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Del Olmo M, Kalashnikov A, Schmal C, Kramer A, Herzel H. Coupling allows robust mammalian redox circadian rhythms despite heterogeneity and noise. Heliyon 2024; 10:e24773. [PMID: 38312577 PMCID: PMC10835301 DOI: 10.1016/j.heliyon.2024.e24773] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2023] [Revised: 12/06/2023] [Accepted: 01/14/2024] [Indexed: 02/06/2024] Open
Abstract
Circadian clocks are endogenous oscillators present in almost all cells that drive daily rhythms in physiology and behavior. There are two mechanisms that have been proposed to explain how circadian rhythms are generated in mammalian cells: through a transcription-translation feedback loop (TTFL) and based on oxidation/reduction reactions, both of which are intrinsically stochastic and heterogeneous at the single cell level. In order to explore the emerging properties of stochastic and heterogeneous redox oscillators, we simplify a recently developed kinetic model of redox oscillations to an amplitude-phase oscillator with 'twist' (period-amplitude correlation) and subject to Gaussian noise. We show that noise and heterogeneity alone lead to fast desynchronization, and that coupling between noisy oscillators can establish robust and synchronized rhythms with amplitude expansions and tuning of the period due to twist. Coupling a network of redox oscillators to a simple model of the TTFL also contributes to synchronization, large amplitudes and fine-tuning of the period for appropriate interaction strengths. These results provide insights into how the circadian clock compensates randomness from intracellular sources and highlight the importance of noise, heterogeneity and coupling in the context of circadian oscillators.
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Affiliation(s)
- Marta Del Olmo
- Institute for Theoretical Biology - Humboldt Universität zu Berlin and Charité Universitätsmedizin Berlin, Philippstraße 13, 10115 Berlin, Germany
| | - Anton Kalashnikov
- Institute for Theoretical Biology - Humboldt Universität zu Berlin and Charité Universitätsmedizin Berlin, Philippstraße 13, 10115 Berlin, Germany
| | - Christoph Schmal
- Institute for Theoretical Biology - Humboldt Universität zu Berlin and Charité Universitätsmedizin Berlin, Philippstraße 13, 10115 Berlin, Germany
| | - Achim Kramer
- Institute for Medical Immunology - Laboratory of Chronobiology, Charité Universitätsmedizin Berlin, Charitéplatz 1, 10117 Berlin, Germany
| | - Hanspeter Herzel
- Institute for Theoretical Biology - Humboldt Universität zu Berlin and Charité Universitätsmedizin Berlin, Philippstraße 13, 10115 Berlin, Germany
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3
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Poe AR, Mace KD, Kayser MS. Getting into rhythm: developmental emergence of circadian clocks and behaviors. FEBS J 2021; 289:6576-6588. [PMID: 34375504 DOI: 10.1111/febs.16157] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2021] [Revised: 06/30/2021] [Accepted: 08/09/2021] [Indexed: 11/28/2022]
Abstract
Circadian clocks keep time to coordinate diverse behaviors and physiological functions. While molecular circadian rhythms are evident during early development, most behavioral rhythms, such as sleep-wake, do not emerge until far later. Here, we examine the development of circadian clocks, outputs, and behaviors across phylogeny, with a particular focus on Drosophila. We explore potential mechanisms for how central clocks and circadian output loci establish communication, and discuss why from an evolutionary perspective sleep-wake and other behavioral rhythms emerge long after central clocks begin keeping time.
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Affiliation(s)
- Amy R Poe
- Department of Psychiatry, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA.,Chronobiology and Sleep Institute, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - Kyla D Mace
- Department of Psychiatry, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA.,Pharmacology Graduate Group, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - Matthew S Kayser
- Department of Psychiatry, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA.,Chronobiology and Sleep Institute, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA.,Department of Neuroscience, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
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4
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Manz KM, Siemann JK, McMahon DG, Grueter BA. Patch-clamp and multi-electrode array electrophysiological analysis in acute mouse brain slices. STAR Protoc 2021; 2:100442. [PMID: 33899023 PMCID: PMC8056272 DOI: 10.1016/j.xpro.2021.100442] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Patch-clamp and multi-electrode array electrophysiology techniques are used to measure dynamic functional properties of neurons. Whole-cell and cell-attached patch-clamp recordings in brain slices can be performed in voltage-clamp and current-clamp configuration to reveal cell-type-specific synaptic and cellular parameters governing neurotransmission. Multi-electrode array electrophysiology can provide spike activity recordings from multiple neurons, enabling larger sample sizes, and long-term recordings. We provide our guide to preparing acute rodent brain slices with example experiments and analyses intended for novice and expert electrophysiologists. For complete details on the use and execution of this protocol, please refer to Manz et al. (2020b). Viable and efficient preparation of mouse brain tissue Comprehensive material source for acute brain slice electrophysiology Detailed approach to whole-cell patch-clamp recording of neurons Utility and application of multi-electrode array electrophysiology in mouse brain
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Affiliation(s)
- Kevin M Manz
- Medical Scientist Training Program, Vanderbilt University, Nashville, TN 37232, USA.,Vanderbilt Brain Institute, Vanderbilt University, Nashville, TN 37232, USA.,Department of Anesthesiology, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Justin K Siemann
- Vanderbilt Brain Institute, Vanderbilt University, Nashville, TN 37232, USA.,Department of Biological Sciences, Vanderbilt University, Nashville, TN 3732, USA
| | - Douglas G McMahon
- Vanderbilt Brain Institute, Vanderbilt University, Nashville, TN 37232, USA.,Department of Biological Sciences, Vanderbilt University, Nashville, TN 3732, USA.,Department of Pharmacology, Vanderbilt University, Nashville, TN 37232, USA
| | - Brad A Grueter
- Vanderbilt Brain Institute, Vanderbilt University, Nashville, TN 37232, USA.,Department of Anesthesiology, Vanderbilt University Medical Center, Nashville, TN 37232, USA.,Vanderbilt Center for Addiction Research, Vanderbilt University, Nashville, TN 37232, USA.,Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232, USA.,Anesthesiology Research Division, Vanderbilt University School of Medicine, 2213 Garland Avenue, P435H MRB IV, Nashville, TN 37232-0413, USA
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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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Ruiz-Gayo M, Olmo ND. Interaction Between Circadian Rhythms, Energy Metabolism, and Cognitive Function. Curr Pharm Des 2020; 26:2416-2425. [PMID: 32156228 DOI: 10.2174/1381612826666200310145006] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2019] [Accepted: 02/11/2020] [Indexed: 11/22/2022]
Abstract
The interaction between meal timing and light regulates circadian rhythms in mammals and not only determines the sleep-wake pattern but also the activity of the endocrine system. Related with that, the necessity to fulfill energy needs is a driving force that requires the participation of cognitive skills whose performance has been shown to undergo circadian variations. These facts have led to the concept that cognition and feeding behaviour can be analysed from a chronobiological perspective. In this context, research carried out during the last two decades has evidenced the link between feeding behaviour/nutritional habits and cognitive processes, and has highlighted the impact of circadian disorders on cognitive decline. All that has allowed hypothesizing a tight relationship between nutritional factors, chronobiology, and cognition. In this connection, experimental diets containing elevated amounts of fat and sugar (high-fat diets; HFDs) have been shown to alter in rodents the circadian distribution of meals, and to have a negative impact on cognition and motivational aspects of behaviour that disappear when animals are forced to adhere to a standard temporal eating pattern. In this review, we will present relevant studies focussing on the effect of HFDs on cognitive aspects of behaviour, paying particular attention to the influence that chronobiological alterations caused by these diets may have on hippocampaldependent cognition.
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Affiliation(s)
- Mariano Ruiz-Gayo
- Department of Health and Pharmaceutical Sciences, School of Pharmacy, Universidad San Pablo-CEU, CEU Universities, Madrid, Spain
| | - Nuria D Olmo
- Department of Health and Pharmaceutical Sciences, School of Pharmacy, Universidad San Pablo-CEU, CEU Universities, Madrid, Spain
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7
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Michel S, Meijer JH. From clock to functional pacemaker. Eur J Neurosci 2019; 51:482-493. [PMID: 30793396 PMCID: PMC7027845 DOI: 10.1111/ejn.14388] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2018] [Revised: 01/23/2019] [Accepted: 02/11/2019] [Indexed: 12/17/2022]
Abstract
In mammals, the central pacemaker that coordinates 24‐hr rhythms is located in the suprachiasmatic nucleus (SCN). Individual neurons of the SCN have a molecular basis for rhythm generation and hence, they function as cell autonomous oscillators. Communication and synchronization among these neurons are crucial for obtaining a coherent rhythm at the population level, that can serve as a pace making signal for brain and body. Hence, the ability of single SCN neurons to produce circadian rhythms is equally important as the ability of these neurons to synchronize one another, to obtain a bona fide pacemaker at the SCN tissue level. In this chapter we will discuss the mechanisms underlying synchronization, and plasticity herein, which allows adaptation to changes in day length. Furthermore, we will discuss deterioration in synchronization among SCN neurons in aging, and gain in synchronization by voluntary physical activity or exercise.
