Role of the Orexin/Hypocretin System in Stress-Related Psychiatric Disorders

Hypocretin modulation of behavioral coping strategies for social stress

Best known for promoting wakefulness and arousal, the neuropeptide hypocretin (Hcrt) also plays an important role in mediating stress responses, including social stress. However, central and systemic manipulation of the Hcrt system has produced diverse behavioral outcomes in animal models. In this review, we first focus on studies where similar manipulations of the Hcrt system led to divergent coping behaviors. We hypothesize that Hcrt differentially facilitates active and passive coping behaviors in response to social stress by acting in different brain regions and on different cell types. We then focus on region and cell type-specific effects of Hcrt in the ventral pallidum, lateral habenula, ventral tegmental area, nucleus accumbens, amygdala, and bed nucleus of the stria terminalis. Overall, the evidence suggests that rather than enhancing or inhibiting behavioral responses to social stress, Hcrt may signal the heightened arousal associated with stressful contexts. The resulting behavioral effects depend on which circuits Hcrt release occurs in and which receptor types are activated. Further study is needed to determine how and why circuit specific activation of Hcrt neurons occurs.

The Aggravating Role of Failing Neuropeptide Networks in the Development of Sporadic Alzheimer's Disease

Alzheimer's disease imposes an increasing burden on aging Western societies. The disorder most frequently appears in its sporadic form, which can be caused by environmental and polygenic factors or monogenic conditions of incomplete penetrance. According to the authors, in the majority of cases, Alzheimer's disease represents an aggravated form of the natural aging of the central nervous system. It can be characterized by the decreased elimination of amyloid β1-42 and the concomitant accumulation of degradation-resistant amyloid plaques. In the present paper, the dysfunction of neuropeptide regulators, which contributes to the pathophysiologic acceleration of senile dementia, is reviewed. However, in the present review, exclusively those neuropeptides or neuropeptide families are scrutinized, and the authors' investigations into their physiologic and pathophysiologic activities have made significant contributions to the literature. Therefore, the pathophysiologic role of orexins, neuromedins, RFamides, corticotrope-releasing hormone family, growth hormone-releasing hormone, gonadotropin-releasing hormone, ghrelin, apelin, and natriuretic peptides are discussed in detail. Finally, the therapeutic potential of neuropeptide antagonists and agonists in the inhibition of disease progression is discussed here.

Optimized ultrasound neuromodulation for non-invasive control of behavior and physiology

Focused ultrasound can non-invasively modulate neural activity, but whether effective stimulation parameters generalize across brain regions and cell types remains unknown. We used focused ultrasound coupled with fiber photometry to identify optimal neuromodulation parameters for four different arousal centers of the brain in an effort to yield overt changes in behavior. Applying coordinate descent, we found that optimal parameters for excitation or inhibition are highly distinct, the effects of which are generally conserved across brain regions and cell types. Optimized stimulations induced clear, target-specific behavioral effects, whereas non-optimized protocols of equivalent energy resulted in substantially less or no change in behavior. These outcomes were independent of auditory confounds and, contrary to expectation, accompanied by a cyclooxygenase-dependent and prolonged reduction in local blood flow and temperature with brain-region-specific scaling. These findings demonstrate that carefully tuned and targeted ultrasound can exhibit powerful effects on complex behavior and physiology.

Restraint stress-induced antinociceptive effects in acute pain: Involvement of orexinergic system in the nucleus accumbens

The complicated relevance between stress and pain has been identified. Neurotransmitters and neuropeptides of various brain areas play a role in this communication. Pain inhibitory response is known as stress-induced analgesia (SIA). The studies demonstrated that the nucleus accumbens (NAc) is critical in modulating pain. As a neuropeptide, orexin is crucially involved in initiating behavioral and physiological responses to threatening and unfeeling stimuli. However, the role of the orexin receptors of the NAc area after exposure to restraint stress (RS) as acute physical stress in the modulation of acute pain is unclear. One hundered twenty adult male albino Wistar rats (230-250 g) were used. Animals were unilaterally implanted with cannulae above the NAc. The SB334867 and TCS OX2 29 were used as antagonists for OX1r and OX2r, respectively. Different doses of the antagonists (1, 3, 10, and 30 nmol/0.5 µl DMSO) were microinjected intra-NAc five minutes before exposure to RS (3 hours). Then, the tail-flick test as a model of acute pain was performed, and the nociceptive threshold (Tail-flick latency; TFL) was measured in 60-minute time set intervals. According to this study's findings, the antinociceptive effects of RS in the tail-flick test were blocked during intra-NAc administration of SB334867 or TCS OX2 29. The RS as acute stress increased TFL and deceased pain-like behavior responses. The 50 % effective dose values of the OX1r and OX2r antagonists were 12.82 and 21.64 nmol, respectively. The result demonstrated contribution of the OX1r into the NAc was more remarkable than that of the OX2r on antinociceptive responses induced by the RS. Besides, in the absence of RS, the TFL was attenuated. The current study's data indicated that OX1r and OX2r into the NAc induced pain modulation responses during RS in acute pain. In conclusion, the findings revealed the involvement of intra-NAc orexin receptors in improving SIA.

Machine learning models to predict ligand binding affinity for the orexin 1 receptor

The orexin 1 receptor (OX1R) is a G-protein coupled receptor that regulates a variety of physiological processes through interactions with the neuropeptides orexin A and B. Selective OX1R antagonists exhibit therapeutic effects in preclinical models of several behavioral disorders, including drug seeking and overeating. However, currently there are no selective OX1R antagonists approved for clinical use, fueling demand for novel compounds that act at this target. In this study, we meticulously curated a dataset comprising over 1300 OX1R ligands using a stringent filter and criteria cascade. Subsequently, we developed highly predictive quantitative structure-activity relationship (QSAR) models employing the optimized hyper-parameters for the random forest machine learning algorithm and twelve 2D molecular descriptors selected by recursive feature elimination with a 5-fold cross-validation process. The predictive capacity of the QSAR model was further assessed using an external test set and enrichment study, confirming its high predictivity. The practical applicability of our final QSAR model was demonstrated through virtual screening of the DrugBank database. This revealed two FDA-approved drugs (isavuconazole and cabozantinib) as potential OX1R ligands, confirmed by radiolabeled OX1R binding assays. To our best knowledge, this study represents the first report of highly predictive QSAR models on a large comprehensive dataset of diverse OX1R ligands, which should prove useful for the discovery and design of new compounds targeting this receptor.

Lateral hypothalamus orexinergic projection to the medial prefrontal cortex modulates chronic stress-induced anhedonia but not anxiety and despair

Chronic stress-induced anxiodepression is a common health problem, however its potential neurocircuitry mechanism remains unclear. We used behavioral, patch-clamp electrophysiology, chemogenetic, and optogenetic approaches to clarify the response of the lateral hypothalamus (LH) and the medial prefrontal cortex (mPFC) to stress, confirmed the structural connections between the LH and mPFC, and investigated the role of the LH-mPFC pathway in chronic stress-induced anxiodepression symptoms. Unpredictable chronic mild stress (UCMS) caused anxiodepression-like behaviors, including anxiety, anhedonia, and despair behaviors. We discovered that the activity of the LH and mPFC was both increased after restraint stress (RS), a stressor of UCMS. Then we found that the orexinergic neurons in the LH predominantly project to the glutamatergic neurons in the mPFC, and the excitability of these neurons were increased after UCMS. In addition, overactivated LH orexinergic terminals in the mPFC induced anhedonia but not anxiety and despair behaviors in naive mice. Moreover, chemogenetically inhibited LH-mPFC orexinergic projection neurons and blocked the orexin receptors in the mPFC alleviated anhedonia but not anxiety and despair behaviors in UCMS-treated mice. Our study identified a new neurocircuit from LH orexinergic neurons to mPFC and revealed its role in regulating anhedonia in response to stress. Overactivation of LHOrx-mPFC pathway selectively mediated chronic stress-induced anhedonia. In normal mice, the LHOrx-mPFC pathway exhibits relatively low activity. However, after chronic stress, the activity of orexinergic neuron in LH is overactivated, leading to an increased release of orexin into the mPFC. This heightened orexin concentration results in increased excitability of the mPFC through OX1R and OX2R, consequently triggering anhedonia.

