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Imamura K, Akagi KI, Miyanoiri Y, Tsujimoto H, Hirokawa T, Ashida H, Murakami K, Inoue A, Suno R, Ikegami T, Sekiyama N, Iwata S, Kobayashi T, Tochio H. Interaction modes of human orexin 2 receptor with selective and nonselective antagonists studied by NMR spectroscopy. Structure 2024; 32:352-361.e5. [PMID: 38194963 DOI: 10.1016/j.str.2023.12.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2023] [Revised: 08/17/2023] [Accepted: 12/13/2023] [Indexed: 01/11/2024]
Abstract
Orexin neuropeptides have many physiological roles in the sleep-wake cycle, feeding behavior, reward demands, and stress responses by activating cognitive receptors, the orexin receptors (OX1R and OX2R), distributed in the brain. There are only subtle differences between OX1R and OX2R in the orthosteric site, which has hindered the rational development of subtype-selective antagonists. In this study, we utilized solution-state NMR to capture the structural plasticity of OX2R labeled with 13CH3-ε-methionine in complex with antagonists. Mutations in the orthosteric site allosterically affected the intracellular tip of TM6. Ligand exchange experiments with the subtype-selective EMPA and the nonselective suvorexant identified three methionine residues that were substantially perturbed. The NMR spectra suggested that the suvorexant-bound state exhibited more structural plasticity than the EMPA-bound state, which has not been foreseen from the close similarity of their crystal structures, providing insights into dynamic features to be considered in understanding the ligand recognition mode.
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Affiliation(s)
- Kayo Imamura
- Department of Biophysics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | - Ken-Ichi Akagi
- Section of Laboratory Equipment, National Institute of Biomedical Innovation, Health, and Nutrition, Osaka 567-0085, Japan
| | - Yohei Miyanoiri
- Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Hirokazu Tsujimoto
- Department of Cell Biology and Medical Chemistry, Graduate School of Medicine, Kyoto University, Kyoto 606-8501, Japan
| | - Takatsugu Hirokawa
- Division of Biomedical Science, Faculty of Medicine, University of Tsukuba, Tsukuba 305-8575, Japan; Transborder Medical Research Center, University of Tsukuba, Tsukuba 305-8575, Japan
| | - Hideo Ashida
- Department of Biophysics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | - Kaori Murakami
- Department of Biophysics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | - Asuka Inoue
- Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Miyagi 980-8578, Japan
| | - Ryoji Suno
- Department of Medical Chemistry, Kansai Medical University, Hirakata 573-1010, Japan
| | - Takahisa Ikegami
- Graduate School of Medical Life Science, Yokohama City University, 1-7-29 Suehiro, Yokohama, Kanagawa 230-0045, Japan
| | - Naotaka Sekiyama
- Department of Biophysics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | - So Iwata
- Department of Cell Biology and Medical Chemistry, Graduate School of Medicine, Kyoto University, Kyoto 606-8501, Japan
| | - Takuya Kobayashi
- Department of Medical Chemistry, Kansai Medical University, Hirakata 573-1010, Japan
| | - Hidehito Tochio
- Department of Biophysics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
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Yamada R, Narita N, Ishikawa T, Kakehi M, Kimura H. The orexin receptor 2 ( OX2R)-selective agonist TAK-994 increases wakefulness without affecting cerebrospinal fluid orexin levels in cynomolgus monkeys. Pharmacol Biochem Behav 2024; 234:173690. [PMID: 38061670 DOI: 10.1016/j.pbb.2023.173690] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/14/2023] [Revised: 12/04/2023] [Accepted: 12/04/2023] [Indexed: 01/01/2024]
Abstract
Orexin A (OX-A) and orexin B are neuropeptides produced in orexin neurons located in the lateral hypothalamus that exert multiple biological functions through the activation of orexin receptor 1 (OX1R) and orexin receptor 2 (OX2R) throughout the central nervous system. OX1R and OX2R have distinct functions: OX1R is involved in reward seeking, whereas OX2R has a pivotal role in sleep/wake regulation. OX2R-selective agonists are in development as novel therapeutic agents for the treatment of hypersomnia. However, their potential to induce orexin release, which may indirectly stimulate both OX1R and OX2R in vivo, is unclear. Herein, we assessed the effects of the OX2R-selective agonist TAK-994 on wakefulness and orexin release in monkeys. Oral administration of TAK-994 at 10 mg/kg in the beginning of the sleep phase (zeitgeber time [ZT] 12) significantly increased wakefulness time in monkeys but did not increase OX-A levels in monkey cisternal cerebrospinal fluid (CSF). Moreover, oral administration of TAK-994 (10 mg/kg) during the active phase (ZT1) did not increase OX-A levels in monkey CSF. These findings indicate that the OX2R agonist TAK-994 selectively activates OX2R in vivo and would not robustly induce spontaneous orexin release during the daytime or nighttime in monkeys.
