1
|
Calligaro H, Shoghi A, Chen X, Kim KY, Yu HL, Khov B, Finander B, Le H, Ellisman MH, Panda S. Ultrastructure of Synaptic Connectivity within Subregions of the Suprachiasmatic Nucleus Revealed by a Genetically Encoded Tag and Serial Blockface Electron Microscopy. eNeuro 2023; 10:ENEURO.0227-23.2023. [PMID: 37500494 PMCID: PMC10449486 DOI: 10.1523/eneuro.0227-23.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2023] [Accepted: 07/01/2023] [Indexed: 07/29/2023] Open
Abstract
The hypothalamic suprachiasmatic nucleus (SCN) is the central circadian pacemaker in vertebrates. The SCN receives photic information exclusively through melanopsin-expressing retinal ganglion cells (mRGCs) to synchronize circadian rhythms with the environmental light cycles. The SCN is composed of two major peptidergic neuron types in the core and shell regions of the SCN. Determining how mRGCs interact with the network of synaptic connections onto and between SCN neurons is key to understand how light regulates the circadian clock and to elucidate the relevant local circuits within the SCN. To map these connections, we used a newly developed Cre-dependent electron microscopy (EM) reporter, APEX2, to label the mitochondria of mRGC axons. Serial blockface scanning electron microscopy was then used to resolve the fine 3D structure of mRGC axons and synaptic boutons in the SCN of a male mouse. The resulting maps reveal patterns of connectomic organization in the core and shell of the SCN. We show that these regions are composed of different neuronal subtypes and differ with regard to the pattern of mRGC input, as the shell receives denser mRGC synaptic input compared with the core. This finding challenges the present view that photic information coming directly from the retina is received primarily by the core region of the SCN.
Collapse
Affiliation(s)
- Hugo Calligaro
- Salk Institute for Biological Studies, La Jolla, CA 92037
| | - Azarin Shoghi
- Salk Institute for Biological Studies, La Jolla, CA 92037
| | - Xinyue Chen
- Salk Institute for Biological Studies, La Jolla, CA 92037
| | - Keun-Young Kim
- Department of Neurosciences, University of California at San Diego School of Medicine, La Jolla, CA 92161
- National Center for Microscopy and Imaging Research, University of California, San Diego, La Jolla, CA 92161
| | - Hsin Liu Yu
- Salk Institute for Biological Studies, La Jolla, CA 92037
| | - Brian Khov
- Salk Institute for Biological Studies, La Jolla, CA 92037
| | | | - Hiep Le
- Salk Institute for Biological Studies, La Jolla, CA 92037
| | - Mark H. Ellisman
- Department of Neurosciences, University of California at San Diego School of Medicine, La Jolla, CA 92161
- National Center for Microscopy and Imaging Research, University of California, San Diego, La Jolla, CA 92161
| | | |
Collapse
|
2
|
Hidayat AS, Lefebvre KA, MacDonald J, Bammler T, Aluru N. Symptomatic and asymptomatic domoic acid exposure in zebrafish (Danio rerio) revealed distinct non-overlapping gene expression patterns in the brain. AQUATIC TOXICOLOGY (AMSTERDAM, NETHERLANDS) 2022; 252:106310. [PMID: 36198224 PMCID: PMC9701550 DOI: 10.1016/j.aquatox.2022.106310] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2022] [Revised: 09/19/2022] [Accepted: 09/20/2022] [Indexed: 06/16/2023]
Abstract
Domoic acid (DA) is a naturally produced neurotoxin synthesized by marine diatoms in the genus Pseudo-nitzschia. DA accumulates in filter-feeders such as shellfish, and can cause severe neurotoxicity when contaminated seafood is ingested, resulting in Amnesic Shellfish Poisoning (ASP) in humans. Overt clinical signs of neurotoxicity include seizures and disorientation. ASP is a significant public health concern, and though seafood regulations have effectively minimized the human risk of severe acute DA poisoning, the effects of exposure at asymptomatic levels are poorly understood. The objective of this study was to determine the effects of exposure to symptomatic and asymptomatic doses of DA on gene expression patterns in the zebrafish brain. We exposed adult zebrafish to either a symptomatic (1.1 ± 0.2 μg DA/g fish) or an asymptomatic (0.31 ± 0.03 µg DA/g fish) dose of DA by intracelomic injection and sampled at 24, 48 and 168 h post-injection. Transcriptional profiling was done using Agilent and Affymetrix microarrays. Our analysis revealed distinct, non-overlapping changes in gene expression between the two doses. We found that the majority of transcriptional changes were observed at 24 h post-injection with both doses. Interestingly, asymptomatic exposure produced more persistent transcriptional effects - in response to symptomatic dose exposure, we observed only one differentially expressed gene one week after exposure, compared to 26 in the asymptomatic dose at the same time (FDR <0.05). GO term analysis revealed that symptomatic DA exposure affected genes associated with peptidyl proline modification and retinoic acid metabolism. Asymptomatic exposure caused differential expression of genes that were associated with GO terms including circadian rhythms and visual system, and also the neuroactive ligand-receptor signaling KEGG pathway. Overall, these results suggest that transcriptional responses are specific to the DA dose and that asymptomatic exposure can cause long-term changes. Further studies are needed to characterize the potential downstream neurobehavioral impacts of DA exposure.
Collapse
Affiliation(s)
- Alia S Hidayat
- MIT-WHOI Joint Program in Oceanography/Applied Ocean Science & Engineering, Cambridge and Woods Hole, MA, USA; Biology Department and Woods Hole Center for Oceans and Human Health, Woods Hole Oceanographic Institution, Woods Hole, MA, USA.
| | - Kathi A Lefebvre
- Environmental and Fisheries Science Division, Northwest Fisheries Science Center, National Marine Fisheries Service, NOAA, Seattle, WA, USA
| | - James MacDonald
- Department of Environmental and Occupational Health, University of Washington, Seattle, WA, USA
| | - Theo Bammler
- Department of Environmental and Occupational Health, University of Washington, Seattle, WA, USA
| | - Neelakanteswar Aluru
- Biology Department and Woods Hole Center for Oceans and Human Health, Woods Hole Oceanographic Institution, Woods Hole, MA, USA
| |
Collapse
|
3
|
Alzate-Correa D, Aten S, Campbell MJ, Hoyt KR, Obrietan K. Light-induced changes in the suprachiasmatic nucleus transcriptome regulated by the ERK/MAPK pathway. PLoS One 2021; 16:e0249430. [PMID: 34191798 PMCID: PMC8244859 DOI: 10.1371/journal.pone.0249430] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2020] [Accepted: 03/17/2021] [Indexed: 11/18/2022] Open
Abstract
The mammalian master circadian pacemaker within the suprachiasmatic nucleus (SCN) maintains tight entrainment to the 24 hr light/dark cycle via a sophisticated clock-gated rhythm in the responsiveness of the oscillator to light. A central event in this light entrainment process appears to be the rapid induction of gene expression via the ERK/MAPK pathway. Here, we used RNA array-based profiling in combination with pharmacological disruption methods to examine the contribution of ERK/MAPK signaling to light-evoked gene expression. Transient photic stimulation during the circadian night, but not during the circadian day, triggered marked changes in gene expression, with early-night light predominately leading to increased gene expression and late-night light predominately leading to gene downregulation. Functional analysis revealed that light-regulated genes are involved in a diversity of physiological processes, including DNA transcription, RNA translation, mRNA processing, synaptic plasticity and circadian timing. The disruption of MAPK signaling led to a marked reduction in light-evoked gene regulation during the early night (32/52 genes) and late night (190/191 genes); further, MAPK signaling was found to gate gene expression across the circadian cycle. Together, these experiments reveal potentially important insights into the transcriptional-based mechanisms by which the ERK/MAPK pathway regulates circadian clock timing and light-evoked clock entrainment.
Collapse
Affiliation(s)
- Diego Alzate-Correa
- Division of Pharmaceutics and Pharmacology, Ohio State University, Columbus, OH, United States of America
| | - Sydney Aten
- Department of Neuroscience, Ohio State University, Columbus, OH, United States of America
| | - Moray J. Campbell
- Division of Pharmaceutics and Pharmacology, Ohio State University, Columbus, OH, United States of America
| | - Kari R. Hoyt
- Division of Pharmaceutics and Pharmacology, Ohio State University, Columbus, OH, United States of America
| | - Karl Obrietan
- Department of Neuroscience, Ohio State University, Columbus, OH, United States of America
| |
Collapse
|
4
|
Jha PK, Bouâouda H, Kalsbeek A, Challet E. Distinct feedback actions of behavioural arousal to the master circadian clock in nocturnal and diurnal mammals. Neurosci Biobehav Rev 2021; 123:48-60. [PMID: 33440199 DOI: 10.1016/j.neubiorev.2020.12.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2020] [Revised: 09/16/2020] [Accepted: 12/10/2020] [Indexed: 12/20/2022]
Abstract
The master clock in the suprachiasmatic nucleus (SCN) of the hypothalamus provides a temporal pattern of sleep and wake that - like many other behavioural and physiological rhythms - is oppositely phased in nocturnal and diurnal animals. The SCN primarily uses environmental light, perceived through the retina, to synchronize its endogenous circadian rhythms with the exact 24 h light/dark cycle of the outside world. The light responsiveness of the SCN is maximal during the night in both nocturnal and diurnal species. Behavioural arousal during the resting period not only perturbs sleep homeostasis, but also acts as a potent non-photic synchronizing cue. The feedback action of arousal on the SCN is mediated by processes involving several brain nuclei and neurotransmitters, which ultimately change the molecular functions of SCN pacemaker cells. Arousing stimuli during the sleeping period differentially affect the circadian system of nocturnal and diurnal species, as evidenced by the different circadian windows of sensitivity to behavioural arousal. In addition, arousing stimuli reduce and increase light resetting in nocturnal and diurnal species, respectively. It is important to address further question of circadian impairments associated with shift work and trans-meridian travel not only in the standard nocturnal laboratory animals but also in diurnal animal models.
Collapse
Affiliation(s)
- Pawan Kumar Jha
- Circadian Clocks and Metabolism Team, Institute of Cellular and Integrative Neurosciences, Centre National de la Recherche Scientifique (CNRS), University of Strasbourg, France; Department of Endocrinology and Metabolism, Amsterdam University Medical Center (AUMC), University of Amsterdam, the Netherlands; Hypothalamic Integration Mechanisms, Netherlands Institute for Neuroscience, Amsterdam, the Netherlands.
| | - Hanan Bouâouda
- Circadian Clocks and Metabolism Team, Institute of Cellular and Integrative Neurosciences, Centre National de la Recherche Scientifique (CNRS), University of Strasbourg, France
| | - Andries Kalsbeek
- Department of Endocrinology and Metabolism, Amsterdam University Medical Center (AUMC), University of Amsterdam, the Netherlands; Hypothalamic Integration Mechanisms, Netherlands Institute for Neuroscience, Amsterdam, the Netherlands
| | - Etienne Challet
- Circadian Clocks and Metabolism Team, Institute of Cellular and Integrative Neurosciences, Centre National de la Recherche Scientifique (CNRS), University of Strasbourg, France
| |
Collapse
|
5
|
Duy PQ, Komal R, Richardson MES, Hahm KS, Fernandez DC, Hattar S. Light Has Diverse Spatiotemporal Molecular Changes in the Mouse Suprachiasmatic Nucleus. J Biol Rhythms 2020; 35:576-587. [PMID: 33030409 PMCID: PMC10046259 DOI: 10.1177/0748730420961214] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
To be physiologically relevant, the period of the central circadian pacemaker, located in the suprachiasmatic nucleus (SCN), has to match the solar day in a process known as circadian photoentrainment. However, little is known about the spatiotemporal molecular changes that occur in the SCN in response to light. In this study, we sought to systematically characterize the circadian and light effects on activity-dependent markers of transcriptional (cFos), translational (pS6), and epigenetic (pH3) activities in the mouse SCN. To investigate circadian versus light influences on these molecular responses, we harvested brains from adult wild-type mice in darkness at different circadian times (CT) or from mice exposed to a 15-min light pulse at the middle of the subjective day (CT6, no phase shifts), early subjective night (CT14, large phase delays), or late subjective night (CT22, small phase advances). We found that cFos and pS6 exhibited rhythmic circadian expression in the SCN with distinct spatial rhythms, whereas pH3 expression was undetectable at all circadian phases. cFos rhythms were largely limited to the SCN shell, whereas pS6 rhythms encompassed the entire SCN. pH3, pS6, and cFos showed gating in response to light; however, we were surprised to find that the expression levels of these markers were not higher at phases when larger phase shifts are observed behaviorally (CT14 versus CT22). We then used animals lacking melanopsin (melanopsin knockout [MKO]), which show deficits in phase delays, to further investigate whether changes in these molecular markers correspond to behavioral phase shifts. Surprisingly, only pS6 showed deficits in MKOs at CT14. Therefore, our previous understanding of the molecular pathways that lead to circadian photoentrainment needs to be revised.
