1
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Tsuno Y, Peng Y, Horike SI, Wang M, Matsui A, Yamagata K, Sugiyama M, Nakamura TJ, Daikoku T, Maejima T, Mieda M. In vivo recording of suprachiasmatic nucleus dynamics reveals a dominant role of arginine vasopressin neurons in circadian pacesetting. PLoS Biol 2023; 21:e3002281. [PMID: 37643163 PMCID: PMC10465001 DOI: 10.1371/journal.pbio.3002281] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Accepted: 07/28/2023] [Indexed: 08/31/2023] Open
Abstract
The central circadian clock of the suprachiasmatic nucleus (SCN) is a network consisting of various types of neurons and glial cells. Individual cells have the autonomous molecular machinery of a cellular clock, but their intrinsic periods vary considerably. Here, we show that arginine vasopressin (AVP) neurons set the ensemble period of the SCN network in vivo to control the circadian behavior rhythm. Artificial lengthening of cellular periods by deleting casein kinase 1 delta (CK1δ) in the whole SCN lengthened the free-running period of behavior rhythm to an extent similar to CK1δ deletion specific to AVP neurons. However, in SCN slices, PER2::LUC reporter rhythms of these mice only partially and transiently recapitulated the period lengthening, showing a dissociation between the SCN shell and core with a period instability in the shell. In contrast, in vivo calcium rhythms of both AVP and vasoactive intestinal peptide (VIP) neurons in the SCN of freely moving mice demonstrated stably lengthened periods similar to the behavioral rhythm upon AVP neuron-specific CK1δ deletion, without changing the phase relationships between each other. Furthermore, optogenetic activation of AVP neurons acutely induced calcium increase in VIP neurons in vivo. These results indicate that AVP neurons regulate other SCN neurons, such as VIP neurons, in vivo and thus act as a primary determinant of the SCN ensemble period.
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Affiliation(s)
- Yusuke Tsuno
- Department of Integrative Neurophysiology, Graduate School of Medical Sciences, Kanazawa University, Kanazawa, Japan
| | - Yubo Peng
- Department of Integrative Neurophysiology, Graduate School of Medical Sciences, Kanazawa University, Kanazawa, Japan
| | - Shin-ichi Horike
- Division of Integrated Omics Research, Research Center for Experimental Modeling of Human Disease, Kanazawa University, Kanazawa, Japan
| | - Mohan Wang
- Department of Integrative Neurophysiology, Graduate School of Medical Sciences, Kanazawa University, Kanazawa, Japan
| | - Ayako Matsui
- Department of Integrative Neurophysiology, Graduate School of Medical Sciences, Kanazawa University, Kanazawa, Japan
| | - Kanato Yamagata
- Child Brain Project, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
| | - Mizuki Sugiyama
- Laboratory of Animal Physiology, School of Agriculture, Meiji University, Kawasaki, Japan
| | - Takahiro J. Nakamura
- Laboratory of Animal Physiology, School of Agriculture, Meiji University, Kawasaki, Japan
| | - Takiko Daikoku
- Division of Animal Disease Model, Research Center for Experimental Modeling of Human Disease, Kanazawa University, Kanazawa, Japan
| | - Takashi Maejima
- Department of Integrative Neurophysiology, Graduate School of Medical Sciences, Kanazawa University, Kanazawa, Japan
| | - Michihiro Mieda
- Department of Integrative Neurophysiology, Graduate School of Medical Sciences, Kanazawa University, Kanazawa, Japan
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2
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Finger AM. In Vitro Assays for Measuring Intercellular Coupling Among Peripheral Circadian Oscillators. Methods Mol Biol 2022; 2482:153-167. [PMID: 35610425 DOI: 10.1007/978-1-0716-2249-0_10] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Circadian clocks can be found in nearly all eukaryotic organisms, as well as certain bacterial strains, including commensal microbiota. Exploring intercellular coupling among cell-autonomous circadian oscillators is crucial for understanding how cellular ensembles generate and sustain coherent circadian rhythms on the tissue level, and thus, rhythmic organ functions. Here we describe a protocol for studying intercellular coupling among peripheral circadian oscillators using three-dimensional spheroid cultures in order to measure coupling strength within peripheral clock networks. We use cell spheroids to simulate in vivo tissue integrity, as well as to increase complexity of cell-cell interactions and the abundance of potential coupling factors. Circadian rhythms are monitored using live-cell imaging of spheroids equipped with circadian reporters over several days.
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Affiliation(s)
- Anna-Marie Finger
- Charité Universitätsmedizin Berlin, Institute for Medical Immunology, Laboratory of Chronobiology, Berlin, Germany.
- Freie Universität Berlin, Berlin, Germany.
- Humboldt-Universität zu Berlin, Berlin, Germany.
- Berlin Institute of Health (BIH), Berlin, Germany.
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3
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Hughes ATL, Samuels RE, Baño-Otálora B, Belle MDC, Wegner S, Guilding C, Northeast RC, Loudon ASI, Gigg J, Piggins HD. Timed daily exercise remodels circadian rhythms in mice. Commun Biol 2021; 4:761. [PMID: 34145388 PMCID: PMC8213798 DOI: 10.1038/s42003-021-02239-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2020] [Accepted: 05/18/2021] [Indexed: 01/26/2023] Open
Abstract
Regular exercise is important for physical and mental health. An underexplored and intriguing property of exercise is its actions on the body’s 24 h or circadian rhythms. Molecular clock cells in the brain’s suprachiasmatic nuclei (SCN) use electrical and chemical signals to orchestrate their activity and convey time of day information to the rest of the brain and body. To date, the long-lasting effects of regular physical exercise on SCN clock cell coordination and communication remain unresolved. Utilizing mouse models in which SCN intercellular neuropeptide signaling is impaired as well as those with intact SCN neurochemical signaling, we examined how daily scheduled voluntary exercise (SVE) influenced behavioral rhythms and SCN molecular and neuronal activities. We show that in mice with disrupted neuropeptide signaling, SVE promotes SCN clock cell synchrony and robust 24 h rhythms in behavior. Interestingly, in both intact and neuropeptide signaling deficient animals, SVE reduces SCN neural activity and alters GABAergic signaling. These findings illustrate the potential utility of regular exercise as a long-lasting and effective non-invasive intervention in the elderly or mentally ill where circadian rhythms can be blunted and poorly aligned to the external world. Using mice with disrupted neuropeptide signaling, Hughes et al. show that daily scheduled voluntary exercise (SVE) promotes suprachiasmatic nuclei (SCN) clock cell synchrony and robust 24 h rhythms in behavior. This study suggests the potential utility of regular exercise as a non-invasive intervention for the elderly or mentally ill, where circadian rhythms can be poorly aligned to the external world.
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Affiliation(s)
- Alun Thomas Lloyd Hughes
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, UK.,School of Biological and Environmental Sciences, Liverpool John Moores University, Liverpool, UK
| | - Rayna Eve Samuels
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, UK
| | - Beatriz Baño-Otálora
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, UK
| | - Mino David Charles Belle
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, UK.,University of Exeter Medical School, Exeter, UK
| | - Sven Wegner
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, UK
| | - Clare Guilding
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, UK.,School of Medical Education, Newcastle University, Newcastle, UK
| | | | | | - John Gigg
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, UK
| | - Hugh David Piggins
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, UK. .,School of Physiology, Pharmacology, and Neuroscience, University of Bristol, Bristol, UK.
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4
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Ribeiro RFN, Cavadas C, Silva MMC. Small-molecule modulators of the circadian clock: Pharmacological potentials in circadian-related diseases. Drug Discov Today 2021; 26:1620-1641. [PMID: 33781946 DOI: 10.1016/j.drudis.2021.03.015] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Revised: 02/20/2021] [Accepted: 03/16/2021] [Indexed: 12/29/2022]
Abstract
Disruption of circadian oscillations has a wide-ranging impact on health, with the potential to induce the development of clock-related diseases. Small-molecule modulators of the circadian clock (SMMCC) target core or noncore clock proteins, modulating physiological effects as a consequence of agonist, inverse agonist, or antagonist interference. These pharmacological modulators are usually identified using chemical screening of large libraries of active compounds. However, target-based screens, chemical optimization, and circadian crystallography have recently assisted in the identification of these compounds. In this review, we focus on established and novel SMMCCs targeting both core and noncore clock proteins, identifying their circadian targets, detailed circadian effects, and specific physiological effects. In addition, we discuss their therapeutic potential for the treatment of diverse clock-related disorders (such as metabolic-associated disorders, autoimmune diseases, mood disorders, and cancer) and as chronotherapeutics. Future perspectives are also considered, such as clinical trials, and potential safety hazards, including those in the absence of clinical trials.
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Affiliation(s)
- Rodrigo F N Ribeiro
- Centre for Neuroscience and Cell Biology (CNC), University of Coimbra, Coimbra, Portugal; Centre for Innovation in Biomedicine and Biotechnology (CIBB), University of Coimbra, Portugal; Faculty of Pharmacy, University of Coimbra, Coimbra, Portugal
| | - Cláudia Cavadas
- Centre for Neuroscience and Cell Biology (CNC), University of Coimbra, Coimbra, Portugal; Centre for Innovation in Biomedicine and Biotechnology (CIBB), University of Coimbra, Portugal; Faculty of Pharmacy, University of Coimbra, Coimbra, Portugal.
| | - Maria Manuel C Silva
- Centre for Neuroscience and Cell Biology (CNC), University of Coimbra, Coimbra, Portugal; Centre for Innovation in Biomedicine and Biotechnology (CIBB), University of Coimbra, Portugal; Faculty of Pharmacy, University of Coimbra, Coimbra, Portugal.
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5
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Cheng AH, Cheng HYM. Genesis of the Master Circadian Pacemaker in Mice. Front Neurosci 2021; 15:659974. [PMID: 33833665 PMCID: PMC8021851 DOI: 10.3389/fnins.2021.659974] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2021] [Accepted: 03/04/2021] [Indexed: 12/13/2022] Open
Abstract
The suprachiasmatic nucleus (SCN) of the hypothalamus is the central circadian clock of mammals. It is responsible for communicating temporal information to peripheral oscillators via humoral and endocrine signaling, ultimately controlling overt rhythms such as sleep-wake cycles, body temperature, and locomotor activity. Given the heterogeneity and complexity of the SCN, its genesis is tightly regulated by countless intrinsic and extrinsic factors. Here, we provide a brief overview of the development of the SCN, with special emphasis on the murine system.