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Affiliation(s)
- Ryuji Yamada
- Neuroscience Drug Discovery Unit, Research, Takeda Pharmaceutical Company Limited, 26-1, Muraoka-Higashi 2-Chome, Fujisawa, Kanagawa 251-8555, Japan
| | - Naohiro Narita
- Drug Metabolism and Pharmacokinetics Laboratory, Research, Takeda Pharmaceutical Company Limited, 26-1, Muraoka-Higashi 2-Chome, Fujisawa, Kanagawa 251-8555, Japan
| | - Takashi Ishikawa
- Neuroscience Drug Discovery Unit, Research, Takeda Pharmaceutical Company Limited, 26-1, Muraoka-Higashi 2-Chome, Fujisawa, Kanagawa 251-8555, Japan
| | - Masaaki Kakehi
- Drug Metabolism and Pharmacokinetics Laboratory, Research, Takeda Pharmaceutical Company Limited, 26-1, Muraoka-Higashi 2-Chome, Fujisawa, Kanagawa 251-8555, Japan
| | - Haruhide Kimura
- Neuroscience Drug Discovery Unit, Research, Takeda Pharmaceutical Company Limited, 26-1, Muraoka-Higashi 2-Chome, Fujisawa, Kanagawa 251-8555, Japan.
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Abstract
Orexin-A and -B (identical to hypocretin-1 and -2) are neuropeptides synthesized in the lateral hypothalamus and perifornical area, and orexin neurons project their axon terminals broadly throughout the entire central nervous system (CNS). The activity of orexins is mediated by two specific G protein-coupled receptors (GPCRs), termed orexin type1 receptor (OX1R) and orexin type2 receptor (OX2R). The orexin system plays a relevant role in various physiological functions, including arousal, feeding, reward, and thermogenesis, and is key to human health. Orexin neurons receive various signals related to environmental, physiological, and emotional stimuli. Previous studies have reported that several neurotransmitters and neuromodulators influence the activation or inhibition of orexin neuron activity. In this review, we summarize the modulating factors of orexin neurons in the sleep/wake rhythm and feeding behavior, particularly in the context of the modulation of appetite, body fluids, and circadian signaling. We also describe the effects of life activity, behavior, and diet on the orexin system. Some studies have observed phenomena that have been verified in animal experiments, revealing the detailed mechanism and neural pathway, while their applications to humans is expected in future research.
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Affiliation(s)
- Takashi Maruyama
- Department of Physiology, School of Medicine, University of Occupational and Environmental Health, Japan.
