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Frontiers of Neurology and Neuroscience 2021Orexins regulate a wide variety of biological functions, most notably the sleep-wake cycle, reward and stress processing, alertness, vigilance, and cognitive... (Review)
Review
Orexins regulate a wide variety of biological functions, most notably the sleep-wake cycle, reward and stress processing, alertness, vigilance, and cognitive functioning. Alterations of central and peripheral orexin levels are linked to conditions such as narcolepsy, anorexia nervosa, age-related cognitive decline, and neurodegenerative disease. Preliminary studies suggest that orexin mimetics can safely promote the wake signal via orexin agonism during the day and that orexin receptor antagonists can promote the sleep signal during the night. Thus, novel orexin therapies have the potential to either improve memory, cognition, and daytime performance directly or indirectly, through promotion of good sleep. The full scope of the therapeutic potential of orexin therapies remains to be elucidated.
Topics: Aging; Alzheimer Disease; Animals; Anorexia Nervosa; Cognitive Dysfunction; Humans; Narcolepsy; Orexin Receptors; Orexins; Parkinson Disease; Sleep
PubMed: 34052810
DOI: 10.1159/000514960 -
Frontiers of Neurology and Neuroscience 2021The hypocretins/orexins are two excitatory neuropeptides, alternately called HCRT1 or orexin-A and HCRT2 or orexin-B, that are the endogenous ligands for two... (Review)
Review
The hypocretins/orexins are two excitatory neuropeptides, alternately called HCRT1 or orexin-A and HCRT2 or orexin-B, that are the endogenous ligands for two G-protein-coupled receptors, HCRTR1/OX1R and HCRTR2/OX2R. Shortly after the discovery of this system, degeneration of hypocretin/orexin-producing neurons was implicated in the etiology of the sleep disorder narcolepsy. The involvement of this system in a disorder characterized by the loss of control over arousal state boundaries also suggested its role as a critical component of endogenous sleep-wake regulatory circuitry. The broad projections of the hypocretin/orexin-producing neurons, along with differential expression of the two receptors in the projection fields of these neurons, suggest distinct roles for these receptors. While HCRTR1/OX1R is associated with regulation of motivation, reward, and autonomic functions, HCRTR2/OX2R is strongly linked to sleep-wake control. The association of hypocretin/orexin with these physiological processes has led to intense interest in the therapeutic potential of compounds targeting these receptors. Agonists and antagonists for the hypocretin/orexin receptors have shown potential for the treatment of disorders of excessive daytime somnolence and nocturnal hyperarousal, respectively, with the first antagonists approved by the US Food and Drug Administration (FDA) in 2014 and 2019 for the treatment of insomnia. These and related compounds have also been useful tools to advance hypocretin/orexin neurobiology.
Topics: Animals; Disorders of Excessive Somnolence; Humans; Orexin Receptor Antagonists; Orexin Receptors; Orexins; Sleep; Sleep Initiation and Maintenance Disorders; Sleep Wake Disorders; Wakefulness
PubMed: 34052813
DOI: 10.1159/000514963 -
Science (New York, N.Y.) Feb 2022Sleep quality declines with age; however, the underlying mechanisms remain elusive. We found that hyperexcitable hypocretin/orexin (Hcrt/OX) neurons drive sleep...
Sleep quality declines with age; however, the underlying mechanisms remain elusive. We found that hyperexcitable hypocretin/orexin (Hcrt/OX) neurons drive sleep fragmentation during aging. In aged mice, Hcrt neurons exhibited more frequent neuronal activity epochs driving wake bouts, and optogenetic activation of Hcrt neurons elicited more prolonged wakefulness. Aged Hcrt neurons showed hyperexcitability with lower KCNQ2 expression and impaired M-current, mediated by KCNQ2/3 channels. Single-nucleus RNA-sequencing revealed adaptive changes to Hcrt neuron loss in the aging brain. Disruption of genes in Hcrt neurons of young mice destabilized sleep, mimicking aging-associated sleep fragmentation, whereas the KCNQ-selective activator flupirtine hyperpolarized Hcrt neurons and rejuvenated sleep architecture in aged mice. Our findings demonstrate a mechanism underlying sleep instability during aging and a strategy to improve sleep continuity.
Topics: Aging; Aminopyridines; Animals; CRISPR-Cas Systems; Electroencephalography; Electromyography; Female; Hypothalamic Area, Lateral; KCNQ2 Potassium Channel; KCNQ3 Potassium Channel; Male; Mice; Narcolepsy; Nerve Tissue Proteins; Neural Pathways; Neurons; Optogenetics; Orexins; Patch-Clamp Techniques; RNA-Seq; Sleep; Sleep Deprivation; Sleep Quality; Wakefulness
PubMed: 35201886
DOI: 10.1126/science.abh3021 -
Nature Communications Jul 2022Humans and animals lacking orexin neurons exhibit daytime sleepiness, sleep attacks, and state instability. While the circuit basis by which orexin neurons contribute to...