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Affiliation(s)
- Arthur H. Cheng
- Department of Biology, University of Toronto Mississauga, Mississauga, ON, Canada
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada
| | - Hai-Ying Mary Cheng
- Department of Biology, University of Toronto Mississauga, Mississauga, ON, Canada
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada
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6
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Lim ASP. Diurnal and seasonal molecular rhythms in the human brain and their relation to Alzheimer disease. HANDBOOK OF CLINICAL NEUROLOGY 2021; 179:271-284. [PMID: 34225968 DOI: 10.1016/b978-0-12-819975-6.00017-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Diurnal and seasonal rhythms influence many aspects of human physiology including brain function. Moreover, altered diurnal and seasonal behavioral and physiological rhythms have been linked to Alzheimer's disease and related dementias (ADRD). Understanding the molecular basis for these links may lead to identification of novel targets to mitigate the negative impact of normal and abnormal diurnal and seasonal rhythms on ADRD or to alleviate the adverse consequences of ADRD on normal diurnal and seasonal rhythms. Diurnally and seasonally rhythmic gene expression and epigenetic modification in the human neocortex may be a key mechanism underlying these links. This chapter will first review the observed epidemiological links between normal and abnormal diurnal and seasonal rhythmicity, cognitive impairment, and ADRD. Then it will review normal diurnal and seasonal rhythms of brain epigenetic modification and gene expression in model organisms. Finally, it will review evidence for diurnal and seasonal rhythms of epigenetic modification and gene expression the human brain in aging, Alzheimer's disease, and other brain disorders.
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Affiliation(s)
- Andrew S P Lim
- Division of Neurology, Department of Medicine, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, ON, Canada.
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7
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Finger AM, Dibner C, Kramer A. Coupled network of the circadian clocks: a driving force of rhythmic physiology. FEBS Lett 2020; 594:2734-2769. [PMID: 32750151 DOI: 10.1002/1873-3468.13898] [Citation(s) in RCA: 46] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2020] [Revised: 07/06/2020] [Accepted: 07/21/2020] [Indexed: 12/15/2022]
Abstract
The circadian system is composed of coupled endogenous oscillators that allow living beings, including humans, to anticipate and adapt to daily changes in their environment. In mammals, circadian clocks form a hierarchically organized network with a 'master clock' located in the suprachiasmatic nucleus of the hypothalamus, which ensures entrainment of subsidiary oscillators to environmental cycles. Robust rhythmicity of body clocks is indispensable for temporally coordinating organ functions, and the disruption or misalignment of circadian rhythms caused for instance by modern lifestyle is strongly associated with various widespread diseases. This review aims to provide a comprehensive overview of our current knowledge about the molecular architecture and system-level organization of mammalian circadian oscillators. Furthermore, we discuss the regulatory roles of peripheral clocks for cell and organ physiology and their implication in the temporal coordination of metabolism in human health and disease. Finally, we summarize methods for assessing circadian rhythmicity in humans.
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Affiliation(s)
- Anna-Marie Finger
- Laboratory of Chronobiology, Charité Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Berlin, Germany.,Berlin Institute of Health (BIH), Berlin, Germany
| | - Charna Dibner
- Division of Endocrinology, Diabetes, Nutrition, and Patient Education, Department of Medicine, University Hospital of Geneva, Geneva, Switzerland.,Department of Cell Physiology and Metabolism, Faculty of Medicine, University of Geneva, Geneva, Switzerland.,Diabetes Center, Faculty of Medicine, University of Geneva, Geneva, Switzerland.,Institute of Genetics and Genomics in Geneva (iGE3), University of Geneva, Geneva, Switzerland
| | - Achim Kramer
- Laboratory of Chronobiology, Charité Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Berlin, Germany.,Berlin Institute of Health (BIH), Berlin, Germany
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8
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Gaspar LS, Álvaro AR, Carmo‐Silva S, Mendes AF, Relógio A, Cavadas C. The importance of determining circadian parameters in pharmacological studies. Br J Pharmacol 2019; 176:2827-2847. [PMID: 31099023 PMCID: PMC6637036 DOI: 10.1111/bph.14712] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2019] [Revised: 03/26/2019] [Accepted: 04/01/2019] [Indexed: 12/25/2022] Open
Abstract
In mammals, most molecular and cellular processes show circadian changes, leading to daily variations in physiology and ultimately in behaviour. Such daily variations induce a temporal coordination of processes that is essential to ensure homeostasis and health. Thus, it is of no surprise that pharmacokinetics (PK) and pharmacodynamics (PD) of many drugs are also subject to circadian variations, profoundly affecting their efficacy and tolerability. Understanding how circadian rhythms influence drug PK, PD, and toxicity might significantly improve treatment efficacy and decrease related side effects. Therefore, it is essential to take circadian variations into account and to determine circadian parameters in pharmacological studies, especially when drugs have a short half-life or target rhythmic processes. This review provides an overview of the current knowledge on circadian rhythms and their relevance to the field of pharmacology. Methodologies to evaluate circadian rhythms in vitro, in rodent models and in humans, from experimental to computational approaches, are described and discussed. Lastly, we aim at alerting the scientific, medical, and regulatory communities to the relevance of the physiological time, as a key parameter to be considered when designing pharmacological studies. This will eventually lead to more successful preclinical and clinical trials and pave the way to a more personalized treatment to the benefit of the patients.
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Affiliation(s)
- Laetitia S. Gaspar
- CNC—Center for Neuroscience and Cell BiologyUniversity of CoimbraCoimbraPortugal
- Center for Innovation in Biomedicine and Biotechnology (CIBB)University of CoimbraCoimbraPortugal
- Institute for Interdisciplinary Research (IIIUC)University of CoimbraCoimbraPortugal
| | - Ana Rita Álvaro
- CNC—Center for Neuroscience and Cell BiologyUniversity of CoimbraCoimbraPortugal
- Center for Innovation in Biomedicine and Biotechnology (CIBB)University of CoimbraCoimbraPortugal
| | - Sara Carmo‐Silva
- CNC—Center for Neuroscience and Cell BiologyUniversity of CoimbraCoimbraPortugal
- Center for Innovation in Biomedicine and Biotechnology (CIBB)University of CoimbraCoimbraPortugal
| | - Alexandrina Ferreira Mendes
- CNC—Center for Neuroscience and Cell BiologyUniversity of CoimbraCoimbraPortugal
- Center for Innovation in Biomedicine and Biotechnology (CIBB)University of CoimbraCoimbraPortugal
- Faculty of PharmacyUniversity of CoimbraCoimbraPortugal
| | - Angela Relógio
- Institute for Theoretical BiologyCharité—Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt—Universität zu Berlin, and Berlin Institute of HealthBerlinGermany
- Medical Department of Hematology, Oncology, and Tumor Immunology, Molecular Cancer Research CenterCharité—Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt—Universität zu Berlin, and Berlin Institute of HealthBerlinGermany
| | - Cláudia Cavadas
- CNC—Center for Neuroscience and Cell BiologyUniversity of CoimbraCoimbraPortugal
- Center for Innovation in Biomedicine and Biotechnology (CIBB)University of CoimbraCoimbraPortugal
- Faculty of PharmacyUniversity of CoimbraCoimbraPortugal
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9
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Wheaton KL, Hansen KF, Aten S, Sullivan KA, Yoon H, Hoyt KR, Obrietan K. The Phosphorylation of CREB at Serine 133 Is a Key Event for Circadian Clock Timing and Entrainment in the Suprachiasmatic Nucleus. J Biol Rhythms 2018; 33:497-514. [PMID: 30175684 DOI: 10.1177/0748730418791713] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Within the suprachiasmatic nucleus (SCN)-the locus of the master circadian clock- transcriptional regulation via the CREB/CRE pathway is implicated in the functioning of the molecular clock timing process, and is a key conduit through which photic input entrains the oscillator. One event driving CRE-mediated transcription is the phosphorylation of CREB at serine 133 (Ser133). Indeed, numerous reporter gene assays have shown that an alanine point mutation in Ser133 reduces CREB-mediated transcription. Here, we sought to examine the contribution of Ser133 phosphorylation to the functional role of CREB in SCN clock physiology in vivo. To this end, we used a CREB knock-in mouse strain, in which Ser133 was mutated to alanine (S/A CREB). Under a standard 12 h light-dark cycle, S/A CREB mice exhibited a marked alteration in clock-regulated wheel running activity. Relative to WT mice, S/A CREB mice had highly fragmented bouts of locomotor activity during the night phase, elevated daytime activity, and a delayed phase angle of entrainment. Further, under free-running conditions, S/A CREB mice had a significantly longer tau than WT mice and reduced activity amplitude. In S/A CREB mice, light-evoked clock entrainment, using both Aschoff type 1 and 6 h "jet lag" paradigms, was markedly reduced relative to WT mice. S/A CREB mice exhibited attenuated transcriptional drive, as assessed by examining both clock-gated and light-evoked gene expression. Finally, SCN slice culture imaging detected a marked disruption in cellular clock phase synchrony following a phase-resetting stimulus in S/A CREB mice. Together, these data indicate that signaling through CREB phosphorylation at Ser133 is critical for the functional fidelity of both SCN timing and entrainment.
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Affiliation(s)
- Kelin L Wheaton
- Division of Pharmaceutics and Pharmaceutical Chemistry, Ohio State University, Columbus, OH
| | | | - Sydney Aten
- Department of Neuroscience, Ohio State University, Columbus, OH
| | - Kyle A Sullivan
- Department of Neuroscience, Ohio State University, Columbus, OH
| | - Hyojung Yoon
- Department of Neuroscience, Ohio State University, Columbus, OH
| | - Kari R Hoyt
- Division of Pharmaceutics and Pharmaceutical Chemistry, Ohio State University, Columbus, OH
| | - Karl Obrietan
- Department of Neuroscience, Ohio State University, Columbus, OH
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10
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Belle MDC, Diekman CO. Neuronal oscillations on an ultra-slow timescale: daily rhythms in electrical activity and gene expression in the mammalian master circadian clockwork. Eur J Neurosci 2018; 48:2696-2717. [PMID: 29396876 DOI: 10.1111/ejn.13856] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2017] [Revised: 01/16/2018] [Accepted: 01/28/2018] [Indexed: 12/17/2022]
Abstract
Neuronal oscillations of the brain, such as those observed in the cortices and hippocampi of behaving animals and humans, span across wide frequency bands, from slow delta waves (0.1 Hz) to ultra-fast ripples (600 Hz). Here, we focus on ultra-slow neuronal oscillators in the hypothalamic suprachiasmatic nuclei (SCN), the master daily clock that operates on interlocking transcription-translation feedback loops to produce circadian rhythms in clock gene expression with a period of near 24 h (< 0.001 Hz). This intracellular molecular clock interacts with the cell's membrane through poorly understood mechanisms to drive the daily pattern in the electrical excitability of SCN neurons, exhibiting an up-state during the day and a down-state at night. In turn, the membrane activity feeds back to regulate the oscillatory activity of clock gene programs. In this review, we emphasise the circadian processes that drive daily electrical oscillations in SCN neurons, and highlight how mathematical modelling contributes to our increasing understanding of circadian rhythm generation, synchronisation and communication within this hypothalamic region and across other brain circuits.