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Affiliation(s)
- Stephan Michel
- Group Neurophysiology, Department of Cell and Chemical Biology, Leiden University Medical Center, Leiden, The Netherlands
| | - Johanna H Meijer
- Group Neurophysiology, Department of Cell and Chemical Biology, Leiden University Medical Center, Leiden, The Netherlands
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8
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Allen CN, Nitabach MN, Colwell CS. Membrane Currents, Gene Expression, and Circadian Clocks. Cold Spring Harb Perspect Biol 2017; 9:cshperspect.a027714. [PMID: 28246182 DOI: 10.1101/cshperspect.a027714] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Neuronal circadian oscillators in the mammalian and Drosophila brain express a circadian clock comprised of interlocking gene transcription feedback loops. The genetic clock regulates the membrane electrical activity by poorly understood signaling pathways to generate a circadian pattern of action potential firing. During the day, Na+ channels contribute an excitatory drive for the spontaneous activity of circadian clock neurons. Multiple types of K+ channels regulate the action potential firing pattern and the nightly reduction in neuronal activity. The membrane electrical activity possibly signaling by changes in intracellular Ca2+ and cyclic adenosine monophosphate (cAMP) regulates the activity of the gene clock. A decline in the signaling pathways that link the gene clock and neural activity during aging and disease may weaken the circadian output and generate significant impacts on human health.
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Affiliation(s)
- Charles N Allen
- Oregon Institute of Occupational Health Sciences and Department of Behavioral Neuroscience, Oregon Health & Science University, Portland, Oregon 97239
| | - Michael N Nitabach
- Department of Cellular and Molecular Physiology and Department of Genetics, Yale School of Medicine, New Haven, Connecticut 06520
| | - Christopher S Colwell
- Department of Psychiatry & Biobehavioral Sciences, University of California, Los Angeles, Los Angeles, California 90024
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9
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Chi-Castañeda D, Ortega A. Clock Genes in Glia Cells: A Rhythmic History. ASN Neuro 2016; 8:8/5/1759091416670766. [PMID: 27666286 PMCID: PMC5037500 DOI: 10.1177/1759091416670766] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2016] [Accepted: 08/22/2016] [Indexed: 11/17/2022] Open
Abstract
Circadian rhythms are periodic patterns in biological processes that allow the organisms to anticipate changes in the environment. These rhythms are driven by the suprachiasmatic nucleus (SCN), the master circadian clock in vertebrates. At a molecular level, circadian rhythms are regulated by the so-called clock genes, which oscillate in a periodic manner. The protein products of clock genes are transcription factors that control their own and other genes’ transcription, collectively known as “clock-controlled genes.” Several brain regions other than the SCN express circadian rhythms of clock genes, including the amygdala, the olfactory bulb, the retina, and the cerebellum. Glia cells in these structures are expected to participate in rhythmicity. However, only certain types of glia cells may be called “glial clocks,” since they express PER-based circadian oscillators, which depend of the SCN for their synchronization. This contribution summarizes the current information about clock genes in glia cells, their plausible role as oscillators and their medical implications.
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Affiliation(s)
- Donají Chi-Castañeda
- Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Ciudad de México, México Soluciones para un México Verde, S.A de C.V., Santa Fé Ciudad de México, México
| | - Arturo Ortega
- Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Ciudad de México, México
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10
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Hastings MH, Herzog ED. Clock Genes, Oscillators, and Cellular Networks in the Suprachiasmatic Nuclei. J Biol Rhythms 2016; 19:400-13. [PMID: 15534320 DOI: 10.1177/0748730404268786] [Citation(s) in RCA: 186] [Impact Index Per Article: 23.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The mammalian SCN contains a biological clock that drives remarkably precise circadian rhythms in vivo and in vitro. Recent advances have revealed molecular and cellular mechanisms required for the generation of these daily rhythms and their synchronization between SCN neurons and to the environmental light cycle. This review of the evidence for a cell-autonomous circadian pacemaker within specialized neurons of the SCN focuses on 6 genes implicated within the pace making mechanism, an additional 4 genes implicated in pathways from the pacemaker, and the intercellular and intracellular mechanisms that synchronize SCN neurons to each other and to solar time.
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Affiliation(s)
- Michael H Hastings
- MRC Laboratory of Molecular Biology, Division of Neurobiology, Cambridge, UK.
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11
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Abstract
The SCN of the mammalian hypothalamus comprises a self-sustained, biological clock that generates endogenous ca. 24-h (circadian) rhythms. Circadian rhythmicity in the SCN originates from the interaction of a defined set of “clock genes” that participate in transcription/translation feedback loops. In order for the SCN to serve as an internal clock that times an internal day corresponding to the external solar day, the intracellular molecular oscillations must be output as physiological signals and be reset by appropriate environmental inputs. Here, the authors consider the mechanisms by which the SCN circadian pacemaker encodes rhythmic output and light input. In particular, they focus on the ionic mechanisms by which SCN neurons encode clock gene output as circa-dian rhythms in spike frequency, as well as cellular and molecular mechanisms by which SCN neurons encode circadian light input through phase heterogeneity in the SCN network. The authors propose that there are 2 distinct classes of ionic mechanisms supporting spike frequency rhythms output—modulation of basal membrane potential and conductance versus modulation of spike production—whereas light input is transformed by cellular communication within the SCN network and encoded by the relative phase relationships among SCN neurons.
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Affiliation(s)
- Sandra J Kuhlman
- Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA
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12
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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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13
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Webb AB, Oates AC. Timing by rhythms: Daily clocks and developmental rulers. Dev Growth Differ 2016; 58:43-58. [PMID: 26542934 PMCID: PMC4832293 DOI: 10.1111/dgd.12242] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2015] [Revised: 09/18/2015] [Accepted: 09/19/2015] [Indexed: 01/10/2023]
Abstract
Biological rhythms are widespread, allowing organisms to temporally organize their behavior and metabolism in advantageous ways. Such proper timing of molecular and cellular events is critical to their development and health. This is best understood in the case of the circadian clock that orchestrates the daily sleep/wake cycle of organisms. Temporal rhythms can also be used for spatial organization, if information from an oscillating system can be recorded within the tissue in a manner that leaves a permanent periodic pattern. One example of this is the "segmentation clock" used by the vertebrate embryo to rhythmically and sequentially subdivide its elongating body axis. The segmentation clock moves with the elongation of the embryo, such that its period sets the segment length as the tissue grows outward. Although the study of this system is still relatively young compared to the circadian clock, outlines of molecular, cellular, and tissue-level regulatory mechanisms of timing have emerged. The question remains, however, is it truly a clock? Here we seek to introduce the segmentation clock to a wider audience of chronobiologists, focusing on the role and control of timing in the system. We compare and contrast the segmentation clock with the circadian clock, and propose that the segmentation clock is actually an oscillatory ruler, with a primary function to measure embryonic space.
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Affiliation(s)
- Alexis B Webb
- The Francis Crick Institute, Mill Hill Laboratory, London, UK
| | - Andrew C Oates
- The Francis Crick Institute, Mill Hill Laboratory, London, UK
- University College London, Gower Street, London, UK
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14
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Hermanstyne TO, Simms CL, Carrasquillo Y, Herzog ED, Nerbonne JM. Distinct Firing Properties of Vasoactive Intestinal Peptide-Expressing Neurons in the Suprachiasmatic Nucleus. J Biol Rhythms 2015; 31:57-67. [PMID: 26712166 DOI: 10.1177/0748730415619745] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The suprachiasmatic nucleus (SCN) regulates daily rhythms in physiology and behavior. Previous studies suggest a critical role for neurons expressing vasoactive intestinal peptide (VIP) in coordinating rhythmicity and synchronization in the SCN. Here we examined the firing properties of VIP-expressing SCN neurons in acute brain slices. Active and passive membrane properties were measured in VIP and in non-VIP neurons during the day and at night. Current-clamp recordings revealed that both VIP and non-VIP neurons were spontaneously active, with higher firing rates during the day than at night. Average firing frequencies, however, were higher in VIP neurons (3.1 ± 0.2 Hz, day and 2.4 ± 0.2 Hz, night) than in non-VIP neurons (1.8 ± 0.2 Hz, day and 0.9 ± 0.2 Hz, night), both day and night. The waveforms of individual action potentials in VIP and non-VIP neurons were also distinct. Action potential durations (APD50) were shorter in VIP neurons (3.6 ± 0.1 ms, day and 2.9 ± 0.1 ms, night) than in non-VIP neurons (4.4 ± 0.3 ms, day and 3.5 ± 0.2 ms, night) throughout the light-dark cycle. In addition, afterhyperpolarization (AHP) amplitudes were larger in VIP neurons (21 ± 0.8 mV, day and 24.9 ± 0.9 mV, night) than in non-VIP neurons (17.2 ± 1.1 mV, day and 20.5 ± 1.2 mV, night) during the day and at night. Furthermore, significant day/night differences were observed in APD50 and AHP amplitudes in both VIP and non-VIP SCN neurons, consistent with rhythmic changes in ionic conductances that contribute to shaping the firing properties of both cell types. The higher day and night firing rates of VIP neurons likely contribute to synchronizing electrical activity in the SCN.
