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Richards J, Gumz ML. Advances in understanding the peripheral circadian clocks. FASEB J 2012; 26:3602-13. [PMID: 22661008 PMCID: PMC3425819 DOI: 10.1096/fj.12-203554] [Citation(s) in RCA: 134] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2012] [Accepted: 05/21/2012] [Indexed: 12/22/2022]
Abstract
In the past decade, it has become increasingly evident that the circadian clock system plays an important role in many physiological processes. The circadian clock can be divided into 2 parts: the central clock, residing in the suprachiasmatic nucleus of the hypothalamus, which receives light cues, and the peripheral clocks that reside in various tissues throughout the body. The peripheral clocks play an integral and unique role in each of their respective tissues, driving the circadian expression of specific genes involved in a variety of physiological functions. The goal of this review is to provide an introduction to and overview of the peripheral clocks, including potential mechanisms, targets, and implications for disease states. The peripheral clocks include the cardiovascular, metabolic, endocrine, immune, and reproductive systems.
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Affiliation(s)
- Jacob Richards
- Department of Medicine and Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida, USA
| | - Michelle L. Gumz
- Department of Medicine and Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida, USA
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52
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Tseng YY, Hunt SM, Heintzen C, Crosthwaite SK, Schwartz JM. Comprehensive modelling of the Neurospora circadian clock and its temperature compensation. PLoS Comput Biol 2012; 8:e1002437. [PMID: 22496627 PMCID: PMC3320131 DOI: 10.1371/journal.pcbi.1002437] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2011] [Accepted: 02/06/2012] [Indexed: 11/19/2022] Open
Abstract
Circadian clocks provide an internal measure of external time allowing organisms to anticipate and exploit predictable daily changes in the environment. Rhythms driven by circadian clocks have a temperature compensated periodicity of approximately 24 hours that persists in constant conditions and can be reset by environmental time cues. Computational modelling has aided our understanding of the molecular mechanisms of circadian clocks, nevertheless it remains a major challenge to integrate the large number of clock components and their interactions into a single, comprehensive model that is able to account for the full breadth of clock phenotypes. Here we present a comprehensive dynamic model of the Neurospora crassa circadian clock that incorporates its key components and their transcriptional and post-transcriptional regulation. The model accounts for a wide range of clock characteristics including: a periodicity of 21.6 hours, persistent oscillation in constant conditions, arrhythmicity in constant light, resetting by brief light pulses, and entrainment to full photoperiods. Crucial components influencing the period and amplitude of oscillations were identified by control analysis. Furthermore, simulations enabled us to propose a mechanism for temperature compensation, which is achieved by simultaneously increasing the translation of frq RNA and decreasing the nuclear import of FRQ protein. Circadian clocks are internal timekeepers that integrate signals from the environment and orchestrate cellular events to occur at the most favourable time of day. Circadian clocks in animals, plants, fungi and bacteria have similar characteristic properties and molecular architecture. They have a periodicity of approximately 24 hours, persist in constant conditions and can be reset by environmental time cues such as light and temperature. Another essential property, whose molecular basis is poorly understood, is that the period is temperature compensated i.e. it remains the same over a range of temperatures. Computational modelling has become a valuable tool to predict and understand the underlying mechanisms of such complex molecular systems, but existing clock models are often restricted in the scope of molecular reactions they cover and in the breadth of conditions they are able to reproduce. We therefore built a comprehensive model of the circadian clock of the fungus Neurospora crassa, which encompasses existing knowledge of the biochemistry of the Neurospora clock. We validated this model against a wide range of experimental phenotypes and then used the model to investigate possible molecular explanations of temperature compensation. Our simulations suggest that temperature compensation of period is achieved by changing the abundance and cellular localisation of a key clock protein.