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Affiliation(s)
- Mino D C Belle
- Institute of Clinical and Biomedical Sciences, University of Exeter Medical School, University of Exeter, Exeter, EX4 4PS, UK
| | - Casey O Diekman
- Department of Mathematical Sciences, New Jersey Institute of Technology, Newark, NJ, USA.,Institute for Brain and Neuroscience Research, New Jersey Institute of Technology, Newark, NJ, USA
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11
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Lai B, Zou J, Lin Z, Qu Z, Song A, Xu Y, Gao X. Haploinsufficiency of hnRNP U Changes Activity Pattern and Metabolic Rhythms. THE AMERICAN JOURNAL OF PATHOLOGY 2017; 188:173-183. [PMID: 29128567 DOI: 10.1016/j.ajpath.2017.09.017] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/26/2017] [Revised: 08/26/2017] [Accepted: 09/21/2017] [Indexed: 12/25/2022]
Abstract
The neuropeptides arginine vasopressin (Avp) and vasoactive intestinal polypeptide (Vip) are critical for the communication and coupling of suprachiasmatic nucleus neurons, which organize daily rhythms of physiology and behavior in mammals. However, how these peptides are regulated remains uncharacterized. We found that heterogeneous nuclear ribonucleoprotein U (hnRNP U) is essential for the expression of Avp and Vip. Loss of one copy of the Hnrnpu gene resulted in fragmented locomotor activities and disrupted metabolic rhythms. Hnrnpu+/- mice were more active than wild-type mice in the daytime but more inactive at night. These phenotypes were partially rescued by microinfusion of Avp and Vip into free-moving animals. In addition, hnRNP U modulated Avp and Vip via directly binding to their promoters together with brain and muscle Arnt-like protein-1/circadian locomotor output cycles kaput heterodimers. Our work identifies hnRNP U as a novel regulator of the circadian pacemaker and provides new insights into the mechanism of rhythm output.
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Affiliation(s)
- Beibei Lai
- State Key Laboratory of Pharmaceutical Biotechnology and MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Collaborative Innovation Center of Genetics and Development, Nanjing University, Nanjing, China
| | - Jianghuan Zou
- State Key Laboratory of Pharmaceutical Biotechnology and MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Collaborative Innovation Center of Genetics and Development, Nanjing University, Nanjing, China
| | - Zhaoyu Lin
- State Key Laboratory of Pharmaceutical Biotechnology and MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Collaborative Innovation Center of Genetics and Development, Nanjing University, Nanjing, China
| | - Zhipeng Qu
- State Key Laboratory of Pharmaceutical Biotechnology and MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Collaborative Innovation Center of Genetics and Development, Nanjing University, Nanjing, China
| | - Anying Song
- State Key Laboratory of Pharmaceutical Biotechnology and MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Collaborative Innovation Center of Genetics and Development, Nanjing University, Nanjing, China
| | - Ying Xu
- Medical College of Soochou University, Suzhou, China.
| | - Xiang Gao
- State Key Laboratory of Pharmaceutical Biotechnology and MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Collaborative Innovation Center of Genetics and Development, Nanjing University, Nanjing, China.
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12
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Bailes HJ, Milosavljevic N, Zhuang LY, Gerrard EJ, Nishiguchi T, Ozawa T, Lucas RJ. Optogenetic interrogation reveals separable G-protein-dependent and -independent signalling linking G-protein-coupled receptors to the circadian oscillator. BMC Biol 2017; 15:40. [PMID: 28506231 PMCID: PMC5430609 DOI: 10.1186/s12915-017-0380-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2017] [Accepted: 04/26/2017] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Endogenous circadian oscillators distributed across the mammalian body are synchronised among themselves and with external time via a variety of signalling molecules, some of which interact with G-protein-coupled receptors (GPCRs). GPCRs can regulate cell physiology via pathways originating with heterotrimeric G-proteins or β-arrestins. We applied an optogenetic approach to determine the contribution of these two signalling modes on circadian phase. RESULTS We employed a photopigment (JellyOp) that activates Gαs signalling with better selectivity and higher sensitivity than available alternatives, and a point mutant of this pigment (F112A) biased towards β-arrestin signalling. When expressed in fibroblasts, both native JellyOp and the F112A arrestin-biased mutant drove light-dependent phase resetting in the circadian clock. Shifts induced by the two opsins differed in their circadian phase dependence and the degree to which they were associated with clock gene induction. CONCLUSIONS Our data imply separable G-protein and arrestin inputs to the mammalian circadian clock and establish a pair of optogenetic tools suitable for manipulating Gαs- and β-arrestin-biased signalling in live cells.
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Affiliation(s)
- Helena J Bailes
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, UK
| | - Nina Milosavljevic
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, UK.
| | - Ling-Yu Zhuang
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, UK
| | - Elliot J Gerrard
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, UK
| | | | - Takeaki Ozawa
- Department of Chemistry, The University of Tokyo, Tokyo, Japan
| | - Robert J Lucas
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, UK
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13
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Evans JA. Collective timekeeping among cells of the master circadian clock. J Endocrinol 2016; 230:R27-49. [PMID: 27154335 PMCID: PMC4938744 DOI: 10.1530/joe-16-0054] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/11/2016] [Accepted: 05/06/2016] [Indexed: 01/09/2023]
Abstract
The suprachiasmatic nucleus (SCN) of the anterior hypothalamus is the master circadian clock that coordinates daily rhythms in behavior and physiology in mammals. Like other hypothalamic nuclei, the SCN displays an impressive array of distinct cell types characterized by differences in neurotransmitter and neuropeptide expression. Individual SCN neurons and glia are able to display self-sustained circadian rhythms in cellular function that are regulated at the molecular level by a 24h transcriptional-translational feedback loop. Remarkably, SCN cells are able to harmonize with one another to sustain coherent rhythms at the tissue level. Mechanisms of cellular communication in the SCN network are not completely understood, but recent progress has provided insight into the functional roles of several SCN signaling factors. This review discusses SCN organization, how intercellular communication is critical for maintaining network function, and the signaling mechanisms that play a role in this process. Despite recent progress, our understanding of SCN circuitry and coupling is far from complete. Further work is needed to map SCN circuitry fully and define the signaling mechanisms that allow for collective timekeeping in the SCN network.
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Affiliation(s)
- Jennifer A Evans
- Department of Biomedical SciencesMarquette University, Milwaukee, WI, USA
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14
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Evans JA, Gorman MR. In synch but not in step: Circadian clock circuits regulating plasticity in daily rhythms. Neuroscience 2016; 320:259-80. [PMID: 26861419 DOI: 10.1016/j.neuroscience.2016.01.072] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2015] [Revised: 01/26/2016] [Accepted: 01/27/2016] [Indexed: 11/16/2022]
Abstract
The suprachiasmatic nucleus (SCN) is a network of neural oscillators that program daily rhythms in mammalian behavior and physiology. Over the last decade much has been learned about how SCN clock neurons coordinate together in time and space to form a cohesive population. Despite this insight, much remains unknown about how SCN neurons communicate with one another to produce emergent properties of the network. Here we review the current understanding of communication among SCN clock cells and highlight a collection of formal assays where changes in SCN interactions provide for plasticity in the waveform of circadian rhythms in behavior. Future studies that pair analytical behavioral assays with modern neuroscience techniques have the potential to provide deeper insight into SCN circuit mechanisms.
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Affiliation(s)
- J A Evans
- Department of Biomedical Sciences, Marquette University, Milwaukee, WI, USA.
| | - M R Gorman
- Department of Psychology, University of San Diego, La Jolla, CA, USA
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15
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Hughes ATL, Croft CL, Samuels RE, Myung J, Takumi T, Piggins HD. Constant light enhances synchrony among circadian clock cells and promotes behavioral rhythms in VPAC2-signaling deficient mice. Sci Rep 2015; 5:14044. [PMID: 26370467 PMCID: PMC4642707 DOI: 10.1038/srep14044] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2015] [Accepted: 08/14/2015] [Indexed: 12/22/2022] Open
Abstract
Individual neurons in the suprachiasmatic nuclei (SCN) contain an intracellular molecular clock and use intercellular signaling to synchronize their timekeeping activities so that the SCN can coordinate brain physiology and behavior. The neuropeptide vasoactive intestinal polypeptide (VIP) and its VPAC2 receptor form a key component of intercellular signaling systems in the SCN and critically control cellular coupling. Targeted mutations in either the intracellular clock or intercellular neuropeptide signaling mechanisms, such as VIP-VPAC2 signaling, can lead to desynchronization of SCN neuronal clocks and loss of behavioral rhythms. An important goal in chronobiology is to develop interventions to correct deficiencies in circadian timekeeping. Here we show that extended exposure to constant light promotes synchrony among SCN clock cells and the expression of ~24 h rhythms in behavior in mice in which intercellular signaling is disrupted through loss of VIP-VPAC2 signaling. This study highlights the importance of SCN synchrony for the expression of rhythms in behavior and reveals how non-invasive manipulations in the external environment can be used to overcome neurochemical communication deficits in this important brain system.
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Affiliation(s)
- Alun T L Hughes
- Faculty of Life Sciences, University of Manchester, Manchester, UK
| | - Cara L Croft
- Faculty of Life Sciences, University of Manchester, Manchester, UK
| | - Rayna E Samuels
- Faculty of Life Sciences, University of Manchester, Manchester, UK
| | - Jihwan Myung
- RIKEN Brain Science Institute, Wako, Saitama, Japan
| | - Toru Takumi
- RIKEN Brain Science Institute, Wako, Saitama, Japan
| | - Hugh D Piggins
- Faculty of Life Sciences, University of Manchester, Manchester, UK
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16
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Belle MDC. Circadian Tick-Talking Across the Neuroendocrine System and Suprachiasmatic Nuclei Circuits: The Enigmatic Communication Between the Molecular and Electrical Membrane Clocks. J Neuroendocrinol 2015; 27:567-76. [PMID: 25845396 PMCID: PMC4973835 DOI: 10.1111/jne.12279] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/26/2014] [Revised: 03/25/2015] [Accepted: 03/26/2015] [Indexed: 12/15/2022]
Abstract
As with many processes in nature, appropriate timing in biological systems is of paramount importance. In the neuroendocrine system, the efficacy of hormonal influence on major bodily functions, such as reproduction, metabolism and growth, relies on timely communication within and across many of the brain's homeostatic systems. The activity of these circuits is tightly orchestrated with the animal's internal physiological demands and external solar cycle by a master circadian clock. In mammals, this master clock is located in the hypothalamic suprachiasmatic nucleus (SCN), where the ensemble activity of thousands of clock neurones generates and communicates circadian time cues to the rest of the brain and body. Many regions of the brain, including areas with neuroendocrine function, also contain local daily clocks that can provide feedback signals to the SCN. Although much is known about the molecular processes underpinning endogenous circadian rhythm generation in SCN neurones and, to a lesser extent, extra-SCN cells, the electrical membrane clock that acts in partnership with the molecular clockwork to communicate circadian timing across the brain is poorly understood. The present review focuses on some circadian aspects of reproductive neuroendocrinology and processes involved in circadian rhythm communication in the SCN, aiming to identify key gaps in our knowledge of cross-talk between our daily master clock and neuroendocrine function. The intention is to highlight our surprisingly limited understanding of their interaction in the hope that this will stimulate future work in these areas.
