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Ouaidat S, Amaral IM, Monteiro DG, Harati H, Hofer A, El Rawas R. Orexins/Hypocretins: Gatekeepers of Social Interaction and Motivation. Int J Mol Sci 2024; 25:2609. [PMID: 38473854 DOI: 10.3390/ijms25052609] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2024] [Revised: 02/12/2024] [Accepted: 02/20/2024] [Indexed: 03/14/2024] Open
Abstract
Ever since the discovery of the brain's orexin/hypocretin system, most research was directed toward unveiling its contribution to the normal functioning of individuals. The investigation of reward-seeking behaviors then gained a lot of attention once the distribution of orexinergic neurons was revealed. Here, we discuss findings on the involvement of orexins in social interaction, a natural reward type. While some studies have succeeded in defining the relationship between orexin and social interaction, the controversy regarding its nature (direct or inverse relation) raises questions about what aspects have been overlooked until now. Upon examining the literature, we identified a research gap concerning conditions influencing the impact of orexins on social behavior expression. In this review, we introduce a number of factors (e.g., stress, orexin's source) that must be considered while studying the role of orexins in social interaction. Furthermore, we refer to published research to investigate the stage at which orexins affect social interaction and we highlight the nucleus accumbens (NAc) shell's role in social interaction and other rewarding behaviors. Finally, the underlying orexin molecular pathway influencing social motivation in particular illnesses is proposed. We conclude that orexin's impact on social interaction is multifactorial and depends on specific conditions available at a time.
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Affiliation(s)
- Sara Ouaidat
- Division of Psychiatry I, Department of Psychiatry, Psychotherapy, Psychosomatics and Medical Psychology, Medical University Innsbruck, 6020 Innsbruck, Austria
- Neuroscience Research Center, Faculty of Medical Sciences, Lebanese University, Beirut P.O. Box 1533, Lebanon
| | - Inês M Amaral
- Division of Psychiatry I, Department of Psychiatry, Psychotherapy, Psychosomatics and Medical Psychology, Medical University Innsbruck, 6020 Innsbruck, Austria
| | - Diogo G Monteiro
- Division of Psychiatry I, Department of Psychiatry, Psychotherapy, Psychosomatics and Medical Psychology, Medical University Innsbruck, 6020 Innsbruck, Austria
| | - Hayat Harati
- Neuroscience Research Center, Faculty of Medical Sciences, Lebanese University, Beirut P.O. Box 1533, Lebanon
| | - Alex Hofer
- Division of Psychiatry I, Department of Psychiatry, Psychotherapy, Psychosomatics and Medical Psychology, Medical University Innsbruck, 6020 Innsbruck, Austria
| | - Rana El Rawas
- Division of Psychiatry I, Department of Psychiatry, Psychotherapy, Psychosomatics and Medical Psychology, Medical University Innsbruck, 6020 Innsbruck, Austria
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Grafe LA, Geng E, Corbett B, Urban K, Bhatnagar S. Sex- and Stress-Dependent Effects on Dendritic Morphology and Spine Densities in Putative Orexin Neurons. Neuroscience 2019; 418:266-278. [PMID: 31442567 DOI: 10.1016/j.neuroscience.2019.08.026] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2019] [Revised: 08/11/2019] [Accepted: 08/13/2019] [Indexed: 01/23/2023]
Abstract
We recently found that non-stressed female rats have higher basal prepro-orexin expression and activation of orexinergic neurons compared to non-stressed males, which lead to impaired habituation to repeated restraint stress at the behavioral, neural, and endocrine level. Here, we extended our study of sex differences in the orexin system by examining spine densities and dendritic morphology in putative orexin neurons in adult male and female rats that were exposed to 5 consecutive days of 30-min restraint. Analysis of spine distribution and density indicated that putative orexinergic neurons in control non-stressed females had significantly more dendritic spines than those in control males, and the majority of these were mushroom spines. This morphological finding may suggest more excitatory input onto orexin neurons in female rats. As orexin neurons are known to promote the hypothalamic-pituitary-adrenal response, this morphological change in orexin neurons could underlie the impaired habituation to repeated stress in female rats. Dendritic complexity did not differ between non-stressed males and females, however repeated restraint stress decreased total dendritic length, nodes, and branching primarily in males. Thus, reduced dendritic complexity of putative orexinergic neurons is observed in males but not in females after 5days of repeated restraint stress. This morphological change might be reflective of decreased orexin system function, which may allow males to habituate more fully to repeated restraint than females. These results extend our understanding of the role of orexin neurons in regulating habituation and demonstrate changes in putative orexin cell morphology and spines that may underlie sex differences in habituation.