The role of orexin in Parkinson's disease

Emerging evidence has implicated the orexin system in non-motor pathogenesis of Parkinson's disease. It has also been suggested the orexin system is involved in the modulation of motor control, further implicating the orexin system in Parkinson's disease. Parkinson's disease is the second most common neurodegenerative disease with millions of people suffering worldwide with motor and non-motor symptoms, significantly affecting their quality of life. Treatments are based solely on symptomatic management and no cure currently exists. The orexin system has the potential to be a treatment target in Parkinson's disease, particularly in the non-motor stage. In this review, the most current evidence on the orexin system in Parkinson's disease and its potential role in motor and non-motor symptoms of the disease is summarized. This review begins with a brief overview of Parkinson's disease, animal models of the disease, and the orexin system. This leads into discussion of the possible roles of orexin neurons in Parkinson's disease and levels of orexin in the cerebral spinal fluid and plasma in Parkinson's disease and animal models of the disease. The role of orexin is then discussed in relation to symptoms of the disease including motor control, sleep, cognitive impairment, psychological behaviors, and the gastrointestinal system. The neuroprotective effects of orexin are also summarized in preclinical models of the disease.

Male mice engaging differently in emotional eating present distinct plasmatic and neurological profiles

Objective: Stressed individuals tend to turn to calorie-rich food, also known as 'comfort food' for the temporary relief it provides. The emotional eating drive is highly variable among subjects. Using a rodent model, we explored the plasmatic and neurobiological differences between 'high and low emotional eaters' (HEE and LEE).Methods: 40 male mice were exposed for 5 weeks to a protocol of unpredictable chronic mild stress. Every 3 or 4 days, they were submitted to a 1-h restraint stress, immediately followed by a 3-h period during which a choice between chow and chocolate sweet cereals was proposed. The dietary intake was measured by weighing. Plasmatic and neurobiological characteristics were compared in mice displaying high vs low intakes.Results: Out of 40 mice, 8 were considered as HEE because of their high post-stress eating score, and 8 as LEE because of their consistent low intake. LEE displayed higher plasma corticosterone and lower levels of NPY than HEE, but acylated and total ghrelin were similar in both groups. In the brain, the abundance of NPY neurons in the arcuate nucleus of the hypothalamus was similar in both groups, but was higher in the ventral hippocampus and the basal lateral amygdala of LEE. The lateral hypothalamus LEE had also more orexin (OX) positive neurons. Both NPY and OX are orexigenic peptides and mood regulators.Discussion: Emotional eating difference was reflected in plasma and brain structures implicated in emotion and eating regulation. These results concur with the psychological side of food consumption.

Mild Traumatic Brain Injury Affects Orexin/Hypocretin Physiology Differently in Male and Female Mice

Traumatic brain injury (TBI) is known to affect the physiology of neural circuits in several brain regions, which can contribute to behavioral changes after injury. Disordered sleep is a behavior that is often seen after TBI, but there is little research into how injury affects the circuitry that contributes to disrupted sleep regulation. Orexin/hypocretin neurons (hereafter referred to as orexin neurons) located in the lateral hypothalamus normally stabilize wakefulness in healthy animals and have been suggested as a source of dysregulated sleep behavior. Despite this, few studies have examined how TBI affects orexin neuron circuitry. Further, almost no animal studies of orexin neurons after TBI have included female animals. Here, we address these gaps by studying changes to orexin physiology using ex vivo acute brain slices and whole-cell patch clamp recording. We hypothesized that orexin neurons would have reduced afferent excitatory activity after injury. Ultimately, this hypothesis was supported but there were additional physiological changes that occurred that we did not originally hypothesize. We studied physiological properties in orexin neurons approximately 1 week after mild traumatic brain injury (mTBI) in 6-8-week-old male and female mice. mTBI was performed with a lateral fluid percussion injury between 1.4 and 1.6 atmospheres. Mild TBI increased the size of action potential afterhyperpolarization in orexin neurons from female mice, but not male mice and reduced the action potential threshold in male mice, but not in female mice. Mild TBI reduced afferent excitatory activity and increased afferent inhibitory activity onto orexin neurons. Alterations in afferent excitatory activity occurred in different parameters in male and female animals. The increased afferent inhibitory activity after injury is more pronounced in recordings from female animals. Our results indicate that mTBI changes the physiology of orexin neuron circuitry and that these changes are not the same in male and female animals.

Associations between psychiatric comorbid disorders and executive dysfunctions in hypocretin-1 deficient pediatric narcolepsy type1

OBJECTIVE/BACKGROUND

Psychiatric symptoms and cognitive deficits add significantly to impairment in academic achievement and quality of life in patients with narcolepsy. The primary aim of this study was to evaluate the prevalence of psychiatric disorders and executive dysfunctions, secondly to explore the association between psychiatric comorbidity, executive dysfunctions, subjective and objective sleep measures, and severity of cerebrospinal fluid (CSF) hypocretin-1 deficiency in pediatric narcolepsy type 1 (PNT1).

PATIENTS/METHODS

Cross-sectional study of 59 consecutively included PNT1 patients (age: 6-20 years; 34:25 girls: boys; 54/59 H1N1 (Pandemrix®)-vaccinated). Core narcolepsy symptoms including subjective sleepiness, polysomnography and multiple sleep latency test results, CSF hypocretin-1 levels, psychiatric disorders (by semistructured diagnostic interview Kaufmann Schedule for Affective Disorders and Schizophrenia Present and Lifetime version (KSADS)), and executive dysfunction (by Behavior Rating of Executive Function (BRIEF)) were assessed.

RESULTS

52.5% of the patients had one or more psychiatric comorbid disorder, and 64.7% had executive dysfunction in a clinically relevant range, with no sex difference in prevalence, while older age was associated with poorer executive function (p=0.013). Having any psychiatric comorbid disorder was associated with poorer executive functions (p=0.001). CSF hypocretin-1 deficiency severity was significantly associated with presence of psychiatric comorbidity (p=0.022) and poorer executive functions (p=0.030), and poorer executive functions was associated with subjective sleepiness (p=0.009).

CONCLUSIONS

The high occurrence of, and association between, psychiatric comorbidity and executive dysfunction underlines the importance of close attention to both these comorbidities in clinical care of NT1.

Characteristics of Seltorexant-Innovative Agent Targeting Orexin System for the Treatment of Depression and Anxiety

Twenty-five years have passed since the discovery of the orexin system, during which time we have learned more and more about it. A number of studies have been conducted showing the role of the orexin system in insomnia, as well as its potential use in the treatment of obesity and depression. In this review, we present the role of the orexin system in the development of depressive illness and show the characteristics of seltorexant, a potential drug for the treatment of depression. This review describes the structure and synthesis of the compound as well as its pharmacodynamics and pharmacokinetics. Pre-clinical and clinical studies are also described, including side effects. There is evidence that the use of seltorexant is considered safe, with no clear or major clinically significant side effects, which makes it a promising candidate for the treatment of depression and anxiety disorders.