| | - Yoichi Ueta
- Department of Physiology, School of Medicine, University of Occupational and Environmental Health, Japan
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Yadav A, Singh SK, Sarkar D. Localization and expression of Orexin B (OXB) and its type 2 receptor ( OX2R) in mouse testis during postnatal development. Peptides 2023; 164:170979. [PMID: 36841281 DOI: 10.1016/j.peptides.2023.170979] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/22/2022] [Revised: 02/04/2023] [Accepted: 02/22/2023] [Indexed: 02/26/2023]
Abstract
The orexins (OXs) were first reported in hypothalamus of rat, and they play an important role in diverse physiological actions. The OXs consist of orexin A (OXA) and orexin B (OXB) peptides and their actions are mediated via two G-protein-coupled receptors, orexin 1 receptor (OX1R) and orexin 2 receptor (OX2R), respectively. Presence of OXA and OX1R has been also reported in peripheral organs like reproductive tissues. These findings, therefore, highlight a possible role of OXs and their receptors in male reproductive health. Though, expression and localization of OXB and OX2R in the testis and their role in spermatogenesis are not finally clarified. Herein, we elucidated the localization and the patterns of expression of OXB and OX2R in Parkes mice testes during postnatal development. Results suggest that the precursor prepro-orexin (PPO), OXB and OX2R are expressed at the transcript and protein levels in mouse testis throughout the postnatal development. Immunostaining further showed the localization of OXB and OX2R both in interstitium and tubular compartments of the testis. On 7 day postpartum (7 dpp), only spermatogonia showed immunoreactivity of OXB and OX2R, while at 14, 28, 42 and 90 dpp, immunolocalization of OXB and OX2R were noted in the seminiferous tubules, especially in leptotene, pachytene spermatocytes, round and elongating spermatids, and in Leydig cells and Sertoli cells. The immunoreactivity of OXB and OX2R appeared to be stage-specific in adult mouse testis. The results suggest the expression of OXB and OX2R in mouse testis and their possible regulatory role in spermatogenesis and steroidogenesis.
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Affiliation(s)
- Anupam Yadav
- Department of Zoology, Institute of Science, Banaras Hindu University, Varanasi 221005, India
| | - Shio Kumar Singh
- Department of Zoology, Institute of Science, Banaras Hindu University, Varanasi 221005, India
| | - Debarshi Sarkar
- Department of Zoology, School of Basic Sciences, Central University of Punjab, VPO-Ghudda, Bathinda 151401, India.
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Dong YJ, Jiang NH, Zhan LH, Teng X, Fang X, Lin MQ, Xie ZY, Luo R, Li LZ, Li B, Zhang BB, Lv GY, Chen SH. Soporific effect of modified Suanzaoren Decoction on mice models of insomnia by regulating Orexin-A and HPA axis homeostasis. Biomed Pharmacother 2021; 143:112141. [PMID: 34509822 DOI: 10.1016/j.biopha.2021.112141] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Revised: 08/26/2021] [Accepted: 08/31/2021] [Indexed: 12/12/2022] Open
Abstract
AIM Modified Suanzaoren Decoction (MSZRD) is obtained by improving Suanzaoren Decoction (SZRT), a traditional Chinese herbal prescription that has been used to treat insomnia for more than thousands of years. Our previous study showed that MSZRD can improve the gastrointestinal discomfort related insomnia by regulating Orexin-A. This study is the first study to evaluate the effects and possible mechanisms of MSZRD in mice with insomnia caused by p-chlorophenylalanine (PCPA) combined with multifactor random stimulation. METHODS After 14 days of multifactor stimulation to ICR mice, a PCPA suspension (30 mg/mL) was injected intraperitoneally for two consecutive days to establish an insomnia model. Three different doses of MSZRD (3.6, 7.2, and 14.4 g/kg/day) were given to ICR mice for 24 days. The food intake and back temperature were measured, and behavioral tests and pentobarbital sodium-induced sleep tests were conducted. The levels of Orexin-A, corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH), and adrenocortical hormones (CORT) in the serum and 5-hydroxytryptamine (5-HT), dopamine (DA), and norepinephrine (NE) in hypothalamus were measured using enzyme-linked immunosorbent assay (ELISA) kits. The levels of γ-aminobutyric acid (GABA) and glutamic acid (Glu) were measured by high-performance liquid chromatography (HPLC). The expression of 5HT1A receptor (5-HTRIA) and orexin receptor 2 antibody (OX2R) was measured by Western blot (WB) and immunohistochemical staining (ICH). Hematoxylin and eosin (H&E) staining and Nissl staining were used to assess the histological changes in hypothalamus tissue. RESULTS Of note, MSZRD can shorten the sleep latency of insomnia mice (P < 0.05, 0.01), prolonged the sleep duration of mice (P < 0.05, 0.01), and improve the circadian rhythm disorder relative to placebo-treated animals. Furthermore, MSZRD effectively increased the content of 5-HT and 5-HTR1A protein in the hypothalamus of insomnia mice (P < 0.05, 0.01), while downregulated the content of DA and NE (P < 0.05, 0.01). Importantly, serum GABA concentration was increased by treatment with MSZRD (P < 0.05), as reflected by a decreased Glu/GABA ratio (P < 0.05). Moreover, MSZRD decreased the levels of CORT, ACTH, and CRH related hormones in HPA axis (P < 0.05, 0.01). At the same time, MSZRD significantly downregulated the serum Orexin-A content in insomnia mice (P < 0.05), as well as hypothalamic OX2R expression (P < 0.05). In addition, MSZRD also improved the histopathological changes in hypothalamus in insomnia mice. CONCLUSION MSZRD has sleep-improvement effect in mice model of insomnia. The mechanism may be that regulating the expression of Orexin-A affects the homeostasis of HPA axis and the release of related neurotransmitters in mice with insomnia.