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Affiliation(s)
- Laura A Grafe
- Department of Psychology, Bryn Mawr College, Bryn Mawr, PA 19010, USA
| | - Eric Geng
- Department of Anesthesiology and Critical Care, Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA
| | - Brian Corbett
- Department of Anesthesiology and Critical Care, Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA
| | - Kimberly Urban
- Department of Anesthesiology and Critical Care, Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA
| | - Seema Bhatnagar
- Department of Anesthesiology and Critical Care, Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA; University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, USA.
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Shariq AS, Rosenblat JD, Alageel A, Mansur RB, Rong C, Ho RC, Ragguett RM, Pan Z, Brietzke E, McIntyre RS. Evaluating the role of orexins in the pathophysiology and treatment of depression: A comprehensive review. Prog Neuropsychopharmacol Biol Psychiatry 2019; 92:1-7. [PMID: 30576764 DOI: 10.1016/j.pnpbp.2018.12.008] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/25/2018] [Revised: 12/14/2018] [Accepted: 12/17/2018] [Indexed: 10/27/2022]
Abstract
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.
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Affiliation(s)
- Aisha S Shariq
- Mood Disorders Psychopharmacology Unit, University Health Network, Toronto, ON M5T 2S8, Canada; Department of Psychiatry, Texas Tech University Health Science Center, Paul L. Foster SOM, El Paso, TX 79905, USA
| | - Joshua D Rosenblat
- Mood Disorders Psychopharmacology Unit, University Health Network, Toronto, ON M5T 2S8, Canada; Department of Psychiatry, University of Toronto, Toronto, ON M5S 1A1, Canada
| | - Asem Alageel
- Mood Disorders Psychopharmacology Unit, University Health Network, Toronto, ON M5T 2S8, Canada; Department of Psychiatry, College of Medicine, Imam University, Riyadh, Saudi Arabia
| | - Rodrigo B Mansur
- Mood Disorders Psychopharmacology Unit, University Health Network, Toronto, ON M5T 2S8, Canada; Department of Psychiatry, University of Toronto, Toronto, ON M5S 1A1, Canada
| | - Carola Rong
- Mood Disorders Psychopharmacology Unit, University Health Network, Toronto, ON M5T 2S8, Canada
| | - Roger C Ho
- National University of Singapore, 119077, Singapore; National University of Hong Kong, 999077, Hong Kong
| | - Renee-Marie Ragguett
- Mood Disorders Psychopharmacology Unit, University Health Network, Toronto, ON M5T 2S8, Canada
| | - Zihang Pan
- Mood Disorders Psychopharmacology Unit, University Health Network, Toronto, ON M5T 2S8, Canada; Institute of Medical Science, University of Toronto, Toronto, ON M5S 1A1, Canada
| | - Elisa Brietzke
- Mood Disorders Psychopharmacology Unit, University Health Network, Toronto, ON M5T 2S8, Canada; Research Group in Molecular and Behavioral Neuroscience of Bipolar Disorder, Department of Psychiatry, Universidade Federal de São Paulo (UNIFESP), São Paulo 14021-001, Brazil
| | - Roger S McIntyre
- Mood Disorders Psychopharmacology Unit, University Health Network, Toronto, ON M5T 2S8, Canada; Department of Psychiatry, University of Toronto, Toronto, ON M5S 1A1, Canada; Department of Pharmacology, University of Toronto, Toronto, ON M5S 1A1, Canada; Brain and Cognition Discovery Foundation (BCDF), Toronto, ON M5T 2S8, Canada.
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Abstract
The neuropeptides orexins are important in regulating the neurobiological systems that respond to stressful stimuli. Furthermore, orexins are known to play a role many of the phenotypes associated with stress-related mental illness such as changes in cognition, sleep-wake states, and appetite. Interestingly, orexins are altered in stress-related psychiatric disorders such as Major Depressive Disorder and Anxiety Disorders. Thus, orexins may be a potential target for treatment of these disorders. In this review, we will focus on what is known about the role of orexins in acute and repeated stress, in stress-induced phenotypes relevant to psychiatric illness in preclinical models, and in stress-related psychiatric illness in humans. We will also briefly discuss how orexins may contribute to sex differences in the stress response and subsequent phenotypes relevant to mental health, as many stress-related psychiatric disorders are twice as prevalent in women.
