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Karmarkar SW, Tischkau SA. Influences of the circadian clock on neuronal susceptibility to excitotoxicity. Front Physiol 2013; 4:313. [PMID: 24204346 PMCID: PMC3817863 DOI: 10.3389/fphys.2013.00313] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2013] [Accepted: 10/12/2013] [Indexed: 11/13/2022] Open
Abstract
Stroke is the third leading cause of death and the primary cause of morbidity in the United States, thus posing an enormous burden on the healthcare system. The factors that determine the risk of an individual toward precipitation of an ischemic event possess a strong circadian component as does the ischemic event itself. This predictability provided a window of opportunity toward the development of chronopharmaceuticals which provided much better clinical outcomes. Experiments from our lab showed for the first time that neuronal susceptibility to ischemic events follows a circadian pattern; hippocampal neurons being most susceptible to an ischemic insult occurring during peak activity in a rodent model of global cerebral ischemia. We also demonstrated that the SCN2.2 cells (like their in vivo counterpart) are resistant to excitotoxicity by glutamate and that this was dependent on activation of ERK signaling. We are currently working on elucidating the complete neuroprotective pathway that provides a barricade against glutamate toxicity in the SCN2.2 cells. Our future experiments will be engaged in hijacking the neuroprotective mechanism in the SCN2.2 cells and applying it to glutamate-susceptible entities in an effort to prevent their death in the presence of excitotoxicity. Despite the advancement in chronopharmaceuticals, optimal clinical outcome with minimal adverse events are difficult to come by at an affordable price. Superior treatment options require a better understanding of molecular mechanisms that define the disease, including the role of the circadian clock.
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Affiliation(s)
- Sumedha W Karmarkar
- Department of Pharmacology, Southern Illinois University School of Medicine Springfield, IL, USA
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102
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Schroeder AM, Colwell CS. How to fix a broken clock. Trends Pharmacol Sci 2013; 34:605-19. [PMID: 24120229 PMCID: PMC3856231 DOI: 10.1016/j.tips.2013.09.002] [Citation(s) in RCA: 96] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2013] [Revised: 09/10/2013] [Accepted: 09/11/2013] [Indexed: 12/29/2022]
Abstract
Fortunate are those who rise out of bed to greet the morning light well rested with the energy and enthusiasm to drive a productive day. Others, however, depend on hypnotics for sleep and require stimulants to awaken lethargic bodies. Sleep/wake disruption is a common occurrence in healthy individuals throughout their lifespan and is also a comorbid condition to many diseases (neurodegenerative) and psychiatric disorders (depression and bipolar). There is growing concern that chronic disruption of the sleep/wake cycle contributes to more serious conditions including diabetes (type 2), cardiovascular disease, and cancer. A poorly functioning circadian system resulting in misalignments in the timing of clocks throughout the body may be at the root of the problem for many people. In this article we discuss environmental (light therapy) and lifestyle changes (scheduled meals, exercise, and sleep) as interventions to help fix a broken clock. We also discuss the challenges and potential for future development of pharmacological treatments to manipulate this key biological system.
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Affiliation(s)
- Analyne M Schroeder
- Laboratory of Circadian and Sleep Medicine, Department of Psychiatry and Biobehavioral Sciences, University of California Los Angeles, Los Angeles, CA 90024, USA
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103
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Kallingal GJ, Mintz EM. Site-specific effects of gastrin-releasing peptide in the suprachiasmatic nucleus. Eur J Neurosci 2013; 39:630-9. [PMID: 24528136 DOI: 10.1111/ejn.12411] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2013] [Accepted: 10/07/2013] [Indexed: 11/29/2022]
Abstract
The effects of gastrin-releasing peptide (GRP) on the circadian clock in the suprachiasmatic nucleus (SCN) are dependent on the activation of N-methyl-d-aspartate (NMDA) receptors in the SCN. In this study, the interaction between GRP, glutamate and serotonin in the regulation of circadian phase in Syrian hamsters was evaluated. Microinjection of GRP into the third ventricle induced c-fos and p-ERK expression throughout the SCN. Coadministration of an NMDA antagonist or 8-hydroxy-2-di-n-propylamino-tetralin [a serotonin (5-HT)1A,7 agonist, DPAT] with GRP limited c-fos expression in the SCN to a region dorsal to GRP cell bodies. Similar to the effects of NMDA antagonists, DPAT attenuated GRP-induced phase shifts in the early night, suggesting that the actions of serotonin on the photic phase shifting mechanism occur downstream from retinorecipient cells. c-fos and p-ERK immunoreactivity in the supraoptic (SON) and paraventricular hypothalamic nuclei also increased following ventricular microinjection of GRP. Because of this finding, a second set of experiments was designed to test a potential role for the SON in the regulation of clock function. Syrian hamsters were given microinjections of GRP into the peri-SON during the early night. GRP-induced c-fos activity in the SCN was similar to that following ventricular administration of GRP. GRP or bicuculline (a γ-aminobutyric acidA antagonist) administered near the SON during the early night elicited phase delays of circadian activity rhythms. These data suggest that GRP-induced phase-resetting is dependent on levels of glutamatergic and serotonergic neurotransmission in the SCN and implicate activity in the SON as a potential regulator of photic signaling in the SCN.
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Affiliation(s)
- George J Kallingal
- Department of Biological Sciences and School of Biomedical Sciences, Kent State University, Kent, OH, USA
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104
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Yamada Y, Prosser RA. Copper chelation and exogenous copper affect circadian clock phase resetting in the suprachiasmatic nucleus in vitro. Neuroscience 2013; 256:252-61. [PMID: 24161278 DOI: 10.1016/j.neuroscience.2013.10.033] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2013] [Revised: 10/14/2013] [Accepted: 10/14/2013] [Indexed: 10/26/2022]
Abstract
Light stimulates specialized retinal ganglion cells to release glutamate (Glu) onto circadian clock neurons of the suprachiasmatic nucleus (SCN). Glu resets the phase of the SCN circadian clock by activating N-methyl-d-aspartate receptors (NMDAR) causing either delays or advances in the clock phase, depending on early- or late-night stimulation, respectively. In addition, these Glu-induced phase shifts require tropomyosin receptor kinase B (TrkB) receptor activity. Previous studies show that copper (Cu) released at hippocampal synapses can inhibit NMDAR activity, and application of exogenous Cu likewise inhibits NMDAR activity. We investigated the effects of Cu in acute SCN brain slices prepared from C57BL/6Nhsd adult, male mice using treatments that decrease or increase available Cu levels in vitro and recorded neuronal activity on the following day. When bath-applied for 10 min at zeitgeber time (ZT) 16 (where ZT0=lights-on in the donor animal colony), the Cu-specific chelators tetrathiomolybdate (TTM) and bathocuproine disulfonate each induce ∼2.5-3-h phase delays in circadian neuronal activity rhythms, similarly to Glu-induced phase delays. Co-application of 10 μM CuCl2, but not 10 μM CoCl₂ blocks TTM-induced phase delays. Furthermore, TTM causes phase advances when applied at ZT23. At both application times, TTM-induced phase shifts are blocked by NMDA or TrkB receptor antagonists. Surprisingly, bath-application of 10 μM Cu alone also induces phase shifts in analogous experiments at ZT16 and ZT23. Inhibiting NMDAR does not block Cu-induced phase shifts. TrkB inhibition blocks Cu-induced phase delays but not phase advances. Thus, increasing and decreasing Cu availability appear to shift the SCN clock phase through different mechanisms, at least at the receptor level. We propose that Cu plays a role in the SCN circadian clock by modulating Glu signaling.
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Affiliation(s)
- Y Yamada
- University of Tennessee, Knoxville, Department of Biochemistry, Cellular and Molecular Biology, Knoxville, TN 37996, USA
| | - R A Prosser
- University of Tennessee, Knoxville, Department of Biochemistry, Cellular and Molecular Biology, Knoxville, TN 37996, USA.
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105
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Franken P. A role for clock genes in sleep homeostasis. Curr Opin Neurobiol 2013; 23:864-72. [DOI: 10.1016/j.conb.2013.05.002] [Citation(s) in RCA: 95] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2013] [Revised: 05/01/2013] [Accepted: 05/11/2013] [Indexed: 11/27/2022]
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106
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Ko ML, Shi L, Huang CCY, Grushin K, Park SY, Ko GYP. Circadian phase-dependent effect of nitric oxide on L-type voltage-gated calcium channels in avian cone photoreceptors. J Neurochem 2013; 127:314-28. [PMID: 23895452 DOI: 10.1111/jnc.12384] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2013] [Revised: 07/19/2013] [Accepted: 07/25/2013] [Indexed: 12/20/2022]
Abstract
Nitric oxide (NO) plays an important role in phase-shifting of circadian neuronal activities in the suprachiasmatic nucleus and circadian behavior activity rhythms. In the retina, NO production is increased in a light-dependent manner. While endogenous circadian oscillators in retinal photoreceptors regulate their physiological states, it is not clear whether NO also participates in the circadian regulation of photoreceptors. In this study, we demonstrate that NO is involved in the circadian phase-dependent regulation of L-type voltage-gated calcium channels (L-VGCCs). In chick cone photoreceptors, the L-VGCCα1 subunit expression and the maximal L-VGCC currents are higher at night, and both Ras-mitogen-activated protein kinase (MAPK)-extracellular signal-regulated kinase (Erk) and Ras-phosphatidylinositol 3 kinase (PI3K)-protein kinase B (Akt) are part of the circadian output pathways regulating L-VGCCs. The NO-cGMP-protein kinase G (PKG) pathway decreases L-VGCCα1 subunit expression and L-VGCC currents at night, but not during the day, and exogenous NO donor or cGMP decreases the phosphorylation of Erk and Akt at night. The protein expression of neural NO synthase (nNOS) is also under circadian control, with both nNOS and NO production being higher during the day. Taken together, NO/cGMP/PKG signaling is involved as part of the circadian output pathway to regulate L-VGCCs in cone photoreceptors. In cone photoreceptors, the protein expression of neural nitric oxide synthase (nNOS) and NO production are under circadian control. NO-cGMP-protein kinase G (PKG) signaling serves in the circadian output pathway to regulate the circadian rhythms of L-type voltage-gated calcium channels (L-VGCCs) in part through regulating the phosphorylation states of extracellular-signal-regulated kinase (Erk) and protein kinase B (Akt).
