Orexin and psychiatric symptoms in suicide attempters

Development and validation of a machine learning model for prediction of comorbid major depression disorder among narcolepsy type 1

BACKGROUND

Major depression disorder (MDD) forms a common psychiatric comorbidity among patients with narcolepsy type 1 (NT1), yet its impact on patients with NT1 is often overlooked by neurologists. Currently, there is a lack of effective methods for accurately predicting MDD in patients with NT1.

OBJECTIVE

This study utilized machine learning (ML) algorithms to identify critical variables and developed the prediction model for predicting MDD in patients with NT1.

METHODS

The study included 267 NT1 patients from four sleep centers. The diagnosis of comorbid MDD was based on Diagnostic and Statistical Manual of Mental Disorders fifth edition (DSM-5). ML models, including six full models and six compact models, were developed using a training set. The performance of these models was compared in the testing set, and the optimal model was evaluated in the testing set. Various evaluation metrics, such as Area under the receiver operating curve (AUC), precision-recall (PR) curve and calibration curve were employed to assess and compare the performance of the ML models. Model interpretability was demonstrated using SHAP.

RESULT

In the testing set, the logistic regression (LG) model demonstrated superior performance compared to other ML models based on evaluation metrics such as AUC, PR curve, and calibration curve. The top eight features used in the LG model, ranked by feature importance, included social impact scale (SIS) score, narcolepsy severity scale (NSS) score, total sleep time, body mass index (BMI), education years, age of onset, sleep efficiency, sleep latency.

CONCLUSION

The study yielded a straightforward and practical ML model for the early identification of MDD in patients with NT1. A web-based tool for clinical applications was developed, which deserves further verification in diverse clinical settings.

TGR5-mediated lateral hypothalamus-dCA3-dorsolateral septum circuit regulates depressive-like behavior in male mice

Although bile acids play a notable role in depression, the pathological significance of the bile acid TGR5 membrane-type receptor in this disorder remains elusive. Using depression models of chronic social defeat stress and chronic restraint stress in male mice, we found that TGR5 in the lateral hypothalamic area (LHA) predominantly decreased in GABAergic neurons, the excitability of which increased in depressive-like mice. Upregulation of TGR5 or inhibition of GABAergic excitability in LHA markedly alleviated depressive-like behavior, whereas down-regulation of TGR5 or enhancement of GABAergic excitability facilitated stress-induced depressive-like behavior. TGR5 also bidirectionally regulated excitability of LHA GABAergic neurons via extracellular regulated protein kinases-dependent Kv4.2 channels. Notably, LHA GABAergic neurons specifically innervated dorsal CA3 (dCA3) CaMKIIα neurons for mediation of depressive-like behavior. LHA GABAergic TGR5 exerted antidepressant-like effects by disinhibiting dCA3 CaMKIIα neurons projecting to the dorsolateral septum (DLS). These findings advance our understanding of TGR5 and the LHAGABA→dCA3CaMKIIα→DLSGABA circuit for the development of potential therapeutic strategies in depression.

Assessing resting-state brain functional connectivity in adolescents and young adults with narcolepsy using functional near-infrared spectroscopy

This study aimed to elucidate the alterations in the prefrontal cortex's functional connectivity and network topology in narcolepsy patients using functional near-infrared spectroscopy (fNIRS). Twelve narcolepsy-diagnosed patients from Guangxi Zhuang Autonomous Region's People's Hospital Sleep Medicine Department and 11 matched healthy controls underwent resting fNIRS scans. Functional connectivity and graph theory analyses were employed to assess the prefrontal cortex network's properties and their correlation with clinical features. Results indicated increased functional connectivity in these adolescent and young adult patients with narcolepsy, with significant variations in metrics like average degree centrality and node efficiency, particularly in the left middle frontal gyrus. These alterations showed correlations with clinical symptoms, including depression and sleep efficiency. However, the significance of these findings was reduced post False Discovery Rate adjustment, suggesting a larger sample size is needed for validation. In conclusion, the study offers initial observations that alterations in the prefrontal cortex's functional connectivity may potentially act as a neurobiological indicator of narcolepsy, warranting further investigation with a larger cohort to substantiate these findings and understand the underlying mechanisms.

Possible role of exercise therapy on depression: Effector neurotransmitters as key players

About 280 million people suffer from depression as the most common neurological disorder and the most common cause of death worldwide. Exercise with serotonin released in the brain by the 5-HT3-IGF-1 mechanism can lead to antidepressant effects. Swimming exercise has antidepressant effects by increasing the sensitivity of serotonin 5-HT2 receptors and postsynaptic 5-HT1A receptors, increasing 5-HT and 5HIAA levels, increasing TPH and serotonin, and decreasing inflammatory levels of IFN-γ and TNF-α. Anaerobic and aerobic exercises increase beta-endorphin, enkephalin, and dynorphin and have antidepressant effects. Exercise by increasing dopamine, D1R, and D2R leads to the expression of BDNF and activation of TrkB and has antidepressant behavior. Exercise leads to a significant increase in GABAAR (γ2 and α2 subunits) and reduces neurodegenerative disorders caused by GABA imbalance through anti-inflammatory pathways. By increasing glutamate and PGC1α and reducing glutamatergic neurotoxicity, exercise enhances neurogenesis and synaptogenesis and prevents neurodegeneration and the onset of depression. Irisin release during exercise shows an important role in depression by increasing dopamine, BDNF, NGF, and IGF-1 and decreasing inflammatory mediators such as IL-6 and IL-1β. In addition, exercise-induced orexin and NPY can increase hippocampal neurogenesis and relieve depression. After exercise, the tryptophan to large neutral amino acids (TRP/LNAA) ratio and the tryptophan to branched-chain amino acids (BCAA) ratio increase, which may have antidepressant effects. The expression of M5 receptor and nAChR α7 increases after exercise and significantly increases dopamine and acetylcholine and ameliorates depression. It appears that during exercise, muscarinic receptors can reduce depression through dopamine in the absence of acetylcholine. Therefore, exercise can be used to reduce depression by affecting neurotransmitters, neuromodulators, cytokines, and/or neurotrophins.

Major Depressive Disorder Prediction Based on Sleep-Wake Disorders Symptoms in US Adolescents: A Machine Learning Approach from National Sleep Research Resource

Background

There is substantial evidence from previous studies that abnormalities in sleep parameters associated with depression are demonstrated in almost all stages of sleep architecture. Patients with symptoms of sleep-wake disorders have a much higher risk of developing major depressive disorders (MDD) compared to those without.

Objective

The aim of the present study is to establish and compare the performance of different machine learning models based on sleep-wake disorder symptoms data and to select the optimal model to interpret the importance of sleep-wake disorder symptoms to predict MDD occurrence in adolescents.