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Affiliation(s)
- Tracey O Hermanstyne
- Departments of Developmental Biology and Medicine, Washington University School of Medicine, Saint Louis, MO
| | - Carrie L Simms
- Department of Biology, Washington University, St. Louis, MO
| | - Yarimar Carrasquillo
- Departments of Developmental Biology and Medicine, Washington University School of Medicine, Saint Louis, MO National Center for Complementary and Alternative Medicine, NIH 35 Convent Drive Building 35A, Room 1E-410, Bethesda, MD 20892, USA
| | - Erik D Herzog
- Department of Biology, Washington University, St. Louis, MO
| | - Jeanne M Nerbonne
- Departments of Developmental Biology and Medicine, Washington University School of Medicine, Saint Louis, MO
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16
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Meijer JH, Michel S. Neurophysiological Analysis of the Suprachiasmatic Nucleus. Methods Enzymol 2015; 552:75-102. [DOI: 10.1016/bs.mie.2014.11.001] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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Mercieca C, Kirwan JR. The intelligent use of systemic glucocorticoids in rheumatoid arthritis. Expert Rev Clin Immunol 2013; 10:143-57. [PMID: 24308837 DOI: 10.1586/1744666x.2014.864236] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Glucocorticoids (GC) have potent anti-inflammatory and immunomodulatory effects and are widely used in the management of rheumatoid arthritis in combination with other disease-modifying anti-rheumatoid drugs. Concern about the risk of adverse effects may be to some extent misplaced as low to moderate doses of GC have different mechanisms of action and risk profiles compared with high doses. This review discusses the current understanding about the different modes of action of GC, their strong disease-modifying properties and the efforts at improving the therapeutic ratio of GC through the development of new drugs which promise greater safety such as selective GC receptor agonists, liposomal GC and modified-release (MR) prednisone.
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Affiliation(s)
- Cecilia Mercieca
- University of Bristol Academic Rheumatology Unit, Bristol Royal Infirmary, Bristol BS2 8HW, UK
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18
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The effects of bilateral lesions of the mesencephalic trigeminal sensory nucleus on nocturnal feeding and related behaviors in mice. Life Sci 2013; 93:681-6. [PMID: 24063988 DOI: 10.1016/j.lfs.2013.09.015] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2013] [Revised: 07/26/2013] [Accepted: 09/09/2013] [Indexed: 11/20/2022]
Abstract
AIMS The mesencephalic trigeminal sensory nucleus (Me5), which receives signals originating from oral proprioceptors and projects its fibers to the hypothalamus, regulates mastication and modulates satiation. Because the Me5 neurons display circadian rhythms in circadian mPer1 gene expression and bilateral Me5 lesions change feeding and exploratory behavior profiles, we speculated that Me5 may influence the daily timing of feeding. Therefore, we explored the effects of bilateral caudal Me5 lesions on the circadian profiles of feeding and its related behaviors. MAIN METHODS We measured the activities of feeding, drinking, and locomotion for 24h using an automated feeding behavior measurement apparatus and analyzed the mRNA expression levels of hypothalamic orexigenic and anorexigenic signaling molecules in both Me5-lesioned and sham-operated mice. KEY FINDINGS Food and water intake and locomotor activity decreased significantly in Me5-lesioned mice during the dark phase without affecting these total indexes when measured over the entire day. Analysis of the mRNA expression levels of hypothalamic orexigenic and anorexigenic signaling molecules showed that prepro-orexin (orexin) mRNA in the perifornical area was significantly decreased during the dark phase only in Me5-lesioned mice. SIGNIFICANCE Bilateral caudal Me5 lesions alter the nocturnal properties of food and water intake and locomotor activity in mice and decrease the mRNA expression level of orexin in the perifornical area during the dark phase. These results suggest that Me5 activity may influence the nocturnal properties of feeding and its related behaviors by adjusting the activity of orexin neurons in the perifornical area.
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Mordel J, Karnas D, Pévet P, Isope P, Challet E, Meissl H. The output signal of Purkinje cells of the cerebellum and circadian rhythmicity. PLoS One 2013; 8:e58457. [PMID: 23505510 PMCID: PMC3591352 DOI: 10.1371/journal.pone.0058457] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2012] [Accepted: 02/04/2013] [Indexed: 02/07/2023] Open
Abstract
Measurement of clock gene expression has recently provided evidence that the cerebellum, like the master clock in the SCN, contains a circadian oscillator. The cerebellar oscillator is involved in anticipation of mealtime and possibly resides in Purkinje cells. However, the rhythmic gene expression is likely transduced into a circadian cerebellar output signal to exert an effective control of neuronal brain circuits that are responsible for feeding behavior. Using electrophysiological recordings from acute and organotypic cerebellar slices, we tested the hypothesis whether Purkinje cells transmit a circadian modulated signal to their targets in the brain. Extracellular recordings from brain slices revealed the typical discharge pattern previously described in vivo in single cell recordings showing basically a tonic or a trimodal-like firing pattern. However, in acute sagittal cerebellar slices the average spike rate of randomly selected Purkinje cells did not exhibit significant circadian variations, irrespective of their specific firing pattern. Also, frequency and amplitude of spontaneous inhibitory postsynaptic currents and the amplitude of GABA- and glutamate-evoked currents did not vary with circadian time. Long-term recordings using multielectrode arrays (MEA) allowed to monitor neuronal activity at multiple sites in organotypic cerebellar slices for several days to weeks. With this recording technique we observed oscillations of the firing rate of cerebellar neurons, presumably of Purkinje cells, with a period of about 24 hours which were stable for periods up to three days. The daily renewal of culture medium could induce circadian oscillations of the firing rate of Purkinje cells, a feature that is compatible with the behavior of slave oscillators. However, from the present results it appears that the circadian expression of cerebellar clock genes exerts only a weak influence on the electrical output of cerebellar neurons.
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Affiliation(s)
- Jérôme Mordel
- Neuroanatomical Department, Max Planck Institute for Brain Research, Frankfurt/M, Germany
- CNRS UPR3212, Institute for Cellular and Integrative Neuroscience, Strasbourg, France
| | - Diana Karnas
- Neuroanatomical Department, Max Planck Institute for Brain Research, Frankfurt/M, Germany
- CNRS UPR3212, Institute for Cellular and Integrative Neuroscience, Strasbourg, France
| | - Paul Pévet
- CNRS UPR3212, Institute for Cellular and Integrative Neuroscience, Strasbourg, France
| | - Philippe Isope
- CNRS UPR3212, Institute for Cellular and Integrative Neuroscience, Strasbourg, France
| | - Etienne Challet
- CNRS UPR3212, Institute for Cellular and Integrative Neuroscience, Strasbourg, France
| | - Hilmar Meissl
- Neuroanatomical Department, Max Planck Institute for Brain Research, Frankfurt/M, Germany
- * E-mail:
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20
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Abstract
The master coordinator of daily schedules in mammals, located in the ventral hypothalamus, is the suprachiasmatic nucleus (SCN). This relatively small population of neurons and glia generates circadian rhythms in physiology and behavior and synchronizes them to local time. Recent advances have begun to define the roles of specific cells and signals (e.g., peptides, amino acids, and purine derivatives) within this network that generate and synchronize daily rhythms. Here we focus on the best-studied signals between neurons and between glia in the mammalian circadian system with an emphasis on time-of-day pharmacology. Where possible, we highlight how commonly used drugs affect the circadian system.
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Abstract
The highly coordinated output of the hypothalamic biological clock does not only govern the daily rhythm in sleep/wake (or feeding/fasting) behaviour but also has direct control over many aspects of hormone release. In fact, a significant proportion of our current understanding of the circadian clock has its roots in the study of the intimate connections between the hypothalamic clock and multiple endocrine axes. This chapter will focus on the anatomical connections used by the mammalian biological clock to enforce its endogenous rhythmicity on the rest of the body, using a number of different hormone systems as a representative example. Experimental studies have revealed a highly specialised organisation of the connections between the mammalian circadian clock neurons and neuroendocrine as well as pre-autonomic neurons in the hypothalamus. These complex connections ensure a logical coordination between behavioural, endocrine and metabolic functions that will help the organism adjust to the time of day most efficiently. For example, activation of the orexin system by the hypothalamic biological clock at the start of the active phase not only ensures that we wake up on time but also that our glucose metabolism and cardiovascular system are prepared for this increased activity. Nevertheless, it is very likely that the circadian clock present within the endocrine glands plays a significant role as well, for instance, by altering these glands' sensitivity to specific stimuli throughout the day. In this way the net result of the activity of the hypothalamic and peripheral clocks ensures an optimal endocrine adaptation of the metabolism of the organism to its time-structured environment.
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Affiliation(s)
- Andries Kalsbeek
- Department of Endocrinology and Metabolism, G2-133, Academic Medical Center of the University of Amsterdam, The Netherlands.