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Affiliation(s)
- Yu-Yao Tseng
- Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
- Manchester Interdisciplinary Biocentre, Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
| | - Suzanne M. Hunt
- Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
| | - Christian Heintzen
- Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
| | - Susan K. Crosthwaite
- Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
- * E-mail: (SKC); (JMS)
| | - Jean-Marc Schwartz
- Manchester Interdisciplinary Biocentre, Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
- * E-mail: (SKC); (JMS)
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53
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Gerstner JR. On the evolution of memory: a time for clocks. Front Mol Neurosci 2012; 5:23. [PMID: 22403527 PMCID: PMC3289401 DOI: 10.3389/fnmol.2012.00023] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2011] [Accepted: 02/11/2012] [Indexed: 12/16/2022] Open
Abstract
Evolutionarily, what was the earliest engram? Biology has evolved to encode representations of past events, and in neuroscience, we are attempting to link experience-dependent changes in molecular signaling with cellular processes that ultimately lead to behavioral output. The theory of evolution has guided biological research for decades, and since phylogenetically conserved mechanisms drive circadian rhythms, these processes may serve as common predecessors underlying more complex behavioral phenotypes. For example, the cAMP/MAPK/CREB cascade is interwoven with the clock to trigger circadian output, and is also known to affect memory formation. Time-of-day dependent changes have been observed in long-term potentiation (LTP) within the suprachiasmatic nucleus and hippocampus, along with light-induced circadian phase resetting and fear conditioning behaviors. Together this suggests during evolution, similar processes underlying metaplasticity in more simple circuits may have been redeployed in higher-order brain regions. Therefore, this notion predicts a model that LTP and metaplasticity may exist in neural circuits of other species, through phylogenetically conserved pathways, leading to several testable hypotheses.
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Affiliation(s)
- Jason R Gerstner
- Center for Sleep and Circadian Neurobiology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
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54
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Tucci V. Sleep, circadian rhythms, and interval timing: evolutionary strategies to time information. Front Integr Neurosci 2012; 5:92. [PMID: 22319478 PMCID: PMC3250947 DOI: 10.3389/fnint.2011.00092] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2011] [Accepted: 12/15/2011] [Indexed: 12/16/2022] Open
Affiliation(s)
- Valter Tucci
- Department of Neuroscience and Brain Technologies, Istituto Italiano di Tecnologia Genova, Italy
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55
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Abstract
Neurons in the suprachiasmatic nucleus (SCN) function as part of a central timing circuit that drives daily changes in our behaviour and underlying physiology. A hallmark feature of SCN neuronal populations is that they are mostly electrically silent during the night, start to fire action potentials near dawn and then continue to generate action potentials with a slow and steady pace all day long. Sets of currents are responsible for this daily rhythm, with the strongest evidence for persistent Na(+) currents, L-type Ca(2+) currents, hyperpolarization-activated currents (I(H)), large-conductance Ca(2+) activated K(+) (BK) currents and fast delayed rectifier (FDR) K(+) currents. These rhythms in electrical activity are crucial for the function of the circadian timing system, including the expression of clock genes, and decline with ageing and disease. This article reviews our current understanding of the ionic and molecular mechanisms that drive the rhythmic firing patterns in the SCN.
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Affiliation(s)
- Christopher S Colwell
- Laboratory of Circadian and Sleep Medicine, Department of Psychiatry and Biobehavioral Sciences, David Geffen School of Medicine, University of California Los Angeles, California 90024, USA.