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Affiliation(s)
- Michael L Ko
- Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, Texas, USA
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107
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Abbott SM, Arnold JM, Chang Q, Miao H, Ota N, Cecala C, Gold PE, Sweedler JV, Gillette MU. Signals from the brainstem sleep/wake centers regulate behavioral timing via the circadian clock. PLoS One 2013; 8:e70481. [PMID: 23950941 PMCID: PMC3741311 DOI: 10.1371/journal.pone.0070481] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2013] [Accepted: 06/19/2013] [Indexed: 11/22/2022] Open
Abstract
Sleep-wake cycling is controlled by the complex interplay between two brain systems, one which controls vigilance state, regulating the transition between sleep and wake, and the other circadian, which communicates time-of-day. Together, they align sleep appropriately with energetic need and the day-night cycle. Neural circuits connect brain stem sites that regulate vigilance state with the suprachiasmatic nucleus (SCN), the master circadian clock, but the function of these connections has been unknown. Coupling discrete stimulation of pontine nuclei controlling vigilance state with analytical chemical measurements of intra-SCN microdialysates in mouse, we found significant neurotransmitter release at the SCN and, concomitantly, resetting of behavioral circadian rhythms. Depending upon stimulus conditions and time-of-day, SCN acetylcholine and/or glutamate levels were augmented and generated shifts of behavioral rhythms. These results establish modes of neurochemical communication from brain regions controlling vigilance state to the central circadian clock, with behavioral consequences. They suggest a basis for dynamic integration across brain systems that regulate vigilance states, and a potential vulnerability to altered communication in sleep disorders.
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Affiliation(s)
- Sabra M. Abbott
- Department of Molecular & Integrative Physiology, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America
- College of Medicine University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America
| | - Jennifer M. Arnold
- Department of Molecular & Integrative Physiology, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America
- College of Medicine University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America
| | - Qing Chang
- Psychology, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America
| | - Hai Miao
- Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America
| | - Nobutoshi Ota
- Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America
| | - Christine Cecala
- Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America
| | - Paul E. Gold
- Department of Molecular & Integrative Physiology, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America
- Psychology, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America
- College of Medicine University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America
| | - Jonathan V. Sweedler
- Department of Molecular & Integrative Physiology, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America
- Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America
| | - Martha U. Gillette
- Department of Molecular & Integrative Physiology, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America
- Cell & Developmental Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America
- College of Medicine University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America
- * E-mail:
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108
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Monti JM, BaHammam AS, Pandi-Perumal SR, Bromundt V, Spence DW, Cardinali DP, Brown GM. Sleep and circadian rhythm dysregulation in schizophrenia. Prog Neuropsychopharmacol Biol Psychiatry 2013; 43:209-16. [PMID: 23318689 DOI: 10.1016/j.pnpbp.2012.12.021] [Citation(s) in RCA: 109] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/05/2012] [Revised: 12/04/2012] [Accepted: 12/27/2012] [Indexed: 12/18/2022]
Abstract
Sleep-onset and maintenance insomnia is a common symptom in schizophrenic patients regardless of either their medication status (drug-naive or previously treated) or the phase of the clinical course (acute or chronic). Regarding sleep architecture, the majority of studies indicate that non-rapid eye movement (NREM), N3 sleep and REM sleep onset latency are reduced in schizophrenia, whereas REM sleep duration tends to remain unchanged. Many of these sleep disturbances in schizophrenia appear to be caused by abnormalities of the circadian system as indicated by misalignments of the endogenous circadian cycle and the sleep-wake cycle. Circadian disruption, sleep onset insomnia and difficulties in maintaining sleep in schizophrenic patients could be partly related to a presumed hyperactivity of the dopaminergic system and dysfunction of the GABAergic system, both associated with core features of schizophrenia and with signaling in sleep and wake promoting brain regions. Since multiple neurotransmitter systems within the CNS can be implicated in sleep disturbances in schizophrenia, the characterization of the neurotransmitter systems involved remains a challenging dilemma.
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Affiliation(s)
- Jaime M Monti
- Department of Pharmacology and Therapeutics, Clinics Hospital, Montevideo, 11600, Uruguay
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109
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Abstract
Heme is a prosthetic group best known for roles in oxygen transport, oxidative catalysis, and respiratory electron transport. Recent years have seen the roles of heme extended to sensors of gases such as O2 and NO and cell redox state, and as mediators of cellular responses to changes in intracellular levels of these gases. The importance of heme is further evident from identification of proteins that bind heme reversibly, using it as a signal, e.g. to regulate gene expression in circadian rhythm pathways and control heme synthesis itself. In this minireview, we explore the current knowledge of the diverse roles of heme sensor proteins.
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Affiliation(s)
- Hazel M. Girvan
- From the Manchester Institute of Biotechnology, Faculty of Life Sciences, University of Manchester, Manchester M1 7DN, United Kingdom
| | - Andrew W. Munro
- From the Manchester Institute of Biotechnology, Faculty of Life Sciences, University of Manchester, Manchester M1 7DN, United Kingdom
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110
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Girardet C, Lebrun B, Cabirol-Pol MJ, Tardivel C, François-Bellan AM, Becquet D, Bosler O. Brain-derived neurotrophic factor/TrkB signaling regulates daily astroglial plasticity in the suprachiasmatic nucleus: electron-microscopic evidence in mouse. Glia 2013; 61:1172-7. [PMID: 23640807 DOI: 10.1002/glia.22509] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2012] [Accepted: 03/20/2013] [Indexed: 11/07/2022]
Abstract
Synchronization of circadian rhythms to the 24-h light/dark (L/D) cycle is associated with daily rearrangements of the neuronal-glial network of the suprachiasmatic nucleus of the hypothalamus (SCN), the central master clock orchestrating biological functions in mammals. These anatomical plastic events involve neurons synthesizing vasoactive intestinal peptide (VIP), known as major integrators of photic signals in the retinorecipient region of the SCN. Using an analog-sensitive kinase allele murine model (TrkB(F616A) ), we presently show that the pharmacological blockade of the tropomyosin-related kinase receptor type B (TrkB), the high-affinity receptor of brain-derived neurotrophic factor (BDNF), abolished day/night changes in the dendrite enwrapping of VIP neurons by astrocytic processes (glial coverage), used as an index of SCN plasticity on electron-microscopic sections. Therefore, the BDNF/TrkB signaling pathway exerts a permissive role on the ultrastructural rearrangements that occur in SCN under L/D alternance, an action that could be a critical determinant of the well-established role played by BDNF in the photic regulation of the SCN. In contrast, the extent of glial coverage of non-VIP neighboring dendrites was not different at daytime and nighttime in TrkB(F616A) mice submitted to TrkB inactivation or not receiving any pharmacological treatment. These data not only show that BDNF regulates SCN structural plasticity across the 24-h cycle but also reinforce the view that the daily changes in SCN architecture subserve the light synchronization process.
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Affiliation(s)
- Clémence Girardet
- Aix Marseille Université, CNRS, CRN2M UMR7286, Faculté de Médecine, 13344 cedex 15, Marseille, France
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111
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Bonsall DR, Lall GS. Protein Kinase C Differentially Regulates Entrainment of the Mammalian Circadian Clock. Chronobiol Int 2013; 30:460-9. [DOI: 10.3109/07420528.2012.741170] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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112
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The circadian clock: a framework linking metabolism, epigenetics and neuronal function. Nat Rev Neurosci 2012. [PMID: 23187814 DOI: 10.1038/nrn3393] [Citation(s) in RCA: 104] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The circadian clock machinery is responsible for biological timekeeping on a systemic level. The central clock system controls peripheral clocks through a number of output cues that synchronize the system as a whole. There is growing evidence that changing cellular metabolic states have important effects on circadian rhythms and can thereby influence neuronal function and disease. Epigenetic control has also been implicated in the modulation of biological timekeeping, and cellular metabolism and epigenetic state seem to be closely linked. We discuss the idea that cellular metabolic state and epigenetic mechanisms might work through the circadian clock to regulate neuronal function and influence disease states.
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113
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Granados-Fuentes D, Herzog ED. The clock shop: coupled circadian oscillators. Exp Neurol 2012; 243:21-7. [PMID: 23099412 DOI: 10.1016/j.expneurol.2012.10.011] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2012] [Revised: 09/04/2012] [Accepted: 10/16/2012] [Indexed: 01/10/2023]
Abstract
Daily rhythms in neural activity underlie circadian rhythms in sleep-wake and other daily behaviors. The cells within the mammalian suprachiasmatic nucleus (SCN) are intrinsically capable of 24-h timekeeping. These cells synchronize with each other and with local environmental cycles to drive coherent rhythms in daily behaviors. Recent studies have identified a small number of neuropeptides critical for this ability to synchronize and sustain coordinated daily rhythms. This review highlights the roles of specific intracellular and intercellular signals within the SCN that underlie circadian synchrony.