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Kirwan JR, Buttgereit F. Symptom control with low-dose glucocorticoid therapy for rheumatoid arthritis. Rheumatology (Oxford) 2012; 51 Suppl 4:iv14-20. [DOI: 10.1093/rheumatology/kes085] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Honma S, Ono D, Suzuki Y, Inagaki N, Yoshikawa T, Nakamura W, Honma KI. Suprachiasmatic nucleus: cellular clocks and networks. PROGRESS IN BRAIN RESEARCH 2012; 199:129-141. [PMID: 22877663 DOI: 10.1016/b978-0-444-59427-3.00029-0] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The suprachiasmatic nucleus (SCN), the master circadian clock of mammals, is composed of multiple circadian oscillator neurons. Most of them exhibit significant circadian rhythms in their clock gene expression and spontaneous firing when cultured in dispersed cells, as well as in an organotypic slice. The distribution of periods depends on the SCN tissue organization, suggesting that cell-to-cell interaction is important for synchronization of the constituent oscillator cells. This cell-to-cell interaction involves both synaptic interactions and humoral mediators. Cellular oscillators form at least three separate but mutually coupled regional pacemakers, and two of them are involved in the photoperiodic regulation of behavioral rhythms in mice. Coupling of cellular oscillators in the SCN tissue compensates for the dysfunction due to clock gene mutations, on the one hand, and desynchronization within and between the regional pacemakers that suppresses the coherent rhythm expression from the SCN, on the other hand. The multioscillator pacemaker structure of the SCN is advantageous for responding to a wide range of environmental challenges without losing coherent rhythm outputs.
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Affiliation(s)
- Sato Honma
- Department of Physiology, Hokkaido University Graduate School of Medicine, Sapporo, Japan; Department of Chronomedicine, Hokkaido University Graduate School of Medicine, Sapporo, Japan.
| | - Daisuke Ono
- Department of Physiology, Hokkaido University Graduate School of Medicine, Sapporo, Japan; Advanced Photonic Bioimaging Section, Research Center for Cooperative Projects, Hokkaido University Graduate School of Medicine, Sapporo, Japan
| | - Yohko Suzuki
- Advanced Photonic Bioimaging Section, Research Center for Cooperative Projects, Hokkaido University Graduate School of Medicine, Sapporo, Japan
| | - Natsuko Inagaki
- Department of Physiology, Hokkaido University Graduate School of Medicine, Sapporo, Japan
| | - Tomoko Yoshikawa
- Advanced Photonic Bioimaging Section, Research Center for Cooperative Projects, Hokkaido University Graduate School of Medicine, Sapporo, Japan
| | - Wataru Nakamura
- Department of Physiology, Hokkaido University Graduate School of Medicine, Sapporo, Japan; Department of Chronodentistry, Osaka University Graduate School of Dentistry, Suita, Osaka, Japan
| | - Ken-Ichi Honma
- Department of Chronomedicine, Hokkaido University Graduate School of Medicine, Sapporo, Japan
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24
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Hong JH, Min CH, Jeong B, Kojiya T, Morioka E, Nagai T, Ikeda M, Lee KJ. Intracellular calcium spikes in rat suprachiasmatic nucleus neurons induced by BAPTA-based calcium dyes. PLoS One 2010; 5:e9634. [PMID: 20224788 PMCID: PMC2835761 DOI: 10.1371/journal.pone.0009634] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2009] [Accepted: 02/17/2010] [Indexed: 12/05/2022] Open
Abstract
Background Circadian rhythms in spontaneous action potential (AP) firing frequencies and in cytosolic free calcium concentrations have been reported for mammalian circadian pacemaker neurons located within the hypothalamic suprachiasmatic nucleus (SCN). Also reported is the existence of “Ca2+ spikes” (i.e., [Ca2+]c transients having a bandwidth of 10∼100 seconds) in SCN neurons, but it is unclear if these SCN Ca2+ spikes are related to the slow circadian rhythms. Methodology/Principal Findings We addressed this issue based on a Ca2+ indicator dye (fluo-4) and a protein Ca2+ sensor (yellow cameleon). Using fluo-4 AM dye, we found spontaneous Ca2+ spikes in 18% of rat SCN cells in acute brain slices, but the Ca2+ spiking frequencies showed no day/night variation. We repeated the same experiments with rat (and mouse) SCN slice cultures that expressed yellow cameleon genes for a number of different circadian phases and, surprisingly, spontaneous Ca2+ spike was barely observed (<3%). When fluo-4 AM or BAPTA-AM was loaded in addition to the cameleon-expressing SCN cultures, however, the number of cells exhibiting Ca2+ spikes was increased to 13∼14%. Conclusions/Significance Despite our extensive set of experiments, no evidence of a circadian rhythm was found in the spontaneous Ca2+ spiking activity of SCN. Furthermore, our study strongly suggests that the spontaneous Ca2+ spiking activity is caused by the Ca2+ chelating effect of the BAPTA-based fluo-4 dye. Therefore, this induced activity seems irrelevant to the intrinsic circadian rhythm of [Ca2+]c in SCN neurons. The problems with BAPTA based dyes are widely known and our study provides a clear case for concern, in particular, for SCN Ca2+ spikes. On the other hand, our study neither invalidates the use of these dyes as a whole, nor undermines the potential role of SCN Ca2+ spikes in the function of SCN.
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Affiliation(s)
- Jin Hee Hong
- Center for Cell-dynamics and Department of Physics, Korea University, Seoul, Republic of Korea
| | - Cheol Hong Min
- Center for Cell-dynamics and Department of Physics, Korea University, Seoul, Republic of Korea
| | - Byeongha Jeong
- Center for Cell-dynamics and Department of Physics, Korea University, Seoul, Republic of Korea
| | - Tomoyoshi Kojiya
- Graduate School of Innovative Life Science, Toyama University, Toyama, Japan
| | - Eri Morioka
- Graduate School of Innovative Life Science, Toyama University, Toyama, Japan
| | - Takeharu Nagai
- Laboratory for Nanosystems Physiology, Research Institute for Electronic Science, Hokkaido University, Sapporo, Japan
| | - Masayuki Ikeda
- Graduate School of Innovative Life Science, Toyama University, Toyama, Japan
| | - Kyoung J. Lee
- Center for Cell-dynamics and Department of Physics, Korea University, Seoul, Republic of Korea
- * E-mail:
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25
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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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26
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vanderLeest HT, Vansteensel MJ, Duindam H, Michel S, Meijer JH. PHASE OF THE ELECTRICAL ACTIVITY RHYTHM IN THE SCN IN VITRO NOT INFLUENCED BY PREPARATION TIME. Chronobiol Int 2009; 26:1075-89. [DOI: 10.3109/07420520903227746] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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27
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Functional neuroanatomy of sleep and circadian rhythms. ACTA ACUST UNITED AC 2009; 61:281-306. [PMID: 19695288 DOI: 10.1016/j.brainresrev.2009.08.001] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2009] [Revised: 07/02/2009] [Accepted: 08/07/2009] [Indexed: 11/23/2022]
Abstract
The daily sleep-wake cycle is perhaps the most dramatic overt manifestation of the circadian timing system, and this is especially true for the monophasic sleep-wake cycle of humans. Considerable recent progress has been made in elucidating the neurobiological mechanisms underlying sleep and arousal, and more generally, of circadian rhythmicity in behavioral and physiological systems. This paper broadly reviews these mechanisms from a functional neuroanatomical and neurochemical perspective, highlighting both historical and recent advances. In particular, I focus on the neural pathways underlying reciprocal interactions between the sleep-regulatory and circadian timing systems, and the functional implications of these interactions. While these two regulatory systems have often been considered in isolation, sleep-wake and circadian regulation are closely intertwined processes controlled by extensively integrated neurobiological mechanisms.
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28
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Perreau-Lenz S, Pévet P, Buijs RM, Kalsbeek A. The Biological Clock: The Bodyguard of Temporal Homeostasis. Chronobiol Int 2009; 21:1-25. [PMID: 15129821 DOI: 10.1081/cbi-120027984] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
In order for any organism to function properly, it is crucial that it be table to control the timing of its biological functions. An internal biological clock, located, in mammals, in the suprachiasmatic nucleus of the hypothalamus (SCN), therefore carefully guards this temporal homeostasis by delivering its message of time throughout the body. In view of the large variety of body functions (behavioral, physiological, and endocrine) as well as the large variety in their preferred time of main activity along the light:dark cycle, it seems logical to envision different means of time distribution by the SCN. In the present review, we propose that even though it presents a unimodal circadian rhythm of general electrical and metabolic activity, the SCN seems to use several sorts of output connections that are active at different times along the light:dark cycle to control the rhythmic expression of different body functions. Although the SCN is suggested to use diffusion of synchronizing factors in the rhythmic control of behavioral functions, it also needs neuronal connections for the control of endocrine functions. The distribution of the time-of-day message to neuroendocrine systems is either directly onto endocrine neurons or via intermediate neurons located in specific SCN targets. In addition, the SCN uses its connections with the autonomic nervous system for spreading its time-of-day message, either by setting the sensitivity of endocrine glands (i.e., thyroid, adrenal, ovary) or by directly controlling an endocrine output (i.e., melatonin synthesis). Moreover, the SCN seems to use different neurotransmitters released at different times along the light:dark cycle for each of the different connection types presented. Clearly, the temporal homeostasis of endocrine functions results from a diverse set of biological clock outputs.