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56
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Kudo T, Loh DH, Truong D, Wu Y, Colwell CS. Circadian dysfunction in a mouse model of Parkinson's disease. Exp Neurol 2011; 232:66-75. [PMID: 21864527 DOI: 10.1016/j.expneurol.2011.08.003] [Citation(s) in RCA: 122] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2011] [Revised: 07/25/2011] [Accepted: 08/08/2011] [Indexed: 10/17/2022]
Abstract
Many Parkinson's disease (PD) patients exhibit sleep disorders as part of their symptoms with evidence suggesting that REM sleep disorders may be intimately associated with this disease. Possible dysfunction in the circadian system in PD has received less attention, yet problems in circadian timing are common in neurodegenerative diseases. In the present study, we examined the expression of daily and circadian rhythms in the alpha-synuclein overexpressing (ASO) transgenic line. We found selective deficits in the expression of circadian rhythms of locomotor activity, including lower night-time activity and greater fragmentation in the wheel-running activity in this PD model. These alterations were prominent in young adult (3-4 mo) ASO mice and worsened progressively with age, consistent with prior reports of age-related loss of motor skills. The temporal distribution of sleep was also altered in the ASO mice compared to littermate controls. In the ASO mice, the peak/trough expression of the clock gene PERIOD2 was normal in the master pacemaker of the circadian system: the suprachiasmatic nucleus (SCN); however, the daytime firing rate of SCN neurons was reduced in the mutant mice. Together, this data raises the possibility that a weakening of circadian output is a core feature of PD. The reduction in magnitude of circadian output would be expected to have functional consequences throughout the body.
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Affiliation(s)
- Takashi Kudo
- Department of Psychiatry & Biobehavioral Sciences, University of California-Los Angeles, Los Angeles, CA 90024, USA
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57
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Fast delayed rectifier potassium current: critical for input and output of the circadian system. J Neurosci 2011; 31:2746-55. [PMID: 21414897 DOI: 10.1523/jneurosci.5792-10.2011] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The ability to generate intrinsic circadian rhythms in electrical activity appears to be a key property of central pacemaker neurons and one essential to the function of the circadian timing system. Previous work has demonstrated that suprachiasmatic nucleus (SCN) neurons express the fast delayed rectifier (FDR) potassium current and raise questions about the function of this current. Here, we report that mice lacking both Kcnc1 and Kcnc2 genes [double knock-out (dKO)] fail to express the Kv3.1 and 3.2 channels in the SCN as well as exhibit a greatly reduced FDR current. SCN neurons from these dKO mice exhibit reduced spontaneous activity during the day as well as reduced NMDA-evoked excitatory responses during the night. Interestingly, the daily rhythm in PER2 expression in the SCN was not altered in the dKO mice, although the photic induction of c-Fos was attenuated. Behaviorally, the dKO mice exhibited extremely disrupted daily rhythms in wheel-running behavior. In a light/dark cycle, some of the dKO mice were arrhythmic, whereas others expressed a diurnal rhythm with low amplitude and significant activity during the day. When placed in constant darkness, the dKO mice exhibited low-amplitude, fragmented rhythms and attenuated light responses. Together, these data are consistent with the hypothesis that the FDR current is critical for the generation of robust circadian rhythms in behavior as well as the synchronization of the circadian system to the photic environment.
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58
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Sugimoto T, Morioka N, Sato K, Hisaoka K, Nakata Y. Noradrenergic regulation of period1 expression in spinal astrocytes is involved in protein kinase A, c-Jun N-terminal kinase and extracellular signal-regulated kinase activation mediated by α1- and β2-adrenoceptors. Neuroscience 2011; 185:1-13. [DOI: 10.1016/j.neuroscience.2011.04.024] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2011] [Revised: 04/08/2011] [Accepted: 04/08/2011] [Indexed: 10/18/2022]
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59
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Marshall L, Kirov R, Brade J, Mölle M, Born J. Transcranial electrical currents to probe EEG brain rhythms and memory consolidation during sleep in humans. PLoS One 2011; 6:e16905. [PMID: 21340034 PMCID: PMC3038929 DOI: 10.1371/journal.pone.0016905] [Citation(s) in RCA: 143] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2010] [Accepted: 01/17/2011] [Indexed: 11/18/2022] Open
Abstract
Previously the application of a weak electric anodal current oscillating with a frequency of the sleep slow oscillation (∼0.75 Hz) during non-rapid eye movement sleep (NonREM) sleep boosted endogenous slow oscillation activity and enhanced sleep-associated memory consolidation. The slow oscillations occurring during NonREM sleep and theta oscillations present during REM sleep have been considered of critical relevance for memory formation. Here transcranial direct current stimulation (tDCS) oscillating at 5 Hz, i.e., within the theta frequency range (theta-tDCS) is applied during NonREM and REM sleep. Theta-tDCS during NonREM sleep produced a global decrease in slow oscillatory activity conjoint with a local reduction of frontal slow EEG spindle power (8-12 Hz) and a decrement in consolidation of declarative memory, underlining the relevance of these cortical oscillations for sleep-dependent memory consolidation. In contrast, during REM sleep theta-tDCS appears to increase global gamma (25-45 Hz) activity, indicating a clear brain state-dependency of theta-tDCS. More generally, results demonstrate the suitability of oscillating-tDCS as a tool to analyze functions of endogenous EEG rhythms and underlying endogenous electric fields as well as the interactions between EEG rhythms of different frequencies.