Humans and animals lacking orexin neurons exhibit daytime sleepiness, sleep attacks, and state instability. While the circuit basis by which orexin neurons contribute to consolidated wakefulness remains unclear, existing models posit that orexin neurons provide their wake-stabilizing influence by exerting excitatory tone on other brain arousal nodes. Here we show using in vivo optogenetics, in vitro optogenetic-based circuit mapping, and single-cell transcriptomics that orexin neurons also contribute to arousal maintenance through indirect inhibition of sleep-promoting neurons of the ventrolateral preoptic nucleus. Activation of this subcortical circuit rapidly drives wakefulness from sleep by differentially modulating the activity of ventrolateral preoptic neurons. We further identify and characterize a feedforward circuit through which orexin (and co-released glutamate) acts to indirectly target and inhibit sleep-promoting ventrolateral preoptic neurons to produce arousal. This revealed circuitry provides an alternate framework for understanding how orexin neurons contribute to the maintenance of consolidated wakefulness and stabilize behavioral state.
Topics: Animals; Arousal; Humans; Neurons; Orexins; Sleep; Wakefulness
PubMed: 35851580
DOI: 10.1038/s41467-022-31591-y -
Neuroscience Bulletin Apr 2020Orexins comprise two neuropeptides produced by orexin neurons in the lateral hypothalamus and are released by extensive projections of these neurons throughout the... (Review)
Review
Orexins comprise two neuropeptides produced by orexin neurons in the lateral hypothalamus and are released by extensive projections of these neurons throughout the central nervous system. Orexins bind and activate their associated G protein-coupled orexin type 1 receptors (OX1Rs) and OX2Rs and act on numerous physiological processes, such as sleep-wake regulation, feeding, reward, emotion, and motivation. Research on the development of orexin receptor antagonists has dramatically increased with the approval of suvorexant for the treatment of primary insomnia. In the present review, we discuss recent findings on the involvement of the orexin system in the pathophysiology of psychiatric disorders, including sleep disorders, depression, anxiety, and drug addiction. We discuss the actions of orexin receptor antagonists, including selective OX1R antagonists (SORA1s), selective OX2R antagonists (SORA2s), and dual OX1/2R antagonists (DORAs), in the treatment of these disorders based on both preclinical and clinical evidence. SORA2s and DORAs have more pronounced efficacy in the treatment of sleep disorders, whereas SORA1s may be promising for the treatment of anxiety and drug addiction. We also discuss potential challenges and opportunities for the application of orexin receptor antagonists to clinical interventions.
Topics: Animals; Humans; Mental Disorders; Orexin Receptor Antagonists; Orexin Receptors; Orexins
PubMed: 31782044
DOI: 10.1007/s12264-019-00447-9 -
Neuropsychopharmacology Reports Dec 2021Most conventional insomnia medications are gamma-aminobutylic acid receptor agonists. However, physical dependence is a concern and one of the major limiting factors for... (Meta-Analysis)
Meta-Analysis Review
Most conventional insomnia medications are gamma-aminobutylic acid receptor agonists. However, physical dependence is a concern and one of the major limiting factors for long-term treatment. The dual orexin receptor antagonists, suvorexant and lemborexant, were recently approved for treating chronic insomnia, giving a novel pharmacotherapeutic option. Because there are no comparative studies on these drugs, a network meta-analysis was conducted, which is suitable for comparing interventions. According to this analysis, 5- and 10-mg lemborexant were superior to 20-mg suvorexant because of the greater improvement in initiating sleep after 1-week administration. Furthermore, 5-mg lemborexant (not 10 mg) and suvorexant were similarly well tolerated, without requiring discontinuation due to adverse events. We also overviewed the pharmacological and pharmacokinetic properties of lemborexant and suvorexant that may support these clinical outcomes. When compared to suvorexant, lemborexant quickly binds to the orexin receptors. The time to reach the maximum concentration after multiple administrations is shorter for lemborexant than for suvorexant. Considering these results, we recommend 5-mg lemborexant as an initial treatment for insomnia, followed by 10-mg lemborexant or suvorexant.
Topics: Humans; Network Meta-Analysis; Orexin Receptor Antagonists; Orexin Receptors; Orexins; Sleep Initiation and Maintenance Disorders
PubMed: 34553844
DOI: 10.1002/npr2.12205 -
Frontiers in Endocrinology 2020
Topics: Fear; Humans; Neoplasms; Orexin Receptors; Orexins
PubMed: 32582031
DOI: 10.3389/fendo.2020.00357 -
Nature Sep 2023Only recently have more specific circuit-probing techniques become available to inform previous reports implicating the rodent hippocampus in orexigenic appetitive...
Only recently have more specific circuit-probing techniques become available to inform previous reports implicating the rodent hippocampus in orexigenic appetitive processing. This function has been reported to be mediated at least in part by lateral hypothalamic inputs, including those involving orexigenic lateral hypothalamic neuropeptides, such as melanin-concentrating hormone. This circuit, however, remains elusive in humans. Here we combine tractography, intracranial electrophysiology, cortico-subcortical evoked potentials, and brain-clearing 3D histology to identify an orexigenic circuit involving the lateral hypothalamus and converging in a hippocampal subregion. We found that low-frequency power is modulated by sweet-fat food cues, and this modulation was specific to the dorsolateral hippocampus. Structural and functional analyses of this circuit in a human cohort exhibiting dysregulated eating behaviour revealed connectivity that was inversely related to body mass index. Collectively, this multimodal approach describes an orexigenic subnetwork within the human hippocampus implicated in obesity and related eating disorders.