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114
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Biological Timekeeping. Sleep Med Clin 2012. [DOI: 10.1016/j.jsmc.2012.06.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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115
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Artinian L, Zhong L, Yang H, Rehder V. Nitric oxide as intracellular modulator: internal production of NO increases neuronal excitability via modulation of several ionic conductances. Eur J Neurosci 2012; 36:3333-43. [PMID: 22913584 DOI: 10.1111/j.1460-9568.2012.08260.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Nitric oxide (NO) has been shown to regulate neuronal excitability in the nervous system, but little is known as to whether NO, which is synthesized in certain neurons, also serves functional roles within NO-producing neurons themselves. We investigated this possibility by using a nitric oxide synthase (NOS)-expressing neuron, and studied the role of intrinsic NO production on neuronal firing properties in single-cell culture. B5 neurons of the pond snail Helisoma trivolvis fire spontaneous action potentials (APs), but once the intrinsic activity of NOS was inhibited, neurons became hyperpolarized and were unable to fire evoked APs. These striking long-term effects could be attributed to intrinsic NO acting on three types of conductances, a persistent sodium current (I(NaP) ), voltage-gated Ca currents (I(Ca) ) and small-conductance calcium-activated potassium (SK) channels. We show that NOS inhibitors 7-nitroindazole and S-methyl-l-thiocitrulline resulted in a decrease in I(NaP) , and that their hyperpolarizing and inhibiting effects on spontaneous spiking were mimicked by the inhibitor of I(NaP) , riluzole. Moreover, inhibition of NOS, soluble guanylate cyclase (sGC) or protein kinase G (PKG) attenuated I(Ca) , and blocked spontaneous and depolarization-induced spiking, suggesting that intrinsic NO controlled I(Ca) via the sGC/PKG pathway. The SK channel inhibitor apamin partially prevented the hyperpolarization observed after inhibition of NOS, suggesting a downregulation of SK channels by intrinsic NO. Taken together, we describe a novel mechanism by which neurons utilize their self-produced NO as an intrinsic modulator of neuronal excitability. In B5 neurons, intrinsic NO production is necessary to maintain spontaneous tonic and evoked spiking activity.
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Affiliation(s)
- Liana Artinian
- Department of Biology, Georgia State University, Atlanta, GA 30302-4010, USA
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116
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Lall GS, Atkinson LA, Corlett SA, Broadbridge PJ, Bonsall DR. Circadian entrainment and its role in depression: a mechanistic review. J Neural Transm (Vienna) 2012; 119:1085-96. [PMID: 22798027 DOI: 10.1007/s00702-012-0858-z] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2012] [Accepted: 06/27/2012] [Indexed: 12/24/2022]
Abstract
The natural rotation of the earth generates an environmental day-night cycle that repeats every 24 h. This daily transition from dawn to dusk provides one of the most important time cues to which the majority of organisms synchronise their activity. Under these conditions, natural light, a photic stimulus, provides the principal entraining cue. In mammals, an endogenous circadian pacemaker located within the suprachiasmatic nucleus (SCN) of the hypothalamus acts as a coordinating centre to align physiological activity with the environmental light-dark cycle. However, the SCN also receives regulatory input from a number of behavioural, non-photic, cues such as physical activity, social interactions and feeding routines. The unique ability of the SCN to integrate both photic and non-photic cues allows it to generate a rhythm that is tailored to the individual and entrained to the environment. Here, we review the key neurotransmitter systems involved in both photic and non-photic transmission to the SCN and their interactions that assist in generating an entrained output rhythm. We also consider the impact on health of a desynchronised circadian system with a focus on depressive affective disorders and current therapies aimed at manipulating the relationship between photic and non-photic SCN regulators.
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Affiliation(s)
- G S Lall
- Medway School of Pharmacy, University of Kent, Chatham ME4 4TB, UK.
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117
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Duffield GE, Mikkelsen JD, Ebling FJP. Conserved expression of the glutamate NMDA receptor 1 subunit splice variants during the development of the Siberian hamster suprachiasmatic nucleus. PLoS One 2012; 7:e37496. [PMID: 22675426 PMCID: PMC3365105 DOI: 10.1371/journal.pone.0037496] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2011] [Accepted: 04/23/2012] [Indexed: 11/19/2022] Open
Abstract
Glutamate neurotransmission and the N-methyl-D-aspartate receptor (NMDAR) are central to photic signaling to the master circadian pacemaker located in the hypothalamic suprachiasmatic nucleus (SCN). NMDARs also play important roles in brain development including visual input circuits. The functional NMDAR is comprised of multiple subunits, but each requiring the NR1 subunit for normal activity. The NR1 can be alternatively spliced to produce isoforms that confer different functional properties on the NMDAR. The SCN undergoes extensive developmental changes during postnatal life, including synaptogenesis and acquisition of photic signaling. These changes are especially important in the highly photoperiodic Siberian hamster, in which development of sensitivity to photic cues within the SCN could impact early physiological programming. In this study we examined the expression of NR1 isoforms in the hamster at different developmental ages. Gene expression in the forebrain was quantified by in situ hybridization using oligonucleotide probes specific to alternatively spliced regions of the NR1 heteronuclear mRNA, including examination of anterior hypothalamus, piriform cortex, caudate-putamen, thalamus and hippocampus. Gene expression analysis within the SCN revealed the absence of the N1 cassette, the presence of the C2 cassette alone and the combined absence of C1 and C2 cassettes, indicating that the dominant splice variants are NR1-2a and NR1-4a. Whilst we observe changes at different developmental ages in levels of NR1 isoform probe hybridization in various forebrain structures, we find no significant changes within the SCN. This suggests that a switch in NR1 isoform does not underlie or is not produced by developmental changes within the hamster SCN. Consistency of the NR1 isoforms would ensure that the response of the SCN cells to photic signals remains stable throughout life, an important aspect of the function of the SCN as a responder to environmental changes in quality/quantity of light over the circadian day and annual cycle.
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Affiliation(s)
- Giles E Duffield
- Department of Biological Sciences, University of Notre Dame, Notre Dame, Indiana, United States of America.
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118
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Balakrishnan A, Tavakkolizadeh A, Rhoads DB. Circadian clock genes and implications for intestinal nutrient uptake. J Nutr Biochem 2012; 23:417-22. [PMID: 22417783 DOI: 10.1016/j.jnutbio.2012.01.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2011] [Revised: 11/30/2011] [Accepted: 01/26/2012] [Indexed: 01/29/2023]
Abstract
There has recently been increasing interest in the phenomenon of circadian rhythmicity. We have used circadian rhythms as a means to understanding the regulation of glucose absorption in the intestine. We and others have previously demonstrated rhythmicity in intestinal glucose uptake, mediated by rhythmicity in the expression of the sodium glucose cotransporter 1. Rhythmicity of clock gene expression was subsequently confirmed in the intestine, a phenomenon also demonstrated in other viscera. Clock genes have since been shown via a combination of in vitro and in vivo techniques to play a role in the transcriptional regulation of key absorptive proteins.
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Affiliation(s)
- Anita Balakrishnan
- Department of Surgery, Brigham and Women's Hospital, and Department of Surgery, Harvard Medical School, Boston, Massachusetts 02115, USA.
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119
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Gerstner JR. On the evolution of memory: a time for clocks. Front Mol Neurosci 2012; 5:23. [PMID: 22403527 PMCID: PMC3289401 DOI: 10.3389/fnmol.2012.00023] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2011] [Accepted: 02/11/2012] [Indexed: 12/16/2022] Open
Abstract
Evolutionarily, what was the earliest engram? Biology has evolved to encode representations of past events, and in neuroscience, we are attempting to link experience-dependent changes in molecular signaling with cellular processes that ultimately lead to behavioral output. The theory of evolution has guided biological research for decades, and since phylogenetically conserved mechanisms drive circadian rhythms, these processes may serve as common predecessors underlying more complex behavioral phenotypes. For example, the cAMP/MAPK/CREB cascade is interwoven with the clock to trigger circadian output, and is also known to affect memory formation. Time-of-day dependent changes have been observed in long-term potentiation (LTP) within the suprachiasmatic nucleus and hippocampus, along with light-induced circadian phase resetting and fear conditioning behaviors. Together this suggests during evolution, similar processes underlying metaplasticity in more simple circuits may have been redeployed in higher-order brain regions. Therefore, this notion predicts a model that LTP and metaplasticity may exist in neural circuits of other species, through phylogenetically conserved pathways, leading to several testable hypotheses.
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Affiliation(s)
- Jason R Gerstner
- Center for Sleep and Circadian Neurobiology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
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120
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Meijer JH, Colwell CS, Rohling JHT, Houben T, Michel S. Dynamic neuronal network organization of the circadian clock and possible deterioration in disease. PROGRESS IN BRAIN RESEARCH 2012; 199:143-162. [PMID: 22877664 DOI: 10.1016/b978-0-444-59427-3.00009-5] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
In mammals, the suprachiasmatic nuclei (SCNs) function as a circadian pacemaker that drives 24-h rhythms in physiology and behavior. The SCN is a multicellular clock in which the constituent oscillators show dynamics in their functional organization and phase coherence. Evidence has emerged that plasticity in phase synchrony among SCN neurons determines (i) the amplitude of the rhythm, (ii) the response to continuous light, (iii) the capacity to respond to seasonal changes, and (iv) the phase-resetting capacity. A decrease in circadian amplitude and phase-resetting capacity is characteristic during aging and can be a result of disease processes. Whether the decrease in amplitude is caused by a loss of synchronization or by a loss of single-cell rhythmicity remains to be determined and is important for the development of strategies to ameliorate circadian disorders.