Behavioral phenotype, intestinal microbiome, and brain neuronal activity of male serotonin transporter knockout mice

The serotonin transporter (5-HTT) plays a critical role in the regulation of serotonin neurotransmission. Mice genetically deficient in 5-HTT expression have been used to study the physiological functions of 5-HTT in the brain and have been proposed as a potential animal model for neuropsychiatric and neurodevelopmental disorders. Recent studies have provided evidence for a link between the gut-brain axis and mood disorders. However, the effects of 5-HTT deficiency on gut microbiota, brain function, and behavior remain to be fully characterized. Here we investigated the effects of 5-HTT deficiency on different types of behavior, the gut microbiome, and brain c-Fos expression as a marker of neuronal activation in response to the forced swim test for assessing depression-related behavior in male 5-HTT knockout mice. Behavioral analysis using a battery of 16 different tests showed that 5-HTT-/- mice exhibited markedly reduced locomotor activity, decreased pain sensitivity, reduced motor function, increased anxiety-like and depression-related behavior, altered social behavior in novel and familiar environments, normal working memory, enhanced spatial reference memory, and impaired fear memory compared to 5-HTT+/+ mice. 5-HTT+/- mice showed slightly reduced locomotor activity and impaired social behavior compared to 5-HTT+/+ mice. Analysis of 16S rRNA gene amplicons showed that 5-HTT-/- mice had altered gut microbiota abundances, such as a decrease in Allobaculum, Bifidobacterium, Clostridium sensu stricto, and Turicibacter, compared to 5-HTT+/+ mice. This study also showed that after exposure to the forced swim test, the number of c-Fos-positive cells was higher in the paraventricular thalamus and lateral hypothalamus and was lower in the prefrontal cortical regions, nucleus accumbens shell, dorsolateral septal nucleus, hippocampal regions, and ventromedial hypothalamus in 5-HTT-/- mice than in 5-HTT+/+ mice. These phenotypes of 5-HTT-/- mice partially recapitulate clinical observations in humans with major depressive disorder. The present findings indicate that 5-HTT-deficient mice serve as a good and valid animal model to study anxiety and depression with altered gut microbial composition and abnormal neuronal activity in the brain, highlighting the importance of 5-HTT in brain function and the mechanisms underlying the regulation of anxiety and depression.

Dual Cannabinoid and Orexin Regulation of Anhedonic Behaviour Caused by Prolonged Restraint Stress

The endocannabinoid and orexin systems share many biological functions, including wakefulness, stress response, reward processing, and mood. While these systems work against one another with respect to arousal, chronic stress-induced downregulation of both systems often leads to anhedonia or the inability to experience pleasure from natural rewards. In the current study, a 24 h restraint stress test (24 h RST) reduced sucrose preference in adult male and female C57BL/6 mice. Prior to the stressor, subsets of mice were intraperitoneally administered cannabinoid and orexin receptor agonists, antagonists, and combinations of these drugs. Restraint mice that received the cannabinoid receptor type 1 (CB1R) antagonist SR141716A, orexin receptor type 2 (OX2R) agonist YNT-185, and the combination of SR141716A and YNT-185, exhibited less anhedonia compared to vehicle/control mice. Thus, the 24 h RST likely decreased orexin signaling, which was then restored by YNT-185. Receptor colocalization analysis throughout mesocorticolimbic brain regions revealed increased CB1R-OX1R colocalization from SR141716A and YNT-185 treatments. Although a previous study from our group showed additive cataleptic effects between CP55,940 and the dual orexin receptor antagonist (TCS-1102), the opposite combination of pharmacological agents proved additive for sucrose preference. Taken together, these results reveal more of the complex interactions between the endocannabinoid and orexin systems.

Chronic orexin-1 receptor blockage attenuates depressive behaviors and provokes PSD-95 expression in a rat model of depression

Depression is a devastating mood disorder affecting more than 300 million people worldwide. Almost 30 % of patients still suffer from treatment resistant depression. Although many reports support the involvement of orexin in the pathophysiology of depression, the precise role of orexin is still unclear. In this study, we evaluated the role of the orexin 1 receptor (Orx₁R) on depressive behaviors and the alterations in postsynaptic density-95 (PSD-95) protein in the chronic mild stress (CMS) model of depression. Fifty-four male Wistar rats were randomly allocated to 6 groups; Control, CMS, acute SB-334867 (SB), CMS+SB, chronic SB (CSB) and CMS+CSB. Rats were exposed to one or two unpredictable stressors each day for three weeks for the induction of CMS. Intracerebroventricular (icv) injection of SB-334867, a selective Orx₁R antagonist, was performed either 30 min before behavioral tests (acute) or once daily for 14 days (chronic). Behavioral despair was assessed by immobility time in the forced swim test (FST), sucrose consumption in sucrose preference test (SPT), and the number of crosses in the open field test (OFT) on days 1, 11, and 22 of the experiment. Finally, rats were decapitated, and brain tissue of the hippocampus (HPC) and prefrontal cortex (PFC) were collected, and the relative expression of PSD-95 was evaluated by western blotting. The CMS model rats showed a significant increase in FST immobility time (P = 0.001) and a decrease in locomotion (P = 0.04) and sucrose preference (P = 0.039). Chronic application of SB decreased immobility time to the control values (P = 0.001) and diminished locomotion (P = 0.047) and sucrose preference (P = 0.042) in comparison to the CMS group. Acute SB reversed just the immobility time (P ≤ 0.006). Chronic SB treatment increased the relative PSD-95 expression in PFC (P = 0.001). Hence, chronic antagonism of Orx₁R alleviates depressive behaviors induced by CMS and improves PSD-95 expression in PFC.

Alexithymia, impulsiveness, emotion, and eating dyscontrol: similarities and differences between narcolepsy type 1 and type 2

Non-sleep symptoms, as depression, anxiety and overweight, are often encountered in narcoleptic patients. The purposes of this study are to evaluate mood, impulsiveness, emotion, alexithymia, and eating behavior in patients with narcolepsy type 1 (NT1) and narcolepsy type 2 (NT2) compared to healthy controls and to investigate possible correlations between clinical-demographic data, polysomnographic parameters, and subjective questionnaires. Consecutive patients affected by NT1 and NT2 underwent to Patient Health Questionnaire-9, Generalized Anxiety Disorder-7 Scale, Barratt Impulsivity Scale-11, Difficulties in Emotion Regulation Scale, Toronto Alexithymia Scale, and Eating Disorder Evaluation Questionnaire. Daytime sleepiness was assessed using Epworth sleepiness score. Data were compared with controls. Fourteen NT1, 10 NT2, and 24 healthy subjects were enrolled. Toronto Alexithymia Scale total score was significantly higher in NT1 than NT2. Compared to controls, NT1 patients exhibited significantly higher scores at Patient Health Questionnaire-9 and Difficulties in Emotion Regulation Scale. A positive correlation between hypnagogic hallucinations and Difficulties in emotion regulation was found. NT1 and NT2 share several psycho-emotional aspects, but whereas NT1 patients exhibit more depressive mood and emotion dysregulation compared to controls, alexithymic symptoms are more prominent in NT1 than NT2. Hypnagogic hallucinations, emotion dysregulation, and alexithymia appear to be correlated, supporting the hypothesis of mutual interaction of the above areas in narcolepsy.

Opioid Use Disorder, Sleep Deficiency, and Ventilatory Control: Bidirectional Mechanisms and Therapeutic Targets

Opioid use continues to rise globally. So too do the associated adverse consequences. Opioid use disorder (OUD) is a chronic and relapsing brain disease characterized by loss of control over opioid use and impairments in cognitive function, mood, pain perception, and autonomic activity. Sleep deficiency, a term that encompasses insufficient or disrupted sleep due to multiple potential causes, including sleep disorders, circadian disruption, and poor sleep quality or structure due to other medical conditions and pain, is present in 75% of patients with OUD. Sleep deficiency accompanies OUD across the spectrum of this addiction. The focus of this concise clinical review is to highlight the bidirectional mechanisms between OUD and sleep deficiency and the potential to target sleep deficiency with therapeutic interventions to promote long-term, healthy recovery among patients in OUD treatment. In addition, current knowledge on the effects of opioids on sleep quality, sleep architecture, sleep-disordered breathing, sleep apnea endotypes, ventilatory control, and implications for therapy and clinical practice are highlighted. Finally, an actionable research agenda is provided to evaluate the basic mechanisms of the relationship between sleep deficiency and OUD and the potential for behavioral, pharmacologic, and positive airway pressure treatments targeting sleep deficiency to improve OUD treatment outcomes.

