression of nicotine withdrawal

BACKGROUND

Hypocretin (orexin) signaling is involved in drug addiction. In this study, we investigated the role of these hypothalamic neuropeptides in nicotine withdrawal by using behavioral and neuroanatomical approaches.

METHODS

Nicotine withdrawal syndrome was precipitated by mecamylamine (2 mg/kg, subcutaneous) in C57BL/6J nicotine-dependent mice (25 mg/kg/day for 14 days) pretreated with the hypocretin receptor 1 (Hcrtr-1) antagonist SB334867 (5 and 10 mg/kg, intraperitoneal), the hypocretin receptor 2 antagonist TCSOX229 (5 and 10 mg/kg, intraperitoneal), and in preprohypocretin knockout mice. c-Fos expression was analyzed in several brain areas related to nicotine dependence by immunofluorescence techniques. Retrograde tracing with rhodamine-labeled fluorescent latex microspheres was used to determine whether the hypocretin neurons project directly to the paraventricular nucleus of the hypothalamus (PVN), and SB334867 was locally administered intra-PVN (10 nmol/side) to test the specific involvement of Hcrtr-1 in this brain area during nicotine withdrawal.

RESULTS

Somatic signs of nicotine withdrawal were attenuated in mice pretreated with SB334867 and in preprohypocretin knockout mice. No changes were found in TCSOX229 pretreated animals. Nicotine withdrawal increased the percentage of hypocretin cells expressing c-Fos in the perifornical, dorsomedial, and lateral hypothalamus. In addition, the increased c-Fos expression in the PVN during withdrawal was dependent on hypocretin transmission through Hcrtr-1 activation. Hypocretin neurons directly innervate the PVN and the local infusion of SB334867 into the PVN decreased the expression of nicotine withdrawal.

CONCLUSIONS

These data demonstrate that hypocretin signaling acting on Hcrtr-1 in the PVN plays a crucial role in the expression of nicotine withdrawal.

Plasticity in neurons synthesizing wake/arousal promoting hormone hypocretin/orexin

The hypothalamus is a critical brain structure regulating physiological functions essential to the survival of individuals and species. One of the striking characteristics of this brain region is the abundance of nerve cells (neurons) expressing a great numbers of neurotransmitters and neuromodulators, among which are hormones released into the blood stream through brain neuroendocrinological routes. The neurons in the lateral hypothalamus take part in intra- and extrahypothalamic circuits controlling basic physiological functions essential for the well being of animal bodies (such as cardiovascular function, respiratory function, immune responses, etc.), animal behaviors required for the maintenance of the survival of individuals (food foraging, flight, fight, etc.) and species (reproductive function), and higher brain functions (learning and memory, mental state, etc.). Hypocretin (also called orexin) comprises of two neuropeptides exclusively synthesized by neurons in the perifornical/lateral hypothalamus. Although hypocretin/orexin was initially found to enhance food intake, it is now clear that the functions mediated by hypocretin/orexin are well beyond what were originally proposed. Specifically, hypocretin/orexin is a crucial promoter of wakefulness; deficiency in the hypocretin/orexin system leads to diseases and disorders such as narcolepsy. It is clear that neurons synthesizing hypocretin/orexin are consistently under regulation originating from various parts of the brain and that the status of activity in hypocretin/orexin neurons is closely related with the nutritional and behavioral state of animals. Therefore, the demand to make adaptive changes in hypocretin/orexin neurons to accommodate the changes in the external environment and behavioral state of animals is expected. The latest developments in the studies of plasticity in hypocretin/orexin neurons under the challenges from environmental and behavioral factors have dramatically shaped the understanding of the roles of hypocretin/orexin neurons in the maintenance of the survival of animals. More importantly, the studies of plasticity in hypocretin/orexin neurons as the consequence of physiological, behavioral, and environmental challenges may shed new insight on the understanding and treatment of sleep disorders (such as insomnia).

CSF-hypocretin-1 levels in patients with major depressive disorder compared to healthy controls

Depressive patients exhibit symptoms of impaired regulation of wakefulness with hyperarousal and agitation as well as difficulties to falling asleep and preserving sleep continuity. Changes in hypocretin (hcrt) levels as polypeptides with impact on arousal and sleep-wake-regulation have been discussed in affective disorders but have not been investigated in patients with solely unipolar depression in comparison to healthy controls. In the present study, cerebrospinal fluid (CSF) levels of hcrt-1 for the first time were analyzed in patients with major depressive disorder (MDD) without psychiatric comorbidities and compared with levels in healthy controls. In 17 inpatients with MDD (mean Hamilton Depression Rating Scale 13.9 ± 7.4) and 10 healthy controls, CSF-hcrt-1 levels were measured using a fluorescence immunoassay (FIA). The mean hcrt-1 CSF levels in patients with MDD (74.3 ± 17.8pg/ml) did not differ compared to that of healthy controls (82.8 ± 22.1pg/ml). Hcrt-1 levels did not correlate with the severity of depressive episode, the symptoms of depression or the number of episodes. Although autonomic and neurohumoral signs of hyperarousal are common in MDD, hcrt-1 levels in CSF were not found to be altered in MDD compared to healthy controls. Whether hcrt-1 levels are altered in depressive patients exhibiting impaired vigilance regulation has to be investigated in further studies combining measures of CSF-hcrt-1 with electroencephalography.

Narcolepsy with hypocretin/orexin deficiency, infections and autoimmunity of the brain

The loss of hypothalamic hypocretin/orexin (hcrt) producing neurons causes narcolepsy with cataplexy. An autoimmune basis for the disease has long been suspected and recent results have greatly strengthened this hypothesis. Narcolepsy with hcrt deficiency is now known to be associated with a Human Leukocyte Antigen (HLA) and T-cell receptor (TCR) polymorphisms, suggesting that an autoimmune process targets a single peptide unique to hcrt-cells via specific HLA-peptide-TCR interactions. Recent data have shown a robust seasonality of disease onset in children and associations with Streptococcus Pyogenes, and influenza A H1N1-infection and H1N1-vaccination, pointing towards processes such as molecular mimicry or bystander activation as crucial for disease development. We speculate that upper airway infections may be common precipitants of a whole host of CNS autoimmune complications including narcolepsy.

The new link between gut-brain axis and neuropsychiatric disorders

PURPOSE OF REVIEW

Although the cause of most neuropsychiatric disorders remains uncertain, new data offer alternative explanations warranting further validations. This review summarizes some recent findings that may localize the origin of eating disorders as well as some other neuropsychiatric disorders outside the brain and discuss their cause as a possible dysfunction of the gut-brain axis involving the humoral immune system.

RECENT FINDINGS

The gut microbiota has been identified as the main source of highest biological variability confined in an individual and also provides constant antigenic stimulation shaping up the physiological immune response. Furthermore, molecular mimicry has been shown among microbial proteins including gut microbiota and several key neuropeptides involved in the regulation of motivated behavior and emotion. Immunoglobulins reactive with these neuropeptides have been identified in humans, and their levels or affinities were associated with neuropsychiatric conditions including anxiety, depression, eating and sleep disorders.

SUMMARY

Cross-reacting immunoglobulins may bind both microbial sequences and neuropeptides, thereby constituting a particular way of signaling between the gut and the brain. Alteration of this link may contribute to several neuropsychiatric disorders, emphasizing the key role of nutrition among other factors influencing gut content and intestinal permeability.