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Affiliation(s)
- Ying-Jie Dong
- Collaborative Innovation Center of Yangtze River Delta Region Green Pharmaceuticals, Zhejiang University of Technology, No. 18, Chaowang Road, Xiacheng District, Hangzhou, Zhejiang 310014, China
| | - Ning-Hua Jiang
- The Second Affiliated Hospital of Jiaxing University, No. 1518, Huancheng North Road, Nanhu District, Jaxing, Zhejiang 314001, China
| | - Liang-Hui Zhan
- Collaborative Innovation Center of Yangtze River Delta Region Green Pharmaceuticals, Zhejiang University of Technology, No. 18, Chaowang Road, Xiacheng District, Hangzhou, Zhejiang 310014, China
| | - Xi Teng
- Collaborative Innovation Center of Yangtze River Delta Region Green Pharmaceuticals, Zhejiang University of Technology, No. 18, Chaowang Road, Xiacheng District, Hangzhou, Zhejiang 310014, China
| | - Xi Fang
- Collaborative Innovation Center of Yangtze River Delta Region Green Pharmaceuticals, Zhejiang University of Technology, No. 18, Chaowang Road, Xiacheng District, Hangzhou, Zhejiang 310014, China
| | - Min-Qiu Lin
- Collaborative Innovation Center of Yangtze River Delta Region Green Pharmaceuticals, Zhejiang University of Technology, No. 18, Chaowang Road, Xiacheng District, Hangzhou, Zhejiang 310014, China
| | - Zhi-Yi Xie
- Collaborative Innovation Center of Yangtze River Delta Region Green Pharmaceuticals, Zhejiang University of Technology, No. 18, Chaowang Road, Xiacheng District, Hangzhou, Zhejiang 310014, China
| | - Rong Luo
- Collaborative Innovation Center of Yangtze River Delta Region Green Pharmaceuticals, Zhejiang University of Technology, No. 18, Chaowang Road, Xiacheng District, Hangzhou, Zhejiang 310014, China
| | - Lin-Zi Li
- Collaborative Innovation Center of Yangtze River Delta Region Green Pharmaceuticals, Zhejiang University of Technology, No. 18, Chaowang Road, Xiacheng District, Hangzhou, Zhejiang 310014, China
| | - Bo Li
- Collaborative Innovation Center of Yangtze River Delta Region Green Pharmaceuticals, Zhejiang University of Technology, No. 18, Chaowang Road, Xiacheng District, Hangzhou, Zhejiang 310014, China
| | - Bei-Bei Zhang
- Center for Food Evaluation, State Administrition for Market Regulation, No. 188 Western Road of South Fourth Ring Road, Fengtai District, Beijing 100070, China.
| | - Gui-Yuan Lv
- College of Pharmaceutical Science, Zhejiang Chinese Medical University, No. 548, Binwen Road, Binjiang District, Hangzhou, Zhejiang 310053, China.
| | - Su-Hong Chen
- Collaborative Innovation Center of Yangtze River Delta Region Green Pharmaceuticals, Zhejiang University of Technology, No. 18, Chaowang Road, Xiacheng District, Hangzhou, Zhejiang 310014, China.