Escitalopram alters the hypothalamic OX system but does not affect its up-regulation induced by early-life stress in adult rats

We hypothesized that there is a relationship between the orexinergic system (OX) alterations and changes elicited by escitalopram or venlafaxine in adult rats subjected to maternal separation (MS). This animal model of childhood adversity induces long-lasting consequences in adult physiology and behavior. Male Wistar rats from the control and MS groups were injected with escitalopram or venlafaxine (10 mg/kg) IP from postnatal day (PND) 69-89. Adult rats were subjected to behavioral assessment, estimation of hypothalamic-pituitary-adrenal (HPA) axis activity and analysis of the OX system (quantitative PCR and immunohistochemistry) in the hypothalamus and amygdala. MS caused anxiety- and depressive-like behavior, endocrine stress-related response, and up-regulation of the OX system in the hypothalamus. Escitalopram, but not venlafaxine, increased the activity of hypothalamic OX system in the control rats and both drugs had no effect on OXs in the MS group. The disturbed signaling of the OX pathway may be significant for harmful long-term consequences of early-life stress. Our data show that the normal brain and brain altered by MS respond differently to escitalopram. Presumably, anti-anxiety and antidepressant effects of this drug do not depend on the activity of hypothalamic OX system.

Pediatric Narcolepsy-A Practical Review

Pediatric narcolepsy is a chronic sleep-wakefulness disorder. Its symptoms frequently begin in childhood. This review article examined the literature for research reporting on the effects of treatment of pediatric narcolepsy, as well as proposed etiology and diagnostic tools. Symptoms of pediatric narcolepsy include excessive sleepiness and cataplexy. In addition, rapid-eye-movement-related phenomena such as sleep paralysis, sleep terror, and hypnagogic or hypnapompic hallucinations can also occur. These symptoms impaired children's function and negatively influenced their social interaction, studying, quality of life, and may further lead to emotional and behavioral problems. Therefore, early diagnosis and intervention are essential for children's development. Moreover, there are differences in clinical experiences between Asian and Western population. The treatment of pediatric narcolepsy should be comprehensive. In this article, we review pediatric narcolepsy and its treatment approach: medication, behavioral modification, and education/mental support. Pharmacological treatment including some promising newly-developed medication can decrease cataplexy and daytime sleepiness in children with narcolepsy. Other forms of management such as psychosocial interventions involve close cooperation between children, school, family, medical personnel, and can further assist their adjustment.

Hypocretins (orexins): The ultimate translational neuropeptides

The hypocretins (Hcrts), also known as orexins, are two neuropeptides produced exclusively in the lateral hypothalamus. They act on two specific receptors that are widely distributed across the brain and involved in a myriad of neurophysiological functions that include sleep, arousal, feeding, reward, fear, anxiety and cognition. Hcrt cell loss in humans leads to narcolepsy with cataplexy (narcolepsy type 1), a disorder characterized by intrusions of sleep into wakefulness, demonstrating that the Hcrt system is nonredundant and essential for sleep/wake stability. The causal link between Hcrts and arousal/wakefulness stabilisation has led to the development of a new class of drugs, Hcrt receptor antagonists to treat insomnia, based on the assumption that blocking orexin-induced arousal will facilitate sleep. This has been clinically validated: currently, two Hcrt receptor antagonists are approved to treat insomnia (suvorexant and lemborexant), with a New Drug Application recently submitted to the US Food and Drug Administration for a third drug (daridorexant). Other therapeutic applications under investigation include reduction of cravings in substance-use disorders and prevention of neurodegenerative disorders such as Alzheimer's disease, given the apparent bidirectional relationship between poor sleep and worsening of the disease. Circuit neuroscience findings suggest that the Hcrt system is a hub that integrates diverse inputs modulating arousal (e.g., circadian rhythms, metabolic status, positive and negative emotions) and conveys this information to multiple output regions. This neuronal architecture explains the wealth of physiological functions associated with Hcrts and highlights the potential of the Hcrt system as a therapeutic target for a number of disorders. We discuss present and future possible applications of drugs targeting the Hcrt system for the treatment of circuit-related neuropsychiatric and neurodegenerative conditions.

Orexin 1 Receptor Antagonism in the Basolateral Amygdala Shifts the Balance From Pro- to Antistress Signaling and Behavior

BACKGROUND

Stress produces differential behavioral responses through select molecular modifications to specific neurocircuitry elements. The orexin (Orx) system targets key components of this neurocircuitry in the basolateral amygdala (BLA).

METHODS

We assessed the contribution of intra-BLA Orx1 receptors (Orx1Rs) in the expression of stress-induced phenotypes of mice. Using the Stress Alternatives Model, a social stress paradigm that produces two behavioral phenotypes, we characterized the role of intra-BLA Orx1R using acute pharmacological inhibition (SB-674042) and genetic knockdown (AAV-U6-Orx1R-shRNA) strategies.

RESULTS

In the BLA, we observed that Orx1R (Hcrtr1) messenger RNA is predominantly expressed in CamKIIα+ glutamatergic neurons and rarely in GABAergic (gamma-aminobutyric acidergic) cells. While there is a slight overlap in Hcrtr1 and Orx2 receptor (Hcrtr2) messenger RNA expression in the BLA, we find that these receptors are most often expressed in separate cells. Antagonism of intra-BLA Orx1R after phenotype formation shifted behavioral expression from stress-sensitive (Stay) to stress-resilient (Escape) responses, an effect that was mimicked by genetic knockdown. Acute inhibition of Orx1R in the BLA also reduced contextual and cued fear freezing responses in Stay animals. This phenotype-specific behavioral change was accompanied by biased molecular transcription favoring Hcrtr2 over Hcrtr1 and Mapk3 over Plcb1 cell signaling cascades and enhanced Bdnf messenger RNA.

CONCLUSIONS

Functional reorganization of intra-BLA gene expression is produced by antagonism of Orx1R, which promotes elevated Hcrtr2, greater Mapk3, and increased Bdnf expression. Together, these results provide evidence for a receptor-driven mechanism that balances pro- and antistress responses within the BLA.

Hypothalamic deep brain stimulation as a strategy to manage anxiety disorders

SignificanceAnxiety disorders are among the most prevalent mental illnesses worldwide. Despite significant advances in their treatment, many patients remain treatment resistant. Thus, new treatment modalities and targets are much needed. Therefore, we developed a deep brain stimulation therapy that targets a recently identified anxiety center in the lateral hypothalamus. We show that this therapy rapidly silences anxiety-implicated neurons and immediately relieves diverse anxiety symptoms in a variety of stressful situations. This therapeutic effect occurs without acute or chronic side effects that are typical of many existing treatments, such as physical sedation or memory deficits. These findings identify a clinically applicable new therapeutic strategy for helping patients to manage treatment-resistant anxiety.

Hypocretin in locus coeruleus and dorsal raphe nucleus mediates inescapable footshock stimulation (IFS)-induced REM sleep alteration

Hypocretin (hcrt) is a stress-reacting neuropeptide mediating arousal and energy homeostasis. An inescapable footshock stimulation (IFS) could initiate the hcrt release from the lateral hypothalamus (LHA) and suppresses rapid eye movement (REM) sleep in rodents. However, the effects of the IFS-induced hcrts on REM-off nuclei, the locus coeruleus (LC) and dorsal raphe nucleus (DRN), remained unclear. We hypothesized that the hcrt projections from the LHA to LC or DRN mediate IFS-induced sleep disruption. Our results demonstrated that the IFS increased hcrt expression and the neuronal activities in the LHA, hypothalamus, brainstem, thalamus, and amygdala. Suppressions of REM sleep and slow wave activity during non-REM (NREM) sleep caused by the high expression of hcrts were blocked when a non-specific and dual hcrt receptor antagonist was administered into the LC or DRN. Furthermore, the IFS also caused an elevated innate anxiety, but was limitedly influenced by the hcrt antagonist. This result suggests that the increased hcrt concentrations in the LC and DRN mediate stress-induced sleep disruptions and might partially involve IFS-induced anxiety.

Do orexin/hypocretin neurons signal stress or reward?