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29
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Abstract
The circadian clock in the suprachiasmatic nuclei (SCN) is composed of thousands of oscillator neurons, each dependent on the cell-autonomous action of a defined set of circadian clock genes. A major question is still how these individual oscillators are organized into a biological clock that produces a coherent output capable of timing all the different daily changes in behavior and physiology. We investigated which anatomical connections and neurotransmitters are used by the biological clock to control the daily release pattern of a number of hormones. The picture that emerged shows projections contacting target neurons in the medial hypothalamus surrounding the SCN. The activity of these pre-autonomic and neuro-endocrine target neurons is controlled by differentially timed waves of vasopressin, GABA, and glutamate release from SCN terminals, among other factors. Together our data indicate that, with regard to the timing of their main release period within the LD cycle, at least four subpopulations of SCN neurons should be discernible. The different subgroups do not necessarily follow the phenotypic differences among SCN neurons. Thus, different subgroups can be found within neuron populations containing the same neurotransmitter. Remarkably, a similar distinction of four differentially timed subpopulations of SCN neurons was recently also discovered in experiments determining the temporal patterns of rhythmicity in individual SCN neurons by way of the electrophysiology or clock gene expression. Moreover, the specialization of the SCN may go as far as a single body structure, i.e., the SCN seems to contain neurons that specifically target the liver, pineal gland, and adrenal gland.
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Affiliation(s)
- A Kalsbeek
- Netherlands Institute for Brain Research, Hypothalamic Integration Mechanisms, Amsterdam, The Netherlands.
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30
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Abstract
The circadian clock in the suprachiasmatic nuclei (SCN) is composed of thousands of oscillator neurons, each of which is dependent on the cell-autonomous action of a defined set of circadian clock genes. A major question is still how these individual oscillators are organized into a biological clock producing a coherent output that is able to time all the different daily changes in behavior and physiology. We investigated which anatomical connections and neurotransmitters are used by the biological clock to control the daily release pattern of a number of hormones. The picture that emerged shows projections contacting target neurons in the medial hypothalamus surrounding the SCN. The activity of these pre-autonomic and neuro-endocrine target neurons is controlled by differentially timed waves of, among others, vasopressin, GABA, and glutamate release from SCN terminals. Together our data indicate that, with regard to the timing of their main release period within the light-dark (LD) cycle, at least 4 subpopulations of SCN neurons should be discerned. The different subgroups do not necessarily follow the phenotypic differences among SCN neurons. Thus, different subgroups can be found within neuron populations containing the same neurotransmitter. Remarkably, a similar distinction of 4 differentially timed subpopulations of SCN neurons was recently also discovered in experiments determining the temporal patterns of rhythmicity in individual SCN neurons by way of the electrophysiology or clock gene expression. Moreover, the specialization of the SCN may go as far as a single body structure; i.e., the SCN seems to contain neurons that specifically target the liver, pineal, and adrenal.
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Affiliation(s)
- A Kalsbeek
- Netherlands Institute for Brain Research, Hypothalamic Integration Mechanisms, Amsterdam, The Netherlands.
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31
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Chappell PE, Goodall CP, Tonsfeldt KJ, White RS, Bredeweg E, Latham KL. Modulation of gonadotrophin-releasing hormone secretion by an endogenous circadian clock. J Neuroendocrinol 2009; 21:339-45. [PMID: 19187466 DOI: 10.1111/j.1365-2826.2009.01845.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The mechanisms mediating positive feedback effects of oestradiol on pre-ovulatory gonadotrophin releasing-hormone (GnRH) surge generation in female mammals, although well-explored, are still incompletely understood. In addition to binding to and signalling through classical nuclear receptor-mediated pathways in afferent hypothalamic neurones, recent evidence suggests that ovarian steroids may use membrane-bound receptors or nonclassical signalling pathways to directly influence cell function leading to the generation of GnRH surge secretion. We review recent investigations into the role of the endogenous molecular circadian clock on modulation of GnRH gene expression and neuropeptide secretion, and will explore potential molecular mechanisms by which ovarian steroids may directly induce secretory changes at the level of the GnRH neurone, examining closely whether circadian clock gene oscillations may be involved.
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Affiliation(s)
- P E Chappell
- Department of Zoology, Oregon State University, Corvallis, OR 97331, USA.
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32
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Kent J, Meredith AL. BK channels regulate spontaneous action potential rhythmicity in the suprachiasmatic nucleus. PLoS One 2008; 3:e3884. [PMID: 19060951 PMCID: PMC2586654 DOI: 10.1371/journal.pone.0003884] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2008] [Accepted: 11/13/2008] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Circadian ( approximately 24 hr) rhythms are generated by the central pacemaker localized to the suprachiasmatic nucleus (SCN) of the hypothalamus. Although the basis for intrinsic rhythmicity is generally understood to rely on transcription factors encoded by "clock genes", less is known about the daily regulation of SCN neuronal activity patterns that communicate a circadian time signal to downstream behaviors and physiological systems. Action potentials in the SCN are necessary for the circadian timing of behavior, and individual SCN neurons modulate their spontaneous firing rate (SFR) over the daily cycle, suggesting that the circadian patterning of neuronal activity is necessary for normal behavioral rhythm expression. The BK K(+) channel plays an important role in suppressing spontaneous firing at night in SCN neurons. Deletion of the Kcnma1 gene, encoding the BK channel, causes degradation of circadian behavioral and physiological rhythms. METHODOLOGY/PRINCIPAL FINDINGS To test the hypothesis that loss of robust behavioral rhythmicity in Kcnma1(-/-) mice is due to the disruption of SFR rhythms in the SCN, we used multi-electrode arrays to record extracellular action potentials from acute wild-type (WT) and Kcnma1(-/-) slices. Patterns of activity in the SCN were tracked simultaneously for up to 3 days, and the phase, period, and synchronization of SFR rhythms were examined. Loss of BK channels increased arrhythmicity but also altered the amplitude and period of rhythmic activity. Unexpectedly, Kcnma1(-/-) SCNs showed increased variability in the timing of the daily SFR peak. CONCLUSIONS/SIGNIFICANCE These results suggest that BK channels regulate multiple aspects of the circadian patterning of neuronal activity in the SCN. In addition, these data illustrate the characteristics of a disrupted SCN rhythm downstream of clock gene-mediated timekeeping and its relationship to behavioral rhythms.
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Affiliation(s)
- Jack Kent
- Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
| | - Andrea L. Meredith
- Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
- * E-mail:
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33
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Hughes ATL, Guilding C, Lennox L, Samuels RE, McMahon DG, Piggins HD. Live imaging of altered period1 expression in the suprachiasmatic nuclei of Vipr2-/- mice. J Neurochem 2008; 106:1646-57. [PMID: 18554318 PMCID: PMC2658715 DOI: 10.1111/j.1471-4159.2008.05520.x] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Vasoactive intestinal polypeptide and its receptor, VPAC2, play important roles in the functioning of the brain’s circadian clock in the suprachiasmatic nuclei (SCN). Mice lacking VPAC2 receptors (Vipr2−/−) show altered circadian rhythms in locomotor behavior, neuronal firing rate, and clock gene expression, however, the nature of molecular oscillations in individual cells is unclear. Here, we used real-time confocal imaging of a destabilized green fluorescent protein (GFP) reporter to track the expression of the core clock gene Per1 in live SCN-containing brain slices from wild-type (WT) and Vipr2−/− mice. Rhythms in Per1-driven GFP were detected in WT and Vipr2−/− cells, though a significantly lower number and proportion of cells in Vipr2−/− slices expressed detectable rhythms. Further, Vipr2−/− cells expressed significantly lower amplitude oscillations than WT cells. Within each slice, the phases of WT cells were synchronized whereas cells in Vipr2−/− slices were poorly synchronized. Most GFP-expressing cells, from both genotypes, expressed neither vasopressin nor vasoactive intestinal polypeptide. Pharmacological blockade of VPAC2 receptors in WT SCN slices partially mimicked the Vipr2−/− phenotype. These data demonstrate that intercellular communication via the VPAC2 receptor is important for SCN neurons to sustain robust, synchronous oscillations in clock gene expression.
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Affiliation(s)
- Alun T L Hughes
- Faculty of Life Sciences, University of Manchester, Manchester, UK
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34
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Circadian mPer1 gene expression in mesencephalic trigeminal nucleus cultures. Brain Res 2008; 1214:84-93. [DOI: 10.1016/j.brainres.2008.03.041] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2007] [Revised: 03/06/2008] [Accepted: 03/13/2008] [Indexed: 11/17/2022]
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Fahrenkrug J, Popovic N, Georg B, Brundin P, Hannibal J. Decreased VIP and VPAC2 receptor expression in the biological clock of the R6/2 Huntington's disease mouse. J Mol Neurosci 2008; 31:139-48. [PMID: 17478887 DOI: 10.1385/jmn/31:02:139] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2006] [Revised: 11/30/1999] [Accepted: 11/01/2006] [Indexed: 12/31/2022]
Abstract
Huntington's disease (HD) is a fatal genetic neurodegenerative disorder caused by a CAG triplet repeat expansion in the gene encoding the protein huntingtin. The most studied model of HD, the R6/2 transgenic mouse, replicates many features of the disease. In addition to motor, cognitive, and endocrine dysfunctions, these mice exhibit a progressive disruption of circadian rhythms. This is accompanied by an altered expression of the circadian clock genes in the suprachiasmatic nucleus/nuclei (SCN), the principal circadian pacemaker in the brain. The neuropeptide vasoactive intestinal polypeptide (VIP) and its receptor VPAC2 are highly expressed in the SCN, and VIPergic signaling plays an essential role in maintenance of ongoing circadian rhythmicity. We found a marked reduction in both VIP mRNA and VPAC2 receptor mRNA, quantified by RT-PCR, as well as a decrease in VIP immunostaining in the SCN of R6/2 mice. These changes were coupled to a disruption of circadian rhythm. We observed no loss of neurons in the SCN and therefore suggest that the changes in VIP and VPAC2 receptor are due to their decreased expression. In conclusion, we propose that impaired VIPergic signaling is an additional candidate mechanism for disruption of circadian rhythms in R6/2 mice.
