scholarly journals Mechanisms of Communication in the Mammalian Circadian Timing System

2019 ◽  
Vol 20 (2) ◽  
pp. 343 ◽  
Author(s):  
Mariana Astiz ◽  
Isabel Heyde ◽  
Henrik Oster
Keyword(s):  
Current Knowledge ◽  
The Body ◽  
Dark Cycle ◽  
Timing System ◽  
Circadian Timing System ◽  
Neuroendocrine Mechanisms ◽  
Peripheral Clocks ◽  
Central Pacemaker ◽  
And Function ◽  
Therapeutic Settings

24-hour rhythms in physiology and behaviour are organized by a body-wide network of endogenous circadian clocks. In mammals, a central pacemaker in the hypothalamic suprachiasmatic nucleus (SCN) integrates external light information to adapt cellular clocks in all tissues and organs to the external light-dark cycle. Together, central and peripheral clocks co-regulate physiological rhythms and functions. In this review, we outline the current knowledge about the routes of communication between the environment, the main pacemakers and the downstream clocks in the body, focusing on what we currently know and what we still need to understand about the communication mechanisms by which centrally and peripherally controlled timing signals coordinate physiological functions and behaviour. We highlight recent findings that shed new light on the internal organization and function of the SCN and neuroendocrine mechanisms mediating clock-to-clock coupling. These findings have implications for our understanding of circadian network entrainment and for potential manipulations of the circadian clock system in therapeutic settings.

Transient circadian internal desynchronization after light-dark phase shift in monkeys

1977 ◽  
Vol 232 (1) ◽  
pp. R31-R37 ◽  
Author(s):  
M. C. Moore-Ede ◽  
D. A. Kass ◽  
J. A. Herd
Keyword(s):  
Body Temperature ◽  
Saimiri Sciureus ◽  
Cycle Phase ◽  
Dark Phase ◽  
Dark Cycle ◽  
Water Excretion ◽  
Urinary Potassium ◽  
Timing System ◽  
Internal Desynchronization ◽  
Circadian Timing System

In four conscious chair-acclimatized squirrel monkeys (Saimiri sciureus) studied with lights on (600 lx) from 0800 to 2000 h daily (LD 12:12), prominent 24-h rhythms in feeding, drinking, activity, body temperature, and urinary potassium, sodium, and water excretion were seen. When the monkeys were subjected to 36 h of darkness followed by 36 h of light each variable demonstrated a circadian rhythm which was not passively dependent on the light-dark cycle. After the 24-h light-dark cycle was abruptly phase-delayed by 8 h, all the rhythms resynchronized with the new light-dark cycle phase, demonstrating that light-dark cycles are an effective zeitgeber. However, the resynchronization of the rhythms of feeding, drinking, activity, and body temperature was 90% complete within approximately 2 days while the 90% resynchronization of the urinary rhythms took approximately 5 days. These results suggest that the circadian timing system in S. sciureus may consist of several spontaneously oscillating units which can become transiently uncoupled during pertubations of environmental time cues.

Cortisol-mediated synchrinization of circadian rhythm in urinary potassium excretion

1977 ◽  
Vol 233 (5) ◽  
pp. R230-R238 ◽  
Author(s):  
M. C. Moore-ede ◽  
W. S. Schmelzer ◽  
D. A. Kass ◽  
J. A. Herd
Keyword(s):  
Circadian Rhythm ◽  
Saimiri Sciureus ◽  
Potassium Excretion ◽  
Dark Cycle ◽  
Urinary Potassium ◽  
Timing System ◽  
Daily Dose ◽  
Circadian Timing System ◽  
Free Running ◽  
Renal Potassium Excretion