Hypothalamic neurons that produce the peptide transmitters orexins/hypocretins (HONs) broadcast their predominantly neuroexcitatory outputs to the entire brain via their extremely wide axonal projections. HONs were originally reported to be activated by food deprivation, and to stimulate arousal, energy expenditure, and eating. This led to extensive studies of HONs in the context of nutrient-sensing and energy balance control. While activation of HONs by body energy depletion continues to be supported by experimental evidence, it has also become clear that HONs are robustly activated not only by nutrient depletion, but also by diverse sensory stimuli (both neutral and those associated with rewarding or aversive events), seemingly unrelated to each other or to energy balance. One theory that could unify these findings is that all these stimuli signal "stress" - defined either as a potentially harmful state, or an awareness of reward deficiency. If HON activity is conceptualized as a cumulative representation of stress, then many of the reported HONs outputs - including EEG arousal, sympathetic activation, place avoidance, and exploratory behaviours - could be viewed as logical stress-counteracting responses. We discuss evidence for and against this unifying theory of HON function, including the alterations in HON activity observed in anxiety and depression disorders. We propose that, in order to orchestrate stress-countering responses, HONs need to coactivate motivation and aversion brain systems, and the impact of HON stimulation on affective states may be perceived as rewarding or aversive depending on the baseline HON activity.

Hypothalamic structural integrity and temporal complexity of cortical information processing at rest in migraine without aura patients between attacks

The hypothalamus has been attributed an important role during the premonitory phase of a migraine attack. Less is known about the role played by the hypothalamus in the interictal period and its relationship with the putative neurocognitive networks previously identified in the pathophysiology of migraine. Our aim was to test whether the hypothalamic microstructure would be altered during the interictal period and whether this co-existed with aberrant connectivity at cortical level. We collected multimodal MRI data from 20 untreated patients with migraine without aura between attacks (MO) and 20 healthy controls (HC) and studied fractional anisotropy, mean (MD), radial (RD), and axial diffusivity of the hypothalamus ROI as a whole from diffusion tensor imaging (DTI). Moreover, we performed an exploratory analysis of the same DTI metrics separately for the anterior and posterior hypothalamic ROIs bilaterally. From resting-state functional MRI, we estimated the Higuchi's fractal dimension (FD), an index of temporal complexity sensible to describe non-periodic patterns characterizing BOLD signature. Finally, we correlated neuroimaging findings with migraine clinical features. In comparison to HC, MO had significantly higher MD, AD, and RD values within the hypothalamus. These findings were confirmed also in the exploratory analysis on the sub-regions of the hypothalamus bilaterally, with the addition of lower FA values on the posterior ROIs. Patients showed higher FD values within the salience network (SN) and the cerebellum, and lower FD values within the primary visual (PV) network compared to HC. We found a positive correlation between cerebellar and SN FD values and severity of migraine. Our findings of hypothalamic abnormalities between migraine attacks may form part of the neuroanatomical substrate that predisposes the onset of the prodromal phase and, therefore, the initiation of an attack. The peculiar fractal dimensionality we found in PV, SN, and cerebellum may be interpreted as an expression of abnormal efficiency demand of brain networks devoted to the integration of sensory, emotional, and cognitive information related to the severity of migraine.

Stress and central autonomic network

The central autonomic network (CAN) plays a critical role in the stress response, which is triggered by challenges on the homeostasis (physiological stressors) or unpleasant social or environmental situations. This review focuses on the role of areas of the CAN including the insular and anterior cingulate cortices, extended amygdala, hypothalamus, periaqueductal gray and locus coeruleus in the stress response. These areas are interconnected and affect sympathetic or parasympathetic output via their influence on premotor or preganglionic autonomic neurons in the lower brainstem and spinal cord. The insula integrates multiple inputs to create a sense of the physiological state of the body, whereas the anterior cingulate initiates predictive visceromotor commands. The amygdala and bed nucleus of the stria terminalis provide automatic emotional tagging and trigger automatic survival responses to threat via their outputs to the hypothalamus, periaqueductal gray, and lower brainstem. Several regions of the hypothalamus, including the paraventricular nucleus, dorsomedial nucleus and lateral hypothalamic area participate in different patterns of stress response according to the type of stimulus and projections to premotor and preganglionic autonomic neurons. The periaqueductal gray initiates different patterns of autonomic, pain modulatory, and motor responses, including the "fight or flight" or "playing dead" responses. The locus coeruleus promotes emotional learning in the amygdala associated with states of anxiety. Neurons of the C1 area of the rostral ventrolateral medulla elicit sympathoexcitatory responses to internal stressors such as hypoxia and inflammation. The ventromedial medulla, including the nucleus raphe pallidus, initiates sympathoexcitatory responses to social and other external stressors.

Pathophysiological Bases of Comorbidity in Migraine

Despite that it is commonly accepted that migraine is a disorder of the nervous system with a prominent genetic basis, it is comorbid with a plethora of medical conditions. Several studies have found bidirectional comorbidity between migraine and different disorders including neurological, psychiatric, cardio- and cerebrovascular, gastrointestinal, metaboloendocrine, and immunological conditions. Each of these has its own genetic load and shares some common characteristics with migraine. The bidirectional mechanisms that are likely to underlie this extensive comorbidity between migraine and other diseases are manifold. Comorbid pathologies can induce and promote thalamocortical network dysexcitability, multi-organ transient or persistent pro-inflammatory state, and disproportionate energetic needs in a variable combination, which in turn may be causative mechanisms of the activation of an ample defensive system with includes the trigeminovascular system in conjunction with the neuroendocrine hypothalamic system. This strategy is designed to maintain brain homeostasis by regulating homeostatic needs, such as normal subcortico-cortical excitability, energy balance, osmoregulation, and emotional response. In this light, the treatment of migraine should always involves a multidisciplinary approach, aimed at identifying and, if necessary, eliminating possible risk and comorbidity factors.

Orexins (hypocretins): The intersection between homeostatic and hedonic feeding

Orexins are hypothalamic neuropeptides originally discovered to play a role in the regulation of feeding behaviour. The broad connections of orexin neurons to mesocorticolimbic circuitry suggest they may play a role in mediating reward-related behaviour beyond homeostatic feeding. Here, we review the role of orexin in a variety of eating-related behaviour, with a focus on reward and motivation, and the neural circuits driving these effects. One emerging finding is the involvement of orexins in hedonic and appetitive behaviour towards palatable food, in addition to their role in homeostatic feeding. This review discusses the brain circuitry and possible mechanisms underlying the role of orexins in these behaviours. Overall, there is a marked bias in the literature towards studies involving male subjects. As such, future work needs to be done to involve female subjects. In summary, orexins play an important role in driving motivation for high salient rewards such as highly palatable food and may serve as the intersection between homeostatic and hedonic feeding.

Cocaine-Seeking Behavior Induced by Orexin A Administration in the Posterior Paraventricular Nucleus of the Thalamus Is Not Long-Lasting: Neuroadaptation of the Orexin System During Cocaine Abstinence

Hypothalamic orexin (Orx) projections to the paraventricular nucleus of the thalamus (PVT) have received growing interest because of their role in drug-seeking behavior. Using an established model of cocaine dependence (i.e., long access [LgA] to cocaine), we previously showed that OrxA injections in the posterior PVT (pPVT) reinstated extinguished cocaine-seeking behavior in rats after an intermediate period of abstinence (2-3 weeks). Considering the long-lasting nature of drug-seeking behavior, the present study examined whether the priming effect of intra-pPVT OrxA administration was preserved after a period of protracted abstinence (4-5 weeks) in rats that self-administered cocaine under LgA conditions. Furthermore, to better understand whether a history of cocaine dependence affects the Orx system-particularly the hypothalamic Orx↔pPVT connection-the number of Orx-expressing cells in the lateral hypothalamus (LH), dorsomedial hypothalamus (DMH), and perifornical area (PFA) and number of orexin receptor 1 (OrxR1)- and OrxR2-expressing cells in the pPVT were quantified. Orexin A administration in the pPVT induced cocaine-seeking behavior after intermediate abstinence, as reported previously. At protracted abstinence, however, the priming effect of OrxA was absent. A higher number of cells that expressed Orx was observed in the LH/DMH/PFA at both intermediate and protracted abstinence. In the pPVT, the number of OrxR2-expressing cells was significantly higher only at intermediate abstinence, with no changes in the number of OrxR1-expressing cells. These data build on our previous findings that the hypothalamic Orx↔pPVT connection is strongly recruited shortly after cocaine abstinence and demonstrate that the priming effect of OrxA is not long lasting. Furthermore, these findings suggest that throughout abstinence, the Orx↔pPVT connection undergoes neuroadaptive changes, reflected by alterations of the number of OrxR2-expressing cells in the pPVT.