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Orexin 2 receptor stimulation enhances resilience, while orexin 2 inhibition promotes susceptibility, to social stress, anxiety and depression. Neuropharmacology 2018; 143:79-94. [PMID: 30240784 DOI: 10.1016/j.neuropharm.2018.09.016] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2018] [Revised: 08/28/2018] [Accepted: 09/11/2018] [Indexed: 02/08/2023]
Abstract
Knockdown of orexin/hypocretin 2 receptor (Orx2) in the basolateral amygdala (BLA) affects anxious and depressive behavior. We use a new behavioral paradigm, the Stress Alternatives Model (SAM), designed to improve translational impact. The SAM induces social stress in adult male mice by aggression from larger mice, allowing for adaptive decision-making regarding escape. In this model, mice remain (Stay) in the oval SAM arena or escape from social aggression (Escape) via routes only large enough for the smaller mouse. We hypothesized intracerebroventricular (icv) stimulation of Orx2 receptors would be anxiolytic and antidepressive in SAM-related social behavior and the Social Interaction/Preference (SIP) test. Conversely, we predicted that icv antagonism of Orx2 receptors would promote anxious and depressive behavior in these same tests. Anxious behaviors such as freezing (both cued and conflict) and startle are exhibited more often in Stay compared with Escape phenotype mice. Time spent attentive to the escape route is more frequent in Escape mice. In Stay mice, stimulation of Orx2 receptors reduces fear conditioning, conflict freezing and startle, and promotes greater attention to the escape hole. This anxiolysis was accompanied by activation of a cluster of inhibitory neurons in the amygdala. A small percentage of those Stay mice also begin escaping; whereas Escape is reversed by the Orx2 antagonist. Escape mice were also Resilient, and Stay mice Susceptible to stress (SIP), with both conditions reversed by Orx2 antagonism or stimulation respectively. Together, these results suggest that the Orx2 receptor may be a useful potential target for anxiolytic or antidepressive therapeutics.
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Grafe LA, Bhatnagar S. The contribution of orexins to sex differences in the stress response. Brain Res 2018; 1731:145893. [PMID: 30081036 DOI: 10.1016/j.brainres.2018.07.026] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2018] [Revised: 06/22/2018] [Accepted: 07/12/2018] [Indexed: 02/07/2023]
Abstract
Women are twice as likely as men to suffer from stress-related psychiatric disorders, such as post-traumatic stress disorder (PTSD) and Major Depressive Disorder (MDD), however, the biological basis of these sex differences is not fully understood. Interestingly, orexins are known to be dysregulated in these disorders. This review first discusses the important role of orexins regulating the response to stress. Next, we review the evidence for sex differences in the orexin system, in which the majority of both preclinical and clinical studies have reported higher orexin system expression in females. Finally, we discuss the functional consequences of these sex differences in orexin expression. Most importantly, the preclinical literature reveals that higher orexin system activity in females contributes to exaggerated neuroendocrine and behavioral responses to stress. In sum, the available data suggests that orexins may be important in the etiology of stress-related psychiatric disorders that present differently in men and women. Thus, targeting orexins could potentially ameliorate many phenotypes of stress-related illness in a sex-specific way.
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Affiliation(s)
- Laura A Grafe
- Department of Anesthesiology and Critical Care, Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA
| | - Seema Bhatnagar
- Department of Anesthesiology and Critical Care, Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA; The University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, USA.