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Affiliation(s)
- Johanna H Meijer
- Laboratory for Neurophysiology, Department of Molecular Cell Biology, Leiden University Medical Center, Leiden, The Netherlands.
| | - Christopher S Colwell
- Laboratory for Neurophysiology, Department of Molecular Cell Biology, Leiden University Medical Center, Leiden, The Netherlands; Laboratory of Circadian and Sleep Medicine, Department of Psychiatry and Biobehavioral Sciences, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
| | - Jos H T Rohling
- Laboratory for Neurophysiology, Department of Molecular Cell Biology, Leiden University Medical Center, Leiden, The Netherlands
| | - Thijs Houben
- Laboratory for Neurophysiology, Department of Molecular Cell Biology, Leiden University Medical Center, Leiden, The Netherlands
| | - Stephan Michel
- Laboratory for Neurophysiology, Department of Molecular Cell Biology, Leiden University Medical Center, Leiden, The Netherlands
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121
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Direct cellular peptidomics of hypothalamic neurons. Front Neuroendocrinol 2011; 32:377-86. [PMID: 21334363 PMCID: PMC3165142 DOI: 10.1016/j.yfrne.2011.02.005] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/22/2010] [Revised: 02/10/2011] [Accepted: 02/14/2011] [Indexed: 11/23/2022]
Abstract
The chemical complexity of cell-to-cell communication has emerged as a fundamental challenge to understanding brain systems. This is certainly true for the hypothalamus, where neuropeptide signals are heterogeneous, localized and dynamic. Thus far, most hypothalamic peptidomic studies have centered on the entire structure; however, recent advances in collection strategies and analytical technologies have enabled direct, high-resolution peptidomic profiles focused on two regions of interest, the suprachiasmatic and supraoptic nuclei, including their sub-regions and individual cells. Suites of peptides now can be identified and probed for function. High spatial and analytical sensitivities reveal that discrete hypothalamic nuclei have distinct peptidomic signatures. Peptidomic discovery not only reveals unanticipated complexity, but also peptides previously unknown that act as key circuit components. Analysis of tissue releasates identifies peptides secreted into the extracellular environment and available for transmitting intercellular signals. Direct sampling techniques define peptide-releasate profiles in spatial, temporal and event-dependent patterns. These approaches are providing remarkable new insights into the complexity of neuropeptidergic cell-to-cell signaling central to neuroendocrine physiology.
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122
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Abstract
Neurons in the suprachiasmatic nucleus (SCN) function as part of a central timing circuit that drives daily changes in our behaviour and underlying physiology. A hallmark feature of SCN neuronal populations is that they are mostly electrically silent during the night, start to fire action potentials near dawn and then continue to generate action potentials with a slow and steady pace all day long. Sets of currents are responsible for this daily rhythm, with the strongest evidence for persistent Na(+) currents, L-type Ca(2+) currents, hyperpolarization-activated currents (I(H)), large-conductance Ca(2+) activated K(+) (BK) currents and fast delayed rectifier (FDR) K(+) currents. These rhythms in electrical activity are crucial for the function of the circadian timing system, including the expression of clock genes, and decline with ageing and disease. This article reviews our current understanding of the ionic and molecular mechanisms that drive the rhythmic firing patterns in the SCN.
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Affiliation(s)
- Christopher S Colwell
- Laboratory of Circadian and Sleep Medicine, Department of Psychiatry and Biobehavioral Sciences, David Geffen School of Medicine, University of California Los Angeles, California 90024, USA.
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123
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Karmarkar SW, Bottum KM, Krager SL, Tischkau SA. ERK/MAPK is essential for endogenous neuroprotection in SCN2.2 cells. PLoS One 2011; 6:e23493. [PMID: 21858143 PMCID: PMC3157406 DOI: 10.1371/journal.pone.0023493] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2011] [Accepted: 07/18/2011] [Indexed: 11/24/2022] Open
Abstract
Background Glutamate (Glu) is essential to central nervous system function; however excessive Glu release leads to neurodegenerative disease. Strategies to protect neurons are underdeveloped, in part due to a limited understanding of natural neuroprotective mechanisms, such as those present in the suprachiasmatic nucleus (SCN). This study tests the hypothesis that activation of ERK/MAPK provides essential protection to the SCN after exposure to excessive Glu using the SCN2.2 cells as a model. Methodology Immortalized SCN2.2 cells (derived from SCN) and GT1-7 cells (neurons from the neighboring hypothalamus) were treated with 10 mM Glu in the presence or absence of the ERK/MAPK inhibitor PD98059. Cell death was assessed by Live/Dead assay, MTS assay and TUNEL. Caspase 3 activity was also measured. Activation of MAPK family members was determined by immunoblot. Bcl2, neuritin and Bid mRNA (by quantitative-PCR) and protein levels (by immunoblot) were also measured. Principal Findings As expected Glu treatment increased caspase 3 activity and cell death in the GT1-7 cells, but Glu alone did not induce cell death or affect caspase 3 activity in the SCN2.2 cells. However, pretreatment with PD98059 increased caspase 3 activity and resulted in cell death after Glu treatment in SCN2.2 cells. This effect was dependent on NMDA receptor activation. Glu treatment in the SCN2.2 cells resulted in sustained activation of the anti-apoptotic pERK/MAPK, without affecting the pro-apoptotic p-p38/MAPK. In contrast, Glu exposure in GT1-7 cells caused an increase in p-p38/MAPK and a decrease in pERK/MAPK. Bcl2-protein increased in SCN2.2 cells following Glu treatment, but not in GT1-7 cells; bid mRNA and cleaved-Bid protein increased in GT1-7, but not SCN2.2 cells. Conclusions Facilitation of ERK activation and inhibition of caspase activation promotes resistance to Glu excitotoxicity in SCN2.2 cells. Significance Further research will explore ERK/MAPK as a key molecule in the prevention of neurodegenerative processes.
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Affiliation(s)
- Sumedha W. Karmarkar
- Department of Pharmacology, Southern Illinois University School of Medicine, Springfield, Illinois, United States of America
| | - Kathleen M. Bottum
- Department of Internal Medicine, Southern Illinois University School of Medicine, Springfield Illinois, United States of America
| | - Stacey L. Krager
- Department of Internal Medicine, Southern Illinois University School of Medicine, Springfield Illinois, United States of America
| | - Shelley A. Tischkau
- Department of Pharmacology, Southern Illinois University School of Medicine, Springfield, Illinois, United States of America
- * E-mail:
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124
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Fast delayed rectifier potassium current: critical for input and output of the circadian system. J Neurosci 2011; 31:2746-55. [PMID: 21414897 DOI: 10.1523/jneurosci.5792-10.2011] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The ability to generate intrinsic circadian rhythms in electrical activity appears to be a key property of central pacemaker neurons and one essential to the function of the circadian timing system. Previous work has demonstrated that suprachiasmatic nucleus (SCN) neurons express the fast delayed rectifier (FDR) potassium current and raise questions about the function of this current. Here, we report that mice lacking both Kcnc1 and Kcnc2 genes [double knock-out (dKO)] fail to express the Kv3.1 and 3.2 channels in the SCN as well as exhibit a greatly reduced FDR current. SCN neurons from these dKO mice exhibit reduced spontaneous activity during the day as well as reduced NMDA-evoked excitatory responses during the night. Interestingly, the daily rhythm in PER2 expression in the SCN was not altered in the dKO mice, although the photic induction of c-Fos was attenuated. Behaviorally, the dKO mice exhibited extremely disrupted daily rhythms in wheel-running behavior. In a light/dark cycle, some of the dKO mice were arrhythmic, whereas others expressed a diurnal rhythm with low amplitude and significant activity during the day. When placed in constant darkness, the dKO mice exhibited low-amplitude, fragmented rhythms and attenuated light responses. Together, these data are consistent with the hypothesis that the FDR current is critical for the generation of robust circadian rhythms in behavior as well as the synchronization of the circadian system to the photic environment.
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125
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Meijer JH, Michel S, Vanderleest HT, Rohling JHT. Daily and seasonal adaptation of the circadian clock requires plasticity of the SCN neuronal network. Eur J Neurosci 2011; 32:2143-51. [PMID: 21143668 DOI: 10.1111/j.1460-9568.2010.07522.x] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Circadian rhythms are an essential property of many living organisms, and arise from an internal pacemaker, or clock. In mammals, this clock resides in the suprachiasmatic nucleus (SCN) of the hypothalamus, and generates an intrinsic circadian rhythm that is transmitted to other parts of the CNS. We will review the evidence that basic adaptive functions of the circadian system rely on functional plasticity in the neuronal network organization, and involve a change in phase relation among oscillatory neurons. We will illustrate this for: (i) photic entrainment of the circadian clock to the light-dark cycle; and (ii) seasonal adaptation of the clock to changes in day length. Molecular studies have shown plasticity in the phase relation between the ventral and dorsal SCN during adjustment to a shifted environmental cycle. Seasonal adaptation relies predominantly on plasticity in the phase relation between the rostral and caudal SCN. Electrical activity is integrated in the SCN, and appears to reflect the sum of the differently phased molecular expression patterns. While both photic entrainment and seasonal adaptation arise from a redistribution of SCN oscillatory activity patterns, different neuronal coupling mechanisms are employed, which are reviewed in the present paper.
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Affiliation(s)
- Johanna H Meijer
- Department of Molecular Cell Biology, Laboratory for Neurophysiology, Leiden University Medical Center, PO Box 9600, 2300 RC Leiden, The Netherlands.