Methods

We derived data for this work from 2020 to 2021 Assessing Nocturnal Sleep/Wake Effects on Risk of Suicide Phase I Study from National Sleep Research Resource. Using demographic and sleep-wake disorder symptoms data as predictors and the occurrence of MDD measured base on the center for epidemiologic studies depression scale as an outcome, the following six machine learning predictive models were developed: eXtreme Gradient Boosting model (XGBoost), Light Gradient Boosting mode, AdaBoost, Gaussian Naïve Bayes, Complement Naïve Bayes, and multilayer perceptron. The models' performance was assessed using the AUC and other metrics, and the final model's predictor importance ranking was explained.

Results

XGBoost is the optimal predictive model in comprehensive performance with the AUC of 0.804 in the test set. All sleep-wake disorder symptoms were significantly positively correlated with the occurrence of adolescent MDD. The insomnia severity was the most important predictor compared with the other predictors in this study.

Conclusion

This machine learning predictive model based on sleep-wake disorder symptoms can help to raise the awareness of risk of symptoms between sleep-wake disorders and MDD in adolescents and improve primary care and prevention.

The Orexin/Hypocretin System, the Peptidergic Regulator of Vigilance, Orchestrates Adaptation to Stress

The orexin/hypocretin neuropeptide family has emerged as a focal point of neuroscientific research following the discovery that this family plays a crucial role in a variety of physiological and behavioral processes. These neuropeptides serve as powerful neuromodulators, intricately shaping autonomic, endocrine, and behavioral responses across species. Notably, they serve as master regulators of vigilance and stress responses; however, their roles in food intake, metabolism, and thermoregulation appear complementary and warrant further investigation. This narrative review provides a journey through the evolution of our understanding of the orexin system, from its initial discovery to the promising progress made in developing orexin derivatives. It goes beyond conventional boundaries, striving to synthesize the multifaceted activities of orexins. Special emphasis is placed on domains such as stress response, fear, anxiety, and learning, in which the authors have contributed to the literature with original publications. This paper also overviews the advancement of orexin pharmacology, which has already yielded some promising successes, particularly in the treatment of sleep disorders.

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.

Orexinergic neurons modulate stress coping responses in mice

Stress is a critical precipitating factor for major depression. However, individual responses to the same stressor vary widely, possibly owing to individual variations in stress resilience. Nevertheless, the factors that determine stress susceptibility and resilience remain poorly understood. Orexin neurons have been implicated in the control of stress-induced arousal. Therefore, we investigated whether orexin-expressing neurons are involved in the regulation of stress resilience in male mice. We found that the level of c-fos expression was significantly different in susceptible versus resilient mice in the learned helplessness test (LHT). Furthermore, activating orexinergic neurons induced resilience in the susceptible group, and this resilience was also consistently observed in other behavioral tests. However, activating orexinergic neurons during the induction period (during inescapable stress exposure) did not affect stress resilience in the escape test. In addition, analyses using pathway-specific optic stimulation revealed that activating orexinergic projections to the medial part of the nucleus accumbens (NAc) alone mediated a decrease in anxiety but was not sufficient to induce resilience in the LHT. Collectively, our data suggest that orexinergic projections to multiple targets control diverse and flexible stress-related behaviors in response to various stressors.

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.

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.

Neurobiology of the Orexin System and Its Potential Role in the Regulation of Hedonic Tone

Orexin peptides comprise two neuropeptides, orexin A and orexin B, that bind two G-protein coupled receptors (GPCRs), orexin receptor 1 (OXR1) and orexin receptor 2 (OXR2). Although cell bodies that produce orexin peptides are localized in a small area comprising the lateral hypothalamus and adjacent regions, orexin-containing fibres project throughout the neuraxis. Although orexins were initially described as peptides that regulate feeding behaviour, research has shown that orexins are involved in diverse functions that range from the modulation of autonomic functions to higher cognitive functions, including reward-seeking, behaviour, attention, cognition, and mood. Furthermore, disruption in orexin signalling has been shown in mood disorders that are associated with low hedonic tone or anhedonia, including depression, anxiety, attention deficit hyperactivity disorder, and addiction. Notably, projections of orexin neurons overlap circuits involved in the modulation of hedonic tone. Evidence shows that orexins may potentiate hedonic behaviours by increasing the feeling of pleasure or reward to various signalling, whereas dysregulation of orexin signalling may underlie low hedonic tone or anhedonia. Further, orexin appears to play a key role in regulating behaviours in motivationally charged situations, such as food-seeking during hunger, or drug-seeking during withdrawal. Therefore, it would be expected that dysregulation of orexin expression or signalling is associated with changes in hedonic tone. Further studies investigating this association are warranted.

Psychological status and serum uric acid levels in narcolepsy with type 1: A case-control study

BACKGROUND

The relationship between uric acid and patients with type 1 (NT1) remains unclear. UA may contribute to the development of depression. Depression is also common in NT1. Our study aimed to evaluate serum levels of UA, creatinine, and UA/Cr ratio, and examine the association of serum UA levels with psychological status in NT1 patients.

METHODS

This is a case-control study conducted on 48 patients diagnosed with NT1 and 40 healthy controls (HC). The 17-item Hamilton Depression Rating (HAMD-17) was used as screening tools for depressive symptoms for patients with NT1. Serum UA, creatinine, and UA/Cr ratio were measured. In addition, the correction of UA status and scores of depressive scales was statistically analyzed.

RESULTS

Approximately 70% of all subjects with NT1 had depression or depressive symptoms compared with the HC group, the serum UA levels and UA/Cr ratios were higher in patients with NT1 (p < 0.05). In addition, there was a negative correlation between UA levels and HAMD-17 scores in NT1 patients (r = -0.334; p = 0.020).

CONCLUSION

We found that serum UA levels were higher in patients with NT1, and the serum UA levels were negatively correlated with depressive symptom scores. Further well-designed prospective cohort studies are needed to determine the causality of the correlation and to further clarify the pathophysiological mechanisms of UA in NT1 patients.

Changes in the Orexin System in Rats Exhibiting Learned Helplessness Behaviors

Orexin-A (OX-A) and orexin-B (OX-B) are neuropeptides produced in the hypothalamus. Preclinical and clinical studies suggest that depression and anxiety are associated with the orexin system. In the current study, we used the learned helplessness (LH) animal model of depression to identify rats displaying LH behaviors (LH rats) and those that did not (No-LH rats). We compared the number of orexin-containing neurons in the hypothalamus of LH, No-LH, and control rats. Orexin peptides, orexin receptor 1 (OXR1) and 2 (OXR2) in brain areas involved in major depression and serum OX-A and corticosterone (CORT) concentrations were quantified and compared between rat groups. We found that LH and No-LH rats displayed higher serum OX-A concentrations compared with control rats. Comparison between LH and No-LH rats revealed that No-LH rats had significantly higher OX-A levels in the brain, more OX-A neurons, and more OX-A neuron activation. LH rats had more OX-B neurons and more OX-B neuron activation. Orexin peptides and receptors in the brain areas involved in major depression exhibited different patterns in LH and NoLH rats. Our findings revealed that activation of OX-A neurons could promote resilient behaviors under stressful situations and OX-A and OX-B neuropeptides exhibit dissimilar functions in LH behaviors.