Collapse
Affiliation(s)
- Phan Q Duy
- Section on Light and Circadian Rhythms, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland.,Medical Scientist Training Program, Yale University School of Medicine, New Haven, Connecticut
| | - Ruchi Komal
- Section on Light and Circadian Rhythms, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland
| | | | - Katie S Hahm
- Section on Light and Circadian Rhythms, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland
| | - Diego C Fernandez
- Section on Light and Circadian Rhythms, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland
| | - Samer Hattar
- Section on Light and Circadian Rhythms, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland
| |
Collapse
|
6
|
Silva CC, Domínguez R. Clock control of mammalian reproductive cycles: Looking beyond the pre-ovulatory surge of gonadotropins. Rev Endocr Metab Disord 2020; 21:149-163. [PMID: 31828563 DOI: 10.1007/s11154-019-09525-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Several aspects of the physiology and behavior of organisms are expressed rhythmically with a 24-h periodicity and hence called circadian rhythms. Such rhythms are thought to be an adaptive response that allows to anticipate cyclic events in the environment. In mammals, the circadian system is a hierarchically organized net of endogenous oscillators driven by the hypothalamic suprachiasmatic nucleus (SCN). This system is synchronized by the environment throughout afferent pathways and in turn it organizes the activity of tissues by means of humoral secretions and neuronal projections. It has been shown that reproductive cycles are regulated by the circadian system. In rodents, the lesion of the SCN results on alterations of the estrous cycle, sexual behavior, tonic and phasic secretion of gonadotropin releasing hormone (GnRH)/gonadotropins and in the failure of ovulation. Most of the studies regarding the circadian control of reproduction, in particular of ovulation, have only focused on the participation of the SCN in the triggering of the proestrus surge of gonadotropins. Here we review aspects of the evolution and organization of the circadian system with particular focus on its relationship with the reproductive cycle of laboratory rodents. Experimental evidence of circadian control of neuroendocrine events indispensable for ovulation that occur prior to proestrus are discussed. In order to offer a working model of the circadian regulation of reproduction, its participation on aspects ranging from gamete production, neuroendocrine regulation, sexual behavior, mating coordination, pregnancy and deliver of the product should be assessed experimentally.
Collapse
Affiliation(s)
- Carlos-Camilo Silva
- Chronobiology of Reproduction Research Lab-UIBR, Facultad de Estudios Superiores Zaragoza, Universidad Nacional Autónoma de México, México City, Mexico
- Programa de Doctorado en Ciencias Biomédicas, Universidad Nacional Autónoma de México, México City, Mexico
| | - Roberto Domínguez
- Chronobiology of Reproduction Research Lab-UIBR, Facultad de Estudios Superiores Zaragoza, Universidad Nacional Autónoma de México, México City, Mexico.
| |
Collapse
|
7
|
Daut RA, Fonken LK. Circadian regulation of depression: A role for serotonin. Front Neuroendocrinol 2019; 54:100746. [PMID: 31002895 PMCID: PMC9826732 DOI: 10.1016/j.yfrne.2019.04.003] [Citation(s) in RCA: 90] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Revised: 03/13/2019] [Accepted: 04/15/2019] [Indexed: 01/11/2023]
Abstract
Synchronizing circadian (24 h) rhythms in physiology and behavior with the environmental light-dark cycle is critical for maintaining optimal health. Dysregulation of the circadian system increases susceptibility to numerous pathological conditions including major depressive disorder. Stress is a common etiological factor in the development of depression and the circadian system is highly interconnected to stress-sensitive neurotransmitter systems such as the serotonin (5-hydroxytryptamine, 5-HT) system. Thus, here we propose that stress-induced perturbation of the 5-HT system disrupts circadian processes and increases susceptibility to depression. In this review, we first provide an overview of the basic components of the circadian system. Next, we discuss evidence that circadian dysfunction is associated with changes in mood in humans and rodent models. Finally, we provide evidence that 5-HT is a critical factor linking dysregulation of the circadian system and mood. Determining how these two systems interact may provide novel therapeutic targets for depression.
Collapse
Affiliation(s)
- Rachel A Daut
- Department of Psychology and Neuroscience, Center for Neuroscience, University of Colorado Boulder, Boulder, CO 80309, USA
| | - Laura K Fonken
- University of Texas at Austin, Division of Pharmacology and Toxicology, Austin, TX 78712, USA.
| |
Collapse
|
8
|
Vitale JA, Bonato M, La Torre A, Banfi G. Heart Rate Variability in Sport Performance: Do Time of Day and Chronotype Play A Role? J Clin Med 2019; 8:jcm8050723. [PMID: 31117327 PMCID: PMC6571903 DOI: 10.3390/jcm8050723] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2019] [Revised: 05/10/2019] [Accepted: 05/20/2019] [Indexed: 12/20/2022] Open
Abstract
A reliable non-invasive method to assess autonomic nervous system activity involves the evaluation of the time course of heart rate variability (HRV). HRV may vary in accordance with the degree and duration of training, and the circadian fluctuation of this variable is crucial for human health since the heart adapts to the needs of different activity levels during sleep phases or in the daytime. In the present review, time-of-day and chronotype effect on HRV in response to acute sessions of physical activity are discussed. Results are sparse and controversial; however, it seems that evening-type subjects have a higher perturbation of the autonomic nervous system (ANS), with slowed vagal reactivation and higher heart rate values in response to morning exercise than morning types. Conversely, both chronotype categories showed similar ANS activity during evening physical tasks, suggesting that this time of day seems to perturb the HRV circadian rhythm to a lesser extent. The control for chronotype and time-of-day effect represents a key strategy for individual training schedules, and, in perspective, for primary injury prevention.
Collapse
Affiliation(s)
| | - Matteo Bonato
- IRCCS Istituto Ortopedico Galeazzi, Via Riccardo Galeazzi 4, 20161 Milan, Italy.
- Department of Biomedical Sciences for Health, Università degli Studi di Milano, Via Giuseppe Colombo 71, 20133 Milan, Italy.
| | - Antonio La Torre
- IRCCS Istituto Ortopedico Galeazzi, Via Riccardo Galeazzi 4, 20161 Milan, Italy.
- Department of Biomedical Sciences for Health, Università degli Studi di Milano, Via Giuseppe Colombo 71, 20133 Milan, Italy.
| | - Giuseppe Banfi
- IRCCS Istituto Ortopedico Galeazzi, Via Riccardo Galeazzi 4, 20161 Milan, Italy.
- Vita-Salute San Raffaele University, Via Olgettina 58, 20132 Milan, Italy.
| |
Collapse
|
9
|
A Symphony of Signals: Intercellular and Intracellular Signaling Mechanisms Underlying Circadian Timekeeping in Mice and Flies. Int J Mol Sci 2019; 20:ijms20092363. [PMID: 31086044 PMCID: PMC6540063 DOI: 10.3390/ijms20092363] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2019] [Revised: 05/10/2019] [Accepted: 05/10/2019] [Indexed: 12/11/2022] Open
Abstract
The central pacemakers of circadian timekeeping systems are highly robust yet adaptable, providing the temporal coordination of rhythms in behavior and physiological processes in accordance with the demands imposed by environmental cycles. These features of the central pacemaker are achieved by a multi-oscillator network in which individual cellular oscillators are tightly coupled to the environmental day-night cycle, and to one another via intercellular coupling. In this review, we will summarize the roles of various neurotransmitters and neuropeptides in the regulation of circadian entrainment and synchrony within the mammalian and Drosophila central pacemakers. We will also describe the diverse functions of protein kinases in the relay of input signals to the core oscillator or the direct regulation of the molecular clock machinery.
Collapse
|
10
|
Timothy JWS, Klas N, Sanghani HR, Al-Mansouri T, Hughes ATL, Kirshenbaum GS, Brienza V, Belle MDC, Ralph MR, Clapcote SJ, Piggins HD. Circadian Disruptions in the Myshkin Mouse Model of Mania Are Independent of Deficits in Suprachiasmatic Molecular Clock Function. Biol Psychiatry 2018; 84:827-837. [PMID: 28689605 PMCID: PMC6218650 DOI: 10.1016/j.biopsych.2017.04.018] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/16/2016] [Revised: 04/06/2017] [Accepted: 04/27/2017] [Indexed: 11/25/2022]
Abstract
BACKGROUND Alterations in environmental light and intrinsic circadian function have strong associations with mood disorders. The neural origins underpinning these changes remain unclear, although genetic deficits in the molecular clock regularly render mice with altered mood-associated phenotypes. METHODS A detailed circadian and light-associated behavioral characterization of the Na+/K+-ATPase α3 Myshkin (Myk/+) mouse model of mania was performed. Na+/K+-ATPase α3 does not reside within the core circadian molecular clockwork, but Myk/+ mice exhibit concomitant disruption in circadian rhythms and mood. The neural basis of this phenotype was investigated through molecular and electrophysiological dissection of the master circadian pacemaker, the suprachiasmatic nuclei (SCN). Light input and glutamatergic signaling to the SCN were concomitantly assessed through behavioral assays and calcium imaging. RESULTS In vivo assays revealed several circadian abnormalities including lengthened period and instability of behavioral rhythms, and elevated metabolic rate. Grossly aberrant responses to light included accentuated resetting, accelerated re-entrainment, and an absence of locomotor suppression. Bioluminescent recording of circadian clock protein (PERIOD2) output from ex vivo SCN revealed no deficits in Myk/+ molecular clock function. Optic nerve crush rescued the circadian period of Myk/+ behavior, highlighting that afferent inputs are critical upstream mediators. Electrophysiological and calcium imaging SCN recordings demonstrated changes in the response to glutamatergic stimulation as well as the electrical output indicative of altered retinal input processing. CONCLUSIONS The Myshkin model demonstrates profound circadian and light-responsive behavioral alterations independent of molecular clock disruption. Afferent light signaling drives behavioral changes and raises new mechanistic implications for circadian disruption in affective disorders.