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126
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An S, Irwin RP, Allen CN, Tsai C, Herzog ED. Vasoactive intestinal polypeptide requires parallel changes in adenylate cyclase and phospholipase C to entrain circadian rhythms to a predictable phase. J Neurophysiol 2011; 105:2289-96. [PMID: 21389307 DOI: 10.1152/jn.00966.2010] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Circadian oscillations in the suprachiasmatic nucleus (SCN) depend on transcriptional repression by Period (PER)1 and PER2 proteins within single cells and on vasoactive intestinal polypeptide (VIP) signaling between cells. Because VIP is released by SCN neurons in a circadian pattern, and, after photic stimulation, it has been suggested to play a role in the synchronization to environmental light cycles. It is not known, however, if or how VIP entrains circadian gene expression or behavior. Here, we tested candidate signaling pathways required for VIP-mediated entrainment of SCN rhythms. We found that single applications of VIP reset PER2 rhythms in a time- and dose-dependent manner that differed from light. Unlike VIP-mediated signaling in other cell types, simultaneous antagonism of adenylate cyclase and phospholipase C activities was required to block the VIP-induced phase shifts of SCN rhythms. Consistent with this, VIP rapidly increased intracellular cAMP in most SCN neurons. Critically, daily VIP treatment entrained PER2 rhythms to a predicted phase angle within several days, depending on the concentration of VIP and the interval between VIP applications. We conclude that VIP entrains circadian timing among SCN neurons through rapid and parallel changes in adenylate cyclase and phospholipase C activities.
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Affiliation(s)
- Sungwon An
- Department of Biology, Washington University, St. Louis, MO 63130-4899, USA
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127
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Therapeutic Options in the Management of Sleep Disorders in Visually Impaired Children: A Systematic Review. Clin Ther 2011; 33:168-81. [DOI: 10.1016/j.clinthera.2011.03.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/07/2011] [Indexed: 11/17/2022]
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128
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Girardet C, Becquet D, Blanchard MP, François-Bellan AM, Bosler O. Neuroglial and synaptic rearrangements associated with photic entrainment of the circadian clock in the suprachiasmatic nucleus. Eur J Neurosci 2010; 32:2133-42. [DOI: 10.1111/j.1460-9568.2010.07520.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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129
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Lukat-Rodgers GS, Correia C, Botuyan MV, Mer G, Rodgers KR. Heme-based sensing by the mammalian circadian protein CLOCK. Inorg Chem 2010; 49:6349-65. [PMID: 20666392 DOI: 10.1021/ic902388q] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Heme is emerging as a key player in the synchrony of circadian-coupled transcriptional regulation. Current evidence suggests that levels of circadian-linked transcription are regulated in response to both the availability of intracellular heme and heme-based sensing of carbon monoxide (CO) and possibly nitric oxide (NO). The protein CLOCK is central to the regulation and maintenance of circadian rhythms in mammals. CLOCK comprises two PAS domains, each with a heme binding site. Our studies focus on the functionality of the murine CLOCK PAS-A domain (residues 103-265). We show that CLOCK PAS-A binds iron(III) protoporhyrin IX to form a complex with 1:1 stoichiometry. Optical absorbance and resonance Raman studies reveal that the heme of ferric CLOCK PAS-A is a six-coordinate, low-spin complex whose resonance Raman signature is insensitive to pH over the range of protein stability. Ferrous CLOCK PAS-A is a mixture of five-coordinate, high-spin and six-coordinate, low-spin complexes. Ferrous CLOCK PAS-A forms complexes with CO and NO. Ferric CLOCK PAS-A undergoes reductive nitrosylation in the presence of NO to generate a CLOCK PAS-A-NO, which is a five-coordinate {FeNO}(7) complex. Formation of the highly stable {FeNO}(7) heme complex from either ferrous or ferric heme makes possible the binding of NO at very low concentration, a characteristic of NO sensors. Comparison of the spectroscopic properties and CO-binding kinetics of CLOCK PAS-A with other CO sensor proteins reveals that CLOCK PAS-A exhibits chemical properties consistent with a heme-based gas sensor protein.
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Affiliation(s)
- Gudrun S Lukat-Rodgers
- Department of Chemistry and Biochemistry, North Dakota State University, Fargo, North Dakota 58102, USA
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130
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Abstract
Circadian clocks control a variety of neuronal, behavioral and physiological responses, via transcriptional regulation of an appreciable portion of the genome. We describe the complex communication network between the brain-specific central clock and the tissue-specific peripheral clocks that serve to synchronize the organism to both external and internal demands. In addition, we discuss and speculate on how epigenetic processes are involved in creating transcriptional environments that are permissive to tissue-specific gene expression programs, which work in concert with the circadian machinery. Accumulating data show that chromatin remodeling events may be critical for providing specificity and plasticity in circadian regulation, and metabolic cues may be involved in directing such epigenetic events. A detailed understanding of the communication cues between the central and peripheral clocks is crucial for a more complete understanding of the circadian system and the several levels of control that are implicated in maintaining biological timekeeping.
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131
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Atkins N, Mitchell JW, Romanova EV, Morgan DJ, Cominski TP, Ecker JL, Pintar JE, Sweedler JV, Gillette MU. Circadian integration of glutamatergic signals by little SAAS in novel suprachiasmatic circuits. PLoS One 2010; 5:e12612. [PMID: 20830308 PMCID: PMC2935382 DOI: 10.1371/journal.pone.0012612] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2010] [Accepted: 08/03/2010] [Indexed: 12/03/2022] Open
Abstract
Background Neuropeptides are critical integrative elements within the central circadian clock in the suprachiasmatic nucleus (SCN), where they mediate both cell-to-cell synchronization and phase adjustments that cause light entrainment. Forward peptidomics identified little SAAS, derived from the proSAAS prohormone, among novel SCN peptides, but its role in the SCN is poorly understood. Methodology/Principal Findings Little SAAS localization and co-expression with established SCN neuropeptides were evaluated by immunohistochemistry using highly specific antisera and stereological analysis. Functional context was assessed relative to c-FOS induction in light-stimulated animals and on neuronal circadian rhythms in glutamate-stimulated brain slices. We found that little SAAS-expressing neurons comprise the third most abundant neuropeptidergic class (16.4%) with unusual functional circuit contexts. Little SAAS is localized within the densely retinorecipient central SCN of both rat and mouse, but not the retinohypothalamic tract (RHT). Some little SAAS colocalizes with vasoactive intestinal polypeptide (VIP) or gastrin-releasing peptide (GRP), known mediators of light signals, but not arginine vasopressin (AVP). Nearly 50% of little SAAS neurons express c-FOS in response to light exposure in early night. Blockade of signals that relay light information, via NMDA receptors or VIP- and GRP-cognate receptors, has no effect on phase delays of circadian rhythms induced by little SAAS. Conclusions/Significance Little SAAS relays signals downstream of light/glutamatergic signaling from eye to SCN, and independent of VIP and GRP action. These findings suggest that little SAAS forms a third SCN neuropeptidergic system, processing light information and activating phase-shifts within novel circuits of the central circadian clock.
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Affiliation(s)
- Norman Atkins
- Neuroscience Program, University of Illinois, Urbana, Illinois, United States of America
| | - Jennifer W. Mitchell
- Department of Cell and Developmental Biology, University of Illinois, Urbana, Illinois, United States of America
| | - Elena V. Romanova
- Beckman Institute for Advanced Science and Technology, University of Illinois, Urbana, Illinois, United States of America
| | - Daniel J. Morgan
- Department of Cell Biology and Neuroscience, University of Medicine and Dentistry of New Jersey, Newark, New Jersey, United States of America
| | - Tara P. Cominski
- Department of Cell Biology and Neuroscience, University of Medicine and Dentistry of New Jersey, Newark, New Jersey, United States of America
| | - Jennifer L. Ecker
- Department of Biology, The Johns Hopkins University, Baltimore, Maryland, United States of America
| | - John E. Pintar
- Department of Cell Biology and Neuroscience, University of Medicine and Dentistry of New Jersey, Newark, New Jersey, United States of America
| | - Jonathan V. Sweedler
- Neuroscience Program, University of Illinois, Urbana, Illinois, United States of America
- Beckman Institute for Advanced Science and Technology, University of Illinois, Urbana, Illinois, United States of America
- Department of Chemistry, University of Illinois, Urbana, Illinois, United States of America
| | - Martha U. Gillette
- Neuroscience Program, University of Illinois, Urbana, Illinois, United States of America
- Department of Cell and Developmental Biology, University of Illinois, Urbana, Illinois, United States of America
- Beckman Institute for Advanced Science and Technology, University of Illinois, Urbana, Illinois, United States of America
- * E-mail:
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132
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Hatori M, Panda S. The emerging roles of melanopsin in behavioral adaptation to light. Trends Mol Med 2010; 16:435-46. [PMID: 20810319 DOI: 10.1016/j.molmed.2010.07.005] [Citation(s) in RCA: 123] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2010] [Revised: 07/10/2010] [Accepted: 07/13/2010] [Indexed: 12/14/2022]
Abstract
The adaptation of behavior and physiology to changes in the ambient light level is of crucial importance to life. These adaptations include the light modulation of neuroendocrine function and temporal alignment of physiology and behavior to the day:night cycle by the circadian clock. These non-image-forming (NIF) responses can function independent of rod and cone photoreceptors but depend on ocular light reception, suggesting the participation of novel photoreceptors in the eye. The discovery of melanopsin in intrinsically photosensitive retinal ganglion cells (ipRGCs) and genetic proof for its important role in major NIF responses have offered an exciting entry point to comprehend how mammals adapt to the light environment. Here, we review the recent advances in our understanding of the emerging roles of melanopsin and ipRGCs. These findings now offer new avenues to understand the role of ambient light in sleep, alertness, dependent physiologies and potential pharmacological intervention as well as lifestyle modifications to improve the quality of life.