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Sekste EA, Lebedev AA, Bychkov ER, Airapetov MI, Gramota KE, Thyssen IY, Shabanov PD. [Increase in the level of orexin receptor 1 (OX1R) mRNA in the brain structures of rats prone to impulsivity in behavior]. Biomed Khim 2021; 67:411-417. [PMID: 34730554 DOI: 10.18097/pbmc20216705411] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Orexin and its receptors are involved in the mechanisms of pathological craving for alcohol and psychoactive drugs. The orexin system is also involved in the mechanisms of non-chemical forms of addiction: binge eating and gambling. The aim of this work was to study the level of orexin receptor mRNA in the hypothalamus, hippocampus, and prefrontal cortex of rats prone to impulsivity in behavior in a model for studying the elements of gambling addiction (a variant of the Iowa Gambling Task test). Brain structures were isolated on the 22nd day of the experiment. The expression of the OX1R gene was higher in the hypothalamus by 122% and in the hippocampus by 149% in rats that preferred to receive a high reward, but with a low probability as compared with a group of animals that preferred a low level of reinforcement, but with a 100% probability. In the prefrontal cortex, on the contrary, no significant changes were observed in the level of OX1R mRNA. The level of OX2R mRNA insignificantly changed in the hypothalamus, hippocampus, and prefrontal cortex of rats prone to impulsivity in behavior. The data indicate involvement of OX1R in the hypothalamus and hippocampus in mechanisms mediating impulsive behavior and the choice of the significance of positive reinforcement in terms of its varying strength and probability.
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Affiliation(s)
- E A Sekste
- Institute of Experimental Medicine, St. Petersburg, Russia
| | - A A Lebedev
- Institute of Experimental Medicine, St. Petersburg, Russia
| | - E R Bychkov
- Institute of Experimental Medicine, St. Petersburg, Russia
| | - M I Airapetov
- Institute of Experimental Medicine, St. Petersburg, Russia; St. Petersburg State Medical Pediatric University, St. Petersburg, Russia
| | - K E Gramota
- Institute of Experimental Medicine, St. Petersburg, Russia
| | - I Yu Thyssen
- Institute of Experimental Medicine, St. Petersburg, Russia
| | - P D Shabanov
- Institute of Experimental Medicine, St. Petersburg, Russia; Kirov Military Medical Academy, St. Petersburg, Russia
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Abstract
Orexins are hypothalamic neuropeptides that were initially identified in the rat brain as endogenous ligands for an (previously) orphan G-protein-coupled receptor (GPCR). They are multitasking peptides involved in many physiological functions, including regulation of feeding behavior, wakefulness and autonomic/neuroendocrine functions, and sleep/wakefulness states in mammals. There are two isopeptides of orexin, orexin A and orexin B, which are produced from a common precursor peptide, prepro-orexin. Structures of orexins, as well as orexin genes, are highly conserved throughout mammalian species, suggesting strong evolutionary pressure that maintains the structures. Their lengths and structure suggested that orexin B is the ancestral form of the orexin neuropeptide. In mammals, orexins bind to two subtypes of GPCRs, i.e., orexin 1 receptor (OX1R) and orexin 2 receptor (OX2R). Phylogenetically, the orexin system is present exclusively in vertebrates. In genomes of species outside mammals, there is only one orexin receptor, which is similar to OX2R, suggesting that OX2R is the prototype receptor for orexins. OX1R is likely to have evolved during early mammalian evolution. Orexin-producing neurons (orexin neurons) are mainly located in the lateral hypothalamic area (LHA) in mammals and are also found in hypothalamic regions in many other vertebrates. Orexins are likely to be closely related to the regulation of active, motivated behavior in many species. The orexin system seems to have evolved as a system that supports active and purposeful behavior which is closely related with wakefulness.