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Affiliation(s)
- M. D. C. Belle
- Faculty of Life SciencesUniversity of ManchesterManchesterUK
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17
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Mieda M, Ono D, Hasegawa E, Okamoto H, Honma KI, Honma S, Sakurai T. Cellular clocks in AVP neurons of the SCN are critical for interneuronal coupling regulating circadian behavior rhythm. Neuron 2015; 85:1103-16. [PMID: 25741730 DOI: 10.1016/j.neuron.2015.02.005] [Citation(s) in RCA: 170] [Impact Index Per Article: 18.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2014] [Revised: 12/10/2014] [Accepted: 01/19/2015] [Indexed: 01/06/2023]
Abstract
The suprachiasmatic nucleus (SCN), the primary circadian pacemaker in mammals, is a network structure composed of multiple types of neurons. Here, we report that mice with a Bmal1 deletion specific to arginine vasopressin (AVP)-producing neurons showed marked lengthening in the free-running period and activity time of behavior rhythms. When exposed to an abrupt 8-hr advance of the light/dark cycle, these mice reentrained faster than control mice did. In these mice, the circadian expression of genes involved in intercellular communications, including Avp, Prokineticin 2, and Rgs16, was drastically reduced in the dorsal SCN, where AVP neurons predominate. In slices, dorsal SCN cells showed attenuated PER2::LUC oscillation with highly variable and lengthened periods. Thus, Bmal1-dependent oscillators of AVP neurons may modulate the coupling of the SCN network, eventually coupling morning and evening behavioral rhythms, by regulating expression of multiple factors important for the network property of these neurons.
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Affiliation(s)
- Michihiro Mieda
- Department of Molecular Neuroscience and Integrative Physiology, Faculty of Medicine, Kanazawa University, 13-1 Takara-machi, Kanazawa, Ishikawa 920-8640, Japan.
| | - Daisuke Ono
- Photonic Bioimaging Section, Research Center for Cooperative Projects, Hokkaido University Graduate School of Medicine, N-15, W-7, Kita-ku, Sapporo, Hokkaido 060-8638, Japan
| | - Emi Hasegawa
- Department of Molecular Neuroscience and Integrative Physiology, Faculty of Medicine, Kanazawa University, 13-1 Takara-machi, Kanazawa, Ishikawa 920-8640, Japan
| | - Hitoshi Okamoto
- Laboratory for Developmental Gene Regulation, RIKEN Brain Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Ken-Ichi Honma
- Department of Chronomedicine, Hokkaido University Graduate School of Medicine, N-15, W-7, Kita-ku, Sapporo, Hokkaido 060-8638, Japan
| | - Sato Honma
- Department of Chronomedicine, Hokkaido University Graduate School of Medicine, N-15, W-7, Kita-ku, Sapporo, Hokkaido 060-8638, Japan
| | - Takeshi Sakurai
- Department of Molecular Neuroscience and Integrative Physiology, Faculty of Medicine, Kanazawa University, 13-1 Takara-machi, Kanazawa, Ishikawa 920-8640, Japan
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18
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Loh DH, Kuljis DA, Azuma L, Wu Y, Truong D, Wang HB, Colwell CS. Disrupted reproduction, estrous cycle, and circadian rhythms in female mice deficient in vasoactive intestinal peptide. J Biol Rhythms 2014; 29:355-69. [PMID: 25252712 DOI: 10.1177/0748730414549767] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The female reproductive cycle is gated by the circadian timing system and may be vulnerable to disruptions in the circadian system. Prior work suggests that vasoactive intestinal peptide (VIP)-expressing neurons in the suprachiasmatic nucleus (SCN) are one pathway by which the circadian clock can influence the estrous cycle, but the impact of the loss of this peptide on reproduction has not been assessed. In the present study, we first examine the impact of the genetic loss of the neuropeptide VIP on the reproductive success of female mice. Significantly, mutant females produce about half the offspring of their wild-type sisters even when mated to the same males. We also find that VIP-deficient females exhibit a disrupted estrous cycle; that is, ovulation occurs less frequently and results in the release of fewer oocytes compared with controls. Circadian rhythms of wheel-running activity are disrupted in the female mutant mice, as is the spontaneous electrical activity of dorsal SCN neurons. On a molecular level, the VIP-deficient SCN tissue exhibits lower amplitude oscillations with altered phase relationships between the SCN and peripheral oscillators as measured by PER2-driven bioluminescence. The simplest explanation of our data is that the loss of VIP results in a weakened SCN oscillator, which reduces the synchronization of the female circadian system. These results clarify one of the mechanisms by which disruption of the circadian system reduces female reproductive success.
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Affiliation(s)
- D H Loh
- Laboratory of Circadian and Sleep Medicine, Department of Psychiatry and Biobehavioral Sciences, University of California-Los Angeles, California
| | - D A Kuljis
- Laboratory of Circadian and Sleep Medicine, Department of Psychiatry and Biobehavioral Sciences, University of California-Los Angeles, California Department of Neurobiology, University of California-Los Angeles
| | - L Azuma
- Laboratory of Circadian and Sleep Medicine, Department of Psychiatry and Biobehavioral Sciences, University of California-Los Angeles, California
| | - Y Wu
- Laboratory of Circadian and Sleep Medicine, Department of Psychiatry and Biobehavioral Sciences, University of California-Los Angeles, California
| | - D Truong
- Laboratory of Circadian and Sleep Medicine, Department of Psychiatry and Biobehavioral Sciences, University of California-Los Angeles, California
| | - H B Wang
- Laboratory of Circadian and Sleep Medicine, Department of Psychiatry and Biobehavioral Sciences, University of California-Los Angeles, California
| | - C S Colwell
- Laboratory of Circadian and Sleep Medicine, Department of Psychiatry and Biobehavioral Sciences, University of California-Los Angeles, California
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19
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Stepanyuk AR, Belan PV, Kononenko NI. A model for the fast synchronous oscillations of firing rate in rat suprachiasmatic nucleus neurons cultured in a multielectrode array dish. PLoS One 2014; 9:e106152. [PMID: 25192180 PMCID: PMC4156468 DOI: 10.1371/journal.pone.0106152] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2014] [Accepted: 08/03/2014] [Indexed: 12/27/2022] Open
Abstract
When dispersed and cultured in a multielectrode dish (MED), suprachiasmatic nucleus (SCN) neurons express fast oscillations of firing rate (FOFR; fast relative to the circadian cycle), with burst duration ∼10 min, and interburst interval varying from 20 to 60 min in different cells but remaining nevertheless rather regular in individual cells. In many cases, separate neurons in distant parts of the 1 mm recording area of a MED exhibited correlated FOFR. Neither the mechanism of FOFR nor the mechanism of their synchronization among neurons is known. Based on recent data implicating vasoactive intestinal polypeptide (VIP) as a key intercellular synchronizing agent, we built a model in which VIP acts as both a feedback regulator to generate FOFR in individual neurons, and a diffusible synchronizing agent to produce coherent electrical output of a neuronal network. In our model, VIP binding to its (VPAC2) receptors acts through Gs G-proteins to activate adenylyl cyclase (AC), increase intracellular cAMP, and open cyclic-nucleotide-gated (CNG) cation channels, thus depolarizing the cell and generating neuronal firing to release VIP. In parallel, slowly developing homologous desensitization and internalization of VPAC2 receptors terminates elevation of cAMP and thereby provides an interpulse silent interval. Through mathematical modeling, we show that this VIP/VPAC2/AC/cAMP/CNG-channel mechanism is sufficient for generating reliable FOFR in single neurons. When our model for FOFR is combined with a published model of synchronization of circadian rhythms based on VIP/VPAC2 and Per gene regulation synchronization of circadian rhythms is significantly accelerated. These results suggest that (a) auto/paracrine regulation by VIP/VPAC2 and intracellular AC/cAMP/CNG-channels are sufficient to provide robust FOFR and synchrony among neurons in a heterogeneous network, and (b) this system may also participate in synchronization of circadian rhythms.
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Affiliation(s)
- Andrey R. Stepanyuk
- Bogomoletz Institute of Physiology, Kiev, Ukraine
- State Key Laboratory of Molecular and Cellular Biology, Kiev, Ukraine
- * E-mail:
| | - Pavel V. Belan
- Bogomoletz Institute of Physiology, Kiev, Ukraine
- State Key Laboratory of Molecular and Cellular Biology, Kiev, Ukraine
| | - Nikolai I. Kononenko
- Bogomoletz Institute of Physiology, Kiev, Ukraine
- State Key Laboratory of Molecular and Cellular Biology, Kiev, Ukraine
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20
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Acute suppressive and long-term phase modulation actions of orexin on the mammalian circadian clock. J Neurosci 2014; 34:3607-21. [PMID: 24599460 DOI: 10.1523/jneurosci.3388-13.2014] [Citation(s) in RCA: 93] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Circadian and homeostatic neural circuits organize the temporal architecture of physiology and behavior, but knowledge of their interactions is imperfect. For example, neurons containing the neuropeptide orexin homeostatically control arousal and appetitive states, while neurons in the suprachiasmatic nuclei (SCN) function as the brain's master circadian clock. The SCN regulates orexin neurons so that they are much more active during the circadian night than the circadian day, but it is unclear whether the orexin neurons reciprocally regulate the SCN clock. Here we show both orexinergic innervation and expression of genes encoding orexin receptors (OX1 and OX2) in the mouse SCN, with OX1 being upregulated at dusk. Remarkably, we find through in vitro physiological recordings that orexin predominantly suppresses mouse SCN Period1 (Per1)-EGFP-expressing clock cells. The mechanisms underpinning these suppressions vary across the circadian cycle, from presynaptic modulation of inhibitory GABAergic signaling during the day to directly activating leak K(+) currents at night. Orexin also augments the SCN clock-resetting effects of neuropeptide Y (NPY), another neurochemical correlate of arousal, and potentiates NPY's inhibition of SCN Per1-EGFP cells. These results build on emerging literature that challenge the widely held view that orexin signaling is exclusively excitatory and suggest new mechanisms for avoiding conflicts between circadian clock signals and homeostatic cues in the brain.
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21
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22
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Fahrenkrug J, Georg B, Hannibal J, Jørgensen HL. Altered rhythm of adrenal clock genes, StAR and serum corticosterone in VIP receptor 2-deficient mice. J Mol Neurosci 2012; 48:584-96. [PMID: 22622901 DOI: 10.1007/s12031-012-9804-7] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2012] [Accepted: 05/03/2012] [Indexed: 12/31/2022]
Abstract
The circadian time-keeping system consists of clocks in the suprachiasmatic nucleus (SCN) and in peripheral organs including an adrenal clock linked to the rhythmic corticosteroid production by regulating steroidogenic acute regulatory protein (StAR). Clock cells contain an autonomous molecular oscillator based on a group of clock genes and their protein products. Mice lacking the VPAC2 receptor display disrupted circadian rhythm of physiology and behaviour, and therefore, we using real-time RT-PCR quantified (1) the mRNAs for the clock genes Per1 and Bmal1 in the adrenal gland and SCN, (2) the adrenal Star mRNA and (3) the serum corticosterone concentration both during a light/dark (L/D) cycle and at constant darkness in wild type (WT) and VPAC2 receptor-deficient mice (VPAC2-KO). We also examined if PER1 and StAR were co-localised in the adrenal steroidogenic cells. Per1 and Bmal1 mRNA showed a 24-h rhythmic expression in the adrenal of WT mice under L/D and dark conditions. During a L/D cycle, the adrenal clock gene rhythm in VPAC2-KO mice was phase-advanced by approximately 6 h compared to WT mice and became arrhythmic in constant darkness. A significant 24-h rhythmic variation in the adrenal Star mRNA expression and circulating corticosterone concentration was similarly phase-advanced during the L/D cycle. The loss of adrenal clock gene rhythm in the VPAC2 receptor knockout mice after transfer into constant darkness was accompanied by disappearance of rhythmicity in Star mRNA expression and serum corticosterone concentration. Double immunohistochemistry showed that the PER1 protein and StAR were co-localised in the same steroidogenic cells. Circulating corticosterone plays a role in the circadian timing system and the misaligned corticosterone rhythm in the VPAC2 receptor knockout mice could be involved in their abnormal rhythms of physiology.