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Affiliation(s)
- Megumi Hatori
- The Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, CA 92037, USA
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133
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Francl JM, Kaur G, Glass JD. Roles of light and serotonin in the regulation of gastrin-releasing peptide and arginine vasopressin output in the hamster SCN circadian clock. Eur J Neurosci 2010; 32:1170-9. [PMID: 20731711 DOI: 10.1111/j.1460-9568.2010.07374.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Daily timing of the mammalian circadian clock of the suprachiasmatic nucleus (SCN) is regulated by photic input from the retina via the retinohypothalamic tract. This signaling is mediated by glutamate, which activates SCN retinorecipient units communicating to pacemaker cells in part through the release of gastrin-releasing peptide (GRP). Efferent signaling from the SCN involves another SCN-containing peptide, arginine vasopressin (AVP). Little is known regarding the mechanisms regulating these peptides, as literature on in vivo peptide release in the SCN is sparse. Here, microdialysis-radioimmunoassay procedures were used to characterize mechanisms controlling GRP and AVP release in the hamster SCN. In animals housed under a 14/10-h light-dark cycle both peptides exhibited daily fluctuations of release, with levels increasing during the morning to peak around midday. Under constant darkness, this pattern persisted for AVP, but rhythmicity was altered for GRP, characterized by a broad plateau throughout the subjective night and early subjective day. Neuronal release of the peptides was confirmed by their suppression with reverse-microdialysis perfusion of calcium blockers and stimulation with depolarizing agents. Reverse-microdialysis perfusion with the 5-HT(1A,7) agonist 8-OH-DPAT ((±)-8-hydroxydipropylaminotetralin hydrobromide) during the day significantly suppressed GRP but had little effect on AVP. Also, perfusion with the glutamate agonist NMDA, or exposure to light at night, increased GRP but did not affect AVP. These analyses reveal distinct daily rhythms of SCN peptidergic activity, with GRP but not AVP release attenuated by serotonergic activation that inhibits photic phase-resetting, and activated by glutamatergic and photic stimulation that mediate this phase-resetting.
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Affiliation(s)
- Jessica M Francl
- Department of Biological Sciences, Kent State University, Kent, OH 44242, USA
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134
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Abstract
Mammalian circadian rhythms are controlled by endogenous biological oscillators, including a master clock located in the hypothalamic suprachiasmatic nuclei (SCN). Since the period of this oscillation is of approximately 24 h, to keep synchrony with the environment, circadian rhythms need to be entrained daily by means of Zeitgeber ("time giver") signals, such as the light-dark cycle. Recent advances in the neurophysiology and molecular biology of circadian rhythmicity allow a better understanding of synchronization. In this review we cover several aspects of the mechanisms for photic entrainment of mammalian circadian rhythms, including retinal sensitivity to light by means of novel photopigments as well as circadian variations in the retina that contribute to the regulation of retinal physiology. Downstream from the retina, we examine retinohypothalamic communication through neurotransmitter (glutamate, aspartate, pituitary adenylate cyclase-activating polypeptide) interaction with SCN receptors and the resulting signal transduction pathways in suprachiasmatic neurons, as well as putative neuron-glia interactions. Finally, we describe and analyze clock gene expression and its importance in entrainment mechanisms, as well as circadian disorders or retinal diseases related to entrainment deficits, including experimental and clinical treatments.
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Affiliation(s)
- Diego A Golombek
- Laboratory of Chronobiology, Department of Science and Technology, University of Quilmes/Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), Quilmes, Argentina.
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135
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Kallingal GJ, Mintz EM. An NMDA antagonist inhibits light but not GRP-induced phase shifts when administered after the phase-shifting stimulus. Brain Res 2010; 1353:106-12. [PMID: 20682305 DOI: 10.1016/j.brainres.2010.07.087] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2010] [Revised: 07/23/2010] [Accepted: 07/26/2010] [Indexed: 10/19/2022]
Abstract
Brief light pulses or microinjection of gastrin-releasing peptide (GRP) into the third ventricle or near the suprachiasmatic nucleus (SCN) induce phase shifts of circadian rhythms during the subjective night. It has previously been reported that these effects are strongly influenced by the activation of N-methyl-d-aspartate (NMDA) receptors and the availability of glutamate. We hypothesized that the photic signaling pathway in the SCN was dependent on glutamate neurotransmission even after the completion of a photic stimulus. Adult male Syrian hamsters equipped with a surgically implanted guide cannula aimed at the SCN region were housed in constant darkness until stable free-running rhythms of wheel-running activity were apparent. Light pulses administered in the early night induced phase delays of circadian rhythms which were attenuated by the co-administration of (+/-)-2-amino-5-phosphonopentanoic acid (AP5), an NMDA antagonist. Microinjection of AP5 also inhibited light-induced shifts, to a lesser extent, immediately after and 15 min after, but not 30 min after the light pulse. A second experiment was designed to test whether AP5 would be able to attenuate GRP-induced shifts 15 min following microinjection of GRP. Phase shifts of animals that received microinjection of AP5 15 min after the administration of GRP were not different from those that received microinjection of GRP and vehicle. These data suggest that glutamate signaling remains necessary for a full photic response in the SCN even after the termination of the photic signal, but that this dependency ends once GRP-dependent signaling is complete.
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Affiliation(s)
- George J Kallingal
- Department of Biological Sciences, Kent State University, Kent, OH 44242, USA
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136
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Wulff K, Gatti S, Wettstein JG, Foster RG. Sleep and circadian rhythm disruption in psychiatric and neurodegenerative disease. Nat Rev Neurosci 2010; 11:589-99. [DOI: 10.1038/nrn2868] [Citation(s) in RCA: 682] [Impact Index Per Article: 45.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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137
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Mizoro Y, Yamaguchi Y, Kitazawa R, Yamada H, Matsuo M, Fustin JM, Doi M, Okamura H. Activation of AMPA receptors in the suprachiasmatic nucleus phase-shifts the mouse circadian clock in vivo and in vitro. PLoS One 2010; 5:e10951. [PMID: 20532181 PMCID: PMC2880614 DOI: 10.1371/journal.pone.0010951] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2010] [Accepted: 05/14/2010] [Indexed: 11/18/2022] Open
Abstract
The glutamatergic neurotransmission in the suprachiasmatic nucleus (SCN) plays a central role in the entrainment of the circadian rhythms to environmental light-dark cycles. Although the glutamatergic effect operating via NMDAR (N-methyl D-aspartate receptor) is well elucidated, much less is known about a role of AMPAR (α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor) in circadian entrainment. Here we show that, in the mouse SCN, GluR2 and GluR4 AMPAR subtypes are abundantly expressed in the retinorecipient area. In vivo microinjection of AMPA in the SCN during the early subjective night phase-delays the behavioral rhythm. In the organotypic SCN slice culture, AMPA application induces phase-dependent phase-shifts of core-clock gene transcription rhythms. These data demonstrate that activation of AMPAR is capable of phase-shifting the circadian clock both in vivo and in vitro, and are consistent with the hypothesis that activation of AMPA receptors is a critical step in the transmission of photic information to the SCN.
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Affiliation(s)
- Yasutaka Mizoro
- Department of Systems Biology, Kyoto University Graduate School of Pharmaceutical Sciences, Kyoto, Japan
| | - Yoshiaki Yamaguchi
- Department of Systems Biology, Kyoto University Graduate School of Pharmaceutical Sciences, Kyoto, Japan
| | - Rena Kitazawa
- Division of Molecular Brain Science, Kobe University Graduate School of Medicine, Kobe, Japan
| | - Hiroyuki Yamada
- Department of Systems Biology, Kyoto University Graduate School of Pharmaceutical Sciences, Kyoto, Japan
| | - Masahiro Matsuo
- Department of Systems Biology, Kyoto University Graduate School of Pharmaceutical Sciences, Kyoto, Japan
| | - Jean-Michel Fustin
- Department of Systems Biology, Kyoto University Graduate School of Pharmaceutical Sciences, Kyoto, Japan
| | - Masao Doi
- Department of Systems Biology, Kyoto University Graduate School of Pharmaceutical Sciences, Kyoto, Japan
| | - Hitoshi Okamura
- Department of Systems Biology, Kyoto University Graduate School of Pharmaceutical Sciences, Kyoto, Japan
- Division of Molecular Brain Science, Kobe University Graduate School of Medicine, Kobe, Japan
- * E-mail:
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138
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Parkash J, d'Anglemont de Tassigny X, Bellefontaine N, Campagne C, Mazure D, Buée-Scherrer V, Prevot V. Phosphorylation of N-methyl-D-aspartic acid receptor-associated neuronal nitric oxide synthase depends on estrogens and modulates hypothalamic nitric oxide production during the ovarian cycle. Endocrinology 2010; 151:2723-35. [PMID: 20371700 PMCID: PMC3112171 DOI: 10.1210/en.2010-0007] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Within the preoptic region, nitric oxide (NO) production varies during the ovarian cycle and has the ability to impact hypothalamic reproductive function. One mechanism for the regulation of NO release mediated by estrogens during the estrous cycle includes physical association of the calcium-activated neuronal NO synthase (nNOS) enzyme with the glutamate N-methyl-d-aspartate (NMDA) receptor channels via the postsynaptic density 95 scaffolding protein. Here we demonstrate that endogenous variations in estrogens levels during the estrous cycle also coincide with corresponding changes in the state of nNOS Ser1412 phosphorylation, the level of association of this isoform with the NMDA receptor/postsynaptic density 95 complex at the plasma membrane, and the activity of NO synthase (NOS). Neuronal NOS Ser1412 phosphorylation is maximal on the afternoon of proestrus when both the levels of estrogens and the physical association of nNOS with NMDA receptors are highest. Estradiol mimicked these effects in ovariectomized (OVX) rats. In addition, the catalytic activity of NOS in membrane protein extracts from the preoptic region, i.e. independent of any functional protein-protein interactions or cell-cell signaling, was significantly increased in estradiol-treated OVX rats compared with OVX rats. Finally, lambda phosphatase-mediated nNOS dephosphorylation dramatically impaired NOS activity in preoptic region protein extracts, thus demonstrating the important role of phosphorylation in the regulation of NO production in the preoptic region. Taken together, these results yield new insights into the regulation of neuron-derived NO production by gonadal steroids within the preoptic region and raise the possibility that changes in nNOS phosphorylation during fluctuating physiological conditions may be involved in the hypothalamic control of key neuroendocrine functions, such as reproduction.