The orexin/hypocretin system in neuropsychiatric disorders: Relation to signs and symptoms

Hypocretin-1 and 2 (or orexin A and B) are neuropeptides exclusively produced by a group of neurons in the lateral and dorsomedial hypothalamus that project throughout the brain. In accordance with this, the two different hypocretin receptors are also found throughout the brain. The hypocretin system is mainly involved in sleep-wake regulation, but also in reward mechanisms, food intake and metabolism, autonomic regulation including thermoregulation, and pain. The disorder most strongly linked to the hypocretin system is the primary sleep disorder narcolepsy type 1 caused by a lack of hypocretin signaling, which is most likely due to an autoimmune process targeting the hypocretin-producing neurons. However, the hypocretin system may also be affected, but to a lesser extent and less specifically, in various other neurological disorders. Examples are neurodegenerative diseases such as Alzheimer's, Huntington's and Parkinson's disease, immune-mediated disorders such as multiple sclerosis, neuromyelitis optica, and anti-Ma2 encephalitis, and genetic disorders such as type 1 diabetus mellitus and Prader-Willi Syndrome. A partial hypocretin deficiency may contribute to the sleep features of these disorders.

Natural language processing of clinical mental health notes may add predictive value to existing suicide risk models

BACKGROUND

This study evaluated whether natural language processing (NLP) of psychotherapy note text provides additional accuracy over and above currently used suicide prediction models.

METHODS

We used a cohort of Veterans Health Administration (VHA) users diagnosed with post-traumatic stress disorder (PTSD) between 2004-2013. Using a case-control design, cases (those that died by suicide during the year following diagnosis) were matched to controls (those that remained alive). After selecting conditional matches based on having shared mental health providers, we chose controls using a 5:1 nearest-neighbor propensity match based on the VHA's structured Electronic Medical Records (EMR)-based suicide prediction model. For cases, psychotherapist notes were collected from diagnosis until death. For controls, psychotherapist notes were collected from diagnosis until matched case's date of death. After ensuring similar numbers of notes, the final sample included 246 cases and 986 controls. Notes were analyzed using Sentiment Analysis and Cognition Engine, a Python-based NLP package. The output was evaluated using machine-learning algorithms. The area under the curve (AUC) was calculated to determine models' predictive accuracy.

RESULTS

NLP derived variables offered small but significant predictive improvement (AUC = 0.58) for patients that had longer treatment duration. A small sample size limited predictive accuracy.

CONCLUSIONS

Study identifies a novel method for measuring suicide risk over time and potentially categorizing patient subgroups with distinct risk sensitivities. Findings suggest leveraging NLP derived variables from psychotherapy notes offers an additional predictive value over and above the VHA's state-of-the-art structured EMR-based suicide prediction model. Replication with a larger non-PTSD specific sample is required.

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.

Sleep Disturbances and Suicidal Behavior

Sleep disturbances, particularly insomnia, nightmares, and excessive daytime sleepiness (EDS), are significant, proximal, and modifiable risk factors for suicidal ideation and behaviors (SIB) and could be targeted for preventative interventions. In this chapter, we review the evidence supporting the association of insomnia, nightmares, and EDS with SIB. We also describe these sleep disturbances in the general population, as well as their association with psychiatric disorders. A PubMed search was conducted to identify the relevant literature. Insomnia is very frequent across mental disorders, but SIB patients are particularly exposed. Specific interventions focused on insomnia are useful in contending suicidal ideation. Nightmares seem to constitute an independent risk factor for SIB, beyond insomnia, particularly in young people and when experienced frequently. The evidence regarding the association of EDS and SIB is less clear and probably explained by the reduction of health-related quality of life and comorbid depression. The mechanisms underlying the relationship between sleep disturbances and SIB as well as the role of potential confounders and future perspectives in this field are also discussed.

Suicidal ideation among nurses: Unique and cumulative effects of different subtypes of sleep problems

BACKGROUND

Nurses have high rates of sleep problems, and higher risk of suicide than the general population. However, there is no empirical evidence showing the extent to which sleep problems among nurses are related to suicidal ideation.

METHODS

Multistage stratified cluster sampling was performed to recruit nurses from tertiary hospitals in Shandong, China. Item 9 of the Patient Health Questionnaire-9 was used to assess suicidal ideation. The Pittsburgh Sleep Quality Index was used to assess different subtypes of sleep problems.

RESULTS

Overall prevalence of suicidal ideation among the sample was 10.8%. Nurses with sleep problems were at high risk for suicidal ideation (^bOR = 1.79, 95% CI = 1.20-2.65). Among different sleep problem subtypes, only "cannot breathe comfortably" was independently related to suicidal ideation. Different subtypes of sleep problems had cumulative effects on suicidal ideation: the more subtypes of sleep problems nurses experienced, the higher the likelihood of suicidal ideation.

LIMITATIONS

The cross-sectional study design prevents inferring causation, and the use of self-report measures may lead to recall bias. Other physical/mental conditions, besides depression, were not assessed. Statistical power may have been insufficient due to the small sub-sample who reported suicidal ideation. Also, the generalizability of the results is limited, as the sample only comprised nurses in tertiary hospitals.

CONCLUSIONS

Nurses experiencing sleep problems were associated with increased likelihood of suicidal ideation. It may be beneficial to incorporate sleep problems into routine screening and intervention for suicide prevention in clinical practice.

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.

A higher body mass index in Chinese inpatients with chronic schizophrenia is associated with elevated plasma orexin-A levels and fewer negative symptoms

Objective: Orexin-A is involved in numerous physiological functions, such as feeding behavior and energy balance. Yet, the associations among the orexin system, weight changes and the clinical symptoms of schizophrenia patients remain uncertain, especially in inpatients with chronic schizophrenia (CS). The purpose of this study was to investigate the relationship between the orexin-A levels, body mass index (BMI) and clinical symptoms of CS inpatients.Methods: Altogether, 324 inpatients were enrolled in our study. The clinical symptoms of all inpatients were measured using a 30-item Positive and Negative Syndrome Scale (PANSS), and then we calculated the BMI of each subject and tested the orexin-A levels by ELISA methods.Results: The orexin-A levels of the CS inpatients in the obesity group (1.24 ± 1.45 ng/ml, n = 52) were significantly higher than those in the non-overweight group (0.85 ± 1.18 ng/ml, n = 176) and the overweight group (0.97 ± 1.15 ng/ml, n = 96). Spearman's correlation analysis showed that higher BMIs were associated with higher plasma orexin-A levels and fewer negative symptoms. Furthermore, the multiple regression analysis indicated that the orexin-A level could be a contributor to BMI (F = 30.21, p < 0.001). However, there was no correlation between plasma orexin-A concentrations and clinical symptoms in our research.Conclusion: A higher plasma orexin-A level may be a factor influencing the BMI of inpatients with CS, and fewer negative symptoms seem to be correlated with higher BMI, but the causality among BMI, orexin-A and clinical symptoms of schizophrenia requires further clinical research.