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Affiliation(s)
- Lisa Marshall
- Department of Neuroendocrinology, University of Lübeck, Lübeck, Germany.
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60
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Wolloscheck T, Spiwoks-Becker I, Rickes O, Holthues H, Spessert R. Phosphodiesterase10A: abundance and circadian regulation in the retina and photoreceptor of the rat. Brain Res 2010; 1376:42-50. [PMID: 21194525 DOI: 10.1016/j.brainres.2010.12.065] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2010] [Revised: 12/14/2010] [Accepted: 12/21/2010] [Indexed: 11/19/2022]
Abstract
Phosphodiesterase10A (PDE10A) is a dual specific cyclic nucleotide phosphodiesterase that is specifically enriched in striatum and which has gained attention as a therapeutic target for psychiatric disorders. The present study shows that PDE10A is also highly expressed in retinal neurons including photoreceptors. The levels of PDE10A transcript and protein display daily rhythms which could be seen in preparations of the whole retina. Corresponding changes in PDE10A mRNA were seen in photoreceptors isolated using laser microdissection. This suggests that the expressional control of the photoreceptor Pde10a gene contributes to the observed cyclicity in the amount of retinal PDE10A. The daily rhythmicity in the retinal PDE10A mRNA amount is retained under constant darkness but can be blocked by constant light or modulated by the lighting regime. It therefore appears to be driven by the endogenous retinal clock system which itself is entrained by light. The findings presented place PDE10A in the context of the visual system and suggest a role of PDE10A in the adaptation of cyclic nucleotide signaling to daily changes in light intensity in retinal neurons including photoreceptors.
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Affiliation(s)
- Tanja Wolloscheck
- Institute of Functional and Clinical Anatomy, University Medical Center of the Johannes Gutenberg University, Saarstraße 19-21, 55099 Mainz, Germany
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61
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Kudo T, Schroeder A, Loh DH, Kuljis D, Jordan MC, Roos KP, Colwell CS. Dysfunctions in circadian behavior and physiology in mouse models of Huntington's disease. Exp Neurol 2010; 228:80-90. [PMID: 21184755 DOI: 10.1016/j.expneurol.2010.12.011] [Citation(s) in RCA: 132] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2010] [Revised: 12/11/2010] [Accepted: 12/14/2010] [Indexed: 10/18/2022]
Abstract
Many patients with Huntington's disease (HD) exhibit disturbances in their daily cycle of sleep and wake as part of their symptoms. These patients have difficulty sleeping at night and staying awake during the day, which has a profound impact on the quality of life of the patients and their care-givers. In the present study, we examined diurnal and circadian rhythms of four models of HD including the BACHD, CAG 140 knock-in and R6/2 CAG 140 and R6/2 CAG 250 lines of mice. The BACHD and both R6/2 lines showed profound circadian phenotypes as measured by wheel-running activity. Focusing on the BACHD line for further analysis, the amplitude of the rhythms in the BACHD mice declined progressively with age. In addition, the circadian regulation of heart rate and body temperature in freely behaving BACHD mice were also disrupted. Furthermore, the distribution of sleep as well as the autonomic regulation of heart rate was disrupted in this HD model. To better understand the mechanistic underpinnings of the circadian disruption, we used electrophysiological tools to record from neurons within the central clock in the suprachiasmatic nucleus (SCN). The BACHD mice exhibit reduced rhythms in spontaneous electrical activity in SCN neurons. Interestingly, the expression of the clock gene PERIOD2 was not altered in the SCN of the BACHD line. Together, this data is consistent with the hypothesis that the HD mutations interfere with the expression of robust circadian rhythms in behavior and physiology. The data raise the possibility that the electrical activity within the central clock itself may be altered in this disease.