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Affiliation(s)
- Shingo Soya
- Faculty of Medicine/International Institute for Integrative Sleep Medicine (WPI-IIIS), University of Tsukuba, Tsukuba, Japan
| | - Takeshi Sakurai
- Faculty of Medicine/International Institute for Integrative Sleep Medicine (WPI-IIIS), University of Tsukuba, Tsukuba, Japan
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Wang QQ, Wang CM, Cheng BH, Yang CQ, Bai B, Chen J. Signaling transduction regulated by 5-hydroxytryptamine 1A receptor and orexin receptor 2 heterodimers. Cell Signal 2018; 54:46-58. [PMID: 30481562 DOI: 10.1016/j.cellsig.2018.11.014] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2018] [Revised: 11/08/2018] [Accepted: 11/15/2018] [Indexed: 12/09/2022]
Abstract
As G-protein-coupled receptors (GPCRs), 5-hydroxytryptamine 1A receptor (5-HT1AR) and orexin receptor 2 (OX2R) regulate the levels of the cellular downstream molecules. The heterodimers of different GPCRs play important roles in various of neurological diseases. Moreover, 5-HT1AR and OX2R are involved in the pathogenesis of neurological diseases such as depression with deficiency of hippocampus plasticity. However, the direct interaction of the two receptors remains elusive. In the present study, we firstly demonstrated the heterodimer formation of 5-HT1AR and OX2R. Exchange protein directly activated by cAMP (Epac) cAMP bioluminescence resonance energy transfer (BRET) biosensor analysis revealed that the expression levels of cellular cAMP significantly increased in HEK293T cells transfected with the two receptors compared with the 5-HT1AR group. Additionally, the cellular level of calcium was upregulated robustly in HEK293T cells co-transfected with 5-HT1AR and OX2R group after agonist treatment. Furthermore, western blotting data showed that 5-HT1AR and OX2R heterodimer decreased the levels of phosphorylation of extracellular signal-regulated kinase (ERK) and cAMP-response element-binding protein (CREB). These results not only unraveled the formation of 5-HT1AR and OX2R heterodimer but also suggested that the heterodimer affected the downstream signaling pathway, which will provide new insights into the function of the two receptors in the brain.
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Affiliation(s)
- Qin-Qin Wang
- Neurobiology Key Laboratory, Jining Medical University, Colleges of Shandong, Jining 272067, PR China
| | - Chun-Mei Wang
- Neurobiology Key Laboratory, Jining Medical University, Colleges of Shandong, Jining 272067, PR China
| | - Bao-Hua Cheng
- Neurobiology Key Laboratory, Jining Medical University, Colleges of Shandong, Jining 272067, PR China
| | - Chun-Qing Yang
- Neurobiology Key Laboratory, Jining Medical University, Colleges of Shandong, Jining 272067, PR China
| | - Bo Bai
- Neurobiology Key Laboratory, Jining Medical University, Colleges of Shandong, Jining 272067, PR China.
| | - Jing Chen
- Neurobiology Key Laboratory, Jining Medical University, Colleges of Shandong, Jining 272067, PR China; Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry CV4 7AL, UK.
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Ikeno T, Yan L. A comparison of the orexin receptor distribution in the brain between diurnal Nile grass rats (Arvicanthis niloticus) and nocturnal mice (Mus musculus). Brain Res 2018; 1690:89-95. [PMID: 29630859 PMCID: PMC5944353 DOI: 10.1016/j.brainres.2018.04.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2018] [Revised: 03/24/2018] [Accepted: 04/02/2018] [Indexed: 11/20/2022]
Abstract
The neuropeptide orexin/hypocretin regulates a wide range of behaviors and physiology through its receptors OX1R and OX2R, or HCRTR-1 and HCRTR-2. Although the distributions of these receptors have been established in nocturnal rodents, their distributions in the brain of diurnal species have not been studied. In the present study, we examined spatial patterns of OX1R and OX2R mRNA expression in diurnal Nile grass rats (Arvicanthis niloticus) by in situ hybridization and compared them with those in nocturnal mice (Mus musculus). Both receptors showed similar spatial patterns between species in most brain regions. However, species-specific expression was found in several regions that are mainly implicated in regulation of sleep/wakefulness, emotion and cognition. OX1R expression was detected in the caudate putamen and ventral tuberomammillary nucleus only in grass rats, while it was detected in the bed nucleus of the stria terminalis, medial division, posteromedial part only in mice. The distribution of OX2R mRNA was mostly consistent between the two species, although it was more widely expressed in the ventral tuberomammillary nucleus in grass rats compared to mice. These results suggest that neuronal pathways of the orexin system differ between chronotypes, and these differences could underlie the distinct profiles in behaviors and physiology between diurnal and nocturnal species.