Depression and suicidal thoughts in untreated and treated narcolepsy: Systematic analysis

OBJECTIVES

To assess the frequency and determinants of depressive symptoms and suicidal thoughts in adults with narcolepsy type 1 (NT1) and controls, as well as the changes after NT1 management and the risk factors of major depressive episode (MDE) and suicide risk (SR) in NT1.

METHODS

Two hundred ninety-seven patients with NT1 (age 39 ± 17 years, 172 drug-free) and 346 controls (age 38 ± 16 years) underwent a comprehensive clinical evaluation including the Beck Depression Inventory-II (BDI-II) self-questionnaire, with 1 item on suicidal thoughts. One hundred one drug-free patients with NT1 completed the BDI-II a second time during treatment. In 162 patients with NT1, the face-to-face Mini International Neuropsychiatric Interview was performed to formally diagnose current MDE and SR.

RESULTS

BDI-II total scores were higher in patients with NT1 than controls and in untreated than treated patients. Patients with moderate to severe BDI-II scores (24.9%) were less educated, were more frequently obese, and had more severe narcolepsy symptoms, more autonomic dysfunctions, and poorer quality of life. Results were unchanged in models adjusted for NT1 medication intake. Suicidal thoughts were more frequent in untreated patients than controls (22.7% vs 12.4%). Patients with suicidal thoughts were more likely to be men and to have more severe narcolepsy symptoms. After narcolepsy management, BDI-II total score and suicidal thoughts decreased. MDE was diagnosed in 29 (18.1%) and SR in 27 (16.9%) patients.

CONCLUSIONS

Depression, depressive symptoms, suicidal thoughts, and SR were frequent in patients with NT1, especially those without treatment, and were associated with NT1 severity. Depressive symptoms and suicidal thoughts improved after NT1 management.

Prevalence of Depression or Depressive Symptoms in Patients with Narcolepsy: a Systematic Review and Meta-Analysis

A meta-analysis was conducted to review the prevalence and associated moderators of depression or depressive symptoms in patients with narcolepsy. An extensive search of the literature yielded 1104 articles and abstracts, of which 31 studies were included in the meta-analysis. Meta-analysis revealed that the overall pooled prevalence of depression or depressive symptoms in patients with narcolepsy was 32% (95% Confidence Interval, 28-36%) with high between-study heterogeneity (Q = 249.77, df = 30, p < 0.001, τ² = 0.0087, I² = 88%). An analysis of 13 studies with healthy control groups indicated that narcolepsy was associated with a significantly increased risk of depression or depressive symptoms (Odds Ratio 3.48, 95% Confidence Interval 2.73-4.45; Q = 41.23, df = 12, p < 0.001, τ² = 0.0087, I² = 70.9%). The prevalence of depression or depressive symptoms in patients with narcolepsy was significantly affected by study design (Q = 5.05, p = 0.02) and recruitment setting (Q = 5.98, p = 0.01), and was marginally affected by age group (Q = 3.44, p = 0.06). The results indicate that narcolepsy patients should be closely monitored for depression and depressive symptoms and that early screening should be considered. However, these conclusions should be tempered because of high variability between studies. The estimates across studies are very inconsistent, indicating the need for larger, multicenter studies, with stringent case definitions.

Involvement of orexinergic system in psychiatric and neurodegenerative disorders: A scoping review

Orexin is a neuropeptide secreted from lateral hypothalamus and pre-frontal cortex concerned in the wakefulness and excitement. This study aimed to review the possible neurobiological effect of orexin. A diversity of search strategies was adopted and assumed which included electronic database searches of Medline and PubMed using MeSH terms, keywords, and title words during the search. Orexin plays a vital role in activation of learning, memory acquisition, and consolidation through activation of monoaminergic system, which affect cognitive flexibility and cognitive function. Orexin stimulates adrenocorticotropin and corticosteroid secretions via activation of central corticotropin-releasing hormone. Cerebrospinal fluid (CSF) and serum orexin serum levels are reduced in depression, schizophrenia, and narcolepsy. However, high orexin serum levels are revealed in drug addictions. Regarding neurodegenerative brain diseases, CSF and serum orexin serum levels are reduced Parkinson disease, Alzheimer dementia, Huntington's disease, amyotrphic lateral sclerosis, and multiple sclerosis. Orexin antagonist leads to significant reduction of sympathetic over-activity during withdrawal syndrome. As well, orexin antagonist improves sleep pattern. Orexinergic system is involved in the different psychiatric and neurological disorders; therefore, targeting of this system could be possible novel pathway in the management of these disorders. In addition, measurement of CSF and serum orexin levels might predict the relapse and withdrawal of addict patients.

Orexin A in adolescents with anxiety disorders

Objectives: The relationships between orexins and stress-related conditions have been well documented in animal studies. However, human studies confirming this relationship are limited. The aim of this study was to investigate the association between orexin-A and anxiety disorders in adolescents. Additionally, we aimed to examine the relationship between orexin-A and cortisol levels in those with anxiety disorders.Methods: A total of 56 medication-free adolescents diagnosed with any anxiety disorder, except for specific phobias, and 32 healthy controls were included in this study. Depression, state and trait anxiety levels of the participants were measured using self-report scales. Orexin-A and cortisol levels were measured by an enzyme-linked immunosorbent assay (ELISA).Results: Analysis of covariance (ANCOVA) indicated that serum orexin-A levels were significantly higher in the anxiety disorder group than in the control group while controlling for age, sex and depression levels. After controlling for age and sex, orexin-A levels were positively and negatively correlated to depression and cortisol levels, respectively. In addition, a positive correlation trend between trait anxiety and orexin-A was found.Conclusions: Orexin-A levels are higher in adolescents with anxiety disorder; however, depressive symptoms should be considered when investigating this relationship.

Reduced serum VGF levels are linked with suicide risk in Chinese Han patients with major depressive disorder

BACKGROUND

VGF (nonacronymic) is a neuropeptide that plays an important role in the pathogenesis of major depressive disorder (MDD). However, no studies have yet investigated VGF levels in patients with MDD who are at risk of suicide. The purpose of the present study was to determine whether serum VGF levels are related to suicide risk in patients with MMD.

METHODS

A total of 107 patients with MDD and 40 normal control participated in the present study. The risk of suicide was assessed using the Nurses Global Assessment of Suicide Risk (NGASR). On this basis, 60 patients were assigned to a high-risk group (NGASR≥9) and 47 were assigned to a low-risk group (NGASR< 9). The severity of depression was measured using the 17-item Hamilton Depression Rating Scale (HDRS). Levels of serum VGF were determined using a double antibody sandwich enzyme-linked immunosorbent assay.