Collapse
Affiliation(s)
- Joseph W S Timothy
- Faculty of Biology, Medicine, and Health, University of Manchester, Manchester
| | - Natasza Klas
- Faculty of Biology, Medicine, and Health, University of Manchester, Manchester
| | | | | | - Alun T L Hughes
- Faculty of Biology, Medicine, and Health, University of Manchester, Manchester
| | - Greer S Kirshenbaum
- Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Canada
| | - Vincent Brienza
- Department of Psychology, University of Toronto, Toronto, Canada
| | - Mino D C Belle
- Faculty of Biology, Medicine, and Health, University of Manchester, Manchester
| | - Martin R Ralph
- Department of Psychology, University of Toronto, Toronto, Canada
| | - Steven J Clapcote
- School of Biomedical Sciences, University of Leeds, Leeds, United Kingdom
| | - Hugh D Piggins
- Faculty of Biology, Medicine, and Health, University of Manchester, Manchester.
| |
Collapse
|
11
|
Zsuga J, More CE, Erdei T, Papp C, Harsanyi S, Gesztelyi R. Blind Spot for Sedentarism: Redefining the Diseasome of Physical Inactivity in View of Circadian System and the Irisin/BDNF Axis. Front Neurol 2018; 9:818. [PMID: 30333788 PMCID: PMC6176117 DOI: 10.3389/fneur.2018.00818] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Accepted: 09/10/2018] [Indexed: 12/18/2022] Open
Abstract
Introduction: The term "diseasome of physical inactivity" was coined by Pedersen to explain clustering of chronic diseases linked to physical inactivity. Accordingly, physical inactivity per se contributes to the accumulation of visceral fat, which, generates chronic low-grade systemic inflammation, contributes to emergence of chronic, non-communicable diseases. Diversity of these disorders posits the possible involvement of a supraphysiological system. Methods: Hypothesis driven literature search and deductive reasoning was used to review relevant literature and formulate a novel theory. Results: We have identified the circadian system, omnipresent in virtually every cell, as a possible vehicle for brain muscle crosstalk, explaining some aspects of the diseasome of physical inactivity This system is hierarchically organized, with the suprachiasmatic nucleus (SCN) being the master clock that entrains to the dark/light cycle and synchronizes subsidiary molecular clocks in the periphery. Insufficient photic entrainment also causes chronic disease evolution. The recently identified irisin, was shown to induce brain-derived neurotrophic factor (BDNF) production in several brain areas. BDNF assumes significant role in gating light's influence in the retinohypothalamic synapse, by having a permissive effect on glutamate signal transduction underlying photic entrainment. Conclusions: Here we provide theoretical evidence to support the hypothesis that irisin may facilitate photic entrainment of the SCN, via BDNF. By this irisin opens up possible pathways for peripheral non-photic entrainment signals to exert influence on the master clock that is otherwise resistant to these. Furthermore, we suggest that intertwining processes of circadian, redox, inflammatory, and myokine systems lay underneath the diseasome of physical inactivity.
Collapse
Affiliation(s)
- Judit Zsuga
- Department of Health System Management and Quality Management in Health Care, Faculty of Public Health, University of Debrecen, Debrecen, Hungary
| | - Csaba E. More
- Department of Psychiatry, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Tamas Erdei
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Csaba Papp
- Department of Health System Management and Quality Management in Health Care, Faculty of Public Health, University of Debrecen, Debrecen, Hungary
| | - Szilvia Harsanyi
- Department of Health System Management and Quality Management in Health Care, Faculty of Public Health, University of Debrecen, Debrecen, Hungary
| | - Rudolf Gesztelyi
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| |
Collapse
|
12
|
Vitale JA, Lombardi G, Weydahl A, Banfi G. Biological rhythms, chronodisruption and chrono-enhancement: The role of physical activity as synchronizer in correcting steroids circadian rhythm in metabolic dysfunctions and cancer. Chronobiol Int 2018; 35:1185-1197. [DOI: 10.1080/07420528.2018.1475395] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Affiliation(s)
- Jacopo Antonino Vitale
- Laboratory of Biological Structure Biomechanics, IRCCS Istituto Ortopedico Galeazzi, Milano, Italia
| | - Giovanni Lombardi
- Laboratory of Experimental Biochemistry & Molecular Biology, IRCCS Istituto Ortopedico Galeazzi, Milano, Italia
| | - Andi Weydahl
- UiT-The Arctic University of Norway, Alta, Norway
| | - Giuseppe Banfi
- Laboratory of Experimental Biochemistry & Molecular Biology, IRCCS Istituto Ortopedico Galeazzi, Milano, Italia
- Vita-Salute San Raffaele University, Milano, Italia
| |
Collapse
|
13
|
Lommen J, Stahr A, Ingenwerth M, Ali AAH, von Gall C. Time-of-day-dependent expression of purinergic receptors in mouse suprachiasmatic nucleus. Cell Tissue Res 2017; 369:579-590. [PMID: 28547658 PMCID: PMC5579179 DOI: 10.1007/s00441-017-2634-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2016] [Accepted: 04/26/2017] [Indexed: 12/22/2022]
Abstract
Purinergic P2X and P2Y receptors are involved in mediating intercellular signalling via purines such as adenosine triphosphate (ATP). P2X and P2Y receptors have been implicated in numerous body functions including learning, memory and sleep. All of these body functions show time-of–day-dependent variations controlled by the master circadian oscillator located in the suprachiasmatic nucleus (SCN). Evidence exists for a role of purinergic signalling in intercellular coupling within SCN. However, few studies have been performed on the expression of purinergic receptors in SCN. Therefore, we analyse the expression of seven P2X (P2X1–7) and eight P2Y (P2Y1–2, 4, 6, 11–14) receptors in mouse SCN and address their time-of-day-dependent variation by using immunohistochemistry and real-time polymerase chain reaction. At the early light phase, P2X and P2Y receptors show a low to moderate, homogenously distributed immunoreaction throughout SCN. P2Y13 reveals strong immunoreaction in fibres within the core region of SCN. From the fifteen analysed P2 receptors, seven exhibit a time-of-day-dependent variation in SCN. P2X1 immunoreaction is very low in the early light phase with a minor increase at the end of the dark phase. P2X4 immunoreaction strongly increases during the dark phase in soma cells in the core region and in a dense network of fibres in the shell region of SCN. P2X3 immunoreaction is moderately elevated during the dark phase. Conversely, immunoreaction for P2Y2, P2Y12 and P2Y14 moderately increases at the early light phase and P2Y6 immunoreaction displays a moderate increase at the mid-light phase. Thus, this study demonstrates a time-of-day-dependent variation of P2 receptors in mouse SCN.
Collapse
Affiliation(s)
- Julian Lommen
- Institute of Anatomy II, Medical Faculty, Heinrich-Heine-University, Moorenstrasse 5, 40225, Düsseldorf, Germany
| | - Anna Stahr
- Institute of Anatomy II, Medical Faculty, Heinrich-Heine-University, Moorenstrasse 5, 40225, Düsseldorf, Germany
| | - Marc Ingenwerth
- Institute of Anatomy II, Medical Faculty, Heinrich-Heine-University, Moorenstrasse 5, 40225, Düsseldorf, Germany.,Institute of Pathology, University of Duisburg-Essen, University Hospital Essen, Hufelandstrasse 55, 45147, Essen, Germany
| | - Amira A H Ali
- Institute of Anatomy II, Medical Faculty, Heinrich-Heine-University, Moorenstrasse 5, 40225, Düsseldorf, Germany
| | - Charlotte von Gall
- Institute of Anatomy II, Medical Faculty, Heinrich-Heine-University, Moorenstrasse 5, 40225, Düsseldorf, Germany.
| |
Collapse
|
14
|
Hanna L, Walmsley L, Pienaar A, Howarth M, Brown TM. Geniculohypothalamic GABAergic projections gate suprachiasmatic nucleus responses to retinal input. J Physiol 2017; 595:3621-3649. [PMID: 28217893 DOI: 10.1113/jp273850] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2016] [Accepted: 02/13/2017] [Indexed: 01/28/2023] Open
Abstract
KEY POINTS Visual input to the suprachiasmatic nucleus circadian clock is critical for animals to adapt their physiology and behaviour in line with the solar day. In addition to direct retinal projections, the clock receives input from the visual thalamus, although the role of this geniculohypothalamic pathway in circadian photoreception is poorly understood. In the present study, we develop a novel brain slice preparation that preserves the geniculohypothalamic pathway to show that GABAergic thalamic neurons inhibit retinally-driven activity in the central clock in a circadian time-dependent manner. We also show that in vivo manipulation of thalamic signalling adjusts specific features of the hypothalamic light response, indicating that the geniculohypothalamic pathway is primarily activated by crossed retinal inputs. Our data provide a mechanism by which geniculohypothalamic signals can adjust the magnitude of circadian and more acute hypothalamic light responses according to time-of-day and establish an important new model for future investigations of the circadian visual system. ABSTRACT Sensory input to the master mammalian circadian clock, the suprachiasmatic nucleus (SCN), is vital in allowing animals to optimize physiology and behaviour alongside daily changes in the environment. Retinal inputs encoding changes in external illumination provide the principle source of such information. The SCN also receives input from other retinorecipient brain regions, primarily via the geniculohypothalamic tract (GHT), although the contribution of these indirect projections to circadian photoreception is currently poorly understood. To address this deficit, in the present study, we established an in vitro mouse brain slice preparation that retains connectivity across the extended circadian system. Using multi-electrode recordings, we first confirm that this preparation retains intact optic projections to the SCN, thalamus and pretectum and a functional GHT. We next show that optogenetic activation of GHT neurons selectively suppresses SCN responses to retinal input, and also that this effect exhibits a pronounced day/night variation and involves a GABAergic mechanism. This inhibitory action was not associated with overt circadian rhythmicity in GHT output, indicating modulation at the SCN level. Finally, we use in vivo electrophysiological recordings alongside pharmacological inactivation or optogenetic excitation to show that GHT signalling actively modulates specific features of the SCN light response, indicating that GHT cells are primarily activated by crossed retinal projections. Taken together, our data establish a new model for studying network communication in the extended circadian system and provide novel insight into the roles of GHT-signalling, revealing a mechanism by which thalamic activity can help gate retinal input to the SCN according to time of day.
Collapse
Affiliation(s)
- Lydia Hanna
- Faculty of Biology Medicine and Health, University of Manchester, Manchester, UK
| | - Lauren Walmsley
- Faculty of Biology Medicine and Health, University of Manchester, Manchester, UK
| | - Abigail Pienaar
- Faculty of Biology Medicine and Health, University of Manchester, Manchester, UK
| | - Michael Howarth
- Faculty of Biology Medicine and Health, University of Manchester, Manchester, UK
| | - Timothy M Brown
- Faculty of Biology Medicine and Health, University of Manchester, Manchester, UK
| |
Collapse
|
15
|
Indic P, Schwartz WJ, Herzog ED, Foley NC, Antle MC. Modeling the Behavior of Coupled Cellular Circadian Oscillators in the Suprachiasmatic Nucleus. J Biol Rhythms 2016; 22:211-9. [PMID: 17517911 DOI: 10.1177/0748730407301238] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The suprachiasmatic nucleus (SCN) in the hypothalamus is the site of the master circadian clock in mammals, a complex tissue composed of multiple, coupled, single-cell circadian oscillators. Mathematical modeling is now providing insights on how individual SCN cells might interact and assemble to create an integrated pacemaker that governs the circadian behavior of whole animals. In this article, we will discuss the neurobiological constraints for modeling SCN behavior, system precision, implications of cellular heterogeneity, and analysis of heterogeneously coupled oscillator networks. Mathematical approaches will be critical for better understanding intercellular interactions within the SCN.
Collapse
Affiliation(s)
- Premananda Indic
- Department of Neurology, University of Massachusetts Medical School, Worcester, MA 01655, USA.
| | | | | | | | | |
Collapse
|
16
|
Abstract
The folliculostellate cells of the mammalian pituitary are non-endocrine cells that are implicated in long-distance communication and paracrine signaling, but to date, these cells have yet to be characterized in teleosts. We found that the stellate cells of the teleost pituitary share many common attributes with mammalian folliculostellate cells. By labeling of stellate cells in live preparations of tilapia pituitaries we investigated their distribution, association with other endocrine cells and their anatomical and functional coupling. In the pars intermedia, stellate cells were arranged around neuronal bundles and their processes extended into the pars distalis. Within the pars distalis, stellate cells formed close associations with FSH cells and, to a lesser degree, with GH and LH cells, suggesting differential paracrine regulation of the two gonadotrope populations. The production of follistatin by stellate cells further corroborates the notion of a paracrine role on FSH release. We also found stellate cells to form gap junctions that enabled dye transfer to neighboring stellate cells, implicating that these cells form a large-scale network that connects distant parts of the pituitary. Our findings represent the first wide-scale study of stellate cells in teleosts and provide valuable information regarding their functional roles in pituitary function.