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Affiliation(s)
- Tomoko Ikeno
- Department of Psychology, Michigan State University, East Lansing, MI 48824, USA.
| | - Lily Yan
- Department of Psychology, Michigan State University, East Lansing, MI 48824, USA; Neuroscience Program, Michigan State University, East Lansing, MI 48824, USA
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Abstract
The discovery of the orexin system represents the single major progress in the sleep field of the last three to four decades. The two orexin peptides and their two receptors play a major role in arousal and sleep/wake cycles. Defects in the orexin system lead to narcolepsy with cataplexy in humans and dogs and can be experimentally reproduced in rodents. At least six orexin receptor antagonists have reached Phase II or Phase III clinical trials in insomnia, five of which are dual orexin receptor antagonists (DORAs) that target both OX1 and OX2 receptors (OX2Rs). All clinically tested DORAs induce and maintain sleep: suvorexant, recently registered in the USA and Japan for insomnia, represents the first hypnotic principle that acts in a completely different manner from the current standard medications. It is clear, however, that in the clinic, all DORAs promote sleep primarily by increasing rapid eye movement (REM) and are almost devoid of effects on slow-wave (SWS) sleep. At present, there is no consensus on whether the sole promotion of REM sleep has a negative impact in patients suffering from insomnia. However, sleep onset REM (SOREM), which has been documented with DORAs, is clearly an undesirable effect, especially for narcoleptic patients and also in fragile populations (e.g. elderly patients) where REM-associated loss of muscle tone may promote an elevated risk of falls. Debate thus remains as to the ideal orexin agent to achieve a balanced increase in REM and non-rapid eye movement (NREM) sleep. Here, we review the evidence that an OX2R antagonist should be at least equivalent, or perhaps superior, to a DORA for the treatment of insomnia. An OX2R antagonist may produce more balanced sleep than a DORA. Rodent sleep experiments show that the OX2R is the primary target of orexin receptor antagonists in sleep modulation. Furthermore, an OX2R antagonist should, in theory, have a lower narcoleptic/cataplexic potential. In the clinic, the situation remains equivocal, since OX2R antagonists are in early stages: MK-1064 has completed Phase I, and MIN202 is currently in clinical Phase II/III trials. However, data from insomnia patients have not yet been released. Promotional material suggests that balanced sleep is indeed induced by MIN-202, whereas in volunteers MK-1064 has been reported to act similarly to DORAs.
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Affiliation(s)
- Laura H Jacobson
- The Florey Institute of Neuroscience and Mental Health, The University of Melbourne, 30 Royal Parade, Parkville, VIC, 3052, Australia
- Department of Pharmacology and Therapeutics, School of Biomedical Sciences, Faculty of Medicine, Dentistry and Health Sciences, The University of Melbourne, Parkville, VIC, 3010, Australia
| | - Sui Chen
- Department of Pharmacology and Therapeutics, School of Biomedical Sciences, Faculty of Medicine, Dentistry and Health Sciences, The University of Melbourne, Parkville, VIC, 3010, Australia
| | - Sanjida Mir
- Department of Pharmacology and Therapeutics, School of Biomedical Sciences, Faculty of Medicine, Dentistry and Health Sciences, The University of Melbourne, Parkville, VIC, 3010, Australia
| | - Daniel Hoyer
- The Florey Institute of Neuroscience and Mental Health, The University of Melbourne, 30 Royal Parade, Parkville, VIC, 3052, Australia.
- Department of Pharmacology and Therapeutics, School of Biomedical Sciences, Faculty of Medicine, Dentistry and Health Sciences, The University of Melbourne, Parkville, VIC, 3010, Australia.
- Department of Chemical Physiology, The Scripps Research Institute, 10550 N. Torrey Pines Road, La Jolla, CA, 92037, USA.
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