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Affiliation(s)
- Jan Fahrenkrug
- Department of Clinical Biochemistry, Bispebjerg University Hospital, Copenhagen NV, Denmark.
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36
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Saint-Mleux B, Bayer L, Eggermann E, Jones BE, Mühlethaler M, Serafin M. Suprachiasmatic modulation of noradrenaline release in the ventrolateral preoptic nucleus. J Neurosci 2007; 27:6412-6. [PMID: 17567801 PMCID: PMC6672428 DOI: 10.1523/jneurosci.1432-07.2007] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
As the major brain circadian pacemaker, the suprachiasmatic nucleus (SCN) is known to influence the timing of sleep and waking. We thus investigated here the effect of SCN stimulation on neurons of the ventrolateral preoptic nucleus (VLPO) thought to be involved in promoting sleep. Using an acute in vitro preparation of the rat anterior hypothalamus/preoptic area, we found that whereas single-pulse stimulations of the SCN evoked standard fast ionotropic IPSPs and EPSPs, train stimulations unexpectedly evoked a long-lasting inhibition (LLI). Such LLIs could also be evoked in VLPO neurons by pressure application of NMDA within the SCN, indicating the specific activation of SCN neurons. This LLI was shown to result from the presynaptic facilitation of noradrenaline release, because it was suppressed in presence of yohimbine, a selective antagonist of alpha2-adrenoreceptors. The LLI depended on the opening of a potassium conductance, because it was annulled at E(K) and could be reversed below E(K). These results show that the SCN can provide an LLI of the sleep-promoting VLPO neurons that could play a role in the circadian organization of the sleep-waking cycle.
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Affiliation(s)
- Benoît Saint-Mleux
- Département de Neurosciences Fondamentales, Centre Médical Universitaire, 1211 Genève 4, Switzerland, and
| | - Laurence Bayer
- Département de Neurosciences Fondamentales, Centre Médical Universitaire, 1211 Genève 4, Switzerland, and
| | - Emmanuel Eggermann
- Département de Neurosciences Fondamentales, Centre Médical Universitaire, 1211 Genève 4, Switzerland, and
| | - Barbara E. Jones
- Department of Neurology and Neurosurgery, McGill University, Montreal Neurological Institute, Montreal, Quebec, Canada H3A 2B4
| | - Michel Mühlethaler
- Département de Neurosciences Fondamentales, Centre Médical Universitaire, 1211 Genève 4, Switzerland, and
| | - Mauro Serafin
- Département de Neurosciences Fondamentales, Centre Médical Universitaire, 1211 Genève 4, Switzerland, and
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37
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Brown TM, Piggins HD. Electrophysiology of the suprachiasmatic circadian clock. Prog Neurobiol 2007; 82:229-55. [PMID: 17646042 DOI: 10.1016/j.pneurobio.2007.05.002] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2006] [Revised: 03/29/2007] [Accepted: 05/30/2007] [Indexed: 01/28/2023]
Abstract
In mammals, an internal timekeeping mechanism located in the suprachiasmatic nuclei (SCN) orchestrates a diverse array of neuroendocrine and physiological parameters to anticipate the cyclical environmental fluctuations that occur every solar day. Electrophysiological recording techniques have proved invaluable in shaping our understanding of how this endogenous clock becomes synchronized to salient environmental cues and appropriately coordinates the timing of a multitude of physiological rhythms in other areas of the brain and body. In this review we discuss the pioneering studies that have shaped our understanding of how this biological pacemaker functions, from input to output. Further, we highlight insights from new studies indicating that, more than just reflecting its oscillatory output, electrical activity within individual clock cells is a vital part of SCN clockwork itself.
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Affiliation(s)
- Timothy M Brown
- Faculty of Life Sciences, Stopford Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK
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38
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Guilding C, Piggins HD. Challenging the omnipotence of the suprachiasmatic timekeeper: are circadian oscillators present throughout the mammalian brain? Eur J Neurosci 2007; 25:3195-216. [PMID: 17552989 DOI: 10.1111/j.1460-9568.2007.05581.x] [Citation(s) in RCA: 237] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The suprachiasmatic nucleus of the hypothalamus (SCN) is the master circadian pacemaker or clock in the mammalian brain. Canonical theory holds that the output from this single, dominant clock is responsible for driving most daily rhythms in physiology and behaviour. However, important recent findings challenge this uniclock model and reveal clock-like activities in many neural and non-neural tissues. Thus, in addition to the SCN, a number of areas of the mammalian brain including the olfactory bulb, amygdala, lateral habenula and a variety of nuclei in the hypothalamus, express circadian rhythms in core clock gene expression, hormone output and electrical activity. This review examines the evidence for extra-SCN circadian oscillators in the mammalian brain and highlights some of the essential properties and key differences between brain oscillators. The demonstration of neural pacemakers outside the SCN has wide-ranging implications for models of the circadian system at a whole-organism level.
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Affiliation(s)
- Clare Guilding
- 3.614 Stopford Building, Faculty of Life Sciences, University of Manchester, Oxford Road, Manchester M13 9PT, UK
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Kuhlman SJ. Biological Rhythms Workshop IB: neurophysiology of SCN pacemaker function. COLD SPRING HARBOR SYMPOSIA ON QUANTITATIVE BIOLOGY 2007; 72:21-33. [PMID: 18419260 DOI: 10.1101/sqb.2007.72.061] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Pacemakers are functional units capable of generating oscillations that synchronize downstream rhythms. In mammals, the suprachiasmatic nucleus (SCN) of the hypothalamus is a circadian pacemaker composed of individual neurons that intrinsically express a near 24-hour rhythm in gene expression. Rhythmic gene expression is tightly coupled to a rhythm in spontaneous firing rate via intrinsic daily regulation of potassium current. Recent progress in the field indicates that SCN pacemaking is a specialized property that emerges from intrinsic features of single cells, structural connectivity among cells, and activity dynamics within the SCN. The focus of this chapter is on how Nature built a functional pacemaker from many individual oscillators that is capable of coordinating the daily timing of essential brain and physiological processes.
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Affiliation(s)
- S J Kuhlman
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA
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40
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Gramowski A, Jügelt K, Stüwe S, Schulze R, McGregor GP, Wartenberg-Demand A, Loock J, Schröder O, Weiss DG. Functional screening of traditional antidepressants with primary cortical neuronal networks grown on multielectrode neurochips. Eur J Neurosci 2006; 24:455-65. [PMID: 16903853 DOI: 10.1111/j.1460-9568.2006.04892.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We optimized the novel technique of multielectrode neurochip recordings for the rapid and efficient screening of neuroactivity. Changes in the spontaneous activity of cultured networks of primary cortical neurons were quantified to evaluate the action of drugs on the firing dynamics of complex network activity. The multiparametric assessment of electrical activity changes caused by psychoactive herbal extracts from Hypericum, Passiflora and Valeriana, and various combinations thereof revealed a receptor-specific and concentration-dependent inhibition of the firing patterns. The spike and burst rates showed significant substance-dependent effects and significant differences in potency. The effects of specific receptor blockades on the inhibitory responses provided evidence that the herbal extracts act on gamma-amino butyric acid (GABA) and serotonin (5-HT) receptors, which are recognized targets of pharmacological antidepressant treatment. A biphasic effect, serotonergic stimulation of activity at low concentrations that is overridden by GABAergic inhibition at higher concentrations, is apparent with Hypericum alone and the triple combination of the extracts. The more potent neuroactivity of the triple combination compared to Hypericum alone and the additive effect of Passiflora and Valeriana suggest a synergy between constituent herbal extracts. The extracts and their combinations affected the set of derived activity parameters in a concomitant manner suggesting that all three constituent extracts and their combinations have largely similar modes of action. This study also demonstrates the sensitivity, selectivity and robustness of neurochip recordings for high content screening of complex mixtures of neuroactive substances and for providing multiparametric information on neuronal activity changes to assess the therapeutic potential of psychoactive substances.
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Affiliation(s)
- Alexandra Gramowski
- Division of Cell Biology and Biosystems Technology, Institute of Biological Sciences, University of Rostock, Albert-Einstein-Strasse, 318059 Rostock, Germany.