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Affiliation(s)
- Jyoti Parkash
- Institut National de la Santé et de la Recherche Médicale, Unité, Bâtiment Biserte, Place de Verdun, 59045 Lille cedex, France
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139
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Stadler F, Schmutz I, Schwaller B, Albrecht U. Lack of calbindin-D28k alters response of the murine circadian clock to light. Chronobiol Int 2010; 27:68-82. [PMID: 20205558 DOI: 10.3109/07420521003648554] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
A strong stimulus adjusting the circadian clock to the prevailing light-dark cycle is light. However, the circadian clock is reset by light only at specific times of the day. The mechanisms mediating such gating of light input to the CNS are not well understood. There is evidence that Ca(2+) ions play an important role in intracellular signaling mechanisms, including signaling cascades stimulated by light. Therefore, Ca(2+) is hypothesized to play a role in the light-mediated resetting of the circadian clock. Calbindin-D28k (CB; gene symbol: Calb1) is a Ca(2+) binding protein implicated in Ca(2+) homeostasis and sensing. The absence of this protein influences Ca(2+) buffering capacity of a cell, alters spatio-temporal aspects of intracellular Ca(2+) signaling, and hence might alter transmission of light information to the circadian clock in neurons of the suprachiasmatic nuclei (SCN). We tested mice lacking a functional Calb1 gene (Calb1(-/-)) and found an increased phase-delay response to light applied at circadian time (CT) 14 in these animals. This is accompanied by elevated induction of Per2 gene expression in the SCN. Period length and circadian rhythmicity were comparable between Calb1(-/-) and wild-type animals. Our findings indicate an involvement of CB in the signaling pathway that modulates the behavioral and molecular response to light.
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Affiliation(s)
- Frédéric Stadler
- Department of Medicine, Unit of Biochemistry, University of Fribourg, 1700 Fribourg, Switzerland
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140
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Bottum K, Poon E, Haley B, Karmarkar S, Tischkau SA. Suprachiasmatic nucleus neurons display endogenous resistance to excitotoxicity. Exp Biol Med (Maywood) 2010; 235:237-46. [PMID: 20404040 DOI: 10.1258/ebm.2009.009244] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A comprehensive understanding of neuroprotective pathways is essential to progress in the battle against numerous neurodegenerative conditions. The hypothalamic suprachiasmatic nucleus (SCN) is endogenously resistant to glutamate (Glu) excitotoxicity in vivo. This study was designed to determine whether immortalized SCN neurons (SCN2.2 cells) retain this characteristic. We first established that SCN2.2 cells retained the ability to respond to Glu. SCN2.2 cells expressed N-methyl-d-aspartate (NMDA) receptor subtypes NR1 and NR2A/2B, suggesting the presence of functional receptors. mRNA for the NMDA receptor subunits NR2A and NR2B were higher in the SCN2.2 than in the control hypothalamic neurons (GT1-7). Specific NMDA receptor antagonists (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate and d-(-)-2-amino-5-phosphonovaleric acid blocked Glu-induced activation of gene expression. SCN2.2 cells were resistant to Glu excitotoxicity compared with GT1-7 neurons as assessed with a mitochondrial function assay, cell death by trypan blue exclusion and apoptosis by terminal deoxynucleotidyl transferase dUTP nick end labeling. SCN2.2 resistance to Glu excitoxicity was retained in the presence of the broad spectrum Glu transport inhibitor, l-trans-pyrrolidine-2,4 dicarboxylate, excluding glial Glu uptake as a major neuroprotective mechanism. Collectively, these observations demonstrate endogenous neuroprotection in SCN2.2 cells; this cell line is resistant to excitotoxicity under conditions that are toxic to other immortalized cell lines. Thus, the SCN2.2 cell line may provide insights into the molecular mechanisms that confer endogenous neuroprotection in the SCN.
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Affiliation(s)
- Kathleen Bottum
- Department of Medicine, Division of Internal Medicine and Psychiatry, Southern Illinois School of Medicine, Springfield, IL 62794-9636, USA
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141
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Kobal AB, Grum DK. Scopoli's work in the field of mercurialism in light of today's knowledge: past and present perspectives. Am J Ind Med 2010; 53:535-47. [PMID: 20112258 DOI: 10.1002/ajim.20798] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
The Idrija Mercury Mine (1490-1994) appointed its first physician, Joannes Antonius Scopoli, in 1754. Most of his descriptions of mercurialism are still relevant today. This study highlights Scopoli's observations on the interaction between elemental mercury (Hg degrees ) and alcohol, on the appearance of lung impairment, insomnia, and depressive mood in mercurialism. This presentation is based on Scopoli's experiences presented in his book, De Hydrargyro Idriensi Tentamina (1761), current knowledge, and our own experience acquired through health monitoring of occupational Hg degrees exposure. Some studies have confirmed Scopoli's observation that alcohol enhances mercurialism and his hypothesis that exposure to high Hg degrees concentrations causes serious lung impairment. Neurobiological studies have highlighted the influence of Hg degrees on sleep disorder and depressive mood observed by Scopoli. Although today's knowledge provides new perspectives of Scopoli's work on mercurialism, his work is still very important and can be considered a part of occupational medicine heritage.
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142
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Clark JP, Kofuji P. Stoichiometry of N-methyl-D-aspartate receptors within the suprachiasmatic nucleus. J Neurophysiol 2010; 103:3448-64. [PMID: 20410362 DOI: 10.1152/jn.01069.2009] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The circadian pacemaker within the suprachiasmatic nucleus (SCN) confers daily rhythms to bodily functions. In nature, the circadian clock will adopt a 24-h period by synchronizing to the solar light/dark cycle. This light entrainment process is mediated, in part, at glutamatergic synapses formed between retinal ganglion afferents and SCN neurons. N-methyl-D-aspartate receptors (NMDARs) located on SCN neurons gate light-induced phase resetting. Despite their importance in circadian physiology, little is known about their functional stoichiometry. We investigated the NR2-subunit composition with whole cell recordings of SCN neurons within the murine hypothalamic brain slice using a combination of subtype-selective NMDAR antagonists and voltage-clamp protocols. We found that extracellular magnesium ([Mg](o)) strongly blocks SCN NMDARs exhibiting affinities and voltage sensitivities associated with NR2A and NR2B subunits. These NMDAR currents were inhibited strongly by NR2B-selective antagonists, Ro 25-6981 (3.5 microM, 55.0 +/- 9.0% block; mean +/- SE) and ifenprodil (10 microM, 55.8 +/- 3.0% block). The current remaining showed decreased [Mg](o) affinities reminiscent of NR2C and NR2D subunits but was highly sensitive to [Zn](o), a potent NR2A blocker, showing a approximately 44.2 +/- 1.1% maximal inhibition at saturating concentrations with an IC(50) of 7.8 +/- 1.1 nM. Considering the selectivity, efficacy, and potency of the drugs used in combination with [Mg](o)-block characteristics of the NMDAR, our data show that both diheteromeric NR2B NMDARs and triheteromeric NR2A NMDARs (paired with an NR2C or NR2D subunits) account for the vast majority of the NMDAR current within the SCN.
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Affiliation(s)
- J P Clark
- Department of Neuroscience, University of Minnesota, 6-145 Jackson Hall, 321 Church St. SE, Minneapolis, MN 55455, USA
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143
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Plano SA, Golombek DA, Chiesa JJ. Circadian entrainment to light-dark cycles involves extracellular nitric oxide communication within the suprachiasmatic nuclei. Eur J Neurosci 2010; 31:876-82. [DOI: 10.1111/j.1460-9568.2010.07120.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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144
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Antle MC, Smith VM, Sterniczuk R, Yamakawa GR, Rakai BD. Physiological responses of the circadian clock to acute light exposure at night. Rev Endocr Metab Disord 2009; 10:279-91. [PMID: 19768549 DOI: 10.1007/s11154-009-9116-6] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Circadian rhythms in physiological, endocrine and metabolic functioning are controlled by a neural clock located in the suprachiasmatic nucleus (SCN). This structure is endogenously rhythmic and the phase of this rhythm can be reset by light information from the eye. A key feature of the SCN is that while it is a small structure containing on the order of about 20,000 cells, it is amazingly heterogeneous. It is likely that anatomical heterogeneity reflects an underlying functional heterogeneity. In this review, we examine the physiological responses of cells in the SCN to light stimuli that reset the phase of the circadian clock, highlighting where possible the spatial pattern of such responses. Increases in intracellular calcium are an important signal in response to light, and this increase triggers many biochemical cascades that mediate responses to light. Furthermore, only some cells in the SCN are actually endogenously rhythmic, and these cells likely do not receive strong direct input from the retina. Therefore, this review also considers how light information is conveyed from the retinorecipient cells to the endogenously rhythmic cells that track circadian phase. A number of neuropeptides, including vasoactive intestinal polypeptide, gastrin-releasing peptide and substance P, may be particularly important in relaying such signals, but other neurochemicals such as GABA and nitric oxide may participate as well. A thorough understanding of the intracellular and intercellular responses to light, as well as the spatial arrangements of such responses may help identify important pharmacological targets for therapeutic interventions to treat sleep and circadian disorders.