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Affiliation(s)
- Takashi Kudo
- Department of Psychiatry & Biobehavioral Sciences, University of California, Los Angeles, Los Angeles, CA 90024, USA
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62
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Brown SA, Pagani L, Cajochen C, Eckert A. Systemic and cellular reflections on ageing and the circadian oscillator: a mini-review. Gerontology 2010; 57:427-34. [PMID: 20980722 DOI: 10.1159/000320673] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2010] [Accepted: 08/26/2010] [Indexed: 11/19/2022] Open
Abstract
From circulation to digestion to excretion, a circadian clock synchronizes most aspects of mammalian physiology with the solar day. During normal ageing, this daily coordination gradually erodes, and during pathological ageing such erosion is exacerbated. Recent experiments suggest that therapies aimed at sustaining circadian function increase quality of life in elderly patients. Hence, a better understanding of the interactions between the circadian clock and ageing - at both cellular and systemic levels - could lead to direct benefits for aged individuals.
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Affiliation(s)
- Steven A Brown
- Department of Pharmacology and Toxicology, University of Zurich, Switzerland. steven.brown @ pharma.uzh.ch
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63
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Sellix MT, Menaker M. Circadian clocks in the ovary. Trends Endocrinol Metab 2010; 21:628-36. [PMID: 20599392 PMCID: PMC2949464 DOI: 10.1016/j.tem.2010.06.002] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/01/2010] [Revised: 06/01/2010] [Accepted: 06/02/2010] [Indexed: 11/22/2022]
Abstract
Clock gene expression has been observed in tissues of the hypothalamic-pituitary-gonadal (HPG) axis. Whereas the contribution of hypothalamic oscillators to the timing of reproductive biology is well known, the role of peripheral oscillators like those in the ovary is less clear. Circadian clocks in the ovary might play a role in the timing of ovulation. Disruption of the clock in ovarian cells or desynchrony between ovarian clocks and circadian oscillators elsewhere in the body may contribute to the onset and progression of various reproductive pathologies. In this paper, we review evidence for clock function in the ovary across a number of species and offer a novel perspective into the role of this clock in normal ovarian physiology and in diseases that negatively affect fertility.
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Affiliation(s)
| | - Michael Menaker
- Corresponding Author: PO Box 400328, University of Virginia, Charlottesville, VA 22904, , Phone: 434-982-5767, Fax: 434-982-5626
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64
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Sukumaran S, Almon RR, DuBois DC, Jusko WJ. Circadian rhythms in gene expression: Relationship to physiology, disease, drug disposition and drug action. Adv Drug Deliv Rev 2010; 62:904-17. [PMID: 20542067 PMCID: PMC2922481 DOI: 10.1016/j.addr.2010.05.009] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2009] [Revised: 05/10/2010] [Accepted: 05/26/2010] [Indexed: 12/26/2022]
Abstract
Circadian rhythms (24h cycles) are observed in virtually all aspects of mammalian function from expression of genes to complex physiological processes. The master clock is present in the suprachiasmatic nucleus (SCN) in the anterior part of the hypothalamus and controls peripheral clocks present in other parts of the body. Components of this core clock mechanism regulate the circadian rhythms in genome-wide mRNA expression, which in turn regulate various biological processes. Disruption of circadian rhythms can be either the cause or the effect of various disorders including metabolic syndrome, inflammatory diseases and cancer. Furthermore, circadian rhythms in gene expression regulate both the action and disposition of various drugs and affect therapeutic efficacy and toxicity based on dosing time. Understanding the regulation of circadian rhythms in gene expression plays an important role in both optimizing the dosing time for existing drugs and in the development of new therapeutics targeting the molecular clock.