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41
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Morin LP, Allen CN. The circadian visual system, 2005. ACTA ACUST UNITED AC 2006; 51:1-60. [PMID: 16337005 DOI: 10.1016/j.brainresrev.2005.08.003] [Citation(s) in RCA: 306] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2005] [Revised: 07/19/2005] [Accepted: 08/09/2005] [Indexed: 11/17/2022]
Abstract
The primary mammalian circadian clock resides in the suprachiasmatic nucleus (SCN), a recipient of dense retinohypothalamic innervation. In its most basic form, the circadian rhythm system is part of the greater visual system. A secondary component of the circadian visual system is the retinorecipient intergeniculate leaflet (IGL) which has connections to many parts of the brain, including efferents converging on targets of the SCN. The IGL also provides a major input to the SCN, with a third major SCN afferent projection arriving from the median raphe nucleus. The last decade has seen a blossoming of research into the anatomy and function of the visual, geniculohypothalamic and midbrain serotonergic systems modulating circadian rhythmicity in a variety of species. There has also been a substantial and simultaneous elaboration of knowledge about the intrinsic structure of the SCN. Many of the developments have been driven by molecular biological investigation of the circadian clock and the molecular tools are enabling novel understanding of regional function within the SCN. The present discussion is an extension of the material covered by the 1994 review, "The Circadian Visual System."
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Affiliation(s)
- L P Morin
- Department of Psychiatry and Graduate Program in Neuroscience, Stony Brook University, Stony Brook, NY 11794, USA.
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42
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Brown TM, Banks JR, Piggins HD. A novel suction electrode recording technique for monitoring circadian rhythms in single and multiunit discharge from brain slices. J Neurosci Methods 2006; 156:173-81. [PMID: 16581136 DOI: 10.1016/j.jneumeth.2006.02.024] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2005] [Revised: 01/12/2006] [Accepted: 02/25/2006] [Indexed: 10/24/2022]
Abstract
The study of spontaneous neuronal discharge for several days in vitro poses substantial technical difficulties not readily addressed by existing methodologies. Here we describe a novel method for recording bioelectrical signals from brain slices, using media-filled, glass micropipettes stabilized at the recording interface by negative pressure. Such electrodes are durable, economical and easily constructed using standard laboratory equipment. Through these suction electrodes, we monitored approximately 24 h oscillations in spontaneous single and multiunit discharge from acutely prepared adult mouse suprachiasmatic nuclei (SCN) slices for up to 4 days in vitro, with very high success rates. Neuronal oscillations exhibited all the characteristics previously determined in SCN recordings using other techniques. Importantly, our electrode assembly enables SCN activity in acutely prepared brain slices to be monitored for substantially longer than with other methodologies. In summary, our data suggest that suction electrodes are likely to provide a favorable alternative to existing methods for recording long-term neuronal activity from brain slices.
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Affiliation(s)
- Timothy M Brown
- Faculty of Life Sciences, University of Manchester, Oxford Road, Manchester M13 9PT, UK
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43
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Abraham U, Prior JL, Granados-Fuentes D, Piwnica-Worms DR, Herzog ED. Independent circadian oscillations of Period1 in specific brain areas in vivo and in vitro. J Neurosci 2006; 25:8620-6. [PMID: 16177029 PMCID: PMC6725522 DOI: 10.1523/jneurosci.2225-05.2005] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Behavioral and physiological circadian rhythms in mammals are controlled by a master pacemaker in the hypothalamic suprachiasmatic nuclei (SCN). Recently, circadian oscillations of hormone secretion, clock gene expression, and electrical activity have been demonstrated in explants of other brain regions. This suggests that some extra-SCN brain regions contain a functional, SCN-independent circadian clock, but in vivo evidence for intrinsic pacemaking is still lacking. We developed a novel method to image bioluminescence in vivo from the main olfactory bulbs (OB) of intact and SCN-lesioned (SCNX) Period1::luciferase rats for 2 d in constant darkness. The OBs expressed circadian rhythms in situ with a reliable twofold increase from day to night, similar to the phase and amplitude of ex vivo rhythms. In vivo cycling persisted for at least 1 month in the absence of the SCN. To assess indirectly in vivo rhythmicity of other brain areas, we measured the phase-dependence of their in vitro rhythms on the time of surgery. Surgery reliably reset the phase of the pineal gland and vascular organ of the lamina terminalis (VOLT) harvested from SCNX rats but had little effect on the phase of the OB. We deduce that the SCN and OB contain self-sustained circadian oscillators, whereas the pineal gland and VOLT are weak oscillators that require input from the SCN to show coordinated circadian rhythms. We conclude that the mammalian brain comprises a diverse set of SCN-dependent and SCN-independent circadian oscillators.
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Affiliation(s)
- Ute Abraham
- Department of Biology, Washington University, St. Louis, Missouri 63130, USA.
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44
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Pakhotin P, Harmar AJ, Verkhratsky A, Piggins H. VIP receptors control excitability of suprachiasmatic nuclei neurones. Pflugers Arch 2005; 452:7-15. [PMID: 16283205 DOI: 10.1007/s00424-005-0003-z] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2005] [Accepted: 09/12/2005] [Indexed: 10/25/2022]
Abstract
The role of vasoactive intestinal polypeptide (VIP) receptors on excitable properties of neurones in slices acutely prepared from the suprachiasmatic nuclei (SCN) of wild-type (WT) and VPAC(2)-receptor-deficient (Vipr2 ( -/- )) mice was studied under voltage clamp with the use of patch-clamp recording in the whole-cell configuration. The resting membrane potential in Vipr2 ( -/- ) neurones was significantly hyperpolarised as compared to WT cells (-60+/-7 vs -72+/-6 mV, p<0.01). Bath application of 100 nM VIP or the VPAC(2) receptor agonist RO 25-1553 triggered a slow inward current in a subpopulation of WT SCN neurones; the VIP-induced current was not affected by slice incubation with 25 microM of bicuculline but disappeared completely when the cells were dialysed with CsCl-containing/K(+)-free solution. Application of VIP or RO 25-1553 to neurones from Vipr2 ( -/- ) mice did not induce currents in all cells tested. Incubation of WT slices with 100 nM VIP or RO 25-1553 resulted in inhibition of fast tetrodotoxin-sensitive sodium currents and delayed rectifier K(+) currents in most of the cells tested. This effect was completely absent in cells from Vipr2 ( -/- ) mice. We postulate that VIP receptors control excitability of SCN neurones at the postsynaptic level by direct modulation of membrane potential via inhibition of K(+) channels and by tonic inhibition of sodium and potassium voltage-gated currents.
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Affiliation(s)
- Pavel Pakhotin
- Faculty of Life Sciences, The University of Manchester, 1.124 Stopford Building, Oxford Road, M13 9PT, Manchester, UK
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Mistlberger RE. Circadian regulation of sleep in mammals: Role of the suprachiasmatic nucleus. ACTA ACUST UNITED AC 2005; 49:429-54. [PMID: 16269313 DOI: 10.1016/j.brainresrev.2005.01.005] [Citation(s) in RCA: 200] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2004] [Revised: 01/07/2005] [Accepted: 01/07/2005] [Indexed: 10/25/2022]
Abstract
Despite significant progress in elucidating the molecular basis for circadian oscillations, the neural mechanisms by which the circadian clock organizes daily rhythms of behavioral state in mammals remain poorly understood. The objective of this review is to critically evaluate a conceptual model that views sleep expression as the outcome of opponent processes-a circadian clock-dependent alerting process that opposes sleep during the daily wake period, and a homeostatic process by which sleep drive builds during waking and is dissipated during sleep after circadian alerting declines. This model is based primarily on the evidence that in a diurnal primate, the squirrel monkey (Saimiri sciureus), ablation of the master circadian clock (the suprachiasmatic nucleus; SCN) induces a significant expansion of total daily sleep duration and a reduction in sleep latency in the dark. According to this model, the circadian clock actively promotes wake but only passively gates sleep; thus, loss of circadian clock alerting by SCN ablation impairs the ability to sustain wakefulness and causes sleep to expand. For comparison, two additional conceptual models are described, one in which the circadian clock actively promotes sleep but not wake, and a third in which the circadian clock actively promotes both sleep and wake, at different circadian phases. Sleep in intact and SCN-damaged rodents and humans is first reviewed, to determine how well the data fit these conceptual models. Neuroanatomical and neurophysiological studies are then reviewed, to examine the evidence for direct and indirect interactions between the SCN circadian clock and sleep-wake circuits. Finally, sleep in SCN-ablated squirrel monkeys is re-examined, to consider its compatibility with alternative models of circadian regulation of sleep. In aggregate, the behavioral and neurobiological evidence suggests that in rodents and humans, the circadian clock actively promotes both wake and sleep, at different phases of the circadian cycle. The hypersomnia of SCN-ablated squirrel monkeys is unique in magnitude, but is not incompatible with a role for the SCN pacemaker in actively promoting sleep.
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Affiliation(s)
- Ralph E Mistlberger
- Department of Psychology, Simon Fraser University, 8888 University Drive, Burnaby, Canada BC V5A 1S6.