RESULTS

Serum VGF levels in the high-risk group (883.34 ± 139.67 pg/mL) were significantly lower than in the low-risk group (1020.56 ± 131.76 pg/mL) and in the control group (1107.00 ± 155.38 pg/mL) (F = 31.90, p < 0.001). In patients with MDD, suicide risk was significantly negatively correlated with VGF levels (r = - 0.55, p = 0.001).

CONCLUSIONS

Reduced serum VGF levels are related to risk of suicide in patients with MDD, so VGF may be a biomarker of suicide risk in MDD.

Resting-state brain network topological properties and the correlation with neuropsychological assessment in adolescent narcolepsy

Study Objectives

To evaluate functional connectivity and topological properties of brain networks, and to investigate the association between brain topological properties and neuropsychiatric behaviors in adolescent narcolepsy.

Methods

Resting-state functional magnetic resonance imaging (fMRI) and neuropsychological assessment were applied in 26 adolescent narcolepsy patients and 30 healthy controls. fMRI data were analyzed in three ways: group independent component analysis and a graph theoretical method were applied to evaluate topological properties within the whole brain. Lastly, network-based statistics was utilized for group comparisons in region-to-region connectivity. The relationship between topological properties and neuropsychiatric behaviors was analyzed with correlation analyses.

Results

In addition to sleepiness, depressive symptoms and impulsivity were detected in adolescent narcolepsy. In adolescent narcolepsy, functional connectivity was decreased between regions of the limbic system and the default mode network (DMN), and increased in the visual network. Adolescent narcolepsy patients exhibited disrupted small-world network properties. Regional alterations in the caudate nucleus (CAU) and posterior cingulate gyrus were associated with subjective sleepiness and regional alterations in the CAU and inferior occipital gyrus were associated with impulsiveness. Remodeling within the salience network and the DMN was associated with sleepiness, depressive feelings, and impulsive behaviors in narcolepsy.

Conclusions

Alterations in brain connectivity and regional topological properties in narcoleptic adolescents were associated with their sleepiness, depressive feelings, and impulsive behaviors.

Orexinergic modulation of serotonin neurons in the dorsal raphe of a diurnal rodent, Arvicanthis niloticus

The hypothalamic neuropeptide, orexin (or hypocretin), is implicated in numerous physiology and behavioral functions, including affective states such as depression and anxiety. The underlying mechanisms and neural circuits through which orexin modulates affective responses remain unclear. The objective of the present study was to test the hypothesis that the serotonin (5-HT) system of the dorsal raphe nucleus (DRN) is a downstream target through which orexin potentially manifests its role in affective states. Using a diurnal rodent, the Nile grass rat (Arvicanthis niloticus), we first characterized the expression of the orexin receptors OX1R and OX2R in the DRN using in situ hybridization. The results revealed distinct distributions of OX1R and OX2R mRNAs, with OX1R predominantly expressed in the dorsal and lateral wings of the DRN that are involved in affective processes, while OX2R was mostly found in the ventral DRN that is more involved in sensory-motor function. We next examined how the orexin-OX1R pathway regulates 5-HT in the DRN and some of its projection sites using a selective OX1R antagonist SB-334867 (10 mg/kg, i.p.). A single injection of SB-334867 decreased 5-HT-ir fibers within the anterior cingulate cortex (aCgC); five once-daily administrations of SB-334867 decreased 5-HT-ir not only in the aCgC but also in the DRN, oval bed nucleus of the stria terminalis (ovBNST), nucleus accumbens shell (NAcSh), and periaqueductal gray (PAG). HPLC analysis revealed that five once-daily administrations of SB-334867 did not affect 5-HT turnover to any of the five sites, although it increased the levels of both 5-HT and 5-HIAA in the NAcSh. These results together suggest that orexinergic modulation of DRN 5-HT neurons via OX1Rs may be one pathway through which orexin regulates mood and anxiety, as well as perhaps other neurobiological processes.

Evaluating the role of orexins in the pathophysiology and treatment of depression: A comprehensive review

Orexins are neuropeptides that are postulated to play a central role in the regulation of the sleep-wake cycle, appetite, affect, and reward circuitry. The objectives of the current review are to comprehensively evaluate (1) the potential role of orexins in the pathophysiology of major depressive disorders (MDD) and (2) the orexin system as a novel target in the treatment of MDD. Dysfunction of the sleep-wake cycle is observed as a central feature of MDD pathophysiology. Orexin system disturbances produce sleep-wake dysfunction, as observed in MDD. Orexin antagonists have been shown to treat insomnia effectively without disrupting normal sleep architecture in both preclinical (e.g., animal models) and clinical studies. Orexin antagonists are generally safe, well-tolerated, and associated with an acceptable long-term adverse effect profile with relatively low propensity for tolerance or dependence. Orexin antagonists have also been shown to possess antidepressant-like properties in some animal models of MDD. Extant evidence indicates that orexin-modulating treatments exert pleiotropic effects on multiple neural systems implicated in the phenomenology of mood disorders and suggests orexins as a promising target for investigation and intervention in mood disorders. To date, no human clinical trials evaluating the antidepressant effects of orexin antagonists in MDD have been completed. Given the promising results from preclinical studies, clinical trials are merited to evaluate the antidepressant effects of orexin antagonists in MDD.

Light as a modulator of emotion and cognition: Lessons learned from studying a diurnal rodent

Light profoundly affects the behavior and physiology of almost all animals, including humans. One such effect in humans is that the level of illumination during the day positively contributes to affective well-being and cognitive function. However, the neural mechanisms underlying the effects of daytime light intensity on affect and cognition are poorly understood. One barrier for progress in this area is that almost all laboratory animal models studied are nocturnal. There are substantial differences in how light affects nocturnal and diurnal species, e.g., light induces sleep in nocturnal mammals but wakefulness in diurnal ones, like humans. Therefore, the mechanisms through which light modulates affect and cognition must differ between the chronotypes. To further understand the neural pathways mediating how ambient light modulates affect and cognition, our recent work has developed a diurnal rodent model, the Nile grass rat (Arvicanthis niloticus), in which daytime light intensity is chronically manipulated in grass rats housed under the same 12:12 hour light/dark cycle. This simulates lighting conditions during summer-like bright sunny days vs. winter-like dim cloudy days. Our work has revealed that chronic dim daylight intensity results in higher depression- and anxiety-like behaviors, as well as impaired spatial learning and memory. Furthermore, we have found that hypothalamic orexin is a mediator of these effects. A better understanding of how changes in daytime light intensity impinge upon the neural substrates involved in affect and cognition will lead to novel preventive and therapeutic strategies for seasonal affective disorder, as well as for non-seasonal emotional or cognitive impairments associated with light deficiency.

Reduced plasma orexin-A levels in patients with bipolar disorder

PURPOSE

Orexins are hypothalamic neuropeptides involved in the regulation of sleep, appetite and arousal. An altered orexin system has been implicated in the pathophysiology of psychiatric disorders. This study aimed to examine whether plasma orexin-A levels differ in patients with schizophrenia, major depressive disorder (MDD), or bipolar disorder (BD) compared to in healthy controls. We also examined the possible correlations between plasma orexin-A levels and clinical variables.