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Affiliation(s)
- Jan Fahrenkrug
- Department of Clinical Biochemistry, Bispebjerg Hospital, University of Copenhagen, Copenhagen 2400, Denmark.
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23
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Wong CCP, Schumann G. Integration of the circadian and stress systems: influence of neuropeptides and implications for alcohol consumption. J Neural Transm (Vienna) 2012; 119:1111-20. [PMID: 22648536 DOI: 10.1007/s00702-012-0829-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2012] [Accepted: 05/10/2012] [Indexed: 12/16/2022]
Abstract
Disruptions in circadian rhythm and stress reactivity are associated with risks of developing neuropsychiatric disorders. The circadian system is organised in a hierarchical manner, whereby the master clock is located at the suprachiasmatic nucleus, a highly conserved brain region that coordinates the oscillations of peripheral clocks. Exposure to psychological stress leads to activation of the hypothalamic-pituitary-adrenal axis. There is growing evidence supporting the interactions between the circadian and stress systems. Anatomically, the circadian and stress signals converge at the paraventricular nucleus (PVN) in the hypothalamus. Genes that are involved in the operation of the circadian and stress systems, including Clock, Period and CRH are expressed in the PVN. In addition, several neuropeptides, including arginin-vasopressin, vasoactive intestinal polypeptide, pituitary adenylate cyclase-activating polypeptide and the neurotransmitter gamma-aminobutyric acid, are present in the PVN. In this review, we will discuss the interaction of circadian genes and stress-response genes at the molecular, neurotransmission and behavioural levels. We will place particular emphasis on the role of neuropeptides in mediating this interaction.
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Affiliation(s)
- Cybele C P Wong
- MRC-SGDP Centre, Institute of Psychiatry, King's College London, 16 De Crespigny Park, London SE5 8AF, UK.
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24
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Iimura T, Nakane A, Sugiyama M, Sato H, Makino Y, Watanabe T, Takagi Y, Numano R, Yamaguchi A. A fluorescence spotlight on the clockwork development and metabolism of bone. J Bone Miner Metab 2012; 30:254-69. [PMID: 21766187 DOI: 10.1007/s00774-011-0295-3] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/09/2011] [Accepted: 06/10/2011] [Indexed: 01/26/2023]
Abstract
Biological phenomena that exhibit periodic activity are often referred as biorhythms or biological clocks. Among these, circadian rhythms, cyclic patterns reflecting a 24-h cycle, are the most obvious in many physiological activities including bone growth and metabolism. In the late 1990s, several clock genes were isolated and their primary structures and functions were identified. The feedback loop model of transcriptional factors was proposed to work as a circadian core oscillator not only in the suprachiasmatic nuclei of the anterior hypothalamus, which is recognized as the mammalian central clock, but also in various peripheral tissues including cartilage and bone. Looking back to embryonic development, the fundamental architecture of skeletal patterning is regulated by ultradian clocks that are defined as biorhythms that cycle more than once every 24 h. As post-genomic approaches, transcriptome analysis by micro-array and bioimaging assays to detect luminescent and fluorescent signals have been exploited to uncover a more comprehensive set of genes and spatio-temporal regulation of the clockwork machinery in animal models. In this review paper, we provide an overview of topics related to these molecular clocks in skeletal biology and medicine, and discuss how fluorescence imaging approaches can contribute to widening our views of this realm of biomedical science.
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Affiliation(s)
- Tadahiro Iimura
- Global Center of Excellence (GCOE) Program, International Research Center for Molecular Science in Tooth and Bone Diseases, Tokyo Medical and Dental University, Tokyo, Japan.
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25
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Hong JH, Jeong B, Min CH, Lee KJ. Circadian waves of cytosolic calcium concentration and long-range network connections in rat suprachiasmatic nucleus. Eur J Neurosci 2012; 35:1417-25. [PMID: 22501027 DOI: 10.1111/j.1460-9568.2012.08069.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The suprachiasmatic nucleus (SCN) is the master clock in mammals governing the daily physiological and behavioral rhythms. It is composed of thousands of clock cells with their own intrinsic periods varying over a wide range (20-28 h). Despite this heterogeneity, an intact SCN maintains a coherent 24 h periodic rhythm through some cell-to-cell coupling mechanisms. This study examined how the clock cells are connected to each other and how their phases are organized in space by monitoring the cytosolic free calcium ion concentration ([Ca(2+)](c)) of clock cells using the calcium-binding fluorescent protein, cameleon. Extensive analysis of 18 different organotypic slice cultures of the SCN showed that the SCN calcium dynamics is coordinated by phase-synchronizing networks of long-range neurites as well as by diffusively propagating phase waves. The networks appear quite extensive and far-reaching, and the clock cells connected by them exhibit heterogeneous responses in their amplitudes and periods of oscillation to tetrodotoxin treatments. Taken together, our study suggests that the network of long-range cellular connectivity has an important role for the SCN in achieving its phase and period coherence.
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Affiliation(s)
- Jin Hee Hong
- Center for Cell Dynamics and Department of Physics, Korea University, Anam-Dong 5-1, Sungbuk-Gu, Seoul 136-713, Korea
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26
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Hughes ATL, Piggins HD. Feedback actions of locomotor activity to the circadian clock. PROGRESS IN BRAIN RESEARCH 2012; 199:305-336. [PMID: 22877673 DOI: 10.1016/b978-0-444-59427-3.00018-6] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
The phase of the mammalian circadian system can be entrained to a range of environmental stimuli, or zeitgebers, including food availability and light. Further, locomotor activity can act as an entraining signal and represents a mechanism for an endogenous behavior to feedback and influence subsequent circadian function. This process involves a number of nuclei distributed across the brain stem, thalamus, and hypothalamus and ultimately alters SCN electrical and molecular function to induce phase shifts in the master circadian pacemaker. Locomotor activity feedback to the circadian system is effective across both nocturnal and diurnal species, including humans, and has recently been shown to improve circadian function in a mouse model with a weakened circadian system. This raises the possibility that exercise may be useful as a noninvasive treatment in cases of human circadian dysfunction including aging, shift work, transmeridian travel, and the blind.
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Affiliation(s)
- Alun T L Hughes
- Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom.
| | - Hugh D Piggins
- Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
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27
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Abstract
In vitro assays have localized circadian pacemakers to individual cells, revealed genetic determinants of rhythm generation, identified molecular players in cell-cell synchronization and determined physiological events regulated by circadian clocks. Although they allow strict control of experimental conditions and reduce the number of variables compared with in vivo studies, they also lack many of the conditions in which cellular circadian oscillators normally function. The present review highlights methods to study circadian timing in cultured mammalian cells and how they have shaped the hypothesis that all cells are capable of circadian rhythmicity.
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Abstract
Humans and other mammals exhibit a remarkable array of cyclical changes in physiology and behaviour. These are often synchronized to the changing environmental light–dark cycle and persist in constant conditions. Such circadian rhythms are controlled by an endogenous clock, located in the suprachiasmatic nuclei of the hypothalamus. This structure and its cells have unique properties, and some of these are reviewed to highlight how this central clock controls and sculpts our daily activities.
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29
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Mohawk JA, Takahashi JS. Cell autonomy and synchrony of suprachiasmatic nucleus circadian oscillators. Trends Neurosci 2011; 34:349-58. [PMID: 21665298 DOI: 10.1016/j.tins.2011.05.003] [Citation(s) in RCA: 158] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2011] [Revised: 05/04/2011] [Accepted: 05/10/2011] [Indexed: 11/18/2022]
Abstract
The suprachiasmatic nucleus (SCN) of the hypothalamus is the site of the master circadian pacemaker in mammals. The individual cells of the SCN are capable of functioning independently from one another and therefore must form a cohesive circadian network through intercellular coupling. The network properties of the SCN lead to coordination of circadian rhythms among its neurons and neuronal subpopulations. There is increasing evidence for multiple interconnected oscillators within the SCN, and in this review we will highlight recent advances in our knowledge of the complex organization and function of the cellular and network-level SCN clock. Understanding the way in which synchrony is achieved between cells in the SCN will provide insight into the means by which this important nucleus orchestrates circadian rhythms throughout the organism.
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Affiliation(s)
- Jennifer A Mohawk
- Department of Neuroscience and Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX 75390-9111, USA
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30
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Loh DH, Dragich JM, Kudo T, Schroeder AM, Nakamura TJ, Waschek JA, Block GD, Colwell CS. Effects of vasoactive intestinal peptide genotype on circadian gene expression in the suprachiasmatic nucleus and peripheral organs. J Biol Rhythms 2011; 26:200-9. [PMID: 21628547 PMCID: PMC3942163 DOI: 10.1177/0748730411401740] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The neuropeptide vasoactive intestinal polypeptide (VIP) has emerged as a key candidate molecule mediating the synchronization of rhythms in clock gene expression within the suprachiasmatic nucleus (SCN). In addition, neurons expressing VIP are anatomically well positioned to mediate communication between the SCN and peripheral oscillators. In this study, we examined the temporal expression profile of 3 key circadian genes: Per1, Per2 , and Bmal1 in the SCN, the adrenal glands and the liver of mice deficient for the Vip gene (VIP KO), and their wild-type counterparts. We performed these measurements in mice held in a light/dark cycle as well as in constant darkness and found that rhythms in gene expression were greatly attenuated in the VIP-deficient SCN. In the periphery, the impact of the loss of VIP varied with the tissue and gene measured. In the adrenals, rhythms in Per1 were lost in VIP-deficient mice, while in the liver, the most dramatic impact was on the phase of the diurnal expression rhythms. Finally, we examined the effects of the loss of VIP on ex vivo explants of the same central and peripheral oscillators using the PER2::LUC reporter system. The VIP-deficient mice exhibited low amplitude rhythms in the SCN as well as altered phase relationships between the SCN and the peripheral oscillators. Together, these data suggest that VIP is critical for robust rhythms in clock gene expression in the SCN and some peripheral organs and that the absence of this peptide alters both the amplitude of circadian rhythms as well as the phase relationships between the rhythms in the SCN and periphery.