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Grafe LA, Eacret D, Dobkin J, Bhatnagar S. Reduced Orexin System Function Contributes to Resilience to Repeated Social Stress. eNeuro 2018; 5:ENEURO.0273-17.2018. [PMID: 29662948 PMCID: PMC5900465 DOI: 10.1523/eneuro.0273-17.2018] [Citation(s) in RCA: 50] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2017] [Revised: 01/31/2018] [Accepted: 02/05/2018] [Indexed: 12/12/2022] Open
Abstract
Exposure to stress increases the risk of developing affective disorders such as depression and post-traumatic stress disorder (PTSD). However, these disorders occur in only a subset of individuals, those that are more vulnerable to the effects of stress, whereas others remain resilient. The coping style adopted to deal with the stressor, either passive or active coping, is related to vulnerability or resilience, respectively. Important neural substrates that mediate responses to a stressor are the orexins. These neuropeptides are altered in the cerebrospinal fluid of patients with stress-related illnesses such as depression and PTSD. The present experiments used a rodent social defeat model that generates actively coping rats and passively coping rats, which we have previously shown exhibit resilient and vulnerable profiles, respectively, to examine if orexins play a role in these stress-induced phenotypes. In situ radiolabeling and qPCR revealed that actively coping rats expressed significantly lower prepro-orexin mRNA compared with passively coping rats. This led to the hypothesis that lower levels of orexins contribute to resilience to repeated social stress. To test this hypothesis, rats first underwent 5 d of social defeat to establish active and passive coping phenotypes. Then, orexin neurons were inhibited before each social defeat for three additional days using designer receptors exclusively activated by designer drugs (DREADDs). Inhibition of orexins increased social interaction behavior and decreased depressive-like behavior in the vulnerable population of rats. Indeed, these data suggest that lowering orexins promoted resilience to social defeat and may be an important target for treatment of stress-related disorders.
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Affiliation(s)
- Laura A. Grafe
- Department of Anesthesiology and Critical Care, Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania 19104
| | - Darrell Eacret
- Department of Anesthesiology and Critical Care, Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania 19104
| | - Jane Dobkin
- Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Seema Bhatnagar
- Department of Anesthesiology and Critical Care, Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania 19104
- Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
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Chien YL, Liu CM, Shan JC, Lee HJ, Hsieh MH, Hwu HG, Chiou LC. Elevated plasma orexin A levels in a subgroup of patients with schizophrenia associated with fewer negative and disorganized symptoms. Psychoneuroendocrinology 2015; 53:1-9. [PMID: 25560205 DOI: 10.1016/j.psyneuen.2014.12.012] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/26/2014] [Revised: 11/29/2014] [Accepted: 12/15/2014] [Indexed: 11/18/2022]
Abstract
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.
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Affiliation(s)
- Yi-Ling Chien
- Department of Psychiatry, College of Medicine, National Taiwan University, Taipei, Taiwan; Department of Psychiatry, National Taiwan University Hospital, Taipei, Taiwan; Graduate Institute of Clinical Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan
| | - Chih-Min Liu
- Department of Psychiatry, College of Medicine, National Taiwan University, Taipei, Taiwan; Department of Psychiatry, National Taiwan University Hospital, Taipei, Taiwan; Graduate Institute of Brain and Mind Sciences, College of Medicine, National Taiwan University, Taipei, Taiwan
| | - Jia-Chi Shan
- Department of Psychiatry, College of Medicine, National Taiwan University, Taipei, Taiwan; Department of Psychiatry, National Taiwan University Hospital, Taipei, Taiwan; Department of Psychiatry, Cathay General Hospital, Taipei, Taiwan
| | - Hsin-Jung Lee
- Department of Pharmacology, College of Medicine, National Taiwan University, Taipei, Taiwan
| | - Ming H Hsieh
- Department of Psychiatry, College of Medicine, National Taiwan University, Taipei, Taiwan; Department of Psychiatry, National Taiwan University Hospital, Taipei, Taiwan; Neurobiology and Cognitive Science Center, College of Medicine, National Taiwan University, Taipei, Taiwan
| | - Hai-Gwo Hwu
- Department of Psychiatry, College of Medicine, National Taiwan University, Taipei, Taiwan; Department of Psychiatry, National Taiwan University Hospital, Taipei, Taiwan; Graduate Institute of Brain and Mind Sciences, College of Medicine, National Taiwan University, Taipei, Taiwan; Neurobiology and Cognitive Science Center, College of Medicine, National Taiwan University, Taipei, Taiwan
| | - Lih-Chu Chiou
- Graduate Institute of Brain and Mind Sciences, College of Medicine, National Taiwan University, Taipei, Taiwan; Department of Pharmacology, College of Medicine, National Taiwan University, Taipei, Taiwan; Neurobiology and Cognitive Science Center, College of Medicine, National Taiwan University, Taipei, Taiwan; Graduate Institute of Pharmacology, College of Medicine, National Taiwan University, Taipei, Taiwan.