Topics: Humans; Body Mass Index; Cohort Studies; Cues; Electrophysiology; Evoked Potentials; Feeding and Eating Disorders; Feeding Behavior; Food; Hippocampus; Obesity; Orexins; Neural Pathways
PubMed: 37648849
DOI: 10.1038/s41586-023-06459-w -
Biochimica Et Biophysica Acta.... Nov 2021Orexin-A (OXA) is a neuropeptide with neuroprotective effect by reducing cerebral ischemia/reperfusion injury (CIRI). Inflammation and apoptosis mediated by astrocyte...
Orexin-A (OXA) is a neuropeptide with neuroprotective effect by reducing cerebral ischemia/reperfusion injury (CIRI). Inflammation and apoptosis mediated by astrocyte activation are the key pathological mechanisms for CIRI. We thus attempted to confirm neuroprotective effects of OXA on astrocytic inflammation and apoptosis in CIRI and clarify the relative mechanisms. A middle cerebral artery occlusion and reperfusion (MCAO/R) rat model and U251 glioma cells model subjected to oxygen glucose deprivation and reperfusion (OGD/R) were established, with or without OXA treatment. Neurological deficit score was determined, and cerebral infarct volume was evaluated by 2,3,5-triphenyltetrazolium chloride (TTC) staining. Western Blot was used to detect the expressions of NF-κB p65, p-p65, p-ERK, p-p38, GFAP, OX1R, IL-1β, TNF-α, IL-6, iNOS, Bcl-2, Bax, CytC, cleaved caspase-9 and cleaved caspase-3 in vivo and in vitro. Pro-inflammatory cytokines in cell supernatant IL-1β, TNF-α and IL-6 were determined by ELISA. Hoechst 33342 staining was used to detect the apoptosis of astrocyte. Immunofluorescent staining was performed to assess the nuclear translocation of p65 and the expression of GFAP. The results showed that OXA significantly improved neurological deficit score and decreased the volume of infarct area in brain. OXA decreased inflammatory mediators, inhibited astrocyte activation and nuclear translocation of NF-κB and phosphorylation of NF-κB, MAPK/ERK and MAPK/p38. Besides, OXA suppressed apoptosis via upregulating the ratio of Bcl-2/Bax and downregulating cytochrome C, cleaved-caspase-9 and cleaved caspase-3. Overall, it was concluded that OXA exerts neuroprotective effect during CIRI through attenuating astrocytes apoptosis, astrocytes activation and pro-inflammatory cytokines production, by Inhibiting OX1R-mediated NF-κB, MAPK/ERK and MAPK/p38 signaling pathways. The progress in our study is helpful to elucidate the molecular mechanisms of OXA neuroprotection, which could lead to the development of new treatment strategies for ischemic stroke.
Topics: Animals; Apoptosis; Astrocytes; Cell Line, Tumor; Cerebral Cortex; Disease Models, Animal; Humans; Infarction, Middle Cerebral Artery; MAP Kinase Signaling System; Male; NF-kappa B; Orexin Receptors; Orexins; Rats; Reperfusion Injury
PubMed: 34358627
DOI: 10.1016/j.bbadis.2021.166230 -
Proceedings of the National Academy of... Aug 2022Narcolepsy type 1 (NT1) is a sleep disorder caused by a loss of orexinergic neurons. Narcolepsy type 2 (NT2) is heterogeneous; affected individuals typically have normal...
Narcolepsy type 1 (NT1) is a sleep disorder caused by a loss of orexinergic neurons. Narcolepsy type 2 (NT2) is heterogeneous; affected individuals typically have normal orexin levels. Following evaluation in mice, the effects of the orexin 2 receptor (OX2R)-selective agonist danavorexton were evaluated in single- and multiple-rising-dose studies in healthy adults, and in individuals with NT1 and NT2. In orexin/ataxin-3 narcolepsy mice, danavorexton reduced sleep/wakefulness fragmentation and cataplexy-like episodes during the active phase. In humans, danavorexton administered intravenously was well tolerated and was associated with marked improvements in sleep latency in both NT1 and NT2. In individuals with NT1, danavorexton dose-dependently increased sleep latency in the Maintenance of Wakefulness Test, up to the ceiling effect of 40 min, in both the single- and multiple-rising-dose studies. These findings indicate that OX2Rs remain functional despite long-term orexin loss in NT1. OX2R-selective agonists are a promising treatment for both NT1 and NT2.
Topics: Adult; Animals; Ataxin-3; Cataplexy; Central Nervous System Stimulants; Disease Models, Animal; Humans; Mice; Narcolepsy; Neurons; Orexin Receptors; Orexins; Phenotype; Wakefulness
PubMed: 35994639
DOI: 10.1073/pnas.2207531119