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Affiliation(s)
- Dawn H. Loh
- Department of Psychiatry and Biobehavioral Sciences, University of California–Los Angeles, Los Angeles, CA
| | - Joanna M. Dragich
- Department of Psychiatry and Biobehavioral Sciences, University of California–Los Angeles, Los Angeles, CA
| | - Takashi Kudo
- Department of Psychiatry and Biobehavioral Sciences, University of California–Los Angeles, Los Angeles, CA
| | - Analyne M. Schroeder
- Department of Psychiatry and Biobehavioral Sciences, University of California–Los Angeles, Los Angeles, CA
| | - Takahiro J. Nakamura
- Department of Psychiatry and Biobehavioral Sciences, University of California–Los Angeles, Los Angeles, CA
| | - James A. Waschek
- Department of Psychiatry and Biobehavioral Sciences, University of California–Los Angeles, Los Angeles, CA
| | - Gene D. Block
- Department of Psychiatry and Biobehavioral Sciences, University of California–Los Angeles, Los Angeles, CA
| | - Christopher S. Colwell
- Department of Psychiatry and Biobehavioral Sciences, University of California–Los Angeles, Los Angeles, CA
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Hughes ATL, Guilding C, Piggins HD. Neuropeptide signaling differentially affects phase maintenance and rhythm generation in SCN and extra-SCN circadian oscillators. PLoS One 2011; 6:e18926. [PMID: 21559484 PMCID: PMC3084722 DOI: 10.1371/journal.pone.0018926] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2011] [Accepted: 03/11/2011] [Indexed: 02/02/2023] Open
Abstract
Circadian rhythms in physiology and behavior are coordinated by the brain's dominant circadian pacemaker located in the suprachiasmatic nuclei (SCN) of the hypothalamus. Vasoactive intestinal polypeptide (VIP) and its receptor, VPAC(2), play important roles in the functioning of the SCN pacemaker. Mice lacking VPAC(2) receptors (Vipr2(-/-)) express disrupted behavioral and metabolic rhythms and show altered SCN neuronal activity and clock gene expression. Within the brain, the SCN is not the only site containing endogenous circadian oscillators, nor is it the only site of VPAC(2) receptor expression; both VPAC(2) receptors and rhythmic clock gene/protein expression have been noted in the arcuate (Arc) and dorsomedial (DMH) nuclei of the mediobasal hypothalamus, and in the pituitary gland. The functional role of VPAC(2) receptors in rhythm generation and maintenance in these tissues is, however, unknown. We used wild type (WT) and Vipr2(-/-) mice expressing a luciferase reporter (PER2::LUC) to investigate whether circadian rhythms in the clock gene protein PER2 in these extra-SCN tissues were compromised by the absence of the VPAC(2) receptor. Vipr2(-/-) SCN cultures expressed significantly lower amplitude PER2::LUC oscillations than WT SCN. Surprisingly, in Vipr2(-/-) Arc/ME/PT complex (Arc, median eminence and pars tuberalis), DMH and pituitary, the period, amplitude and rate of damping of rhythms were not significantly different to WT. Intriguingly, while we found WT SCN and Arc/ME/PT tissues to maintain a consistent circadian phase when cultured, the phase of corresponding Vipr2(-/-) cultures was reset by cull/culture procedure. These data demonstrate that while the main rhythm parameters of extra-SCN circadian oscillations are maintained in Vipr2(-/-) mice, the ability of these oscillators to resist phase shifts is compromised. These deficiencies may contribute towards the aberrant behavior and metabolism associated with Vipr2(-/-) animals. Further, our data indicate a link between circadian rhythm strength and the ability of tissues to resist circadian phase resetting.
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Affiliation(s)
- Alun T L Hughes
- Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom.
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Farnell YF, Shende VR, Neuendorff N, Allen GC, Earnest DJ. Immortalized cell lines for real-time analysis of circadian pacemaker and peripheral oscillator properties. Eur J Neurosci 2011; 33:1533-40. [PMID: 21366728 DOI: 10.1111/j.1460-9568.2011.07629.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In the mammalian circadian system, cell-autonomous clocks in the suprachiasmatic nuclei (SCN) are distinguished from those in other brain regions and peripheral tissues by the capacity to generate coordinated rhythms and drive oscillations in other cells. To further establish in vitro models for distinguishing the functional properties of SCN and peripheral oscillators, we developed immortalized cell lines derived from fibroblasts and the SCN anlage of mPer2 (Luc) knockin mice. Circadian rhythms in luminescence driven by the mPER2::LUC fusion protein were observed in cultures of mPer2 (Luc) SCN cells and in serum-shocked or SCN2.2-co-cultured mPer2 (Luc) fibroblasts. SCN mPer2 (Luc) cells generated self-sustained circadian oscillations that persisted for at least four cycles with periodicities of ≈24 h. Immortalized fibroblasts only showed circadian rhythms of mPER2::LUC expression in response to serum shock or when co-cultured with SCN2.2 cells. Circadian oscillations of luminescence in mPer2 (Luc) fibroblasts decayed after 3-4 cycles in serum-shocked cultures but robustly persisted for 6-7 cycles in the presence of SCN2.2 cells. In the co-culture model, the circadian behavior of mPer2 (Luc) fibroblasts was dependent on the integrity of the molecular clockworks in co-cultured SCN cells as persistent rhythmicity was not observed in the presence of immortalized SCN cells derived from mice with targeted disruption of Per1 and Per2 (Per1(ldc) /Per2 (ldc) ). Because immortalized mPer2 (Luc) SCN cells and fibroblasts retain their indigenous circadian properties, these in vitro models will be valuable for real-time comparisons of clock gene rhythms in SCN and peripheral oscillators and identifying the diffusible signals that mediate the distinctive pacemaking function of the SCN.
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Affiliation(s)
- Yuhua F Farnell
- Department of Neuroscience and Experimental Therapeutics, Texas A&M University Health Science Center, College Station, TX 77843, USA
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33
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Savelyev SA, Larsson KC, Johansson AS, Lundkvist GBS. Slice preparation, organotypic tissue culturing and luciferase recording of clock gene activity in the suprachiasmatic nucleus. J Vis Exp 2011:2439. [PMID: 21372784 PMCID: PMC3197397 DOI: 10.3791/2439] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
Abstract
A central circadian (~24 hr) clock coordinating daily rhythms in physiology and behavior resides in the suprachiasmatic nucleus (SCN) located in the anterior hypothalamus. The clock is directly synchronized by light via the retina and optic nerve. Circadian oscillations are generated by interacting negative feedback loops of a number of so called "clock genes" and their protein products, including the Period (Per) genes. The core clock is also dependent on membrane depolarization, calcium and cAMP 1. The SCN shows daily oscillations in clock gene expression, metabolic activity and spontaneous electrical activity. Remarkably, this endogenous cyclic activity persists in adult tissue slices of the SCN 2-4. In this way, the biological clock can easily be studied in vitro, allowing molecular, electrophysiological and metabolic investigations of the pacemaker function. The SCN is a small, well-defined bilateral structure located right above the optic chiasm 5. In the rat it contains ~8.000 neurons in each nucleus and has dimensions of approximately 947 μm (length, rostrocaudal axis) x 424 μm (width) x 390 μm (height) 6. To dissect out the SCN it is necessary to cut a brain slice at the specific level of the brain where the SCN can be identified. Here, we describe the dissecting and slicing procedure of the SCN, which is similar for mouse and rat brains. Further, we show how to culture the dissected tissue organotypically on a membrane 7, a technique developed for SCN tissue culture by Yamazaki et al.8. Finally, we demonstrate how transgenic tissue can be used for measuring expression of clock genes/proteins using dynamic luciferase reporter technology, a method that originally was used for circadian measurements by Geusz et al.9. We here use SCN tissues from the transgenic knock-in PERIOD2::LUCIFERASE mice produced by Yoo et al.10. The mice contain a fusion protein of PERIOD (PER) 2 and the firefly enzyme LUCIFERASE. When PER2 is translated in the presence of the substrate for luciferase, i.e. luciferin, the PER2 expression can be monitored as bioluminescence when luciferase catalyzes the oxidation of luciferin. The number of emitted photons positively correlates to the amount of produced PER2 protein, and the bioluminescence rhythms match the PER2 protein rhythm in vivo10. In this way the cyclic variation in PER2 expression can be continuously monitored real time during many days. The protocol we follow for tissue culturing and real-time bioluminescence recording has been thoroughly described by Yamazaki and Takahashi 11.
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Affiliation(s)
- Sergey A Savelyev
- Swedish Medical Nanoscience Center, Department of Neuroscience, Karolinska Institutet
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Brown TM, Wynne J, Piggins HD, Lucas RJ. Multiple hypothalamic cell populations encoding distinct visual information. J Physiol 2011; 589:1173-94. [PMID: 21224225 DOI: 10.1113/jphysiol.2010.199877] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Environmental illumination profoundly influences mammalian physiology and behaviour through actions on a master circadian oscillator in the suprachiasmatic nuclei (SCN) and other hypothalamic nuclei. The retinal and central mechanisms that shape daily patterns of light-evoked and spontaneous activity in this network of hypothalamic cells are still largely unclear. Similarly, the exact nature of the sensory information conveyed by such cells is unresolved. Here we set out to address these issues, through multielectrode recordings from the hypothalamus of red cone knockin mice (Opn1mwR). With this powerful mouse model, the photoreceptive origins of any response can be readily identified on the basis of their relative sensitivity to short and long wavelength light. Our experiments revealed that the firing pattern of many hypothalamic cells was influenced by changes in light levels and/or according to the steady state level of illumination. These ‘contrast' and ‘irradiance' responses were driven primarily by cone and melanopsin photoreceptors respectively, with rods exhibiting a much more subtle influence. Individual hypothalamic neurons differentially sampled from these information streams, giving rise to four distinct response types. The most common response phenotype in the SCN itself was sustained activation. Cells with this behaviour responded to all three photoreceptor classes in a manner consistent with their distinct contributions to circadian photoentrainment. These ‘sustained' cells were also unique in our sample in expressing circadian firing patterns with highest activity during the mid projected day. Surprisingly, we also found a minority of SCN neurons that lacked the melanopsin-derived irradiance signal and responded only to light transitions, allowing for the possibility that rod–cone contrast signals may be routed to SCN output targets without influencing neighbouring circadian oscillators. Finally, an array of cells extending throughout the periventricular hypothalamus and ventral thalamus were excited or inhibited solely according to the activity of melanopsin. These cells appeared to convey a filtered version of the visual signal, suitable for modulating physiology/behaviour purely according to environmental irradiance. In summary, these findings reveal unexpectedly widespread hypothalamic cell populations encoding distinct qualities of visual information.
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Affiliation(s)
- Timothy M Brown
- Faculty of Life Sciences, AV Hill Building, University of Manchester, Manchester M13 9PT, UK
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35
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Intrinsic regulation of spatiotemporal organization within the suprachiasmatic nucleus. PLoS One 2011; 6:e15869. [PMID: 21249213 PMCID: PMC3017566 DOI: 10.1371/journal.pone.0015869] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2010] [Accepted: 12/03/2010] [Indexed: 11/19/2022] Open
Abstract
The mammalian pacemaker in the suprachiasmatic nucleus (SCN) contains a population of neural oscillators capable of sustaining cell-autonomous rhythms in gene expression and electrical firing. A critical question for understanding pacemaker function is how SCN oscillators are organized into a coherent tissue capable of coordinating circadian rhythms in behavior and physiology. Here we undertake a comprehensive analysis of oscillatory function across the SCN of the adult PER2::LUC mouse by developing a novel approach involving multi-position bioluminescence imaging and unbiased computational analyses. We demonstrate that there is phase heterogeneity across all three dimensions of the SCN that is intrinsically regulated and extrinsically modulated by light in a region-specific manner. By investigating the mechanistic bases of SCN phase heterogeneity, we show for the first time that phase differences are not systematically related to regional differences in period, waveform, amplitude, or brightness. Furthermore, phase differences are not related to regional differences in the expression of arginine vasopressin and vasoactive intestinal polypeptide, two key neuropeptides characterizing functionally distinct subdivisions of the SCN. The consistency of SCN spatiotemporal organization across individuals and across planes of section suggests that the precise phasing of oscillators is a robust feature of the pacemaker important for its function.