PATIENTS AND METHODS

All participants were Japanese. The sample consisted of 80 patients with schizophrenia (42 women, 52.5%; mean age 36.8 years), 80 patients with MDD (43 women, 53.8%; 43.7 years), and 40 patients with BD (24 women, 60%; 41.1 years), as well as 80 healthy controls (48 women, 60%; 47.0 years). Plasma orexin-A levels were quantified by an enzyme-linked immunosorbent assay.

RESULTS

Mean orexin-A levels were significantly different across the four diagnostic groups (F=4.09; df=3; p=0.007, η² =0.06). In particular, the patients with BD showed significantly lower orexin-A levels than did the controls. When the median value of the control group (109.8 pg/ml) was set as a cut-off value, subjects whose orexin-A levels were below the cut-off were more common in all psychiatric groups (schizophrenia: 73.8%, x² =9.56, df=1, p=0.003, OR=2.81, 95% CI: 1.45 to 5.45, d=0.57; MDD: 78.5%, x² =14.02, df=1, p<0.001, OR=3.65, 95% CI: 1.82 to 7.29, d=0.72; BD: 87.5%, x² =16.0, df=1, p<0.001, OR=7.00, 95% CI: 2.49 to 19.70, d=1.07). We found no association between plasma orexin-A levels and any clinical symptoms, depression severity, or medication doses.

CONCLUSION

Our results suggest that plasma orexin-A levels are reduced in patients with BD.

Changes In Plasma NPY, IL-1β And Hypocretin In People Who Died By Suicide

PURPOSE

There is growing evidence showing that inflammatory cytokines and neuropeptides may be involved in the pathophysiology of suicidal behavior. However, studies have yielded contradictory data, and no biological markers that help predict suicide have been identified. This study aimed to identify biological patterns, such as NPY, IL-1β and hypocretin plasma levels, in people who died by suicide.

PATIENTS AND METHODS

Twenty-two people who died by suicide compared with 22 controls matched for age and sex were studied. In suicide and control subjects, we estimated the levels of NPY, IL-1β and hypocretin in plasma using enzyme-linked immunosorbent assay. The data are presented as the median (25th-75th percentile).

RESULTS

We found (1) a significant elevation in plasma NPY levels in suicide subjects versus control subjects (suicide: 11.38 (9.380-16.55); controls: 8.95 (7.590-10.93); P=0.013), and plasma NPY concentrations were approximately 62% higher in suicide subjects than those in control subjects; (2) a significant decrease in plasma IL-1β concentrations between suicide and control subjects (suicide: 121.1 (82.97-143.0); controls: 425.9 (233.1-835.3); P<0.001) as well as a decrease in IL-1β concentrations by almost 80%; and (3) no significant difference in plasma hypocretin levels between suicide and control subjects (suicide: 16.62 (13.62-25.77); controls: 21.63 (14.97-29.72); P=0.356).

CONCLUSION

Our results suggest that plasma NPY and IL-1β were related with suicide behavior rather than to suicide causes or suicide method. Specific combinations of plasma biomarkers may discriminate between types of suicidal behaviors and indicate increased risk for future suicide attempts.

Orexin/hypocretin receptor modulation of anxiolytic and antidepressive responses during social stress and decision-making: Potential for therapy

Hypothalmic orexin/hypocretin (Orx) neurons in the lateral and dorsomedial perifornical region (LH-DMH/PeF) innervate broadly throughout the brain, and receive similar inputs. This wide distribution, as well as two Orx peptides (Orx_A and Orx_B) and two Orx receptors (Orx₁ and Orx₂) allow for functionally related but distinctive behavioral outcomes, that include arousal, sleep-wake regulation, food seeking, metabolism, feeding, reward, addiction, and learning. These are all motivational functions, and tie the orexin systems to anxiety and depression as well. We present evidence, that for affective behavior, Orx₁ and Orx₂ receptors appear to have opposing functions. The majority of research on anxiety- and depression-related outcomes has focused on Orx₁ receptors, which appear to have primarily anxiogenic and pro-depressive actions. Although there is significant research suggesting contrary findings, the primary potential for pharmacotherapies linked to the Orx₁ receptor is via antagonists to block anxious and depressive behavior. Dual orexin receptor antagonists have been approved for treatment of sleep disorders, and are likely candidates for adaptation for affect disorder treatments. However, we present evidence here that demonstrates the Orx₂ receptors are anxiolytic and antidepressive. Using a new experimental pre-clinical model of anxious and depressive behavior stimulated by social stress and decision-making that produces two stable behavioral phenotypes, Escape/Resilient and Stay/Susceptible, we tested the effects of intracerebroventricular injections of Orx₂ agonist and antagonist drugs. Over ten behavioral measures, we have demonstrated that Orx₂ agonists promote resilience, as well as anxiolytic and antidepressive behavior. In contrast, Orx₂ antagonists or knockdown kindle anxious and pro-depressive behavior plus increase susceptibility. The results suggest that the Orx₂ receptor may be a useful target for pharmacotherapies to treat anxiety and depression.

The Discovery of Suvorexant, the First Orexin Receptor Drug for Insomnia

Historically, pharmacological therapies have used mechanisms such as γ-aminobutyric acid A (GABA_A) receptor potentiation to drive sleep through broad suppression of central nervous system activity. With the discovery of orexin signaling loss as the etiology underlying narcolepsy, a disorder associated with hypersomnolence, orexin antagonism emerged as an alternative approach to attenuate orexin-induced wakefulness more selectively. Dual orexin receptor antagonists (DORAs) block the activity of orexin 1 and 2 receptors to both reduce the threshold to transition into sleep and attenuate orexin-mediated arousal. Among DORAs evaluated clinically, suvorexant has pharmacokinetic properties engineered for a plasma half-life appropriate for rapid sleep onset and maintenance at low to moderate doses. Unlike GABA_A receptor modulators, DORAs promote both non-rapid eye movement (NREM) and REM sleep, do not disrupt sleep stage-specific quantitative electroencephalogram spectral profiles, and allow somnolence indistinct from normal sleep. The preservation of cognitive performance and the ability to arouse to salient stimuli after DORA administration suggest further advantages over historical therapies.

Comorbidity of narcolepsy and depressive disorders: a nationwide population-based study in Taiwan

OBJECTIVE

Narcolepsy is a chronic sleep disorder that is likely to have neuropsychiatric comorbidities. Depression is a serious mood disorder that affects individuals' daily activities and functions. The current study aimed to investigate the relationship between narcolepsy and depressive disorders.

METHODS

The study consisted of patients diagnosed with narcolepsy between January 2002, and December 2011 (n = 258), and age-matched and gender-matched controls (n = 2580) from Taiwan's National Health Insurance database. Both the patients and the controls were monitored through December 31, 2011, to identify the occurrence of a depressive disorder. A multivariate logistic regression model was used to assess the narcolepsy's potential influence on the comorbidity of a depressive disorder.