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Affiliation(s)
- Siddharth Sukumaran
- Department of Biological Sciences, State University of New York at Buffalo, 14260, United States
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65
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Giusi G, Alo’ R, Crudo M, Di Vito A, Facciolo RM, Canonaco M. Environmental stressors and neurobiological features of marine teleosts: Histamine receptors as targets. Crit Rev Toxicol 2010; 40:620-32. [DOI: 10.3109/10408444.2010.487479] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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66
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Abstract
Circadian misalignment has been implicated in the development of obesity, diabetes mellitus, and cardiovascular disease. Time-of-day-dependent synchronization of organisms with their environment is mediated by circadian clocks. This cell autonomous mechanism has been identified within all cardiovascular-relevant cell types, including cardiomyocytes. Recent molecular- and genetic-based studies suggest that the cardiomyocyte circadian clock influences multiple myocardial processes, including transcription, signaling, growth, metabolism, and contractile function. Following an appreciation of its physiological roles, the cardiomyocyte circadian clock has recently been linked to the pathogenesis of heart disease in response to adverse stresses, such as ischemia/reperfusion, in animal models. The purpose of this review is therefore to highlight recent advances regarding the roles of the cardiomyocyte circadian clock in both myocardial physiology and pathophysiology (ie, health and disease).
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Affiliation(s)
- David J Durgan
- Division of Cardiovascular Diseases, Department of Medicine, University of Alabama at Birmingham, 703 19th Street S., Birmingham, AL 35294, USA
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67
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Itri JN, Vosko AM, Schroeder A, Dragich JM, Michel S, Colwell CS. Circadian regulation of a-type potassium currents in the suprachiasmatic nucleus. J Neurophysiol 2009; 103:632-40. [PMID: 19939959 DOI: 10.1152/jn.00670.2009] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In mammals, the precise circadian timing of many biological processes depends on the generation of oscillations in neural activity of pacemaker cells in the suprachiasmatic nucleus (SCN) of the hypothalamus. Understanding the ionic mechanisms underlying these rhythms is an important goal of research in chronobiology. Previous work has shown that SCN neurons express A-type potassium currents (IAs), but little is known about the properties of this current in the SCN. We sought to characterize some of these properties, including the identities of IA channel subunits found in the SCN and the circadian regulation of IA itself. In this study, we were able to detect significant hybridization for Shal-related family members 1 and 2 (Kv4.1 and 4.2) within the SCN. In addition, we used Western blot to show that the Kv4.1 and 4.2 proteins are expressed in SCN tissue. We further show that the magnitude of the IA current exhibits a diurnal rhythm that peaks during the day in the dorsal region of the mouse SCN. This rhythm seems to be driven by a subset of SCN neurons with a larger peak current and a longer decay constant. Importantly, this rhythm in neurons in the dorsal SCN continues in constant darkness, providing an important demonstration of the circadian regulation of an intrinsic voltage-gated current in mammalian cells. We conclude that the anatomical expression, biophysical properties, and pharmacological profiles measured are all consistent with the SCN IA current being generated by Kv4 channels. Additionally, these data suggest a role for IA in the regulation of spontaneous action potential firing during the transitions between day/night and in the integration of synaptic inputs to SCN neurons throughout the daily cycle.
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Affiliation(s)
- Jason N Itri
- Department of Psychiatry and Biobehavioral Sciences, University of California-Los Angeles, Los Angeles, CA 90024-1759, USA
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