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International Journal of Molecular... May 2020The circadian system is an internal time-keeping system that synchronizes the behavior and physiology of an organism to the 24 h solar day. The master circadian clock,... (Review)
Review
The circadian system is an internal time-keeping system that synchronizes the behavior and physiology of an organism to the 24 h solar day. The master circadian clock, the suprachiasmatic nucleus (SCN), resides in the hypothalamus. It receives information about the environmental light/dark conditions through the eyes and orchestrates peripheral oscillators. Purinergic signaling is mediated by extracellular purines and pyrimidines that bind to purinergic receptors and regulate multiple body functions. In this review, we highlight the interaction between the circadian system and purinergic signaling to provide a better understanding of rhythmic body functions under physiological and pathological conditions.
Topics: Animals; Circadian Clocks; Circadian Rhythm; Humans; Hypothalamus; Models, Neurological; Neurons; Receptors, Purinergic; Signal Transduction; Suprachiasmatic Nucleus
PubMed: 32408622
DOI: 10.3390/ijms21103423 -
The FEBS Journal Nov 2022The brain has a complex structure composed of hundreds of regions, forming networks to cooperate body functions. Therefore, understanding how various brain regions... (Review)
Review
The brain has a complex structure composed of hundreds of regions, forming networks to cooperate body functions. Therefore, understanding how various brain regions communicate with each other and with peripheral organs is important to understand human physiology. The suprachiasmatic nucleus (SCN) in the brain is the circadian pacemaker. The SCN receives photic information from the environment and conveys this to other parts of the brain and body to synchronize all circadian clocks. The circadian clock is an endogenous oscillator that generates daily rhythms in metabolism and physiology in almost all cells via a conserved transcriptional-translational negative feedback loop. So, the information flow from the environment to the SCN to other tissues synchronizes locally distributed circadian clocks to maintain homeostasis. Thus, understanding the circadian networks and how they adjust to environmental changes will better understand human physiology. This review will focus on circadian networks mediated by the SCN to understand how the environment, brain, and peripheral tissues form networks for cooperation.
Topics: Animals; Humans; Circadian Rhythm; Suprachiasmatic Nucleus; Circadian Clocks; Mammals; Brain
PubMed: 34657394
DOI: 10.1111/febs.16233 -
Proceedings of the Japan Academy.... 2010We have demonstrated that in rats activities of various enzymes related to gluconeogenesis and amino acid metabolism show circadian rhythms. Based on these results, we... (Review)
Review
We have demonstrated that in rats activities of various enzymes related to gluconeogenesis and amino acid metabolism show circadian rhythms. Based on these results, we have explored the molecular mechanisms underlying circadian oscillation and phase response to light of the master clock located in the dorsomedial subdivision of the suprachiasmatic nucleus (SCN) and found various proteins closely related to phase response such as BIT/SHPS-1 and those of circadian oscillation, some of which are involved in protein-tyrosine phosphorylation.On the other hand, we have presented several lines of evidence that the ventrolateral subdivision of the SCN includes not only the control center of energy supply to the brain, but also that of homeostasis such as blood glucose, blood pressure, water balance, and body temperature. We have also shown that besides these functions, the latter subdivision is involved in the regulations of hormone secretions such as insulin, glucagon, corticosterone and vasopressin. It has been also shown by electrophysiological means that light exposure to rat eye enhances sympathetic nerve activity, whereas it depresses parasympathetic nerve activity. Thus, environmental light is implicated not only in the phase-shift through the retinohypthalamic tract (RHT), but also control of autonomic nerve activities through the RHT, It is also discussed in this review how the two divisions are interconnected and how environmental light is involved in this interconnection.
Topics: Animals; Autonomic Nervous System; Circadian Rhythm; Eating; Homeostasis; Humans; Light; Suprachiasmatic Nucleus
PubMed: 20431263
DOI: 10.2183/pjab.86.391 -
EBioMedicine Jan 2022Exposure to light affects our physiology and behaviour through a pathway connecting the retina to the circadian pacemaker in the hypothalamus - the suprachiasmatic... (Review)
Review
Exposure to light affects our physiology and behaviour through a pathway connecting the retina to the circadian pacemaker in the hypothalamus - the suprachiasmatic nucleus (SCN). Recent research has identified significant individual differences in the non-visual effects of light,mediated by this pathway. Here, we discuss the fundamentals and individual differences in the non-visual effects of light. We propose a set of actions to improve our evidence database to be more diverse: understanding systematic bias in the evidence base, dedicated efforts to recruit more diverse participants, routine deposition and sharing of data, and development of data standards and reporting guidelines.