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Martelli D, Stanić D, Dutschmann M. The emerging role of the parabrachial complex in the generation of wakefulness drive and its implication for respiratory control. Respir Physiol Neurobiol 2013; 188:318-23. [PMID: 23816598 DOI: 10.1016/j.resp.2013.06.019] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2013] [Revised: 06/24/2013] [Accepted: 06/24/2013] [Indexed: 12/22/2022]
Abstract
The parabrachial complex is classically seen as a major neural knot that transmits viscero- and somatosensory information toward the limbic and thalamic forebrain. In the present review we summarize recent findings that imply an emerging role of the parabrachial complex as an integral part of the ascending reticular arousal system, which promotes wakefulness and cortical activation. The ascending parabrachial projections that target wake-promoting hypothalamic areas and the basal forebrain are largely glutamatergic. Such fast synaptic transmission could be even more significant in promoting wakefulness and its characteristic pattern of cortical activation than the cholinergic or mono-aminergic ascending pathways that have been emphasized extensively in the past. A similar role of the parabrachial complex could also apply for its more established function in control of breathing. Here the parabrachial respiratory neurons may modulate and adapt breathing via the control of respiratory phase transition and upper airway patency, particularly during respiratory and non-respiratory behavior associated with wakefulness.
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Affiliation(s)
- Davide Martelli
- Florey Institute of Neuroscience and Mental Health, Gate 11, Royal Parade, University of Melbourne, Victoria 3052, Australia
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Amygdalar orexinergic–GABAergic interactions regulate anxiety behaviors of the Syrian golden hamster. Behav Brain Res 2011; 218:288-95. [DOI: 10.1016/j.bbr.2010.11.014] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2010] [Revised: 10/22/2010] [Accepted: 11/05/2010] [Indexed: 11/21/2022]
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Rolls A, Schaich Borg J, de Lecea L. Sleep and metabolism: role of hypothalamic neuronal circuitry. Best Pract Res Clin Endocrinol Metab 2010; 24:817-28. [PMID: 21112028 DOI: 10.1016/j.beem.2010.08.002] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Sleep and metabolism are intertwined physiologically and behaviorally, but the neural systems underlying their coordination are still poorly understood. The hypothalamus is likely to play a major role in the regulation sleep, metabolism, and their interaction. And increasing evidence suggests that hypocretin cells in the lateral hypothalamus may provide particularly important contributions. Here we review: 1) direct interactions between biological arousal and metabolic systems in the hypothalamus, and 2) indirect interactions between these two systems mediated by stress or reward, emphasizing the role of hypocretins. An increased understanding of the mechanisms underlying these interactions may provide novel approaches for the treatment of patients with sleep disorders and obesity, as well as suggest new therapeutic strategies for symptoms of aging, stress, or addiction.
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Affiliation(s)
- Asya Rolls
- Department of Psychiatry and Behavioral Sciences, Stanford University School of Medicine, Palo Alto, CA 94304-5742, USA.
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Furlong TM, Vianna DML, Liu L, Carrive P. Hypocretin/orexin contributes to the expression of some but not all forms of stress and arousal. Eur J Neurosci 2009; 30:1603-14. [PMID: 19811530 DOI: 10.1111/j.1460-9568.2009.06952.x] [Citation(s) in RCA: 139] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Hypocretin/orexin has a well-established role in wakefulness and in the maintenance of arousal. Because stress is associated with arousal, it has been proposed that hypocretin is also involved in stress. However, it is not clear if this is true for all forms of stress. To clarify this issue, we compared four conditions combining high arousal with no or low stress (wakefulness and exploration) or high stress (contextual fear and restraint) in the rat. We looked at Fos expression in hypocretin neurons, hypocretin-1 levels in cerebrospinal fluid and cardiovascular and behavioural changes after pharmacological blockade with the dual hypocretin receptor antagonist, almorexant. Fos expression in hypocretin neurons was highest with wakefulness and exploration, also high with fear but not significant with restraint. Hypocretin-1 levels were consistent with this pattern, although the differences were not as marked. Hypocretin receptor blockade with almorexant reduced the pressor, tachycardic and locomotor responses of wakefulness and exploration as well as the pressor and sympathetic component of the tachycardic response of fear. In contrast, almorexant did not reduce the pressor and tachycardic responses of restraint and nor did it reduce the pressor, tachycardic and locomotor responses of another stressor, i.e. cold exposure. Thus, hypocretin is not involved in all forms of stress. Comparison of the different conditions suggests that, regardless of stress, hypocretin involvement occurs when the arousal associated with the response includes increased attention to environmental cues. When it does, hypocretin will at least contribute to the cardiovascular response. The findings are of clinical relevance to some forms of psychological stress.