Collapse
|
17
|
Laermans J, Depoortere I. Chronobesity: role of the circadian system in the obesity epidemic. Obes Rev 2016; 17:108-25. [PMID: 26693661 DOI: 10.1111/obr.12351] [Citation(s) in RCA: 77] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/31/2015] [Revised: 09/25/2015] [Accepted: 10/01/2015] [Indexed: 01/17/2023]
Abstract
Although obesity is considered to result from an imbalance between energy uptake and energy expenditure, the strategy of dietary changes and physical exercise has failed to tackle the global obesity epidemic. In search of alternative and more adequate treatment options, research has aimed at further unravelling the mechanisms underlying this excessive weight gain. While numerous studies are focusing on the neuroendocrine alterations that occur after bariatric Roux-en-Y gastric bypass surgery, an increasing amount of chronobiological studies have started to raise awareness concerning the pivotal role of the circadian system in the development and exacerbation of obesity. This internal timekeeping mechanism rhythmically regulates metabolic and physiological processes in order to meet the fluctuating demands in energy use and supply throughout the 24-h day. This review elaborates on the extensive bidirectional interaction between the circadian system and metabolism and explains how disruption of body clocks by means of shift work, frequent time zone travelling or non-stop consumption of calorie-dense foods can evoke detrimental metabolic alterations that contribute to obesity. Altering the body's circadian rhythms by means of time-related dietary approaches (chrononutrition) or pharmacological substances (chronobiotics) may therefore represent a novel and interesting way to prevent or treat obesity and associated comorbidities.
Collapse
Affiliation(s)
- J Laermans
- Gut Peptide Research Lab, Translational Research Center for Gastrointestinal Disorders (TARGID), University of Leuven, Leuven, Belgium
| | - I Depoortere
- Gut Peptide Research Lab, Translational Research Center for Gastrointestinal Disorders (TARGID), University of Leuven, Leuven, Belgium
| |
Collapse
|
18
|
Glutamate-Dependent BMAL1 Regulation in Cultured Bergmann Glia Cells. Neurochem Res 2015; 40:961-70. [PMID: 25749891 DOI: 10.1007/s11064-015-1551-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Revised: 02/25/2015] [Accepted: 03/02/2015] [Indexed: 10/23/2022]
Abstract
Glutamate, the major excitatory amino acid, activates a wide variety of signal transduction cascades. This neurotransmitter is involved in photic entrainment of circadian rhythms, which regulate physiological and behavioral functions. The circadian clock in vertebrates is based on a transcription-translation feedback loop in which Brain and muscle aryl hydrocarbon receptor nuclear translocator (ARNT)-like protein 1 (BMAL1) acts as transcriptional activator of others clock genes. This protein is expressed in nearly all suprachiasmatic nucleus neurons, as well as in the granular layer of the cerebellum. In this context, we decided to investigate the role of glutamate in the molecular mechanisms involved in the processes of transcription/translation of BMAL1 protein. To this end, primary cultures of chick cerebellar Bergmann glial cells were stimulated with glutamatergic ligands and we found that BMAL1 levels increased in a dose- and time dependent manner. Additionally, we studied the phosphorylation of serine residues in BMAL1 under glutamate stimulation and we were able to detect an increase in the phosphorylation of this protein. The increased expression of BMAL1 is most probably the result of a stabilization of the protein after it has been phosphorylated by the cyclic AMP-dependent protein kinase and/or the Ca(2+)/diacylglycerol dependent protein kinase. The present results strongly suggest that glutamate participates in regulating BMAL1 in glial cells and that these cells might prove to be important in the control of circadian rhythms in the cerebellum.
Collapse
|
19
|
Gompf HS, Fuller PM, Hattar S, Saper CB, Lu J. Impaired circadian photosensitivity in mice lacking glutamate transmission from retinal melanopsin cells. J Biol Rhythms 2015; 30:35-41. [PMID: 25512304 PMCID: PMC4316665 DOI: 10.1177/0748730414561545] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Intrinsically photoreceptive retinal ganglion cells (ipRGCs) contain the photopigment melanopsin and convey retinal light inputs to the circadian system via the retinohypothalamic tract (RHT) projection to the suprachiasmatic nucleus (SCN). The principal neurotransmitter of this projection is glutamate, and ipRGCs use the vesicular glutamate transporter 2 (VGLUT2) to package glutamate into synaptic vesicles. However, these neurons contain other potential neurotransmitters, such as pituitary adenylate cyclase activating polypeptide (PACAP). To test the role of glutamate in mediating ipRGC light inputs into the SCN, we crossed mice in which Cre-recombinase expression is driven by the melanopsin promotor (Opn4(Cre/+)) with mice in which the second exon of VGLUT2 is flanked by loxP sites (VGLUT2(fl/fl)), producing ipRGCs that are unable to package glutamate into synaptic vesicles. Such mice had free-running circadian rhythms that did not entrain to a 12:12 light-dark (12:12 LD) cycle, nor did they show a phase delay after a 45-min light pulse administered at circadian time (CT) 14. A small subset of the mice did appear to entrain to the 12:12 LD cycle with a positive phase angle to lights-off; a similar entrainment pattern could be achieved in free-running mice if they were exposed to a 12:12 LD cycle with light of a greater intensity. Glutamate transmission from the ipRGCs is necessary for normal light entrainment of the SCN at moderate (0.35 W/m(2)) light levels, but residual transmission (possibly by PACAP in ipRGCs or by other RGCs) can weakly entrain animals, particularly at very high (6.53 W/m(2)) light levels, although it may be less effective at suppressing locomotor activity (light masking).
Collapse
Affiliation(s)
- Heinrich S Gompf
- Department of Neurology, Division of Sleep Medicine, Harvard Medical School and Beth Israel Deaconess Medical Center, Boston, MA
| | - Patrick M Fuller
- Department of Neurology, Division of Sleep Medicine, Harvard Medical School and Beth Israel Deaconess Medical Center, Boston, MA
| | - Samer Hattar
- Department of Biology, Johns Hopkins University, Baltimore, MD Department of Neuroscience, Johns Hopkins University, Baltimore, Maryland, MD
| | - Clifford B Saper
- Department of Neurology, Division of Sleep Medicine, Harvard Medical School and Beth Israel Deaconess Medical Center, Boston, MA
| | - Jun Lu
- Department of Neurology, Division of Sleep Medicine, Harvard Medical School and Beth Israel Deaconess Medical Center, Boston, MA
| |
Collapse
|
20
|
Irwin RP, Allen CN. Simultaneous electrophysiological recording and calcium imaging of suprachiasmatic nucleus neurons. J Vis Exp 2013:50794. [PMID: 24335611 DOI: 10.3791/50794] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
Simultaneous electrophysiological and fluorescent imaging recording methods were used to study the role of changes of membrane potential or current in regulating the intracellular calcium concentration. Changing environmental conditions, such as the light-dark cycle, can modify neuronal and neural network activity and the expression of a family of circadian clock genes within the suprachiasmatic nucleus (SCN), the location of the master circadian clock in the mammalian brain. Excitatory synaptic transmission leads to an increase in the postsynaptic Ca(2+) concentration that is believed to activate the signaling pathways that shifts the rhythmic expression of circadian clock genes. Hypothalamic slices containing the SCN were patch clamped using microelectrodes filled with an internal solution containing the calcium indicator bis-fura-2. After a seal was formed between the microelectrode and the SCN neuronal membrane, the membrane was ruptured using gentle suction and the calcium probe diffused into the neuron filling both the soma and dendrites. Quantitative ratiometric measurements of the intracellular calcium concentration were recorded simultaneously with membrane potential or current. Using these methods it is possible to study the role of changes of the intracellular calcium concentration produced by synaptic activity and action potential firing of individual neurons. In this presentation we demonstrate the methods to simultaneously record electrophysiological activity along with intracellular calcium from individual SCN neurons maintained in brain slices.
Collapse
Affiliation(s)
- Robert P Irwin
- Center for Research on Occupational and Environmental Toxicology, Oregon Health & Science University
| | | |
Collapse
|
21
|
Bouchard-Cannon P, Cheng HYM. Scheduled feeding alters the timing of the suprachiasmatic nucleus circadian clock in dexras1-deficient mice. Chronobiol Int 2012; 29:965-81. [PMID: 22928915 PMCID: PMC3707842 DOI: 10.3109/07420528.2012.707264] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Restricted feeding (RF) schedules are potent zeitgebers capable of entraining metabolic and hormonal rhythms in peripheral oscillators in anticipation of food. Behaviorally, this manifests in the form of food anticipatory activity (FAA) in the hours preceding food availability. Circadian rhythms of FAA are thought to be controlled by a food-entrainable oscillator (FEO) outside of the suprachiasmatic nucleus (SCN), the central circadian pacemaker in mammals. Although evidence suggests that the FEO and the SCN are capable of interacting functionally under RF conditions, the genetic basis of these interactions remains to be defined. In this study, using dexras1-deficient (dexras1(-/-)) mice, the authors examined whether Dexras1, a modulator of multiple inputs to the SCN, plays a role in regulating the effects of RF on activity rhythms and gene expression in the SCN. Daytime RF under 12L:12D or constant darkness (DD) resulted in potentiated (but less stable) FAA expression in dexras1(-/-) mice compared with wild-type (WT) controls. Under these conditions, the magnitude and phase of the SCN-driven activity component were greatly perturbed in the mutants. Restoration to ad libitum (AL) feeding revealed a stable phase displacement of the SCN-driven activity component of dexras1(-/-) mice by ~2 h in advance of the expected time. RF in the late night/early morning induced a long-lasting increase in the period of the SCN-driven activity component in the mutants but not the WT. At the molecular level, daytime RF advanced the rhythm of PER1, PER2, and pERK expression in the mutant SCN without having any effect in the WT. Collectively, these results indicate that the absence of Dexras1 sensitizes the SCN to perturbations resulting from restricted feeding.
Collapse
|
22
|
Koletar MM, Cheng HYM, Penninger JM, Ralph MR. Loss ofdexras1Alters Nonphotic Circadian Phase Shifts and Reveals a Role for the Intergeniculate Leaflet (IGL) in Gene-Targeted Mice. Chronobiol Int 2011; 28:553-62. [DOI: 10.3109/07420528.2011.592235] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
|
23
|
Positive and negative modulation of circadian activity rhythms by mGluR5 and mGluR2/3 metabotropic glutamate receptors. Neuropharmacology 2010; 60:209-15. [PMID: 20831878 DOI: 10.1016/j.neuropharm.2010.08.022] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2010] [Revised: 08/25/2010] [Accepted: 08/27/2010] [Indexed: 11/23/2022]
Abstract
Glutamate released from retinal ganglion cells conveys information about the daily light:dark cycle to master circadian pacemaker neurons within the suprachiasmatic nucleus that then synchronize internal circadian rhythms with the external day-length. Glutamate activation of ionotropic glutamate receptors in the suprachiasmatic nucleus is well established, but the function of the metabotropic glutamate receptors that are also located in this nucleus is not known. Therefore, in this study we evaluated agonists and antagonists acting at orthosteric or allosteric sites for mGluR5 and mGluR2/3 metabotropic glutamate receptors for their ability to modulate light-induced phase advances and delays of hamster circadian activity rhythms. mGluR5 allosteric antagonists fenobam, MPEP and MTEP, each 10 mg/kg, potentiated light-induced phase advances of hamster circadian activity rhythms, while the mGluR5 agonists CHPG, (S)-3,5-DHPG or positive allosteric modulator CDPPB had no effect. Neither mGluR5 agonists nor antagonists had any effect on light-induced phase delays of activity rhythms. The competitive mGluR2/3 antagonist LY341495, 10 mg/kg, also potentiated light-induced phase advances, but inhibited light-induced phase delays. The mGluR2/3 agonists LY354740 and LY404039 were without effect on phase advances while a third agonist LY379268, 10 mg/kg, inhibited both light-induced advances and delays. Finally, mGluR2/3 agonists LY379268 and LY404039 also inhibited light-induced phase delays of activity rhythms. These results suggest that during light-induced phase advances, mGluR2/3 and mGluR5 receptors act to negatively modulate the effects of light on the circadian pacemaker or its output(s). mGluR5 receptors do not appear to be involved during light-induced phase delays. In contrast, the role for mGluR2/3 receptors during phase delays is more complicated as both agonists and antagonists inhibit light-induced phase delays. Dysfunctions in human circadian rhythms have been implicated in some forms of depression, and metabotropic glutamate receptor ligands, which are also being evaluated for antidepressant activity, are shown here to be capable of modifying light-induced phase shifts of circadian activity rhythms.