Topics: Circadian Rhythm; Humans; Hypothalamus; Individuality; Retina; Suprachiasmatic Nucleus
PubMed: 35027334
DOI: 10.1016/j.ebiom.2021.103640 -
The Neuroscientist : a Review Journal... Aug 2004The hypothalamic suprachiasmatic nucleus (SCN) has a pivotal role in the mammalian circadian clock. SCN neurons generate circadian rhythms in action potential firing... (Review)
Review
The hypothalamic suprachiasmatic nucleus (SCN) has a pivotal role in the mammalian circadian clock. SCN neurons generate circadian rhythms in action potential firing frequencies and neurotransmitter release, and the core oscillation is thought to be driven by "clock gene" transcription-translation feedback loops. Cytosolic Ca2+ mobilization followed by stimulation of various receptors has been shown to reset the gene transcription cycles in SCN neurons, whereas contribution of steady-state cytosolic Ca2+ levels to the rhythm generation is unclear. Recently, circadian rhythms in cytosolic Ca2+ levels have been demonstrated in cultured SCN neurons. The circadian Ca2+ rhythms are driven by the release of Ca2+ from ryanodine-sensitive internal stores and resistant to the blockade of action potentials. These results raise the possibility that gene translation/transcription loops may interact with autonomous Ca2+ oscillations in the production of circadian rhythms in SCN neurons.
Topics: Animals; CLOCK Proteins; Calcium; Calcium Signaling; Circadian Rhythm; Feedback; Gene Expression Regulation; Genes, Regulator; Humans; Neurons; Suprachiasmatic Nucleus; Trans-Activators
PubMed: 15271259
DOI: 10.1177/10738584031262149 -
Neuron Oct 2021The suprachiasmatic nucleus (SCN) is the master circadian pacemaker in mammals and is entrained by environmental light. However, the molecular basis of the response of...
The suprachiasmatic nucleus (SCN) is the master circadian pacemaker in mammals and is entrained by environmental light. However, the molecular basis of the response of the SCN to light is not fully understood. We used RNA/chromatin immunoprecipitation/single-nucleus sequencing with circadian behavioral assays to identify mouse SCN cell types and explore their responses to light. We identified three peptidergic cell types that responded to light in the SCN: arginine vasopressin (AVP), vasoactive intestinal peptide (VIP), and cholecystokinin (CCK). In each cell type, light-responsive subgroups were enriched for expression of neuronal Per-Arnt-Sim (PAS) domain protein 4 (NPAS4) target genes. Further, mice lacking Npas4 had a longer circadian period under constant conditions, a damped phase response curve to light, and reduced light-induced gene expression in the SCN. Our data indicate that NPAS4 is necessary for normal transcriptional responses to light in the SCN and critical for photic phase-shifting of circadian behavior.
Topics: Animals; Arginine Vasopressin; Basic Helix-Loop-Helix Transcription Factors; Cholecystokinin; Chromatin Immunoprecipitation; Circadian Rhythm; Gene Expression Profiling; Light; Mice; Mice, Knockout; Neurons; Sequence Analysis, RNA; Single-Cell Analysis; Suprachiasmatic Nucleus; Vasoactive Intestinal Peptide
PubMed: 34416169
DOI: 10.1016/j.neuron.2021.07.026 -
Free Radical Biology & Medicine May 2018Oxidation-reduction reactions are essential to life as the core mechanisms of energy transfer. A large body of evidence in recent years presents an extensive and complex... (Review)
Review
Oxidation-reduction reactions are essential to life as the core mechanisms of energy transfer. A large body of evidence in recent years presents an extensive and complex network of interactions between the circadian and cellular redox systems. Recent advances show that cellular redox state undergoes a ~24-h (circadian) oscillation in most tissues and is conserved across the domains of life. In nucleated cells, the metabolic oscillation is dependent upon the circadian transcription-translation machinery and, vice versa, redox-active proteins and cofactors feed back into the molecular oscillator. In the suprachiasmatic nucleus (SCN), a hypothalamic region of the brain specialized for circadian timekeeping, redox oscillation was found to modulate neuronal membrane excitability. The SCN redox environment is relatively reduced in daytime when neuronal activity is highest and relatively oxidized in nighttime when activity is at its lowest. There is evidence that the redox environment directly modulates SCN K channels, tightly coupling metabolic rhythms to neuronal activity. Application of reducing or oxidizing agents produces rapid changes in membrane excitability in a time-of-day-dependent manner. We propose that this reciprocal interaction may not be unique to the SCN. In this review, we consider the evidence for circadian redox oscillation and its interdependencies with established circadian timekeeping mechanisms. Furthermore, we will investigate the effects of redox on ion-channel gating dynamics and membrane excitability. The susceptibility of many different ion channels to modulation by changes in the redox environment suggests that circadian redox rhythms may play a role in the regulation of all excitable cells.