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Affiliation(s)
- Teri M Furlong
- School of Medical Sciences, University of New South Wales, NSW 2052, Australia
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Zeitzer JM, Buckmaster CL, Landolt HP, Lyons DM, Mignot E. Modafinil and γ-hydroxybutyrate have sleep state-specific pharmacological actions on hypocretin-1 physiology in a primate model of human sleep. Behav Pharmacol 2009; 20:643-52. [PMID: 19752724 PMCID: PMC2939929 DOI: 10.1097/fbp.0b013e328331b9db] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Hypocretin-1 is a hypothalamic neuropeptide that is important in the regulation of wake and the lack of which results in the sleep disorder narcolepsy. Using a monkey that has consolidated wake akin to humans, we examined pharmacological manipulation of sleep and wake and its effects on hypocretin physiology. Monkeys were given the sleep-inducing γ-hydroxybutyrate (GHB) and the wake-inducing modafinil both in the morning and in the evening. Cerebrospinal fluid hypocretin-1 concentrations changed significantly in response to the drugs only when accompanied by a behavioral change (GHB-induced sleep in the morning or modafinil-induced wake in the evening). We also found that there was a large (180-fold) interindividual variation in GHB pharmacokinetics that explains variability in sleep induction in response to the drug. Our data indicate that the neurochemical concomitants of sleep and wake are capable of changing the physiological output of hypocretin neurons. Sleep independent of circadian timing is capable of decreasing cerebrospinal fluid hypocretin-1 concentrations. Furthermore, hypocretin neurons do not seem to respond to an 'effort' to remain awake, but rather keep track of time spent awake as a wake-promoting counterbalance to extended wakefulness.
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Affiliation(s)
- Jamie M Zeitzer
- Department of Psychiatry and Behavioral Sciences, Stanford University, Stanford, USA.
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Pasumarthi RK, Fadel J. Activation of orexin/hypocretin projections to basal forebrain and paraventricular thalamus by acute nicotine. Brain Res Bull 2008; 77:367-73. [PMID: 18950690 PMCID: PMC2742411 DOI: 10.1016/j.brainresbull.2008.09.014] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2008] [Revised: 07/11/2008] [Accepted: 09/18/2008] [Indexed: 01/15/2023]
Abstract
Orexin/hypocretin neurons of the lateral hypothalamus/perifornical area project to a diverse array of brain regions and are responsive to a variety of psychostimulant drugs. It has been shown that orexin neurons are activated by systemic nicotine administration suggesting a possible orexinergic contribution to the effects of this drug on arousal and cognitive function. The basal forebrain and paraventricular nucleus of the dorsal thalamus (PVT) both receive orexin inputs and have been implicated in arousal, attention and psychostimulant drug responses. However, it is unknown whether orexin inputs to these areas are activated by psychostimulant drugs such as nicotine. Here, we infused the retrograde tract tracer cholera toxin B subunit (CTb) into either the basal forebrain or PVT of adult male rats. Seven to 10 days later, animals received an acute systemic administration of (-) nicotine hydrogen tartrate or vehicle and were euthanized 2h later. Triple-label immunohistochemistry/immunofluorescence was used to detect Fos expression in retrogradely-labeled orexin neurons. Nicotine increased Fos expression in orexin neurons projecting to both basal forebrain and PVT. The relative activation in lateral and medial banks of retrogradely-labeled orexin neurons was similar following basal forebrain CTb deposits, but was more pronounced in the medial bank following PVT deposits of CTb. Our findings suggest that orexin inputs to the basal forebrain and PVT may contribute to nicotine effects on arousal and cognition and provide further support for the existence of functional heterogeneity across the medial-lateral distribution of orexin neurons.