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36
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Abstract
The mammalian circadian system is a complex hierarchical temporal network which is organized around an ensemble of uniquely coupled cells comprising the principal circadian pacemaker in the suprachiasmatic nucleus of the hypothalamus. This central pacemaker is entrained each day by the environmental light/dark cycle and transmits synchronizing cues to cell-autonomous oscillators in tissues throughout the body. Within cells of the central pacemaker and the peripheral tissues, the underlying molecular mechanism by which oscillations in gene expression occur involves interconnected feedback loops of transcription and translation. Over the past 10 years, we have learned much regarding the genetics of this system, including how it is particularly resilient when challenged by single-gene mutations, how accessory transcriptional loops enhance the robustness of oscillations, how epigenetic mechanisms contribute to the control of circadian gene expression, and how, from coupled neuronal networks, emergent clock properties arise. Here, we will explore the genetics of the mammalian circadian system from cell-autonomous molecular oscillations, to interactions among central and peripheral oscillators and ultimately, to the daily rhythms of behavior observed in the animal.
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37
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Girardet C, Becquet D, Blanchard MP, François-Bellan AM, Bosler O. Neuroglial and synaptic rearrangements associated with photic entrainment of the circadian clock in the suprachiasmatic nucleus. Eur J Neurosci 2010; 32:2133-42. [DOI: 10.1111/j.1460-9568.2010.07520.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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38
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Power A, Hughes ATL, Samuels RE, Piggins HD. Rhythm-promoting actions of exercise in mice with deficient neuropeptide signaling. J Biol Rhythms 2010; 25:235-46. [PMID: 20679493 DOI: 10.1177/0748730410374446] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Daily exercise promotes physical health as well as improvements in mental and neural functions. Studies in intact wild-type (WT) rodents have revealed that the brain's suprachiasmatic nuclei (SCN), site of the main circadian pacemaker, are also responsive to scheduled wheel running. It is unclear, however, if and how animals with a dysfunctional circadian pacemaker respond to exercise. Here, we tested whether scheduled voluntary exercise (SVE) in a running wheel for 6 hours per day could promote neural and behavioral rhythmicity in animals whose circadian competence is compromised through genetically targeted loss of vasoactive intestinal polypeptide (VIP(-/-) mice) or its VPAC(2) receptor (Vipr2(-/-) mice). We report that in constant dark (DD), rhythmic VIP(-/-) and Vipr2(-/-) mice show weak free-running rhythms with a period of <23 hours and all wild-type mice are strongly rhythmic with approximately 23.5-hour periodicity. VIP(-/-) and Vipr2(-/-) mice rapidly (<7 days) synchronize to daily SVE, while WT mice take much longer (>35 days). Following 21 to 50 days of SVE, WT mice show small changes in their rhythms, and most Vipr2(-/-) mice now sustain robust near 24-hour behavioral rhythms, whereas very few VIP(-/-) mice do. This study demonstrates that scheduled daily exercise can markedly improve circadian rhythms in behavioral activity and raises the possibility that this noninvasive approach may be useful as an intervention in clinical etiologies in which there are dysfunctions of circadian time keeping.
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Affiliation(s)
- A Power
- Faculty of Life Sciences, University of Manchester, Oxford Road, Manchester, UK M13 9PT
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39
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Abstract
Mammalian circadian rhythms are controlled by endogenous biological oscillators, including a master clock located in the hypothalamic suprachiasmatic nuclei (SCN). Since the period of this oscillation is of approximately 24 h, to keep synchrony with the environment, circadian rhythms need to be entrained daily by means of Zeitgeber ("time giver") signals, such as the light-dark cycle. Recent advances in the neurophysiology and molecular biology of circadian rhythmicity allow a better understanding of synchronization. In this review we cover several aspects of the mechanisms for photic entrainment of mammalian circadian rhythms, including retinal sensitivity to light by means of novel photopigments as well as circadian variations in the retina that contribute to the regulation of retinal physiology. Downstream from the retina, we examine retinohypothalamic communication through neurotransmitter (glutamate, aspartate, pituitary adenylate cyclase-activating polypeptide) interaction with SCN receptors and the resulting signal transduction pathways in suprachiasmatic neurons, as well as putative neuron-glia interactions. Finally, we describe and analyze clock gene expression and its importance in entrainment mechanisms, as well as circadian disorders or retinal diseases related to entrainment deficits, including experimental and clinical treatments.
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Affiliation(s)
- Diego A Golombek
- Laboratory of Chronobiology, Department of Science and Technology, University of Quilmes/Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), Quilmes, Argentina.
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40
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Guilding C, Hughes ATL, Piggins HD. Circadian oscillators in the epithalamus. Neuroscience 2010; 169:1630-9. [PMID: 20547209 PMCID: PMC2928449 DOI: 10.1016/j.neuroscience.2010.06.015] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2010] [Revised: 06/04/2010] [Accepted: 06/08/2010] [Indexed: 12/28/2022]
Abstract
The habenula complex is implicated in a range of cognitive, emotional and reproductive behaviors, and recently this epithalamic structure was suggested to be a component of the brain's circadian system. Circadian timekeeping is driven in cells by the cyclical activity of core clock genes and proteins such as per2/PER2. There are currently no reports of rhythmic clock gene/protein expression in the habenula and therefore the question of whether this structure has an intrinsic molecular clock remains unresolved. Here, using videomicroscopy imaging and photon-counting of a PER2::luciferase (LUC) fusion protein together with multiunit electrophysiological recordings, we tested the endogenous circadian properties of the mouse habenula in vitro. We show that a circadian oscillator is localized primarily to the medial portion of the lateral habenula. Rhythms in PER2:: LUC bioluminescence here are visualized in single cells and oscillations continue in the presence of the sodium channel blocker, tetrodotoxin, indicating that individual cells have intrinsic timekeeping properties. Ependymal cells lining the dorsal third ventricle also express circadian oscillations of PER2. These findings establish that neurons and non-neuronal cells in the epithalamus express rhythms in cellular and molecular activities, indicating a role for circadian oscillators in the temporal regulation of habenula controlled processes and behavior.
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Affiliation(s)
- C Guilding
- Faculty of Life Sciences, University of Manchester, Manchester, UK
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41
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Pantazopoulos H, Dolatshad H, Davis FC. Chronic stimulation of the hypothalamic vasoactive intestinal peptide receptor lengthens circadian period in mice and hamsters. Am J Physiol Regul Integr Comp Physiol 2010; 299:R379-85. [PMID: 20463182 DOI: 10.1152/ajpregu.00176.2010] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Evidence suggests that circadian rhythms are regulated through diffusible signals generated by the suprachiasmatic nucleus (SCN). Vasoactive intestinal peptide (VIP) is located in SCN neurons positioned to receive photic input from the retinohypothalamic tract and transmit information to other SCN cells and adjacent hypothalamic areas. Studies using knockout mice indicate that VIP is essential for synchrony among SCN cells and for the expression of normal circadian rhythms. To test the hypothesis that VIP is also an SCN output signal, we recorded wheel-running activity rhythms in hamsters and continuously infused the VIP receptor agonist BAY 55-9837 in the third ventricle for 28 days. Unlike other candidate output signals, infusion of BAY 55-9837 did not affect activity levels. Instead, BAY 55-9837 lengthened the circadian period by 0.69 +/- 0.04 h (P < 0.0002 compared with controls). Period returned to baseline after infusions. We analyzed the effect of BAY 55-9837 on cultured SCN from PER2::LUC mice to determine if lengthening of the period by BAY 55-9837 is a direct effect on the SCN. Application of 10 muM BAY 55-9837 to SCN in culture lengthened the period of PER2 luciferase expression (24.73 +/- 0.24 h) compared with control SCN (23.57 +/- 0.26, P = 0.01). In addition, rhythm amplitude was significantly increased, consistent with increased synchronization of SCN neurons. The effect of BAY 55-9837 in vivo on period is similar to the effect of constant light. The present results suggest that VIP-VPAC2 signaling in the SCN may play two roles, synchronizing SCN neurons and setting the period of the SCN as a whole.
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Affiliation(s)
- Harry Pantazopoulos
- Department of Biology, Northeastern University, Boston, Massachusetts 02478, USA
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42
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Circadian control of mouse heart rate and blood pressure by the suprachiasmatic nuclei: behavioral effects are more significant than direct outputs. PLoS One 2010; 5:e9783. [PMID: 20339544 PMCID: PMC2842429 DOI: 10.1371/journal.pone.0009783] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2009] [Accepted: 02/25/2010] [Indexed: 11/19/2022] Open
Abstract
Background Diurnal variations in the incidence of events such as heart attack and stroke suggest a role for circadian rhythms in the etiology of cardiovascular disease. The aim of this study was to assess the influence of the suprachiasmatic nucleus (SCN) circadian clock on cardiovascular function. Methodology/Principal Findings Heart rate (HR), blood pressure (BP) and locomotor activity (LA) were measured in circadian mutant (Vipr2−/−) mice and wild type littermates, using implanted radio-telemetry devices. Sleep and wakefulness were studied in similar mice implanted with electroencephalograph (EEG) electrodes. There was less diurnal variation in the frequency and duration of bouts of rest/activity and sleep/wake in Vipr2−/− mice than in wild type (WT) and short “ultradian” episodes of arousal were more prominent, especially in constant conditions (DD). Activity was an important determinant of circadian variation in BP and HR in animals of both genotypes; altered timing of episodes of activity and rest (as well as sleep and wakefulness) across the day accounted for most of the difference between Vipr2−/− mice and WT. However, there was also a modest circadian rhythm of resting HR and BP that was independent of LA. Conclusions/Significance If appropriate methods of analysis are used that take into account sleep and locomotor activity level, mice are a good model for understanding the contribution of circadian timing to cardiovascular function. Future studies of the influence of sleep and wakefulness on cardiovascular physiology may help to explain accumulating evidence linking disrupted sleep with cardiovascular disease in man.
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Lu W, Meng QJ, Tyler NJC, Stokkan KA, Loudon ASI. A circadian clock is not required in an arctic mammal. Curr Biol 2010; 20:533-7. [PMID: 20226667 DOI: 10.1016/j.cub.2010.01.042] [Citation(s) in RCA: 91] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2009] [Revised: 01/14/2010] [Accepted: 01/15/2010] [Indexed: 01/05/2023]
Abstract
Seasonally breeding mammals use the annual change in the photoperiod cycle to drive rhythmic nocturnal melatonin signals from the pineal gland, providing a critical cue to time seasonal reproduction. Paradoxically, species resident at high latitudes achieve tight regulation of the temporal pattern of growth and reproduction despite the absence of photoperiodic information for most of the year. In this study, we show that the melatonin rhythm of reindeer (Rangifer tarandus) is acutely responsive to the light/dark cycle but not to circadian phase, and also that two key clock genes monitored in reindeer fibroblast cells display little, if any, circadian rhythmicity. The molecular clockwork that normally drives cellular circadian rhythms is evidently weak or even absent in this species, and instead, melatonin-mediated seasonal timing may be driven directly by photic information received at a limited time of year specific to the equinoxes.