Topics: Animals; Circadian Rhythm; Humans; Ion Channels; Neurons; Oxidation-Reduction; Suprachiasmatic Nucleus
PubMed: 29398284
DOI: 10.1016/j.freeradbiomed.2018.01.025 -
Current Opinion in Neurobiology Oct 2013It has been known since the 1970s that the suprachiasmatic nucleus (SCN) is the brain's main biological clock, and since the 1990s that it uses a genetic clock based on... (Review)
Review
It has been known since the 1970s that the suprachiasmatic nucleus (SCN) is the brain's main biological clock, and since the 1990s that it uses a genetic clock based on transcriptional-translational loops to tell time. However, the recent demonstration that many other cells in the brain and the body also make use of the same genetic clock raises the question of how the SCN synchronizes all of the other clocks to arrive at a coherent circadian profile of physiology and behavior. In this review, we re-examine the evidence that the SCN clock is necessary for bringing order to the body's biological rhythms, and the circuitry of the circadian timing system by which it accomplishes this goal. Finally, we review the evidence that under conditions of restricted food availability, other clocks may be able to take over from the SCN to determine rhythms of behavior and physiology.
Topics: Animals; Brain; Circadian Clocks; Circadian Rhythm; Humans; Suprachiasmatic Nucleus
PubMed: 23706187
DOI: 10.1016/j.conb.2013.04.004 -
The Journal of Endocrinology Jul 2016The suprachiasmatic nucleus (SCN) of the anterior hypothalamus is the master circadian clock that coordinates daily rhythms in behavior and physiology in mammals. Like... (Review)
Review
The suprachiasmatic nucleus (SCN) of the anterior hypothalamus is the master circadian clock that coordinates daily rhythms in behavior and physiology in mammals. Like other hypothalamic nuclei, the SCN displays an impressive array of distinct cell types characterized by differences in neurotransmitter and neuropeptide expression. Individual SCN neurons and glia are able to display self-sustained circadian rhythms in cellular function that are regulated at the molecular level by a 24h transcriptional-translational feedback loop. Remarkably, SCN cells are able to harmonize with one another to sustain coherent rhythms at the tissue level. Mechanisms of cellular communication in the SCN network are not completely understood, but recent progress has provided insight into the functional roles of several SCN signaling factors. This review discusses SCN organization, how intercellular communication is critical for maintaining network function, and the signaling mechanisms that play a role in this process. Despite recent progress, our understanding of SCN circuitry and coupling is far from complete. Further work is needed to map SCN circuitry fully and define the signaling mechanisms that allow for collective timekeeping in the SCN network.
Topics: Animals; Cell Communication; Circadian Clocks; Circadian Rhythm; Nerve Net; Neurons; Signal Transduction; Suprachiasmatic Nucleus
PubMed: 27154335
DOI: 10.1530/JOE-16-0054 -
The Yale Journal of Biology and Medicine Jun 2019Circadian rhythms, or biological oscillations of approximately 24 hours, impact almost all aspects of our lives by regulating the sleep-wake cycle, hormone release, body... (Review)
Review
Circadian rhythms, or biological oscillations of approximately 24 hours, impact almost all aspects of our lives by regulating the sleep-wake cycle, hormone release, body temperature fluctuation, and timing of food consumption. The molecular machinery governing these rhythms is similar across organisms ranging from unicellular fungi to insects, rodents, and humans. Circadian entrainment, or temporal synchrony with one's environment, is essential for survival. In mammals, the central circadian pacemaker is located in the suprachiasmatic nucleus (SCN) of the hypothalamus and mediates entrainment to environmental conditions. While the light:dark cycle is the primary environmental cue, arousal-inducing, non-photic signals such as food consumption, exercise, and social interaction are also potent synchronizers. Many of these stimuli enhance dopaminergic signaling suggesting that a cohesive circadian physiology depends on the relationship between circadian clocks and the neuronal circuits responsible for detecting salient events. Here, we review the inner workings of mammalian circadian entrainment, and describe the health consequences of circadian rhythm disruptions with an emphasis on dopamine signaling.
Topics: Animals; Circadian Clocks; Circadian Rhythm; Dopamine; Dopaminergic Neurons; Humans; Photoperiod; Signal Transduction; Suprachiasmatic Nucleus
PubMed: 31249488
DOI: No ID Found