Lateral hypothalamus orexinergic inputs to lateral habenula modulate maladaptation after social defeat stress

Social stress, a common stressor, causes multiple forms of physical and mental dysfunction. Prolonged exposure to social stress is associated with a higher risk of psychological disorders, including anxiety disorders and major depressive disorder (MDD). The orexinergic system is involved in the regulation of multiple motivated behaviors. The current study examined the regulatory effect of orexinergic projections from the lateral hypothalamic area (LHA) to the lateral habenula (LHb) in depression- and anxiety-like behaviors after chronic social defeat stress. When mice were defeated during social interaction, both orexinergic neurons in the LHA and glutamatergic neurons in the LHb were strongly activated, as indicated by the FosTRAP strategy. Infusion of orexin in the LHb significantly alleviated social avoidance and depression-like behaviors induced by chronic social defeat stress. Administration of an orexin receptor 2 antagonist in the LHb further aggravated the depressive phenotype. Photoactivation of orexinergic cell bodies in the LHA or terminals in the LHb relieved anxiety-like behaviors induced by chronic social defeat stress. Collectively, we identified the antidepressant and anxiolytic effects of the circuit from LHA orexinergic neurons to the LHb in response to chronic social stress, providing new evidence of the antidepressant properties of LHA orexin circuits.

Inhibition of Orexin/Hypocretin Neurons Ameliorates Elevated Physical Activity and Energy Expenditure in the A53T Mouse Model of Parkinson's Disease

Aside from the classical motor symptoms, Parkinson's disease also has various non-classical symptoms. Interestingly, orexin neurons, involved in the regulation of exploratory locomotion, spontaneous physical activity, and energy expenditure, are affected in Parkinson's. In this study, we hypothesized that Parkinson's-disease-associated pathology affects orexin neurons and therefore impairs functions they regulate. To test this, we used a transgenic animal model of Parkinson's, the A53T mouse. We measured body composition, exploratory locomotion, spontaneous physical activity, and energy expenditure. Further, we assessed alpha-synuclein accumulation, inflammation, and astrogliosis. Finally, we hypothesized that chemogenetic inhibition of orexin neurons would ameliorate observed impairments in the A53T mice. We showed that aging in A53T mice was accompanied by reductions in fat mass and increases in exploratory locomotion, spontaneous physical activity, and energy expenditure. We detected the presence of alpha-synuclein accumulations in orexin neurons, increased astrogliosis, and microglial activation. Moreover, loss of inhibitory pre-synaptic terminals and a reduced number of orexin cells were observed in A53T mice. As hypothesized, this chemogenetic intervention mitigated the behavioral disturbances induced by Parkinson's disease pathology. This study implicates the involvement of orexin in early Parkinson's-disease-associated impairment of hypothalamic-regulated physiological functions and highlights the importance of orexin neurons in Parkinson's disease symptomology.

Investigation of the effect of the dual orexin receptor antagonist almorexant on ophthalmological, spermatogenic, and hormonal variables in healthy male subjects

BACKGROUND/AIMS

The aim of this single-center, double-blind study was to investigate the effect of a 4-week once daily administration of 200 mg almorexant on tear film break-up time, spermatogenesis, hormone levels, and pancreatic elastase in stool in healthy male subjects.

METHODS

Almorexant 200 mg or matching placebo was administered in the evening for 4 weeks once daily to 56 healthy male subjects. Changes in ophthalmological variables, sperm composition, hormone levels, and pancreatic elastase levels in stool were evaluated periodically up to 8 weeks after discontinuation of drug administration. Blood samples for pharmacokinetic measurements were taken after 4 weeks to confirm compliance to study drug intake.

RESULTS

The results of this study revealed no treatment effects of almorexant, neither on tear film break-up time nor on other ophthalmological variables investigated during this study. Furthermore, spermatogenesis, hormones of the hypothalamic-pituitary-adrenal and -gonadal axes, and endocrine pancreatic secretion were shown to be not affected by a 4-week once daily administration of almorexant.

CONCLUSION

Almorexant was well tolerated and had no effect on the spectrum of pharmacodynamic variables assessed. Ophthalmology and testicular findings detected in preclinical studies were not observed in this clinical study. Therefore, these preclinical findings appear not to be relevant for humans and do not prevent from conducting larger clinical trials with either healthy subjects or patients.

Orexin-A up-regulates dopamine D2 receptor and mRNA in the nucleus accumbens Shell

Orexins-A (OrxA) and -B (OrxB) neuropeptides are synthesized by a group of neurons located in the lateral hypothalamus and adjacent perifornical area, which send their projections to the mesolimbic dopaminergic (DAergic) system including ventral tegmental area and nucleus accumbens (NAc), where orexin receptors are expressed. NAc plays a central role in reward-seeking behavior and drug abuse. NAc-neurons express dopamine-1 (D1R) and dopamine-2 (D2R) receptors. Orexins bind to their two cognate G-protein-coupled receptors, orexin-receptor type-1 (Orx₁R) and type-2 (Orx₂R). Orexin receptor signaling is involved in behaviors such as motivation and addiction. Orexin-containing neurons modulate DAergic activity that is key in synaptic plasticity induced by addictive drugs. However, the effect of OrxA on expression and content of DAergic receptors in NAc is unknown. The purpose of this study was to investigate whether OrxA can alter gene expression and protein levels of D1R/D2R in NAc. Gene expression was evaluated by real-time PCR analysis and protein levels by western blot in rats. The results show that intracerebroventricular (i.c.v.) injection of OrxA increases both gene transcription and protein content of D2R but fails to modify D1R. This effect was also confirmed with OrxA infusion in NAc/Shell. Our results demonstrate for the first time that OrxA induces up-regulation of gene and protein of D2R in NAc. These findings support the hypothesis that OrxA modulates the DAergic transmission and this may serve to understand how orexin signaling enhances DA responses at baseline conditions and in response to psychostimulants.

Increased plasma orexin-A concentrations are associated with the non-motor symptoms in Parkinson's disease patients

BACKGROUND

Orexin, a neuropeptide primarily secreted by neurons in the lateral hypothalamus, has been implicated in Parkinson's disease (PD). Studies on the relationship between plasma orexin-A levels and PD are rare.

OBJECTIVES

This study aimed to assess levels of plasma orexin-A in the progression of PD and to evaluate the correlation between orexin-A levels and non-motor symptoms.

METHODS

Enzyme-linked immunosorbent assay was used to determine plasma orexin-A levels in 117 healthy controls and 121 PD patients, including those with early (n = 68), medium (n = 40) and advanced (n = 13) stages of the disease. Evaluation of motor symptoms and non-motor symptoms in PD patients, such as sleep disorders, cognitive dysfunction, neuropsychiatric symptoms, autonomic nervous dysfunction, hyposmia and PD-related pain, were assessed by the associated scales.

RESULTS

Plasma orexin-A levels were significantly higher in PD patients compared to healthy controls. Orexin-A levels were elevated in early-stage and medium-stage PD compared to healthy controls, but were decreased in advanced-stage PD. Orexin-A levels were negatively correlated with the Unified Parkinson's Disease Rating Scale Part III scores, disease duration, and dopamine receptor agonist doses, and were positively correlated with the Pittsburgh Sleep Quality Index, REM-sleep Behavior Disorder Questionnaire, 14-item Hamilton Anxiety Scale, Mini-Mental State Examination, and Non-motor Symptom Scale items 22-24 scores.

CONCLUSIONS

We found for the first time that plasma orexin-A levels were increased in early-stage and medium-stage PD and were decreased in advanced-stage PD. Furthermore, orexin-A levels were correlated with the non-motor symptoms of insomnia, REM-sleep behavior disorder, anxiety, cognitive dysfunction, and renal dysfunction.