Collapse
|
24
|
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.
Collapse
Affiliation(s)
- George J Kallingal
- Department of Biological Sciences, Kent State University, Kent, OH 44242, USA
| | | |
Collapse
|
25
|
Engelund A, Fahrenkrug J, Harrison A, Hannibal J. Vesicular glutamate transporter 2 (VGLUT2) is co-stored with PACAP in projections from the rat melanopsin-containing retinal ganglion cells. Cell Tissue Res 2010; 340:243-55. [PMID: 20339872 DOI: 10.1007/s00441-010-0950-3] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2009] [Accepted: 02/18/2010] [Indexed: 11/26/2022]
Abstract
The retinal ganglion cell layer of the eye comprises a subtype of cells characterized by their intrinsic photosensitivity and expression of melanopsin (ipRGCs). These cells regulate a variety of non-image-forming (NIF) functions such as light entrainment of circadian rhythms, acute suppression of locomotor activity (masking), and pupillary light reflex. Two neurotransmitters have been identified in ipRGCs, glutamate and pituitary adenylate cyclase-activating polypeptide (PACAP). To date, little is known about their release and interplay. Here, we describe the presence and co-localization of vesicular glutamate transporter 2 (VGLUT2; a marker of glutamate signaling) and PACAP in ipRGCs and their projections in the brain. Nine adult male Wistar rats were assigned to one of three groups; anterograde tracing (n = 3), eye enucleation (n = 3), and untreated (n = 3). Under anaesthesia, rats were transcardially perfusion-fixated, after which the brains and eyes were removed for double immunohistochemical staining using a polyclonal anti-VGLUT2 antibody and a mouse monoclonal anti-PACAP antibody. Results revealed that VGLUT2- and PACAP-immunoreactivity (-ir) were present in ipRGCs and co-localized in their projections in the suprachiasmatic nucleus, the intergeniculate leaflet, and the olivary pretectal nucleus. We conclude that there is evidence to support the use of glutamate and PACAP as neurotransmitters in NIF photoperception by rat ipRGCs, and that these neurotransmitters are co-stored and probably released from the same nerve terminals. Furthermore, we conclude that VGLUT2 is the preferred subtype of vesicular transporter used by these cells.
Collapse
Affiliation(s)
- Anna Engelund
- Department of Clinical Biochemistry, Bispebjerg Hospital, Faculty of Health Sciences, University of Copenhagen, Bispebjerg Bakke 23, DK-2400, Copenhagen, Denmark.
| | | | | | | |
Collapse
|
26
|
Dibner C, Schibler U, Albrecht U. The Mammalian Circadian Timing System: Organization and Coordination of Central and Peripheral Clocks. Annu Rev Physiol 2010; 72:517-49. [DOI: 10.1146/annurev-physiol-021909-135821] [Citation(s) in RCA: 1626] [Impact Index Per Article: 116.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Most physiology and behavior of mammalian organisms follow daily oscillations. These rhythmic processes are governed by environmental cues (e.g., fluctuations in light intensity and temperature), an internal circadian timing system, and the interaction between this timekeeping system and environmental signals. In mammals, the circadian timekeeping system has a complex architecture, composed of a central pacemaker in the brain's suprachiasmatic nuclei (SCN) and subsidiary clocks in nearly every body cell. The central clock is synchronized to geophysical time mainly via photic cues perceived by the retina and transmitted by electrical signals to SCN neurons. In turn, the SCN influences circadian physiology and behavior via neuronal and humoral cues and via the synchronization of local oscillators that are operative in the cells of most organs and tissues. Thus, some of the SCN output pathways serve as input pathways for peripheral tissues. Here we discuss knowledge acquired during the past few years on the complex structure and function of the mammalian circadian timing system.
Collapse
Affiliation(s)
- Charna Dibner
- Division of Endocrinology, Diabetes and Nutrition, Geneva University Hospital (HUG), CH-1211 Geneva-14, Switzerland
| | - Ueli Schibler
- Department of Molecular Biology & NCCR Frontiers in Genetics, Sciences III, University of Geneva, CH-1211 Geneva-4, Switzerland
| | - Urs Albrecht
- Department of Medicine, Division of Biochemistry, University of Fribourg, CH-1700 Fribourg, Switzerland
| |
Collapse
|
27
|
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: 4.2] [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.
Collapse
Affiliation(s)
- Robert P Irwin
- Center for Research on Occupational and Environmental Toxicology (CROET), Oregon Health & Science University, Portland, OR 97239, USA.
| | | |
Collapse
|
28
|
Bendová Z, Sumová A, Mikkelsen JD. Circadian and developmental regulation of N-methyl-d-aspartate-receptor 1 mRNA splice variants and N-methyl-d-aspartate-receptor 3 subunit expression within the rat suprachiasmatic nucleus. Neuroscience 2009; 159:599-609. [PMID: 19361480 DOI: 10.1016/j.neuroscience.2009.01.016] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2008] [Revised: 01/08/2009] [Accepted: 01/09/2009] [Indexed: 10/21/2022]
Abstract
The circadian rhythms of mammals are generated by the circadian clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus. Its intrinsic period is entrained to a 24 h cycle by external cues, mainly by light. Light impinging on the SCN at night causes either advancing or delaying phase shifts of the circadian clock. N-methyl-d-aspartate receptors (NMDAR) are the main glutamate receptors mediating the effect of light on the molecular clockwork in the SCN. They are composed of multiple subunits, each with specific characteristics whose mutual interactions strongly determine properties of the receptor. In the brain, the distribution of NMDAR subunits depends on the region and developmental stage. Here, we report the circadian expression of the NMDAR1 subunit in the adult rat SCN and depict its splice variants that may constitute the functional receptor channel in the SCN. During ontogenesis, expression of two of the NMDAR1 subunit splice variants, as well as the NMDAR3A and 3B subunits, exhibits developmental loss around the time of eye opening. Moreover, we demonstrate the spatial and developmental characteristics of the expression of the truncated splice form of NMDAR1 subunit NR1-E in the brain. Our data suggest that specific properties of the NMDAR subunits we describe within the SCN likely influence the photic transduction pathways mediating the clock entrainment. Furthermore, the developmental changes in NMDAR composition may contribute to the gradual postnatal maturation of the entrainment pathways.
Collapse
Affiliation(s)
- Z Bendová
- Institute of Physiology, Academy of Sciences of the Czech Republic, Prague, Czech Republic.
| | | | | |
Collapse
|
29
|
Fatehi M, Fatehi-Hassanabad Z. Effects of 17beta-estradiol on neuronal cell excitability and neurotransmission in the suprachiasmatic nucleus of rat. Neuropsychopharmacology 2008; 33:1354-64. [PMID: 17687263 DOI: 10.1038/sj.npp.1301523] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
17beta-Estradiol receptors have been found in several brain nuclei including the suprachiasmatic nucleus (SCN) of mammalian species. The SCN is believed to act as brain clock regulating circadian and circannual biological rhythms, such as body temperature, sleep, and mood. Here, we examined whether 17beta-estradiol (E2) could affect cell excitability and synaptic transmission in the SCN. Bath application of E2 (0.03-3 microM) increased the spontaneous firing frequency and depolarized cell membrane of the SCN neurons significantly. Furthermore, E2 (0.03-3 microM) increased (by about 25-150% of control) frequency of the miniature excitatory postsynaptic currents. Amplitude of the evoked excitatory postsynaptic currents was enhanced (by about 32% of control) after exposure to 1 microM E2. The paired-pulse ratio was reduced by E2. These effects were prevented by the estrogen receptor antagonist, ICI 182780. Exposure to the biologically inactive 17alpha-estradiol did not cause any significant changes in the parameters mentioned above. These findings are in favor of an implication of estrogen in modulation of neuronal activity in SCN and possibly regulating circadian rhythms.
Collapse
Affiliation(s)
- Mohammad Fatehi
- Department of Biomedical Sciences, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, PE, Canada.
| | | |
Collapse
|
30
|
Wang LM, Schroeder A, Loh D, Smith D, Lin K, Han JH, Michel S, Hummer DL, Ehlen JC, Albers HE, Colwell CS. Role for the NR2B subunit of the N-methyl-D-aspartate receptor in mediating light input to the circadian system. Eur J Neurosci 2008; 27:1771-9. [PMID: 18380671 PMCID: PMC2586987 DOI: 10.1111/j.1460-9568.2008.06144.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Light information reaches the suprachiasmatic nucleus (SCN) through a subpopulation of retinal ganglion cells that utilize glutamate as a neurotransmitter. A variety of evidence suggests that the release of glutamate then activates N-methyl-D-aspartate (NMDA) receptors within the SCN and triggers a signaling cascade that ultimately leads to phase shifts in the circadian system. In this study, we first sought to explore the role of the NR2B subunit in mediating the effects of light on the circadian system of hamsters and mice. We found that localized microinjection of the NR2B subunit antagonist ifenprodil into the SCN region reduces the magnitude of light-induced phase shifts of the circadian rhythm in wheel-running activity. Next, we found that the NR2B message and levels of phospho-NR2B vary with time of day in SCN tissue using semiquantitative real-time polymerase chain reaction and western blot analysis, respectively. Functionally, we found that blocking the NR2B subunit with ifenprodil significantly reduced the magnitude of NMDA currents recorded in SCN neurons. Ifenprodil also significantly reduced the magnitude of NMDA-induced Ca2+ changes in SCN cells. Together, these results demonstrate that the NR2B subunit is an important component of NMDA receptor-mediated responses within SCN neurons and that this subunit contributes to light-induced phase shifts of the mammalian circadian system.
Collapse
Affiliation(s)
- L M Wang
- Department of Psychiatry and Biobehavioral Sciences, University of California-Los Angeles, 760 Westwood Plaza, Los Angeles, CA 90024-1759, USA
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
31
|
Belenky MA, Yarom Y, Pickard GE. Heterogeneous expression of gamma-aminobutyric acid and gamma-aminobutyric acid-associated receptors and transporters in the rat suprachiasmatic nucleus. J Comp Neurol 2008; 506:708-32. [PMID: 18067149 DOI: 10.1002/cne.21553] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The hypothalamic suprachiasmatic nucleus (SCN) is the primary mammalian circadian clock that regulates rhythmic physiology and behavior. The SCN is composed of a diverse set of neurons arranged in a tight intrinsic network. In the rat, vasoactive intestinal peptide (VIP)- and gastrin-releasing peptide (GRP)-containing neurons are the dominant cell phenotypes of the ventral SCN, and these cells receive photic information from the retina and the intergeniculate leaflet. Neurons expressing vasopressin (VP) are concentrated in the dorsal and medial aspects of the SCN. Although the VIP/GRP and VP cell groups are concentrated in different regions of the SCN, the separation of these cell groups is not absolute. The inhibitory neurotransmitter gamma-aminobutyric acid (GABA) is expressed in most SCN neurons irrespective of their location or peptidergic phenotype. In the present study, immunoperoxidase labeling, immunofluorescence confocal microscopy, and ultrastructural immunocytochemistry were used to examine the spatial distribution of several markers associated with SCN GABAergic neurons. Glutamate decarboxylase, a marker of GABA synthesis, and vesicular GABA transporter were more prominently observed in the ventral SCN. KCC2, a K(+)/Cl(-) cotransporter, was highly expressed in the ventral SCN in association with VIP- and GRP-producing neurons, whereas VP neurons in the dorsal SCN were devoid of KCC2. On the other hand, GABA(B) receptors were observed predominantly in VPergic neurons dorsally, whereas, in the ventral SCN, GABA(B) receptors were associated almost exclusively with retinal afferent fibers and terminals. The differential expression of GABAergic markers within the SCN suggests that GABA may play dissimilar roles in different SCN neuronal phenotypes.