RESULTS

During the study period, 32.7%, 24.8%, and 10.9% of the narcoleptic patients were comorbid with any depressive disorder, dysthymic disorder, and major depressive disorder, respectively. When compared to the control subjects, the patients with narcolepsy were at greater risks of having any depressive disorder (aOR 6.77; 95% CI 4.90-9.37), dysthymic disorder (aOR 6.62; 95% CI 4.61-9.57), and major depressive disorder (aOR 6.83; 95% CI 4.06-11.48). Of the narcoleptic patients that were comorbid with depression, >50% had been diagnosed with depression prior to being diagnosed with narcolepsy.

CONCLUSIONS

This nationwide data study revealed that narcolepsy and depression commonly co-occurred. Since some symptoms of narcolepsy overlapped with those of depressive disorders, the findings serve as a reminder that clinicians must pay attention to the comorbidity of narcolepsy and depression.

Sexually Dimorphic Changes of Hypocretin (Orexin) in Depression

Background

Neurophysiological and behavioral processes regulated by hypocretin (orexin) are severely affected in depression. However, alterations in hypocretin have so far not been studied in the human brain. We explored the hypocretin system changes in the hypothalamus and cortex in depression from male and female subjects.

Methods

We quantified the differences between depression patients and well-matched controls, in terms of hypothalamic hypocretin-1 immunoreactivity (ir) and hypocretin receptors (Hcrtr-receptors)-mRNA in the anterior cingulate cortex (ACC) and dorsolateral prefrontal cortex. In addition, we determined the alterations in the hypocretin system in a frequently used model for depression, the chronic unpredictable mild stress (CUMS) rat.

Results

i) Compared to control subjects, the amount of hypocretin-immunoreactivity (ir) was significantly increased in female but not in male depression patients; ii) hypothalamic hypocretin-ir showed a clear diurnal fluctuation, which was absent in depression; iii) male depressive patients who had committed suicide showed significantly increased ACC Hcrt-receptor-2-mRNA expression compared to male controls; and iv) female but not male CUMS rats showed a highly significant positive correlation between the mRNA levels of corticotropin-releasing hormone and prepro-hypocretin in the hypothalamus, and a significantly increased Hcrt-receptor-1-mRNA expression in the frontal cortex compared to female control rats.

Conclusions

The clear sex-related change found in the hypothalamic hypocretin-1-ir in depression should be taken into account in the development of hypocretin-targeted therapeutic strategies.

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Hypocretin (orexin) changes were studied in human postmortem brain in depression.

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A clear sex-related change was found in the hypothalamic hypocretin-1-immunoreactivity in depression.

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A rat depression model did not reflect the changes in the hypocretin system in the human brain in depression.

The stress systems of depressed patients are put into a higher gear by genetic and developmental factors. Over-reaction of these systems to stressful environmental situations makes people vulnerable to depression and suicide. This is the first postmortem study on changes in a relatively novel stress system in depression, consisting of the hypothalamic hypocretin neurons and hypocretin receptors in the prefrontal cortex. A clear sex-related change was found in the hypothalamic hypocretin-1-immunoreactivity in depression. Evaluation of the hypocretin system in a frequently used depression animal model, i.e. chronic unpredictable mild stress rats, did not replicate changes found in the hypocretin systems in the human brain in depression.

Exercise Influence on Hippocampal Function: Possible Involvement of Orexin-A

In the present article, we provide a brief review of current knowledge regarding the effects induced by physical exercise on hippocampus. Research involving animals and humans supports the view that physical exercise, enhancing hippocampal neurogenesis and function, improves cognition, and regulates mood. These beneficial effects depend on the contribute of more factors including the enhancement of vascularization and upregulation of growth factors. Among these, the BDNF seems to play a significant role. Another putative factor that might contribute to beneficial effects of exercise is the orexin-A. In support of this hypothesis there are the following observations: (1) orexin-A enhances hippocampal neurogenesis and function and (2) the levels of orexin-A increase with physical exercise. The beneficial effects of exercise may represent an important resource to hinder the cognitive decline associated with the aging-related hippocampal deterioration and ameliorate depressive symptoms.

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

Orexins (hypocretins) are critically involved in coordinating appropriate physiological and behavioral responses to aversive and threatening stimuli. Acute stressors engage orexin neurons via direct projections from stress-sensitive brain regions. Orexin neurons, in turn, facilitate adaptive behavior via reciprocal connections as well as via direct projections to the hypophysiotropic neurons that coordinate the hypothalamic-pituitary-adrenal (HPA) axis response to stress. Consequently, hyperactivity of the orexin system is associated with increased motivated arousal and anxiety, and is emerging as a key feature of panic disorder. Accordingly, there has been significant interest in the therapeutic potential of pharmacological agents that antagonize orexin signaling at their receptors for the treatment of anxiety disorders. In contrast, disorders characterized by inappropriately low levels of motivated arousal, such as depression, generally appear to be associated with hypoactivity of the orexin system. This includes narcolepsy with cataplexy, a disorder characterized by the progressive loss of orexin neurons and increased rates of moderate/severe depression symptomology. Here, we provide a comprehensive overview of both clinical and preclinical evidence highlighting the role of orexin signaling in stress reactivity, as well as how perturbations to this system can result in dysregulated behavioral phenotypes.

Elevated plasma orexin A levels in a subgroup of patients with schizophrenia associated with fewer negative and disorganized symptoms

BACKGROUND

Orexin A and B, a pair of hypothalamic neuropeptides also named hypocretin 1 and 2, play a role in the regulation of arousal, appetite, reward, attention, and cognition. Animal studies showed that antipsychotics can activate orexin neurons in a manner correlated with their weight gain liability. However, little is known about the role of orexin in patients with schizophrenia. This study aimed to investigate the correlation of plasma orexin level with clinical symptom profile, neurocognitive functioning and weight gain liability of the antipsychotics taken in patients with schizophrenia.

METHODS

We measured plasma levels of orexin A in 127 patients with schizophrenia and 34 healthy controls by radioimmunoassay. In patients, we assessed clinical symptoms on the Positive and Negative Syndrome Scale and executive function by the Wisconsin Card Sorting test (WCST), and examined their associations with plasma orexin A level.

RESULTS

Patients with schizophrenia had a significantly higher mean orexin A level than healthy controls (60.7±37.9 vs. 38.8±15.5pg/ml). Patients were divided into two subgroups based on their orexin A levels that were distributed in two clusters divided by 80pg/ml. Patients in the high-orexin subgroup had significantly fewer negative and disorganized symptoms, and tended to have fewer perseverative errors, more failure to maintain set yet comparable category achieved on the WCST than the normal-orexin subgroup. There was no significant difference in orexin A levels among patients taking antipsychotics with different weight gain liabilities.