The orexin (hypocretin) neuropeptide system is a target for novel therapeutics to treat cocaine use disorder with alcohol coabuse

An estimated 50-90% of individuals with cocaine use disorder (CUD) also report using alcohol. Cocaine users report coabusing alcohol to 'self-medicate' against the negative emotional side effects of the cocaine 'crash', including the onset of anxiety. Thus, pharmaceutical strategies to treat CUD would ideally reduce the motivational properties of cocaine, alcohol, and their combination, as well as reduce the onset of anxiety during drug withdrawal. The hypothalamic orexin (hypocretin) neuropeptide system offers a promising target, as orexin neurons are critically involved in activating behavioral and physiological states to respond to both positive and negative motivators. Here, we seek to describe studies demonstrating efficacy of orexin receptor antagonists in reducing cocaine, alcohol- and stress-related behaviors, but note that these studies have largely focused on each of these phenomena in isolation. For orexin-based compounds to be viable in the clinical setting, we argue that it is imperative that their efficacy be tested in animal models that account for polysubstance use patterns. To begin to examine this, we present new data showing that rats' preferred level of cocaine intake is significantly increased following chronic homecage access to alcohol. We also report that cocaine intake and motivation are reduced by a selective orexin-1 receptor antagonist when rats have a history of cocaine + alcohol, but not a limited history of cocaine alone. In light of these proof-of-principle data, we outline what we believe to be the key priorities going forward with respect to further examining the orexin system in models of polysubstance use. This article is part of the special issue on Neurocircuitry Modulating Drug and Alcohol Abuse.

Translational evaluation of novel selective orexin-1 receptor antagonist JNJ-61393215 in an experimental model for panic in rodents and humans

Orexin neurons originating in the perifornical and lateral hypothalamic area project to anxiety- and panic-associated neural circuitry, and are highly reactive to anxiogenic stimuli. Preclinical evidence suggests that the orexin system, and particularly the orexin-1 receptor (OX1R), may be involved in the pathophysiology of panic and anxiety. Selective OX1R antagonists thus may constitute a potential new treatment strategy for panic- and anxiety-related disorders. Here, we characterized a novel selective OX1R antagonist, JNJ-61393215, and determined its affinity and potency for human and rat OX1R in vitro. We also evaluated the safety, pharmacokinetic, and pharmacodynamic properties of JNJ-61393215 in first-in-human single- and multiple-ascending dose studies conducted. Finally, the potential anxiolytic effects of JNJ-61393215 were evaluated both in rats and in healthy men using 35% CO₂ inhalation challenge to induce panic symptoms. In the rat CO₂ model of panic anxiety, JNJ-61393215 demonstrated dose-dependent attenuation of CO₂-induced panic-like behavior without altering baseline locomotor or autonomic activity, and had minimal effect on spontaneous sleep. In phase-1 human studies, JNJ-61393215 at 90 mg demonstrated significant reduction (P < 0.02) in CO₂-induced fear and anxiety symptoms that were comparable to those obtained using alprazolam. The most frequently reported adverse events were somnolence and headache, and all events were mild in severity. These results support the safety, tolerability, and anxiolytic effects of JNJ-61393215, and validate CO₂ exposure as a translational cross-species experimental model to evaluate the therapeutic potential of novel anxiolytic drugs.

Targeting the Orexin System for Prescription Opioid Use Disorder

Prescription opioids are potent analgesics that are used for clinical pain management. However, the nonmedical use of these medications has emerged as a major concern because of dramatic increases in abuse and overdose. Therefore, effective strategies to prevent prescription opioid use disorder are urgently needed. The orexin system has been implicated in the regulation of motivation, arousal, and stress, making this system a promising target for the treatment of substance use disorder. This review discusses recent preclinical studies that suggest that orexin receptor blockade could be beneficial for the treatment of prescription opioid use disorder.

Orexin Receptor Antagonists as Emerging Treatments for Psychiatric Disorders

Orexins comprise two neuropeptides produced by orexin neurons in the lateral hypothalamus and are released by extensive projections of these neurons throughout the central nervous system. Orexins bind and activate their associated G protein-coupled orexin type 1 receptors (OX1Rs) and OX2Rs and act on numerous physiological processes, such as sleep-wake regulation, feeding, reward, emotion, and motivation. Research on the development of orexin receptor antagonists has dramatically increased with the approval of suvorexant for the treatment of primary insomnia. In the present review, we discuss recent findings on the involvement of the orexin system in the pathophysiology of psychiatric disorders, including sleep disorders, depression, anxiety, and drug addiction. We discuss the actions of orexin receptor antagonists, including selective OX1R antagonists (SORA1s), selective OX2R antagonists (SORA2s), and dual OX1/2R antagonists (DORAs), in the treatment of these disorders based on both preclinical and clinical evidence. SORA2s and DORAs have more pronounced efficacy in the treatment of sleep disorders, whereas SORA1s may be promising for the treatment of anxiety and drug addiction. We also discuss potential challenges and opportunities for the application of orexin receptor antagonists to clinical interventions.

The Effect of Orexin Receptor Antagonism on Quinpirole-Induced Compulsive-Like Checking Behavior in Rats

The orexinergic system supposedly plays a role in stress circuits for arousing behaviors during anxiety, suggesting that it may play a role also in neural circuits mediating the compulsive behavior characteristic of obsessive-compulsive disorder (OCD). This study aims to investigate the roles of the orexinergic system in the development of OCD behaviors, using as preparation the induction of compulsive checking by chronic treatment with the D2/D3 agonist, quinpirole. Repeated injections of quinpirole (0.5 mg/kg, twice per week for a total of 10 injections) were used to induce compulsive checking. In separate groups of rats, OX1R (SB334867-A; 10 μg i.c.v) and OX2R (TCS-OX2-29; 10 μg i.c.v) receptor antagonists were co-administered together with quinpirole. Checking behavior in a large open field was measured after the first, fifth, and tenth injections of the drugs. SB334867-A attenuated checking behavior and the level of anxiety. TCS-OX2-29 administration ameliorated anxiety but did not block the development of compulsive checking. Orexin 1 receptors seem to play a more critical role than orexin 2 receptors in the induction of compulsive checking. Considering that the quinpirole sensitization model of OCD involves activation of dopamine systems and sensitization to quinpirole, it is suggested that neural interaction between orexigenic and dopamine systems may be important in the pathogenesis of OCD.

Recent perspectives on orexin/hypocretin promotion of addiction-related behaviors

The neuropeptide hypocretin/orexin plays a broad and important role in physiological functions ranging from addiction, stress, and anxiety to sleep, energy metabolism, and homeostatic regulation. A number of recent reviews addressing the importance of orexin for different addictive behaviors, especially the contribution of orexin-1-receptors (Ox1Rs) in responding for intoxicants in higher-motivation individuals and situations, and orexin-2-receptor (Ox2Rs) in stress-related aspects of addictive responding. This may parallel the importance of more lateral orexin neurons in the hypothalamus for reward and more medial for stress and arousal. However, there is clearly also some crossover, which may reflect, in part, where positive and negative conditioning (reward- and relief-seeking) are both present concurrently in established addiction, and also where orexin signaling can differ in subregions of a particular brain region. Here, we attempt to examine and synthesize some of the most recent work addressing orexin functions in addiction, including a particular role for Ox1Rs for driving responding in higher-motivation individuals and under higher levels of effort. While there are some commonalities across addictive substances addressed here (alcohol, cocaine, opiates), there are also some differences, which may relate to several factors including the speed of intoxication with a given substance. Together, recent findings have shed important insight and clues into what a more unified role of Ox1Rs might entail, and critical areas for future work. In addition, these many studies support the development of Ox1R blockers for use in humans to counteract addiction and other disorders of motivation. This article is part of the special issue on Neuropeptides.

Chronic ketamine abuse is associated with orexin-A reduction and ACTH elevation

BACKGROUND

Ketamine has emerged as a major substance of abuse worldwide. Evidence suggests a role of orexin system in reward processing, withdrawal, and stress response. It also interacts with the stress mechanisms of hypothalamic-pituitary-adrenal (HPA) axis to regulate drug-taking behavior. The study aimed to explore the relevance of orexin and stress hormones to chronic ketamine abuse.

METHODS

We enrolled 67 ketamine-dependent (KD) patients and 64 controls. The levels of orexin-A, adrenocorticotropic hormone (ACTH), and cortisol were measured at baseline, 1 week, and 2 weeks after ketamine discontinuation. KD patients were assessed by Beck Depression Inventory, Beck Anxiety Inventory, and Visual Analogue Scale for ketamine craving at baseline.