Collapse
Affiliation(s)
- Michael A Belenky
- Department of Cell/Animal Biology, Institute of Life Sciences, Hebrew University of Jerusalem, Jerusalem, 91904 Israel.
| | | | | |
Collapse
|
32
|
Calcium response to retinohypothalamic tract synaptic transmission in suprachiasmatic nucleus neurons. J Neurosci 2007; 27:11748-57. [PMID: 17959816 DOI: 10.1523/jneurosci.1840-07.2007] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Glutamate released from retinohypothalamic tract (RHT) synapses with suprachiasmatic nucleus (SCN) neurons induces phase changes in the circadian clock presumably by using Ca2+ as a second messenger. We used electrophysiological and Ca2+ imaging techniques to simultaneously record changes in the membrane potential and intracellular calcium concentration ([Ca2+]i) in SCN neurons after stimulation of the RHT at physiologically relevant frequencies. Stimulation of the RHT sufficient to generate an EPSP did not produce detectable changes in [Ca2+]i, whereas EPSP-induced action potentials evoked an increase in [Ca2+]i, suggesting that the change in postsynaptic somatic [Ca2+]i produced by synaptically activated glutamate receptors was the result of membrane depolarization activating voltage-dependent Ca2+ channels. The magnitude of the Ca2+ response was dependent on the RHT stimulation frequency and duration, and on the SCN neuron action potential frequency. Membrane depolarization-induced changes in [Ca2+]i were larger and decayed more quickly in the dendrites than in the soma and were attenuated by nimodipine, suggesting a compartmentalization of Ca2+ signaling and a contribution of L-type Ca2+ channels. RHT stimulation at frequencies that mimicked the output of light-sensitive retinal ganglion cells (RGCs) evoked [Ca2+]i transients in SCN neurons via membrane depolarization and activation of voltage-dependent Ca2+ channels. These data suggest that for Ca2+ to induce phase advances or delays, light-induced signaling from RGCs must augment the underlying oscillatory somatic [Ca2+]i by evoking postsynaptic action potentials in SCN neurons during a period of slow spontaneous firing such as occurs during nighttime.
Collapse
|
33
|
Rash JE, Olson CO, Pouliot WA, Davidson KGV, Yasumura T, Furman CS, Royer S, Kamasawa N, Nagy JI, Dudek FE. Connexin36 vs. connexin32, "miniature" neuronal gap junctions, and limited electrotonic coupling in rodent suprachiasmatic nucleus. Neuroscience 2007; 149:350-71. [PMID: 17904757 PMCID: PMC2245895 DOI: 10.1016/j.neuroscience.2007.06.052] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/06/2007] [Indexed: 11/25/2022]
Abstract
Suprachiasmatic nucleus (SCN) neurons generate circadian rhythms, and these neurons normally exhibit loosely-synchronized action potentials. Although electrotonic coupling has long been proposed to mediate this neuronal synchrony, ultrastructural studies have failed to detect gap junctions between SCN neurons. Nevertheless, it has been proposed that neuronal gap junctions exist in the SCN; that they consist of connexin32 or, alternatively, connexin36; and that connexin36 knockout eliminates neuronal coupling between SCN neurons and disrupts circadian rhythms. We used confocal immunofluorescence microscopy and freeze-fracture replica immunogold labeling to examine the distributions of connexin30, connexin32, connexin36, and connexin43 in rat and mouse SCN and used whole-cell recordings to re-assess electrotonic and tracer coupling. Connexin32-immunofluorescent puncta were essentially absent in SCN but connexin36 was relatively abundant. Fifteen neuronal gap junctions were identified ultrastructurally, all of which contained connexin36 but not connexin32, whereas nearby oligodendrocyte gap junctions contained connexin32. In adult SCN, one neuronal gap junction was >600 connexons, whereas 75% were smaller than 50 connexons, which may be below the limit of detectability by fluorescence microscopy and thin-section electron microscopy. Whole-cell recordings in hypothalamic slices revealed tracer coupling with neurobiotin in <5% of SCN neurons, and paired recordings (>40 pairs) did not reveal obvious electrotonic coupling or synchronized action potentials, consistent with few neurons possessing large gap junctions. However, most neurons had partial spikes or spikelets (often <1 mV), which remained after QX-314 [N-(2,6-dimethylphenylcarbamoylmethyl)triethylammonium bromide] had blocked sodium-mediated action potentials within the recorded neuron, consistent with spikelet transmission via small gap junctions. Thus, a few "miniature" gap junctions on most SCN neurons appear to mediate weak electrotonic coupling between limited numbers of neuron pairs, thus accounting for frequent detection of partial spikes and hypothetically providing the basis for "loose" electrical or metabolic synchronization of electrical activity commonly observed in SCN neuronal populations during circadian rhythms.
Collapse
Affiliation(s)
- J E Rash
- Department of Biomedical Sciences, Colorado State University, Campus Delivery 1617, Fort Collins, CO 80523-1617, USA.
| | | | | | | | | | | | | | | | | | | |
Collapse
|
34
|
Gillette MU, Medanic M, McArthur AJ, Liu C, Ding JM, Faiman LE, Weber ET, Tcheng TK, Gallman EA. Intrinsic neuronal rhythms in the suprachiasmatic nuclei and their adjustment. CIBA FOUNDATION SYMPOSIUM 2007; 183:134-44; discussion 144-53. [PMID: 7656683 DOI: 10.1002/9780470514597.ch8] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The central role of the suprachiasmatic nuclei in regulating mammalian circadian rhythms is well established. We study the temporal organization of neuronal properties in the suprachiasmatic nucleus (SCN) using a rat hypothalamic brain slice preparation. Electrical properties of single neurons are monitored by extra-cellular and whole-cell patch recording techniques. The ensemble of neurons in the SCN undergoes circadian changes in spontaneous activity, membrane properties and sensitivity to phase adjustment. At any point in this cycle, diversity is observed in individual neurons' electrical properties, including firing rate, firing pattern and response to injected current. Nevertheless, the SCN generate stable, near 24 h oscillations in ensemble neuronal firing rate for at least three days in vitro. The rhythm is sinusoidal, with peak activity, a marker of phase, appearing near midday. In addition to these electrophysiological changes, the SCN undergoes sequential changes in vitro in sensitivities to adjustment. During subjective day, the SCN progresses through periods of sensitivity to cyclic AMP, serotonin, neuropeptide Y, and then to melatonin at dusk. During the subjective night, sensitivities to glutamate, cyclic GMP and then neuropeptide Y are followed by a second period of sensitivity to melatonin at dawn. Because the SCN, when maintained in vitro, is under constant conditions and isolated from afferents, these changes must be generated within the clock in the SCN. The changing sensitivities reflect underlying temporal domains that are characterized by specific sets of biochemical and molecular relationships which occur in an ordered sequence over the circadian cycle.
Collapse
Affiliation(s)
- M U Gillette
- Department of Cell & Structural Biology, University of Illinois, Urbana 61801, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
35
|
Hastings MH, Ebling FJ, Grosse J, Herbert J, Maywood ES, Mikkelsen JD, Sumova A. Immediate-early genes and the neural bases of photic and non-photic entrainment. CIBA FOUNDATION SYMPOSIUM 2007; 183:175-89; discussion 190-7. [PMID: 7656685 DOI: 10.1002/9780470514597.ch10] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The expression of immediate-early genes (IEGs) within the mammalian suprachiasmatic nucleus (SCN) identifies individual light-responsive cells of the circadian system. Cells immunoreactive for products of IEGs form a neurochemically heterogeneous population, of which a few are VIP (vasoactive intestinal peptide)-immunoreactive or GRP (gastrin-releasing peptide)-immunoreactive, although the phenotypes of most of the others have yet to be determined. Dual-labelling experiments with anatomical tracers reveal that only a minority of efferent projection neurons of the SCN are immunoreactive for IEG products, and it is likely that the majority of the immunoreactive cells are interneurons or glia. Photic induction of IEGs is mediated via NMDA (N-methyl-D-aspartate) and non-NMDA glutamatergic receptors, the SCN expressing a topographically specific complement of subtypes of the NMDA receptor. Non-photic cues (arousal) can shift the clock but this is not associated with expression of IEGs, demonstrating that the proteins encoded by IEGs are probably involved in transducing photic cues, rather than shifting the clock per se. Their induction provides an anatomically explicit marker for circadian phase and photic sensitivity and so is useful in analyses of circadian function, for example, in the tau mutant hamster. Non-photic phase shifts are accompanied by adrenocortical activation, confirming the importance of arousal in shifting of the clock. The phase-shifting effect of arousal can be blocked by treatment with the serotonin receptor antagonist ketanserin, suggesting that ascending serotonergic input to the forebrain, possibly directly to the SCN, is an important mediator of entrainment by arousal.
Collapse
Affiliation(s)
- M H Hastings
- Department of Anatomy, University of Cambridge, UK
| | | | | | | | | | | | | |
Collapse
|
36
|
Brown TM, Piggins HD. Electrophysiology of the suprachiasmatic circadian clock. Prog Neurobiol 2007; 82:229-55. [PMID: 17646042 DOI: 10.1016/j.pneurobio.2007.05.002] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2006] [Revised: 03/29/2007] [Accepted: 05/30/2007] [Indexed: 01/28/2023]
Abstract
In mammals, an internal timekeeping mechanism located in the suprachiasmatic nuclei (SCN) orchestrates a diverse array of neuroendocrine and physiological parameters to anticipate the cyclical environmental fluctuations that occur every solar day. Electrophysiological recording techniques have proved invaluable in shaping our understanding of how this endogenous clock becomes synchronized to salient environmental cues and appropriately coordinates the timing of a multitude of physiological rhythms in other areas of the brain and body. In this review we discuss the pioneering studies that have shaped our understanding of how this biological pacemaker functions, from input to output. Further, we highlight insights from new studies indicating that, more than just reflecting its oscillatory output, electrical activity within individual clock cells is a vital part of SCN clockwork itself.
Collapse
Affiliation(s)
- Timothy M Brown
- Faculty of Life Sciences, Stopford Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK
| | | |
Collapse
|
37
|
Kallingal GJ, Mintz EM. Glutamatergic activity modulates the phase-shifting effects of gastrin-releasing peptide and light. Eur J Neurosci 2007; 24:2853-8. [PMID: 17156209 DOI: 10.1111/j.1460-9568.2006.05165.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Previous studies have established that microinjection of gastrin-releasing peptide (GRP) into the suprachiasmatic nucleus (SCN) region or third ventricle causes circadian phase shifts similar to those produced by light pulses. Activation of N-methyl-d-aspartate (NMDA) receptors in the SCN region also produces light-like phase shifts. This study was designed to test the effects of (+/-)-2-amino-5-phosphonopentanoic acid (AP5), an NMDA antagonist, and l-trans-pyrrolidine-2,4-dicarboxylic acid (PDC), a glutamate reuptake inhibitor, on GRP-induced phase shifts. Adult male Syrian hamsters equipped with a surgically implanted guide cannula aimed at the third ventricle were housed in constant darkness until stable free-running rhythms of wheel-running activity were apparent. Microinjection of GRP into the third ventricle at circadian time (CT)13 induced large phase delays. These GRP-induced phase delays were completely blocked by co-administration of AP5, suggesting that GRP-induced phase delays require concurrent activation of NMDA receptors. Microinjection of AP5 alone did not induce significant phase shifts. A second set of experiments was designed to test whether GRP-induced phase shifts would be enhanced by PDC. Co-administration of PDC and GRP elicited significantly larger phase delays at CT13 than GRP alone. However, administration of PDC alone did not induce a significant phase shift. Finally, when administered just prior to a light pulse, PDC elicited significantly larger phase delays than light pulse plus vehicle controls. These data suggest that the effects of GRP on the circadian clock phase are highly dependent on the level of excitation provided by activated NMDA receptors.