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Affiliation(s)
- Ravi K. Pasumarthi
- Department of Pharmacology, Physiology and Neuroscience, University of South Carolina School of Medicine, Columbia, SC 29208 USA
| | - Jim Fadel
- Department of Pharmacology, Physiology and Neuroscience, University of South Carolina School of Medicine, Columbia, SC 29208 USA
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Abstract
Advances in molecular biology have led to new peptides and proteins being discovered on a regular basis, including the isolation of a number of neurotransmitter candidates. Rarely, however, do these immediately capture the attention of the scientific community. The isolation and characterization of the orexin/hypocretin peptides a decade ago resulted in a slew of studies that have helped clarified their diverse functions, including prominent roles in arousal and appetitive behavior. A number of recent studies have detailed the role of the orexins/hypocretins in attention and cognition and uncovered an involvement in schizophrenia and the mechanisms of action of antipsychotic drugs (APDs). This issue of Schizophrenia Bulletin presents several articles that review our current understanding and point to future directions for the study of the orexins/hypocretins in schizophrenia and APD actions.
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Affiliation(s)
- Ariel Y Deutch
- Department of Psychiatry, Vanderbilt University Medical Center, Nashville, TN 37212, USA.
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17
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Abstract
In mammals, daily rhythms in behaviour and physiology are driven by a circadian timing system comprised, in a hierarchical way, of a master pacemaker in the suprachiasmatic nuclei (SCN) of the hypothalamus and of peripheral oscillators in most body cells. At the molecular level, in both the SCN and peripheral oscillators, the circadian clock mechanism is built from interconnected feedback loops in gene expression that operate in a cell-autonomous and self-sustained fashion. The SCN clock is mainly entrained by light/dark cycles. By contrast, peripheral oscillators can be strongly affected by daily feeding cycles, which have little effect on the phase of the SCN. However, when feeding schedules are coupled with a caloric restriction, behavioural and physiological circadian rhythms and gene expression in the SCN are shifted and/or entrained to meal-time. Moreover, the reward and motivational value of food can also be a potent synchroniser for the SCN clock. This suggests that energy metabolism and motivational properties of food can influence the clock mechanism of the SCN. Food-related cues may entrain clock genes of the SCN with a direct effect, or be mediated indirectly by another neural or peripheral site. In addition, there may be one or more oscillator sites that would play an integral role as a food-entrained oscillator (FEO), responsible for anticipation of meal-time. The site housing, or the network underlying, this putative FEO is still unknown. The aim of this review is to summarise our current knowledge of the central and peripheral circadian clocks and how they can be entrained by feeding at the physiological and molecular levels.
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Affiliation(s)
- J Mendoza
- Institut des Neurosciences Cellulaires et Intégratives, Département de Neurobiologie des Rythmes UMR7168, CNRS et Université Louis Pasteur, Strasbourg, France.
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18
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Furlong T, Carrive P. Neurotoxic lesions centered on the perifornical hypothalamus abolish the cardiovascular and behavioral responses of conditioned fear to context but not of restraint. Brain Res 2006; 1128:107-19. [PMID: 17126820 DOI: 10.1016/j.brainres.2006.10.058] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2006] [Revised: 10/26/2006] [Accepted: 10/27/2006] [Indexed: 10/23/2022]
Abstract
The aim of this study was to test the role of the perifornical hypothalamus and adjacent areas in the behavioral and cardiovascular responses to two forms of stress, conditioned fear to context and restraint. Of particular interest was the role of the hypocretin (orexin) containing neurons in these responses. Rats implanted with radio-telemetric probes and fear conditioned to a context received bilateral injections of the neurotoxin hypocretin-2-saporin centered on the perifornical area. One week later, the animals were tested for conditioned fear to context and restraint while recording freezing, 22 kHz ultrasonic vocalizations, activity, mean arterial pressure and heart rate. Histological verification revealed that the lesions were not specific since virtually all the neurons within the injection area were lost. Nevertheless, these lesions, which were centered on the perifornical area, markedly reduced all recorded components of the contextual fear response (by 70%) but had no effect on the response to restraint. The lesions also caused a reduction in body weight and reduced the circadian rhythm of the recorded parameters. The results show (i) that hypocretin-2-saporin was not specific enough to produce lesions restricted to the hypocretin system, (ii) that neurons of the perifornical area are necessary for the expression of both the cardiovascular and behavioral components of conditioned fear to context, and (iii) that the same neurons are not necessary for the cardiovascular response to restraint. Thus, the perifornical hypothalamus is critical for some forms of stress but not others. We propose that it is a necessary relay for emotional responses in which the psychological component is stronger than the sensory component.