CONCLUSION

Higher level of orexin A seems to be related to favorable clinical symptom profiles of schizophrenia, but the causal relationship needs further clarification.

The hypocretin/orexin system: an increasingly important role in neuropsychiatry

Hypocretins, also named as orexins, are excitatory neuropeptides secreted by neurons specifically located in lateral hypothalamus and perifornical areas. Orexinergic fibers are extensively distributed in various brain regions and involved in a number of physiological functions, such as arousal, cognition, stress, appetite, and metabolism. Arousal is the most important function of orexin system as dysfunction of orexin signaling leads to narcolepsy. In addition to narcolepsy, orexin dysfunction is associated with serious neural disorders, including addiction, depression, and anxiety. However, some results linking orexin with these disorders are still contradictory, which may result from differences of detection methods or the precision of tools used in measurements; strategies targeted to orexin system (e.g., antagonists to orexin receptors, gene delivery, and cell transplantation) are promising new tools for treatment of neuropsychiatric disorders, though studies are still in a stage of preclinical or clinical research.

Attenuated orexinergic signaling underlies depression-like responses induced by daytime light deficiency

Light has profound effects on mood, as exemplified by seasonal affective disorder (SAD) and the beneficial effects of bright light therapy. However, the underlying neural pathways through which light regulates mood are not well understood. Our previous work has developed the diurnal grass rat, Arvicanthis niloticus, as an animal model of SAD (Leach et al., 2013a,b). By utilizing a 12:12-h dim light:dark (DLD) paradigm that simulates the lower light intensity of winter, we showed that the animals housed in DLD exhibited increased depression-like behaviors in the forced swim test (FST) and sweet solution preference (SSP) compared to animals housed in bright light during the day (BLD). The objective of the present study was to test the hypothesis that light affects mood by acting on the brain orexinergic system in the diurnal grass rat model of SAD. First, orexin A immunoreactivity (OXA-ir) was examined in DLD and BLD grass rats. Results revealed a reduction in the number of OXA-ir neurons in the hypothalamus and attenuated OXA-ir fiber density in the dorsal raphe nucleus of animals in the DLD compared to those in the BLD group. Then, the animals in BLD were treated systemically with SB-334867, a selective orexin 1 receptor (OX1R) antagonist, which led to a depressive phenotype characterized by increased immobility in the FST and a decrease in SSP compared to vehicle-treated controls. Results suggest that attenuated orexinergic signaling is associated with increased depression-like behaviors in grass rats, and support the hypothesis that the orexinergic system mediates the effects of light on mood.

Orexin antagonists for neuropsychiatric disease: progress and potential pitfalls

The tight regulation of sleep/wake states is critical for mental and physiological wellbeing. For example, dysregulation of sleep/wake systems predisposes individuals to metabolic disorders such as obesity and psychiatric problems, including depression. Contributing to this understanding, the last decade has seen significant advances in our appreciation of the complex interactions between brain systems that control the transition between sleep and wake states. Pivotal to our increased understanding of this pathway was the description of a group of neurons in the lateral hypothalamus (LH) that express the neuropeptides orexin A and B (hypocretin, Hcrt-1 and Hcrt-2). Orexin neurons were quickly placed at center stage with the demonstration that loss of normal orexin function is associated with the development of narcolepsy—a condition in which sufferers fail to maintain normal levels of daytime wakefulness. Since these initial seminal findings, much progress has been made in our understanding of the physiology and function of the orexin system. For example, the orexin system has been identified as a key modulator of autonomic and neuroendocrine function, arousal, reward and attention. Notably, studies in animals suggest that dysregulation of orexin function is associated with neuropsychiatric states such as addiction and mood disorders including depression and anxiety. This review discusses the progress associated with therapeutic attempts to restore orexin system function and treat neuropsychiatric conditions such as addiction, depression and anxiety. We also highlight potential pitfalls and challenges associated with targeting this system to treat these neuropsychiatric states.

The hypocretin system and psychiatric disorders

The hypocretin system is constituted by a small group of hypothalamic neurons with widespread connections within the entire central nervous system producing two neuropeptides involved in several key physiological functions such as the regulation of sleep and wakefulness, motor control, autonomic functions, metabolism, feeding behavior, and reward. Narcolepsy with cataplexy is a neurological disorder regarded as a disease model for the selective hypocretin system damage, and also shares several psychopatological traits and comorbidities with psychiatric disorders. We reviewed the available literature on the involvement of the hypocretin system in psychiatric nosography. Different evidences such as cerebrospinal hypocretin-1 levels, genetic polymorphisms of the neuropeptides or their receptors, response to treatments, clinical, experimental and functional data directly or indirectly linked the hypocretin system to schizophrenia, mood, anxiety and eating disorders, as well as to addiction. Future genetic and pharmacological studies will disentangle the hypocretin system role in the field of psychiatry.

The role of neuropeptides in suicidal behavior: a systematic review

There is a growing evidence that neuropeptides may be involved in the pathophysiology of suicidal behavior. A critical review of the literature was conducted to investigate the association between neuropeptides and suicidal behavior. Only articles from peer-reviewed journals were selected for the inclusion in the present review. Twenty-six articles were assessed for eligibility but only 22 studies were included. Most studies have documented an association between suicidality and some neuropeptides such as corticotropin-releasing factor (CRF), VGF, cholecystokinin, substance P, and neuropeptide Y (NPY), which have been demonstrated to act as key neuromodulators of emotional processing. Significant differences in neuropeptides levels have been found in those who have attempted or completed suicide compared with healthy controls or those dying from other causes. Despite cross-sectional associations between neuropeptides levels and suicidal behavior, causality may not be inferred. The implications of the mentioned studies were discussed in this review paper.

Role of orexin in the pathophysiology of depression: potential for pharmacological intervention

Depression is a devastating mental disorder with an increasing impact throughout the world, whereas the efficacy of currently available pharmacological treatment is still limited. Growing evidence from preclinical and clinical studies suggests that orexins (neuropeptides that are also known as hypocretins) and their receptors are involved in the physiopathology of depression. Indeed, the orexinergic system regulates functions that are disturbed in depressive states such as sleep, reward system, feeding behavior, the stress response and monoaminergic neurotransmission. Nevertheless, the precise role of orexins in behavioral and neurophysiological impairments observed in depression is still unclear. Both hypoactivity and hyperactivity of orexin signaling pathways have been found to be associated with depression. These discrepancies in the literature prompted the necessity for additional investigations, as the orexinergic system appears to be a promising target to treat the symptoms of depression. This assumption is underlined by recent data suggesting that pharmacological blockade of orexin receptors induces a robust antidepressant-like effect in an animal model of depression. Further preclinical and clinical studies are needed to progress the overall understanding of the orexinergic alterations in depression, which will eventually translate preliminary observations into real therapeutic potential. The aim of this paper is to provide an overview of human and animal research dedicated to the study of the specific involvement of orexins in depression, and to propose a framework in which disturbances of the orexinergic system are regarded as an integral component of the etiology of depression.