Collapse
Affiliation(s)
- George J Kallingal
- School of Biomedical Sciences, Kent State University, Kent, OH 44242, USA
| | | |
Collapse
|
38
|
HATTAR SAMER, KUMAR MONICA, PARK ALEXANDER, TONG PATRICK, TUNG JONATHAN, YAU KINGWAI, BERSON DAVIDM. Central projections of melanopsin-expressing retinal ganglion cells in the mouse. J Comp Neurol 2006; 497:326-49. [PMID: 16736474 PMCID: PMC2885916 DOI: 10.1002/cne.20970] [Citation(s) in RCA: 687] [Impact Index Per Article: 38.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
A rare type of ganglion cell in mammalian retina is directly photosensitive. These novel retinal photoreceptors express the photopigment melanopsin. They send axons directly to the suprachiasmatic nucleus (SCN), intergeniculate leaflet (IGL), and olivary pretectal nucleus (OPN), thereby contributing to photic synchronization of circadian rhythms and the pupillary light reflex. Here, we sought to characterize more fully the projections of these cells to the brain. By targeting tau-lacZ to the melanopsin gene locus in mice, ganglion cells that would normally express melanopsin were induced to express, instead, the marker enzyme beta-galactosidase. Their axons were visualized by X-gal histochemistry or anti-beta-galactosidase immunofluorescence. Established targets were confirmed, including the SCN, IGL, OPN, ventral division of the lateral geniculate nucleus (LGv), and preoptic area, but the overall projections were more widespread than previously recognized. Targets included the lateral nucleus, peri-supraoptic nucleus, and subparaventricular zone of the hypothalamus, medial amygdala, margin of the lateral habenula, posterior limitans nucleus, superior colliculus, and periaqueductal gray. There were also weak projections to the margins of the dorsal lateral geniculate nucleus. Co-staining with the cholera toxin B subunit to label all retinal afferents showed that melanopsin ganglion cells provide most of the retinal input to the SCN, IGL, and lateral habenula and much of that to the OPN, but that other ganglion cells do contribute at least some retinal input to these targets. Staining patterns after monocular enucleation revealed that the projections of these cells are overwhelmingly crossed except for the projection to the SCN, which is bilaterally symmetrical.
Collapse
Affiliation(s)
- SAMER HATTAR
- Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2105
| | - MONICA KUMAR
- Department of Neuroscience, Brown University, Providence, Rhode Island 02912
| | - ALEXANDER PARK
- Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2105
| | - PATRICK TONG
- Department of Ophthalmology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2105
| | - JONATHAN TUNG
- Department of Neuroscience, Brown University, Providence, Rhode Island 02912
| | - KING-WAI YAU
- Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2105
- Department of Ophthalmology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2105
| | - DAVID M. BERSON
- Department of Neuroscience, Brown University, Providence, Rhode Island 02912
- Correspondence to: David M. Berson, Department of Neuroscience, Box 1953, Brown University, Providence, RI 02912.
| |
Collapse
|
39
|
Morin LP, Allen CN. The circadian visual system, 2005. ACTA ACUST UNITED AC 2006; 51:1-60. [PMID: 16337005 DOI: 10.1016/j.brainresrev.2005.08.003] [Citation(s) in RCA: 306] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2005] [Revised: 07/19/2005] [Accepted: 08/09/2005] [Indexed: 11/17/2022]
Abstract
The primary mammalian circadian clock resides in the suprachiasmatic nucleus (SCN), a recipient of dense retinohypothalamic innervation. In its most basic form, the circadian rhythm system is part of the greater visual system. A secondary component of the circadian visual system is the retinorecipient intergeniculate leaflet (IGL) which has connections to many parts of the brain, including efferents converging on targets of the SCN. The IGL also provides a major input to the SCN, with a third major SCN afferent projection arriving from the median raphe nucleus. The last decade has seen a blossoming of research into the anatomy and function of the visual, geniculohypothalamic and midbrain serotonergic systems modulating circadian rhythmicity in a variety of species. There has also been a substantial and simultaneous elaboration of knowledge about the intrinsic structure of the SCN. Many of the developments have been driven by molecular biological investigation of the circadian clock and the molecular tools are enabling novel understanding of regional function within the SCN. The present discussion is an extension of the material covered by the 1994 review, "The Circadian Visual System."
Collapse
Affiliation(s)
- L P Morin
- Department of Psychiatry and Graduate Program in Neuroscience, Stony Brook University, Stony Brook, NY 11794, USA.
| | | |
Collapse
|
40
|
Moldavan MG, Irwin RP, Allen CN. Presynaptic GABABReceptors Regulate Retinohypothalamic Tract Synaptic Transmission by Inhibiting Voltage-Gated Ca2+Channels. J Neurophysiol 2006; 95:3727-41. [PMID: 16709723 DOI: 10.1152/jn.00909.2005] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Presynaptic GABABreceptor activation inhibits glutamate release from retinohypothalamic tract (RHT) terminals in the suprachiasmatic nucleus (SCN). Voltage-clamp whole cell recordings from rat SCN neurons and optical recordings of Ca2+-sensitive fluorescent probes within RHT terminals were used to examine GABAB-receptor modulation of RHT transmission. Baclofen inhibited evoked excitatory postsynaptic currents (EPSCs) in a concentration-dependent manner equally during the day and night. Blockers of N-, P/Q-, T-, and R-type voltage-dependent Ca2+channels, but not L-type, reduced the EPSC amplitude by 66, 36, 32, and 18% of control, respectively. Joint application of multiple Ca2+channel blockers inhibited the EPSCs less than that predicted, consistent with a model in which multiple Ca2+channels overlap in the regulation of transmitter release. Presynaptic inhibition of EPSCs by baclofen was occluded by ω-conotoxin GVIA (≤72%), mibefradil (≤52%), and ω-agatoxin TK (≤15%), but not by SNX-482 or nimodipine. Baclofen reduced both evoked presynaptic Ca2+influx and resting Ca2+concentration in RHT terminals. Tertiapin did not alter the evoked EPSC and baclofen-induced inhibition, indicating that baclofen does not inhibit glutamate release by activation of Kir3 channels. Neither Ba2+nor high extracellular K+modified the baclofen-induced inhibition. 4-Aminopyridine (4-AP) significantly increased the EPSC amplitude and the charge transfer, and dramatically reduced the baclofen effect. These data indicate that baclofen inhibits glutamate release from RHT terminals by blocking N-, T-, and P/Q-type Ca2+channels, and possibly by activation of 4-AP–sensitive K+channels, but not by inhibition of R- and L-type Ca2+channels or by Kir3 channel activation.
Collapse
Affiliation(s)
- Mykhaylo G Moldavan
- Center for Research on Occupational and Environmental Toxicology, Oregon Health and Science University, Portland 97239-30, USA
| | | | | |
Collapse
|
41
|
Reghunandanan V, Reghunandanan R. Neurotransmitters of the suprachiasmatic nuclei. J Circadian Rhythms 2006; 4:2. [PMID: 16480518 PMCID: PMC1402333 DOI: 10.1186/1740-3391-4-2] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2005] [Accepted: 02/16/2006] [Indexed: 12/04/2022] Open
Abstract
There has been extensive research in the recent past looking into the molecular basis and mechanisms of the biological clock, situated in the suprachiasmatic nuclei (SCN) of the anterior hypothalamus. Neurotransmitters are a very important component of SCN function. Thorough knowledge of neurotransmitters is not only essential for the understanding of the clock but also for the successful manipulation of the clock with experimental chemicals and therapeutical drugs. This article reviews the current knowledge about neurotransmitters in the SCN, including neurotransmitters that have been identified only recently. An attempt was made to describe the neurotransmitters and hormonal/diffusible signals of the SCN efference, which are necessary for the master clock to exert its overt function. The expression of robust circadian rhythms depends on the integrity of the biological clock and on the integration of thousands of individual cellular clocks found in the clock. Neurotransmitters are required at all levels, at the input, in the clock itself, and in its efferent output for the normal function of the clock. The relationship between neurotransmitter function and gene expression is also discussed because clock gene transcription forms the molecular basis of the clock and its working.
Collapse
Affiliation(s)
- Vallath Reghunandanan
- Department of Basic Medical Science, Faculty of Medicine and Health Sciences, University of Malaysia, 93150 Kuching, Malaysia
| | - Rajalaxmy Reghunandanan
- Department of Basic Medical Science, Faculty of Medicine and Health Sciences, University of Malaysia, 93150 Kuching, Malaysia
| |
Collapse
|
42
|
González JA, Dyball REJ. Pinealectomy reduces optic nerve but not intergeniculate leaflet input to the suprachiasmatic nucleus at night. J Neuroendocrinol 2006; 18:146-53. [PMID: 16420284 DOI: 10.1111/j.1365-2826.2005.01395.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The suprachiasmatic nucleus (SCN) of the hypothalamus regulates circadian rhythms in mammals. It receives, among others, direct inputs from the retina and from the thalamic intergeniculate leaflet (IGL). The former sends photic signals to the SCN, whereas the latter probably integrates photic and nonphotic information. To characterise these inputs in vivo, extracellular single-unit recordings were made from the SCN of rats under urethane anaesthesia during electrical stimulation of the optic nerve (OptN) or the IGL region. Cell responses were evaluated by creating peri-stimulus time histograms. Because humoral signals such as melatonin might modulate the activity of the SCN in addition to neural inputs, recordings were also made using pinealectomised (Px) rats to test for a possible role of this hormone in regulating inputs to the SCN. A significantly greater number of cells responded to IGL (60 of 90, 67%) than to OptN (35 of 75, 47%) stimulation in intact animals (chi(2) = 5.905, P = 0.015). The same was true when Px animals were tested (IGL, 82 of 131, 63%; OptN, 31 of 111, 28%; chi(2) = 27.637, P < 0.001). In intact animals, the proportion of cells responsive to IGL stimulation during the day and during the night was not significantly different from the proportion responsive in Px animals. The same was true for OptN stimulation during the day. However, during the night, the proportion of cells responsive to OptN stimulation in intact animals was significantly greater than the proportion responsive in Px animals (chi(2) = 7.127, P = 0.008). Our findings suggest that a lack of melatonin modulates OptN but not IGL inputs to the SCN.
Collapse
Affiliation(s)
- J A González
- Department of Anatomy, University of Cambridge, Downing Street, Cambridge, UK
| | | |
Collapse
|
43
|
Bramley JR, Sollars PJ, Pickard GE, Dudek FE. 5-HT1B Receptor-Mediated Presynaptic Inhibition of GABA Release in the Suprachiasmatic Nucleus. J Neurophysiol 2005; 93:3157-64. [PMID: 15716370 DOI: 10.1152/jn.00770.2004] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The suprachiasmatic nucleus (SCN) receives a dense serotonergic innervation that modulates photic input to the SCN via serotonin 1B (5-HT1B) presynaptic receptors on retinal glutamatergic terminals. However, the majority of 5-HT1B binding sites in the SCN are located on nonretinal terminals and most axonal terminals in the SCN are GABAergic. We therefore tested the hypothesis that 5-HT1B receptors might also be located on SCN GABAergic terminals by examining the effects of the highly selective 5-HT1B receptor agonist CP-93,129 on SCN miniature inhibitory postsynaptic currents (mIPSCs). Whole cell patch-clamp recordings of mIPSCs were obtained from rat and mouse SCN neurons in hypothalamic slices. Using CsCl-containing microelectrodes with QX314, we isolated mPSCs that were sensitive to the GABAA receptor antagonist, bicuculline. Bath application of CP-93,129 (1 μM) decreased the frequency of mIPSCs by an average of 22% ( n = 7) in rat SCN neurons and by an average of 30% ( n = 8) in mouse SCN neurons with no clear effect on mIPSC amplitude. In mice lacking functional 5-HT1B receptors, CP-93,129 (1 μM) had no clear effect on the frequency or the amplitude of mIPSCs recorded in any of the cells tested ( n = 4). The decrease in the frequency of mIPSCs of SCN neurons produced by the selective 5-HT1B receptor agonist CP-93,129 is consistent with the interpretation that 5-HT1B receptors are located on GABA terminals in the SCN and that 5-HT inhibits GABA release via a 5-HT1B presynaptic receptor-mediated mechanism.