RESULTS

Compared with the controls, KD patients had significantly lower orexin-A (0.65 ± 0.12 vs. 0.74 ± 0.10 ng/mL, p < 0.001) and increased ACTH (32.3 ± 16.3 vs. 22.3 ± 11.0 pg/mL, p = 0.008) levels at baseline, whereas cortisol levels were similar between two groups. Levels of the three markers did not correlate with ketamine use variables, craving, depression, or anxiety symptoms. The levels did not alter after 1 or 2 weeks of ketamine discontinuation. Notably, those with higher anxiety had lower orexin-A but increased cortisol levels than did those with lower anxiety.

CONCLUSIONS

This study showed that KD patients had persistent orexin-A reduction and stress hormone dysregulation in early abstinence. The anxious phenotype of KD might be associated with a lower orexin-A expression. These results point to a promising pathway to investigate the neurochemical mechanisms of ketamine addiction.

Mood-related central and peripheral clocks

Mood disorders, including major depression, bipolar disorder, and seasonal affective disorder, are debilitating disorders that affect a significant portion of the global population. Individuals suffering from mood disorders often show significant disturbances in circadian rhythms and sleep. Moreover, environmental disruptions to circadian rhythms can precipitate or exacerbate mood symptoms in vulnerable individuals. Circadian clocks exist throughout the central nervous system and periphery, where they regulate a wide variety of physiological processes implicated in mood regulation. These processes include monoaminergic and glutamatergic transmission, hypothalamic-pituitary-adrenal axis function, metabolism, and immune function. While there seems to be a clear link between circadian rhythm disruption and mood regulation, the mechanisms that underlie this association remain unclear. This review will touch on the interactions between the circadian system and each of these processes and discuss their potential role in the development of mood disorders. While clinical studies are presented, much of the review will focus on studies in animal models, which are attempting to elucidate the molecular and cellular mechanisms in which circadian genes regulate mood.

Suvorexant to treat alcohol use disorder and comorbid insomnia: Plan for a phase II trial

Alcohol use disorder (AUD) is a complex neuropsychiatric disease state in which currently approved pharmacotherapeutics are of relatively low effect at a population level. One reason for this may be that current pharmacotherapeutics focus on the reward pathway in relapse prevention, rather than addressing AUD from a holistic perspective. Importantly, one often overlooked symptom of AUD is sleep disruption. In recent years, an efficient, relatively low risk and economic strategy that has proven successful in other disorders is the repositioning or repurposing of drugs approved for the treatment of other indications. Suvorexant, a dual orexin receptor antagonist, has been licensed for the treatment of insomnia in the USA, Australia and Japan. The orexin system also plays a role in the emotional dysregulation that occurs during withdrawal from alcohol use and in alcohol-seeking behaviours. These two factors prompted the planning of a clinical trial into the use of suvorexant to treat insomnia in alcohol dependent individuals during and 24 weeks post-acute alcohol withdrawal. In this review we outline the comorbid nature of AUD and sleep disruptions. We then highlight the role of the orexin system in both sleep-wake regulation and AUD. Finally, we discuss our plan for a Phase II double blind placebo controlled trial examining the effectiveness of suvorexant for the treatment of comorbid insomnia and AUD.

Targeting the orexin system for prescription opioid use disorder: Orexin-1 receptor blockade prevents oxycodone taking and seeking in rats

Prescription opioids, such as oxycodone, are potent analgesics that are used to treat and manage pain. However, oxycodone is one of the most commonly abused prescription drugs. Finding an effective strategy to prevent prescription opioid use disorder is urgent. Orexin receptors (OrxR1 and OrxR2) have been implicated in the regulation of motivation, arousal, and stress, making them possible targets for the treatment of substance use disorder. To study the significance of environmental stimuli in maintaining the vulnerability to relapse to oxycodone use, resistance to the extinction of oxycodone-seeking behavior that was elicited by an oxycodone-related stimulus was examined. Rats were trained to self-administer oxycodone in the presence of a contextual/discriminative stimulus (S^D). Using this procedure, the rats readily acquired oxycodone self-administration and exhibited increases in physical signs of opioid withdrawal. Following extinction, response-reinstating effects of re-exposure to the S^D perseverated. We then tested whether OrxR blockade prevents oxycodone intake and relapse. The effects of the OrxR1 antagonist SB334867 and OrxR2 antagonist TCSOX229 on oxycodone self-administration were tested. SB334867 significantly decreased oxycodone self-administration, whereas TCSOX229 did not produce any effect. To investigate whether OrxR1 and OrxR2 blockade prevents oxycodone seeking, the rats were tested for the ability of SB334867 and TCSOX229 to prevent the S^D-induced conditioned reinstatement of oxycodone-seeking behavior. SB334867 decreased oxycodone-seeking behavior, whereas TCSOX229 was ineffective. These results suggest that OrxR1 antagonism prevents excessive prescription opioid use and relapse and might be beneficial for the treatment of prescription opioid use disorder.

Pharmacological and chemogenetic orexin/hypocretin intervention ameliorates Hipp-dependent memory impairment in the A53T mice model of Parkinson's disease

Parkinson's disease (PD), classically defined as a progressive motor disorder accompanied with dopaminergic neuron loss and presence of Lewy bodies, is the second most common neurodegenerative disease. PD also has various non-classical symptoms, including cognitive impairments. In addition, inflammation and astrogliosis are recognized as an integral part of PD pathology. The hippocampus (Hipp) is a brain region involved in cognition and memory, and the neuropeptide orexin has been shown to enhance learning and memory. Previous studies show impairments in Hipp-dependent memory in a transgenic mouse model of Parkinson's disease (A53T mice), and we hypothesized that increasing orexin tone will reverse this. To test this, we subjected 3, 5, and 7-month old A53T mice to a Barnes maze and a contextual object recognition test to determine Hipp dependent memory. Inflammation and astrogliosis markers in the Hipp were assessed by immuno-fluorescence densitometry. The data show that early cognitive impairment is coupled with an increase in expression of inflammatory and astrogliosis markers. Next, in two separate experiments, mice were given intra-hippocampal injections of orexin or chemogenetic viral injections of an orexin neuron specific Designer Receptor Exclusively Activated by Designer Drug (DREADD). For the pharmacological approach mice were intracranially treated with orexin A, whereas the chemogenetic approach utilized clozapine N-oxide (CNO). Both pharmacological orexin A intervention as well as chemogenetic activation of orexin neurons ameliorated Hipp-dependent early memory impairment observed in A53T mice. This study implicates orexin in PD-associated cognitive impairment and suggests that exogenous orexin treatment and/or manipulation of endogenous orexin levels may be a potential strategy for addressing early cognitive loss in PD.

Increased neural connectivity between the hypothalamus and cortical resting-state functional networks in chronic migraine

OBJECTIVE

The findings of resting-state functional MRI studies have suggested that abnormal functional integration between interconnected cortical networks characterises the brain of patients with migraine. The aim of this study was to investigate the functional connectivity between the hypothalamus, brainstem, considered as the migraine generator, and the following areas/networks that are reportedly involved in the pathophysiology of migraine: default mode network (DMN), executive control network, dorsal attention system, and primary and dorsoventral visual networks.

METHODS

Twenty patients with chronic migraine (CM) without medication overuse and 20 healthy controls (HCs) were prospectively recruited. All study participants underwent 3-T MRI scans using a 7.5-min resting-state protocol. Using a seed-based approach, we performed a ROI-to-ROI analysis selecting the hypothalamus as the seed.

RESULTS

Compared to HCs, patients with CM showed significantly increased neural connectivity between the hypothalamus and brain areas belonging to the DMN and dorsal visual network. We did not detect any connectivity abnormalities between the hypothalamus and the brainstem. The correlation analysis showed that the severity of the migraine headache was positively correlated with the connectivity strength of the hypothalamus and negatively with the connectivity strength of the medial prefrontal cortex, which belongs to the DMN.

CONCLUSION

These data provide evidence for hypothalamic involvement in large-scale reorganisation at the functional-network level in CM and in proportion with the perceived severity of the migraine pain.