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Affiliation(s)
- Michael C Antle
- Department of Psychology, University of Calgary, 2500 University Drive NW, Calgary, AB, T2N 1N4, Canada.
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145
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Irwin RP, Allen CN. GABAergic signaling induces divergent neuronal Ca2+ responses in the suprachiasmatic nucleus network. Eur J Neurosci 2009; 30:1462-75. [PMID: 19821838 DOI: 10.1111/j.1460-9568.2009.06944.x] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Intercellular communication between gamma-aminobutyric acid (GABA)ergic suprachiasmatic nucleus (SCN) neurons facilitates light-induced phase changes and synchronization of individual neural oscillators within the SCN network. We used ratiometric Ca(2+) imaging techniques to record changes in the intracellular calcium concentration ([Ca(2+)](i)) to study the role of GABA in interneuronal communication and the response of the SCN neuronal network to optic nerve stimulations that mimic entraining light signals. Stimulation of the retinohypothalamic tract (RHT) evoked divergent Ca(2+) responses in neurons that varied regionally within the SCN with a pattern that correlated with those evoked by pharmacological GABA applications. GABA(A) and GABA(B) receptor agonists and antagonists were used to evaluate components of the GABA-induced changes in [Ca(2+)](i). Application of the GABA(A) receptor antagonist gabazine induced changes in baseline [Ca(2+)](i) in a direction opposite to that evoked by GABA, and similarly altered the RHT stimulation-induced Ca(2+) response. GABA application induced Ca(2+) responses varied in time and region within the SCN network. The NKCC1 cotransporter blocker, bumetanide, and L-type calcium channel blocker, nimodipine, attenuated the GABA-induced rise of [Ca(2+)](i). These results suggest that physiological GABA induces opposing effects on [Ca(2+)](i) based on the chloride equilibrium potential, and may play an important role in neuronal Ca(2+) balance, synchronization and modulation of light input signaling in the SCN network.
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Affiliation(s)
- Robert P Irwin
- Center for Research on Occupational and Environmental Toxicology (CROET), Oregon Health & Science University, Portland, OR 97239, USA.
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146
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Mou X, Peterson CB, Prosser RA. Tissue-type plasminogen activator-plasmin-BDNF modulate glutamate-induced phase-shifts of the mouse suprachiasmatic circadian clockin vitro. Eur J Neurosci 2009; 30:1451-60. [DOI: 10.1111/j.1460-9568.2009.06946.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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147
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Shimizu K, Mackenzie SM, Storm DR. SCOP/PHLPP and its functional role in the brain. MOLECULAR BIOSYSTEMS 2009; 6:38-43. [PMID: 20024065 DOI: 10.1039/b911410f] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
SCOP (suprachiasmatic nucleus (SCN) circadian oscillatory protein) was originally identified in 1999 in a differential display screen of the rat SCN for genes whose expression were regulated in a circadian manner (K. Shimizu, M. Okada, A. Takano and K. Nagai, FEBS Lett., 1999, 458, 363-369). The SCN is the principle pacemaker of the circadian clock, and expression of SCOP protein in the SCN was found to oscillate, increasing during the subjective night, even when animals were housed in constant darkness. SCOP interacts with and inhibits multiple proteins important for intracellular signaling, either by directly binding to K-Ras or by dephosphorylating p-Akt and p-PKC. Since the functions of K-Ras, Akt, and PKC are considerably divergent, SCOP may have several roles. We recently discovered that SCOP participates in the formation of long-term hippocampus-dependent memories, and other investigators have examined its role in cell proliferation and survival. In this review, we introduce SCOP from its molecular structure to its physiological functions, focusing mainly on its role in ERK1/2 activation and memory consolidation.
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Affiliation(s)
- Kimiko Shimizu
- Department of Biophysics and Biochemistry, Graduate School of Science, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan
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148
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McElroy B, Zakaria A, Glass JD, Prosser RA. Ethanol modulates mammalian circadian clock phase resetting through extrasynaptic GABA receptor activation. Neuroscience 2009; 164:842-8. [PMID: 19695310 DOI: 10.1016/j.neuroscience.2009.08.020] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2009] [Revised: 08/06/2009] [Accepted: 08/07/2009] [Indexed: 10/20/2022]
Abstract
Ethanol modulates the actions of multiple neurotransmitter systems, including GABA. However, its enhancing effects on GABA signaling typically are seen only at high concentrations. In contrast, although GABA is a prominent neurotransmitter in the circadian clock of the suprachiasmatic nucleus (SCN), we see ethanol modulation of clock phase resetting at low concentrations (<50 mM). A possible explanation is that ethanol enhances GABAergic signaling in the SCN through activating GABA(A) receptors that contain the delta subunit (GABA(Adelta) receptors), which are sensitive to low ethanol concentrations. Therefore, we investigated whether ethanol acts on GABA(Adelta) receptors in the SCN. Here we show that acute application of the GABA(Adelta) receptor antagonist, RO15-4513, to mouse hypothalamic slices containing the SCN prevents ethanol inhibition of nighttime glutamate-induced (photic-like) phase delays of the circadian clock. Diazepam, which enhances activity of GABA(A) receptors containing the gamma subunit (GABA(Agamma) receptors), does not modulate these phase shifts. Moreover, we find that RO15-4513 prevents ethanol enhancement of daytime serotonergic (non-photic) phase advances of the circadian clock. Furthermore, diazepam phase-advances the SCN circadian clock when applied alone in the daytime, while ethanol has no effect by itself at that time. These data support the hypothesis that ethanol acts on GABA(Adelta) receptors in the SCN to modulate photic and non-photic circadian clock phase resetting. They also reveal distinct modulatory roles of different GABA(A) receptor subtypes in circadian clock phase regulation.
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Affiliation(s)
- B McElroy
- Department Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, TN 37996, USA
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149
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Marvin KA, Reinking JL, Lee AJ, Pardee K, Krause HM, Burstyn JN. Nuclear receptors homo sapiens Rev-erbbeta and Drosophila melanogaster E75 are thiolate-ligated heme proteins which undergo redox-mediated ligand switching and bind CO and NO. Biochemistry 2009; 48:7056-71. [PMID: 19405475 DOI: 10.1021/bi900697c] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Nuclear receptors E75, which regulates development in Drosophila melanogaster, and Rev-erbbeta, which regulates circadian rhythm in humans, bind heme within their ligand binding domains (LBD). The heme-bound ligand binding domains of E75 and Rev-erbbeta were studied using electronic absorption, MCD, resonance Raman, and EPR spectroscopies. Both proteins undergo redox-dependent ligand switching and CO- and NO-induced ligand displacement. In the Fe(III) oxidation state, the nuclear receptor hemes are low spin and 6-coordinate with cysteine(thiolate) as one of the two axial heme ligands. The sixth ligand is a neutral donor, presumably histidine. When the heme is reduced to the Fe(II) oxidation state, the cysteine(thiolate) is replaced by a different neutral donor ligand, whose identity is not known. CO binds to the Fe(II) heme in both E75(LBD) and Rev-erbbeta(LBD) opposite a sixth neutral ligand, plausibly the same histidine that served as the sixth ligand in the Fe(III) state. NO binds to the heme of both proteins; however, the NO-heme is 5-coordinate in E75 and 6-coordinate in Rev-erbbeta. These nuclear receptors exhibit coordination characteristics that are similar to other known redox and gas sensors, suggesting that E75 and Rev-erbbeta may function in heme-, redox-, or gas-regulated control of cellular function.
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Affiliation(s)
- Katherine A Marvin
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, USA
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150
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Ullner E, Buceta J, Díez-Noguera A, García-Ojalvo J. Noise-induced coherence in multicellular circadian clocks. Biophys J 2009; 96:3573-81. [PMID: 19413962 DOI: 10.1016/j.bpj.2009.02.031] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2008] [Revised: 01/15/2009] [Accepted: 02/02/2009] [Indexed: 10/20/2022] Open
Abstract
In higher organisms, circadian rhythms are generated by a multicellular genetic clock that is entrained very efficiently to the 24-h light-dark cycle. Most studies done so far of these circadian oscillators have considered a perfectly periodic driving by light, in the form of either a square wave or a sinusoidal modulation. However, in natural conditions, organisms are subject to nonnegligible fluctuations in the light level all through the daily cycle. In this article, we investigate how the interplay between light fluctuations and intercellular coupling affects the dynamics of the collective rhythm in a large ensemble of nonidentical, globally coupled cellular clocks modeled as Goodwin oscillators. On the basis of experimental considerations, we assume an inverse dependence of the cell-cell coupling strength on the light intensity, in such a way that the larger the light intensity, the weaker the coupling. Our results show a noise-induced rhythm generation for constant light intensities at which the clock is arrhythmic in the noise-free case. Importantly, the rhythm shows a resonancelike phenomenon as a function of the noise intensity. Such improved coherence can be only observed at the level of the overt rhythm and not at the level of the individual oscillators, thus suggesting a cooperative effect of noise, coupling, and the emerging synchronization between the oscillators.
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Affiliation(s)
- Ekkehard Ullner
- Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya, Terrassa, Spain.
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