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46
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Barakat MT, O'Hara BF, Cao VH, Heller HC, Ruby NF. Light induces c-fos and per1 expression in the suprachiasmatic nucleus of arrhythmic hamsters. Am J Physiol Regul Integr Comp Physiol 2005; 289:R1381-6. [PMID: 16002555 DOI: 10.1152/ajpregu.00695.2004] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Locomotor activity rhythms in a significant proportion of Siberian hamsters (Phodopus sungorus sungorus) become arrhythmic after the light-dark (LD) cycle is phase-delayed by 5 h. Arrhythmia is apparent within a few days and persists indefinitely despite the presence of the photocycle. The failure of arrhythmic hamsters to regain rhythms while housed in the LD cycle, as well as the lack of any masking of activity, suggested that the circadian system of these animals had become insensitive to light. We tested this hypothesis by examining light-induced gene expression in the suprachiasmatic nucleus (SCN). Several weeks after the phase delay, arrhythmic and re-entrained hamsters were housed in constant darkness (DD) for 24 h and administered a 30-min light pulse 2 h after predicted dark onset because light induces c-fos and per1 genes at this time in entrained animals. Brains were then removed, and tissue sections containing the SCN were processed for in situ hybridization and probed with c-fos and per1 mRNA probes made from Siberian hamster cDNA. Contrary to our prediction, light pulses induced robust expression of both c-fos and per1 in all re-entrained and arrhythmic hamsters. A separate group of animals held in DD for 10 days after the light pulse remained arrhythmic. Thus, even though the SCN of these animals responded to light, neither the LD cycle nor DD restored rhythms, as it does in other species made arrhythmic by constant light (LL). These results suggest that different mechanisms underlie arrhythmicity induced by LL or by a phase delay of the LD cycle. Whereas LL induces arrhythmicity by desynchronizing SCN neurons, phase delay-induced arrhythmicity may be due to a loss of circadian rhythms at the level of individual SCN neurons.
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Affiliation(s)
- Monique T Barakat
- Department of Biological Sciences, 371 Serra Mall, Stanford University, Stanford, California 94305-5020, USA.
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47
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Aton SJ, Block GD, Tei H, Yamazaki S, Herzog ED. Plasticity of circadian behavior and the suprachiasmatic nucleus following exposure to non-24-hour light cycles. J Biol Rhythms 2005; 19:198-207. [PMID: 15155006 DOI: 10.1177/0748730404264156] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Period aftereffects are a form of behavioral plasticity in which the free-running period of circadian behavior undergoes experience-dependent changes. It is unclear whether this plasticity is age dependent and whether the changes in behavioral period relate to changes in the SCN or the retina, 2 known circadian pacemakers in mammals. To determine whether these changes vary with age, Per1-luc transgenic mice (in which the luciferase gene is driven by the Period1 promoter) of different ages were exposed to short (10 h light: 10 h dark, T20) or long (14 h light: 14 h dark, T28) light cycles (T cycles). Recordings of running-wheel activity in constant darkness (DD) revealed that the intrinsic periods of T20 mice were significantly shorter than of T28 mice at all ages. Aftereffects following the shorter light cycle were significantly smaller in mice older than 3 months, corresponding with a decreased ability to entrain to T20. Age did not diminish entrainment or aftereffects in the 28-h light schedule. The behavioral period of pups born in DD depended on the T cycle experienced in utero, showing maternal transference of aftereffects. Recordings of Per1-luc activity from the isolated SCN in vitro revealed that the SCN of young mice expressed aftereffects, but the periods of behavior and SCN were negatively correlated. Enucleation in DD had no effect on behavioral aftereffects, indicating the eyes are not required for aftereffects expression. These data show that circadian aftereffects are an age-dependent form of plasticity mediated by stable changes in the SCN and, importantly, extra-SCN tissues.
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Affiliation(s)
- Sara J Aton
- Department of Biology, Washington University, St. Louis, MO 63130-4899, USA.
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48
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Aton SJ, Colwell CS, Harmar AJ, Waschek J, Herzog ED. Vasoactive intestinal polypeptide mediates circadian rhythmicity and synchrony in mammalian clock neurons. Nat Neurosci 2005; 8:476-83. [PMID: 15750589 PMCID: PMC1628303 DOI: 10.1038/nn1419] [Citation(s) in RCA: 567] [Impact Index Per Article: 29.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2005] [Accepted: 02/15/2005] [Indexed: 11/09/2022]
Abstract
The mammalian suprachiasmatic nucleus (SCN) is a master circadian pacemaker. It is not known which SCN neurons are autonomous pacemakers or how they synchronize their daily firing rhythms to coordinate circadian behavior. Vasoactive intestinal polypeptide (VIP) and the VIP receptor VPAC(2) (encoded by the gene Vipr2) may mediate rhythms in individual SCN neurons, synchrony between neurons, or both. We found that Vip(-/-) and Vipr2(-/-) mice showed two daily bouts of activity in a skeleton photoperiod and multiple circadian periods in constant darkness. Loss of VIP or VPAC(2) also abolished circadian firing rhythms in approximately half of all SCN neurons and disrupted synchrony between rhythmic neurons. Critically, daily application of a VPAC(2) agonist restored rhythmicity and synchrony to VIP(-/-) SCN neurons, but not to Vipr2(-/-) neurons. We conclude that VIP coordinates daily rhythms in the SCN and behavior by synchronizing a small population of pacemaking neurons and maintaining rhythmicity in a larger subset of neurons.
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MESH Headings
- Action Potentials/drug effects
- Action Potentials/physiology
- Analysis of Variance
- Animals
- Animals, Newborn
- Behavior, Animal
- Biological Clocks/physiology
- Cells, Cultured
- Chi-Square Distribution
- Circadian Rhythm/drug effects
- Circadian Rhythm/physiology
- Immunohistochemistry/methods
- In Vitro Techniques
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Motor Activity/genetics
- Neurons/drug effects
- Neurons/physiology
- Peptides, Cyclic/pharmacology
- Receptors, Vasoactive Intestinal Peptide/deficiency
- Receptors, Vasoactive Intestinal Peptide/genetics
- Receptors, Vasoactive Intestinal Peptide, Type II
- Suprachiasmatic Nucleus/cytology
- Time Factors
- Vasoactive Intestinal Peptide/agonists
- Vasoactive Intestinal Peptide/metabolism
- Vasoactive Intestinal Peptide/pharmacology
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Affiliation(s)
- Sara J Aton
- Department of Biology, One Brookings Drive, Washington University, St. Louis, Missouri 63130, USA
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49
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Abstract
Daily oscillations in physiology and behavior are regulated by a brain clock located in the suprachiasmatic nucleus (SCN). Individual cells within this nucleus contain an autonomous molecular clock. Recent discoveries that make use of new molecular and genetic data and tools highlight the conclusion that the SCN is a heterogeneous network of functionally and phenotypically differentiated cells. Neurons within SCN subregions serve distinctly separate functions in regulating the overall activity of the circadian clock: some cells within the SCN rhythmically express "clock" genes, whereas others exhibit induced expression of these genes after the organism has been exposed to a light pulse. The coordinated interaction of these functionally distinct cells is integral to the coherent functioning of the brain clock.
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Affiliation(s)
- Michael C Antle
- Department of Psychology, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada.
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50
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Bhumbra GS, Inyushkin AN, Saeb-Parsy K, Hon A, Dyball REJ. Rhythmic changes in spike coding in the rat suprachiasmatic nucleus. J Physiol 2005; 563:291-307. [PMID: 15611016 PMCID: PMC1665572 DOI: 10.1113/jphysiol.2004.079848] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Revised: 11/23/2004] [Accepted: 12/16/2004] [Indexed: 11/08/2022] Open
Abstract
The suprachiasmatic nucleus is regarded as the main mammalian circadian pacemaker but evidence for rhythmic firing of single units in vivo has been obtained only recently. The present study was undertaken to determine if rhythms could be seen using measures of activity in addition to the mean spike frequency. We investigated whether there were changes in the irregularity of cell activity measured by the disorder of the interspike interval distribution for neurones recorded in vivo and in vitro. By plotting the entropy of the log interval histogram that quantifies the coding capacity for each action potential against the respective zeitgeber time, we describe oscillations of spike activity in vivo. Entropy measures have the advantage over variances in that they quantify aspects of the shape of the distribution and not just the dispersion. One hundred and sixty-six cell recordings from the suprachiasmatic nucleus showed a significant rhythm in entropy with an oscillatory trend in the data (P < 0.001) showing a trough towards the end of the light period and a peak in the mid-dark period. There was a similar rhythm for the cells recorded from the peripheral zone (n = 209, P = 0.037). In separate experiments in vitro, to investigate the relationship between mean spike frequency and entropy, potassium-induced depolarization of cells recorded during the subjective night was correlated with a significant increase in mean spike frequency (r = 0.259, P = 0.011) and a decrease in entropy (r = -0.296, P = 0.004). The negative correlation between the entropy and mean spike frequency of cells recorded in vitro was significantly different from that seen in vivo (F = 15.5, P < 0.001), which may reflect differences in the balance between deterministic and stochastic influences on spike occurrence. The study shows that while there is a rhythm of mean spike frequency, parameters based on the variability of interspike interval distributions also display rhythmic changes over the day-night cycle.
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Affiliation(s)
- G S Bhumbra
- Department of Anatomy, University of Cambridge, Downing Street, Cambridge CB2 3DY, UK
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