Collapse
Affiliation(s)
- Jayne R Bramley
- Dept. of Biomedical Sciences, Anatomy and Neurobiology Section, Colorado State University, Fort Collins, CO 80523, USA
| | | | | | | |
Collapse
|
44
|
Menger GJ, Lu K, Thomas T, Cassone VM, Earnest DJ. Circadian profiling of the transcriptome in immortalized rat SCN cells. Physiol Genomics 2005; 21:370-81. [PMID: 15769907 DOI: 10.1152/physiolgenomics.00224.2004] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Endogenous oscillations in gene expression are a prevalent feature of the circadian clock in the mammalian suprachiasmatic nucleus (SCN) and similar timekeeping systems in other organisms. To determine whether immortalized cells derived from the rat SCN (SCN2.2) retain these intrinsic rhythm-generating properties, oscillatory behavior of the SCN2.2 transcriptome was analyzed and compared with that found in the rat SCN in vivo using rat U34A Affymetrix GeneChips. In SCN2.2 cells, 116 unique genes and 46 ESTs or genes of unknown function exhibited circadian fluctuations with a 1.5-fold or greater difference in their mRNA abundance for two cycles. Many (35%) of these rhythmically regulated genes in SCN2.2 cells also exhibited circadian profiles of mRNA expression in the rat SCN in vivo. Functional analyses and cartography indicate that a diverse set of cellular pathways are strategically regulated by the circadian clock in SCN2.2 cells and that the largest categories of rhythmic genes are those involved in cellular and systems-level communication or in metabolic processes like cellular respiration, fatty acid recycling, and steroid synthesis. Because many of the same genes or nodes within these functional categories were rhythmically expressed in both SCN2.2 cells and the rat SCN, the circadian regulation of these pathways may be important in modulating input to or output from the SCN clock mechanism. In summary, global expression and circadian regulation of the SCN2.2 transcriptome retain many SCN-like properties, suggesting that genes displaying rhythmic profiles in both experimental models may be integral to their function as both circadian oscillators and pacemakers.
Collapse
Affiliation(s)
- Gus J Menger
- Department of Human Anatomy and Medical Neurobiology, Texas A & M University Health Science Center, College of Medicine, Texas 77843-1114, USA
| | | | | | | | | |
Collapse
|
45
|
Marpegán L, Bekinschtein TA, Costas MA, Golombek DA. Circadian responses to endotoxin treatment in mice. J Neuroimmunol 2004; 160:102-9. [PMID: 15710463 DOI: 10.1016/j.jneuroim.2004.11.003] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2004] [Revised: 11/10/2004] [Accepted: 11/10/2004] [Indexed: 11/24/2022]
Abstract
We tested the ability of Escherichia coli lipopolysaccharide (LPS) to phase-shift the activity circadian rhythm in C57Bl/6J mice. Intraperitoneal administration of 25 microg/kg LPS induced photic-like phase delays (-43+/-10 min) during the early subjective night. These delays were non-additive to those induced by light at CT 15, and were reduced by the previous administration of sulfasalazine, a NF-kappaB activation inhibitor. At CT 15, LPS induced c-Fos expression in the dorsal area of the suprachiasmatic nuclei (SCN). Our results suggest that the activation of the immune system should be considered an entraining signal for the murine circadian clock.
Collapse
Affiliation(s)
- Luciano Marpegán
- Departamento de Ciencia y Tecnología, Universidad Nacional de Quilmes, R.S. Peña 180, (1876) Bernal, Buenos Aires, Argentina
| | | | | | | |
Collapse
|
46
|
Menet JS, Vuillez P, Pévet P. Calbindin expression in the hamster suprachiasmatic nucleus depends on day-length. Neuroscience 2004; 122:591-8. [PMID: 14622902 DOI: 10.1016/j.neuroscience.2003.08.020] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The mammalian circadian clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus controls many physiological and behavioral rhythms. The SCN is compartmentalized in two functionally distinct subregions: a dorsomedial subregion that rhythmically expresses clock genes, and a ventrolateral subregion which, in contrast, mainly expresses clock genes at a constant level. In the golden hamster, this ventrolateral part of the SCN contains a subpopulation of neurons expressing calbindin D28k. This subpopulation has recently been implicated in the control of locomotor rhythmicity. Because both the pattern and level of locomotor activity are affected by day-length, we investigated whether photoperiod also affects calbindin expression. We show that calbindin expression is negatively correlated to the day-length. The number of calbindin immunopositive neurons and calbindin mRNA levels were markedly increased in hamsters exposed to short photoperiods (light/dark cycle [LD] 6:18 and LD10:14) when compared with hamster exposed to long photoperiods (LD18:6 and LD14:10). This suggests that calbindin neurons are involved in the encoding of seasonal information by the SCN.
Collapse
Affiliation(s)
- J S Menet
- CNRS-UMR 7518, Neurobiologie des Rythmes, Université Louis Pasteur, IFR Neuroscience 37, 12 rue de l'Université, 67000 Strasbourg, France
| | | | | |
Collapse
|
47
|
Feinstein N, Fritschy JM, Parnas I. Presynaptic membrane of inhibitory crayfish axon terminals is stained by antibodies raised against mammalian GABA(A) receptor subunits alpha3 and beta(2/3). J Comp Neurol 2003; 465:250-62. [PMID: 12949785 DOI: 10.1002/cne.10847] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The opener muscle of the dactyl of the walking leg of crayfish is innervated by one excitatory axon releasing glutamate and one inhibitory axon releasing GABA. Functional GABA(A) receptors are present postsynaptically on the muscle and presynaptically on terminals and release boutons of the excitatory axon, whereas presynaptic GABA(A) autoreceptors have not been reported on terminals or release boutons of the inhibitory axon. Using antibodies raised against mammalian GABA(A) receptor subunits alpha3 and beta(2/3), we obtained highly specific staining of the presynaptic membrane of the inhibitory bouton and of the postsynaptic membrane of the muscle. Using pre- and postembedding techniques, staining was localized to only presynaptic and postsynaptic membranes of synaptic active zones. We also found extrasynaptic receptor subunit immunoreactivity near (up to 100 nm) to the active zones. Staining with antibodies for the alpha3 and beta(2/3) subunits showed colocalization of particles of the two subunits. We suggest that presynaptic inhibitory boutons of the crayfish possess GABA(A)-like autoreceptors composed of at least the alpha3 and beta(2/3) subunits.
Collapse
Affiliation(s)
- N Feinstein
- The Otto Loewi Minerva Center for Cellular and Molecular Neurobiology, The Hebrew University, Jerusalem 91904, Israel
| | | | | |
Collapse
|
48
|
Abstract
The suprachiasmatic nucleus (SCN) is the neuroanatomical locus of the mammalian circadian pacemaker. Here we demonstrate that an abrupt shift in the light/dark (LD) cycle disrupts the synchronous oscillation of circadian components in the rat SCN. The phases of the RNA cycles of the period genes Per1 and Per2 and the cryptochrome gene Cry1 shifted rapidly in the ventrolateral, photoreceptive region of the SCN, but were relatively slow to shift in the dorsomedial region. During the period of desynchrony, the animals displayed increased nighttime rest, the timing of which was inversely correlated with the expression of Per1 mRNA in the dorsomedial SCN. Molecular resynchrony required approximately 6 d after a 10 hr delay and 9 approximately 13 d after a 6 hr advance of the LD cycle and was accompanied by the reemergence of normal rest-activity patterns. This dissociation and slow resynchronization of endogenous oscillators within the SCN after an LD cycle shift suggests a mechanism for the physiological symptoms that constitute jet lag.
Collapse
|
49
|
Belenky MA, Sagiv N, Fritschy JM, Yarom Y. Presynaptic and postsynaptic GABAA receptors in rat suprachiasmatic nucleus. Neuroscience 2003; 118:909-23. [PMID: 12732237 DOI: 10.1016/s0306-4522(03)00062-9] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The mammalian suprachiasmatic nucleus (SCN), the brain's circadian clock, is composed mainly of GABAergic neurons, that are interconnected via synapses with GABA(A) receptors. Here we report on the subcellular localization of these receptors in the SCN, as revealed by an extensively characterized antibody to the alpha 3 subunit of GABA(A) receptors in conjunction with pre- and postembedding electron microscopic immunocytochemistry. GABA(A) receptor immunoreactivity was observed in neuronal perikarya, dendritic processes and axonal terminals. In perikarya and proximal dendrites, GABA(A) receptor immunoreactivity was expressed mainly in endoplasmic reticulum and Golgi complexes, while in the distal part of dendrites, immunoreaction product was associated with postsynaptic plasma membrane. Many GABAergic axonal terminals, as revealed by postembedding immunogold labeling, displayed GABA(A) receptor immunoreactivity, associated mainly with the extrasynaptic portion of their plasma membrane. The function of these receptors was studied in hypothalamic slices using whole-cell patch-clamp recording of the responses to minimal stimulation of an area dorsal to the SCN. Analysis of the evoked inhibitory postsynaptic currents showed that either bath or local application of 100 microM of GABA decreased GABAergic transmission, manifested as a two-fold increase in failure rate. This presynaptic effect, which was detected in the presence of the glutamate receptor blocker 6-cyano-7-nitroquinoxaline-2,3-dione and the selective GABA(B) receptor blocker CGP55845A, appears to be mediated via activation of GABA(A) receptors. Our results thus show that GABA(A) receptors are widely distributed in the SCN and may subserve both pre- and postsynaptic roles in controlling the mammalian circadian clock.
Collapse
Affiliation(s)
- M A Belenky
- Department of Cell and Animal Biology Institute of Life Sciences, Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | | | | | | |
Collapse
|
50
|
Jiao YY, Rusak B. Electrophysiology of optic nerve input to suprachiasmatic nucleus neurons in rats and degus. Brain Res 2003; 960:142-51. [PMID: 12505666 DOI: 10.1016/s0006-8993(02)03804-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Neurons in the mammalian suprachiasmatic nucleus (SCN), the principal pacemaker of the circadian system, receive direct retinal input. Some SCN neurons respond to retinal illumination or optic nerve stimulation with changes in firing rates. In nocturnal rodents, retinal illumination increases firing rates of a large majority and decreases firing rates of a minority of responsive neurons. In two species of diurnal rodent, these proportions are altered or even reversed. Since retinal input to the SCN has been reported to involve release of the excitatory neurotransmitter glutamate, the mechanism mediating suppressions is unknown. We studied responses of neurons in SCN slices from diurnal degus and nocturnal rats to optic nerve stimulation. To test whether suppressions are mediated indirectly by release of the inhibitory neurotransmitter GABA from SCN neurons that are first activated by glutamate release, we attempted to block suppressions by adding to the bath either APV, an antagonist for excitatory glutamate receptors, or bicuculline, a GABA(A) receptor antagonist. If glutamate is the only neurotransmitter released by optic nerves in the SCN, APV should prevent both activations and suppressions in response to optic nerve stimulation. We found that APV had little effect on suppressions although it effectively blocked activations. Bicuculline blocked most suppressions. These findings are inconsistent with a model in which the retina provides only excitatory glutamate input to the SCN via NMDA receptors. Since some retinal fibers in adult mammals contain GABA, it is possible that the retinal innervation of the SCN includes both glutamate- and GABA-containing axons.
Collapse
Affiliation(s)
- Yong-Yi Jiao
- Department of Psychology, Dalhousie University, Halifax, Nova Scotia, Canada
| | | |
Collapse
|