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Affiliation(s)
- Teri Furlong
- Department of Anatomy, School of Medical Sciences, University of New South Wales, Sydney, NSW 2035 Australia
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Singh G, Davenport AP. Neuropeptide B and W: neurotransmitters in an emerging G-protein-coupled receptor system. Br J Pharmacol 2006; 148:1033-41. [PMID: 16847439 PMCID: PMC1752024 DOI: 10.1038/sj.bjp.0706825] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Deorphanised G-protein-coupled receptors represent new and expanding targets for drug development. Neuropeptide B (NPB) and W (NPW) have recently been identified as the cognate endogenous ligands for the orphan receptor GPR7, now designated as NPBW(1). NPB and NPW also bound to a second related orphan receptor, GPR8, now designated as NPBW(2) that is present in humans but not rats or mice. In humans, high levels of NPW mRNA have been visualised in the substantia nigra, whereas moderate expression levels have been detected in the amygdala and hippocampus. In peripheral tissues, expression of NPW mRNA has been confirmed in the progenital system, comprising the kidney, testis, uterus, ovary and placenta, and also in stomach homogenates. Immunocytochemical, molecular biological and autoradiography techniques have revealed a discrete CNS distribution for NPBW(1) in human, mouse and rat. Highest expression of NPBW(1) mRNA and protein was identified in the amygdala and hypothalamic nuclei known to regulate feeding behaviour. [(125)I]-NPW bound with a single high affinity to rat amygdala, K(D)=0.44 nM and 150 fmol mg(-1) protein. Physiological studies demonstrate that intracerebroventricular infusion of NPBW(1) ligands modulates feeding behaviour, regulates the release of corticosterone, prolactin and growth hormone while also manipulating pain pathway. Mouse knockout models of the gene encoding either NPB or NPBW(1) have a gender-specific phenotype, with moderate obesity evident in males but not females. Further investigation is required to elucidate the precise physiological role of NPB and NPW as neurotransmitters.
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Affiliation(s)
- Gurminder Singh
- Clinical Pharmacology Unit, University of Cambridge, Centre for Clinical Investigation, Box 110, Level Six, Addenbrooke's Hospital, Cambridge CB2 2QQ
| | - Anthony P Davenport
- Clinical Pharmacology Unit, University of Cambridge, Centre for Clinical Investigation, Box 110, Level Six, Addenbrooke's Hospital, Cambridge CB2 2QQ
- Author for correspondence:
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Satoh S, Matsumura H, Kanbayashi T, Yoshida Y, Urakami T, Nakajima T, Kimura N, Nishino S, Yoneda H. Expression pattern of FOS in orexin neurons during sleep induced by an adenosine A2A receptor agonist. Behav Brain Res 2006; 170:277-86. [PMID: 16621044 DOI: 10.1016/j.bbr.2006.03.010] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2005] [Revised: 02/24/2006] [Accepted: 03/07/2006] [Indexed: 11/17/2022]
Abstract
The present study examined the expression pattern of FOS in the hypothalamic peptide neurons during the sleep-dominant state induced by an adenosine A2A receptor agonist. The control rats, those that received the microdialysis-perfusion of their ventral striatum with artificial cerebrospinal fluid in the dark-active phase, spent 24% of the 90-min period prior to sacrifice in non-rapid eye movement (non-REM) sleep and 2.3% of that in REM sleep. These rats exhibited FOS, a transcription factor, in 21% of their orexin neurons and in 1.0% of their melanin-concentrating hormone (MCH) neurons in the perifornical/lateral hypothalamic areas. However, the rats perfused with 50 microM CGS21680, an adenosine A2A receptor agonist, spent 60% of the 90-min period prior to sacrifice in non-REM sleep and 11% of that in REM sleep. These rats exhibited FOS in 1.7% of their orexin neurons and FOS in 0.5% of their MCH neurons. When the sleep-dominant state was disturbed by mild stimulation and the rats were kept in the sleepy state by treatment with a sleep-inducing dose of CGS21680, the rats exhibited FOS in 13.3% of their orexin neurons, which percentage was about half of that for the control rats. These results suggest that the sleep-promoting process induced by this adenosine A2A receptor agonist was associated with a decline in the activity of orexin neurons. MCH neurons are not likely to change their activities during this sleep-promoting process.
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Affiliation(s)
- Shinsuke Satoh
- Department of Neuropsychiatry, Osaka Medical College, Takatsuki, Osaka 569-8686, Japan.
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