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Affiliation(s)
- Weiqun Lu
- Faculty of Life Sciences, University of Manchester, Manchester M139PT, UK
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44
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Phase organization of circadian oscillators in extended gate and oscillator models. J Theor Biol 2010; 264:367-76. [PMID: 20144621 DOI: 10.1016/j.jtbi.2010.02.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2009] [Revised: 01/22/2010] [Accepted: 02/02/2010] [Indexed: 11/21/2022]
Abstract
The suprachiasmatic nuclei (SCN) control daily oscillations in physiology and behavior. The gate-oscillator model captures functional heterogeneity in SCN and has been successful in reproducing many features of SCN. This paper investigates the mechanism of phase organization in the gate-oscillator model and finds that only stable fixed points of the phase transition function are essential to phase organization. This obvious finding forms the basis for understanding the complex phase distribution in the gate-oscillator scheme. Extending the model with a dead zone of the phase transition function and the propagation delay of the gate signal which may represent the spatial structure of SCN, the author discusses how some features of experimentally reported phase distribution, such as the existence of anti-phase neurons and fixed phase difference between neurons, could be understood in the framework of the gate-oscillator model. The extended model shows clearly the way in which the interplay between the single-cell property and the property of the network organization influence the phase distribution of SCN neurons.
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45
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Geusz ME, Blakely KT, Hiler DJ, Jamasbi RJ. Elevated mPer1 gene expression in tumor stroma imaged through bioluminescence. Int J Cancer 2010; 126:620-30. [PMID: 19637242 DOI: 10.1002/ijc.24788] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The tumor stroma has significant effects on cancer cell growth and metastasis. Interactions between cancer and stromal cells shape tumor progression through poorly understood mechanisms. One factor regulating tumor growth is the circadian timing system that generates daily physiological rhythms throughout the body. Clock genes such as mPer1 serve in molecular timing events of circadian oscillators and when mutated can disrupt circadian rhythms and accelerate tumor growth. Stimulation of mPer1 by cytokines suggests that the timing of circadian oscillators may be altered by these tumor-derived signals. To explore tumor and stromal interactions, the pattern of mPer1 expression was imaged in tumors generated through subcutaneous injection of Lewis lung carcinoma (LLC) cells. Several imaging studies have used bioluminescent cancer cell lines expressing firefly luciferase to image tumor growth in live mice. In contrast, this study used non-bioluminescent cancer cells to produce tumors within transgenic mice expressing luciferase controlled by the mPer1 gene promoter. Bioluminescence originated only in host cells and was significantly elevated throughout the tumor stroma. It was detected through the skin of live mice or by imaging the tumor directly. No effects on the circadian timing system were detected during three weeks of tumor growth according to wheel-running rhythms. Similarly, no effects on mPer1 expression outside the tumor were found. These results suggest that mPer1 activity may play a localized role in the interactions between cancer and stromal cells. The effects might be exploited clinically by targeting the circadian clock genes of stromal cells.
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Affiliation(s)
- Michael E Geusz
- Department of Biological Sciences, Bowling Green State University, Bowling Green, OH 43403-0208, USA.
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46
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Abstract
The suprachiasmatic nucleus (SCN) is the primary circadian pacemaker in mammals. Individual SCN neurons in dispersed culture can generate independent circadian oscillations of clock gene expression and neuronal firing. However, SCN rhythmicity depends on sufficient membrane depolarization and levels of intracellular calcium and cAMP. In the intact SCN, cellular oscillations are synchronized and reinforced by rhythmic synaptic input from other cells, resulting in a reproducible topographic pattern of distinct phases and amplitudes specified by SCN circuit organization. The SCN network synchronizes its component cellular oscillators, reinforces their oscillations, responds to light input by altering their phase distribution, increases their robustness to genetic perturbations, and enhances their precision. Thus, even though individual SCN neurons can be cell-autonomous circadian oscillators, neuronal network properties are integral to normal function of the SCN.
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Affiliation(s)
- David K Welsh
- Department of Psychiatry, University of California-San Diego, La Jolla, CA 92093, USA.
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47
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Butler MP, Silver R. Basis of robustness and resilience in the suprachiasmatic nucleus: individual neurons form nodes in circuits that cycle daily. J Biol Rhythms 2009; 24:340-52. [PMID: 19755580 DOI: 10.1177/0748730409344800] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
How the cellular elements of the SCN are synchronized to each other is not well understood. We explore circadian oscillations manifest at the level of the cell, the tissue, and the whole animal to better understand intra-SCN synchrony and master clock function of the nucleus. At each level of analysis, responses to variations in operating environment (robustness), and following damage to components of the system (resilience), provide insight into the mechanisms whereby the SCN orchestrates circadian timing. Tissue level rhythmicity reveals circuits associated with an orderly spatiotemporal daily pattern of activity that is not predictable from their cellular elements. Specifically, in stable state, some SCN regions express low amplitude or undetectable rhythms in clock gene expression while others produce high amplitude oscillations. Within the SCN, clock gene expression follows a spatially ordered, repeated pattern of activation and inactivation. This pattern of activation is plastic and subserves responses to changes in external and internal conditions. Just as daily rhythms at the cellular level depend on sequential expression and interaction of clock genes, so too do rhythms at the SCN tissue level depend on sequential activation of local nodes. We hypothesize that individual neurons are organized into nodes that are themselves sequentially activated across the volume of the SCN in a cycle that repeats on a daily basis. We further propose that robustness is expressed in the ability of the SCN to sustain rhythmicity over a wide range of internal and external conditions, and that this reflects plasticity of the underlying nodes and circuits. Resilience is expressed in the ability of SCN cells to oscillate and to sustain activity-related rhythms at the behavioral level. Importantly, other aspects of pacemaker function remain to be examined.
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Affiliation(s)
- Matthew P Butler
- Department of Psychology, Columbia University, New York, New York 10027, USA
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48
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Belle MDC, Diekman CO, Forger DB, Piggins HD. Daily electrical silencing in the mammalian circadian clock. Science 2009; 326:281-4. [PMID: 19815775 DOI: 10.1126/science.1169657] [Citation(s) in RCA: 131] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Neurons in the brain's suprachiasmatic nuclei (SCNs), which control the timing of daily rhythms, are thought to encode time of day by changing their firing frequency, with high rates during the day and lower rates at night. Some SCN neurons express a key clock gene, period 1 (per1). We found that during the day, neurons containing per1 sustain an electrically excited state and do not fire, whereas non-per1 neurons show the previously reported daily variation in firing activity. Using a combined experimental and theoretical approach, we explain how ionic currents lead to the unusual electrophysiological behaviors of per1 cells, which unlike other mammalian brain cells can survive and function at depolarized states.
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Affiliation(s)
- Mino D C Belle
- Faculty of Life Sciences, A. V. Hill Building, University of Manchester, Manchester M13 9PT, UK
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49
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Hickok JR, Tischkau SA. In vivo circadian rhythms in gonadotropin-releasing hormone neurons. Neuroendocrinology 2009; 91:110-20. [PMID: 19786732 PMCID: PMC7068787 DOI: 10.1159/000243163] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/22/2008] [Accepted: 06/18/2009] [Indexed: 11/19/2022]
Abstract
Although it is generally accepted that the circadian clock provides a timing signal for the luteinizing hormone (LH) surge, mechanistic explanations of this phenomenon remain underexplored. It is known, for example, that circadian locomotor output cycles kaput (clock) mutant mice have severely dampened LH surges, but whether this phenotype derives from a loss of circadian rhythmicity in the suprachiasmatic nucleus (SCN) or altered circadian function in gonadotropin-releasing hormone (GnRH) neurons has not been resolved. GnRH neurons can be stimulated to cycle with a circadian period in vitro and disruption of that cycle disturbs secretion of the GnRH decapeptide. We show that both period-2 (PER2) and brain muscle Arnt-like-1 (BMAL1) proteins cycle with a circadian period in the GnRH population in vivo. PER2 and BMAL1 expression both oscillate with a 24-hour period, with PER2 peaking during the night and BMAL1 peaking during the day. The population, however, is not as homogeneous as other oscillatory tissues with only about 50% of the population sharing peak expression levels of BMAL1 at zeitgeber time 4 (ZT4) and PER2 at ZT16. Further, a light pulse that induced a phase delay in the activity rhythm of the GnRH-eGFP mice caused a similar delay in peak expression levels of BMAL1 and PER2. These studies provide direct evidence for a functional circadian clock in native GnRH neurons with a phase that closely follows that of the SCN.
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Affiliation(s)
- Jason R Hickok
- Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, Urbana, Ill 62794-9629, USA
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50
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Guilding C, Hughes ATL, Brown TM, Namvar S, Piggins HD. A riot of rhythms: neuronal and glial circadian oscillators in the mediobasal hypothalamus. Mol Brain 2009; 2:28. [PMID: 19712475 PMCID: PMC2745382 DOI: 10.1186/1756-6606-2-28] [Citation(s) in RCA: 137] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2009] [Accepted: 08/27/2009] [Indexed: 11/20/2022] Open
Abstract
Background In mammals, the synchronized activity of cell autonomous clocks in the suprachiasmatic nuclei (SCN) enables this structure to function as the master circadian clock, coordinating daily rhythms in physiology and behavior. However, the dominance of this clock has been challenged by the observations that metabolic duress can over-ride SCN controlled rhythms, and that clock genes are expressed in many brain areas, including those implicated in the regulation of appetite and feeding. The recent development of mice in which clock gene/protein activity is reported by bioluminescent constructs (luciferase or luc) now enables us to track molecular oscillations in numerous tissues ex vivo. Consequently we determined both clock activities and responsiveness to metabolic perturbations of cells and tissues within the mediobasal hypothalamus (MBH), a site pivotal for optimal internal homeostatic regulation. Results Here we demonstrate endogenous circadian rhythms of PER2::LUC expression in discrete subdivisions of the arcuate (Arc) and dorsomedial nuclei (DMH). Rhythms resolved to single cells did not maintain long-term synchrony with one-another, leading to a damping of oscillations at both cell and tissue levels. Complementary electrophysiology recordings revealed rhythms in neuronal activity in the Arc and DMH. Further, PER2::LUC rhythms were detected in the ependymal layer of the third ventricle and in the median eminence/pars tuberalis (ME/PT). A high-fat diet had no effect on the molecular oscillations in the MBH, whereas food deprivation resulted in an altered phase in the ME/PT. Conclusion Our results provide the first single cell resolution of endogenous circadian rhythms in clock gene expression in any intact tissue outside the SCN, reveal the cellular basis for tissue level damping in extra-SCN oscillators and demonstrate that an oscillator in the ME/PT is responsive to changes in metabolism.
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Affiliation(s)
- Clare Guilding
- Faculty of Life Sciences, University of Manchester, Manchester, UK.
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