Conscious chair-acclimatized squirrel monkeys (Saimiri sciureus) studied with lights on (600 lx) from 0800 to 2000 h daily (LD 12:12) display a prominent circadian rhythm in renal potassium excretion. The characteristics of this rhythm were reproduced in adrenalectomized monkeys by infusing 5 mg cortisol and 0.001 mg aldosterone, or 5 mg cortisol alone, between 0800 and 0900 h daily. When the timing of cortisol adminisration (with or without aldosterone) was phase-delayed by 8 h, the urinary potassium rhythm resynchronized by 80% of the cortisol phase shift, but only after a transient response lasting 3–4 days. With the same daily dose of adrenal steroids given as a continuous infusion throughout each 24 h, urinary potassium excretion showed free-running oscillations no longer synchronized to the light-dark cycle. These results indicate that the cirdacian rhythm of plasma cortisol concentration acts as an internal mediator in the circadian timing system, synchronizing a potentially autonomous oscillation in renal potassium excretion to environmental time cues and to other circadian rhythms within the animal.

scholarly journals Vascular Endothelial Cell Biology: An Update

2019 ◽  
Vol 20 (18) ◽  
pp. 4411 ◽  
Author(s):  
Krüger-Genge ◽  
Blocki ◽  
Franke ◽  
Jung
Keyword(s):  
Endothelial Cells ◽  
Cell Biology ◽  
Current Knowledge ◽  
Regional Blood Flow ◽  
Vascular Endothelial Cell ◽  
Inflammatory Cells ◽  
The Body ◽  
Arterial Tree ◽  
Foreign Materials ◽  
And Function

The vascular endothelium, a monolayer of endothelial cells (EC), constitutes the inner cellular lining of arteries, veins and capillaries and therefore is in direct contact with the components and cells of blood. The endothelium is not only a mere barrier between blood and tissues but also an endocrine organ. It actively controls the degree of vascular relaxation and constriction, and the extravasation of solutes, fluid, macromolecules and hormones, as well as that of platelets and blood cells. Through control of vascular tone, EC regulate the regional blood flow. They also direct inflammatory cells to foreign materials, areas in need of repair or defense against infections. In addition, EC are important in controlling blood fluidity, platelet adhesion and aggregation, leukocyte activation, adhesion, and transmigration. They also tightly keep the balance between coagulation and fibrinolysis and play a major role in the regulation of immune responses, inflammation and angiogenesis. To fulfill these different tasks, EC are heterogeneous and perform distinctly in the various organs and along the vascular tree. Important morphological, physiological and phenotypic differences between EC in the different parts of the arterial tree as well as between arteries and veins optimally support their specified functions in these vascular areas. This review updates the current knowledge about the morphology and function of endothelial cells, particularly their differences in different localizations around the body paying attention specifically to their different responses to physical, biochemical and environmental stimuli considering the different origins of the EC.

scholarly journals Entrainment of peripheral clock genes by cortisol

2012 ◽  
Vol 44 (11) ◽  
pp. 607-621 ◽  
Author(s):  
Panteleimon D. Mavroudis ◽  
Jeremy D. Scheff ◽  
Steve E. Calvano ◽  
Stephen F. Lowry ◽  
Ioannis P. Androulakis
Keyword(s):  
Clock Genes ◽  
Dynamic Regime ◽  
The Body ◽  
Molecular Function ◽  
Frequency Range ◽  
Peripheral Tissues ◽  
Peripheral Clock ◽  
Peripheral Clocks ◽  
Central Pacemaker ◽  
Peripheral Cells

Circadian rhythmicity in mammals is primarily driven by the suprachiasmatic nucleus (SCN), often called the central pacemaker, which converts the photic information of light and dark cycles into neuronal and hormonal signals in the periphery of the body. Cells of peripheral tissues respond to these centrally mediated cues by adjusting their molecular function to optimize organism performance. Numerous systemic cues orchestrate peripheral rhythmicity, such as feeding, body temperature, the autonomic nervous system, and hormones. We propose a semimechanistic model for the entrainment of peripheral clock genes by cortisol as a representative entrainer of peripheral cells. This model demonstrates the importance of entrainer's characteristics in terms of the synchronization and entrainment of peripheral clock genes, and predicts the loss of intercellular synchrony when cortisol moves out of its homeostatic amplitude and frequency range, as has been observed clinically in chronic stress and cancer. The model also predicts a dynamic regime of entrainment, when cortisol has a slightly decreased amplitude rhythm, where individual clock genes remain relatively synchronized among themselves but are phase shifted in relation to the entrainer. The model illustrates how the loss of communication between the SCN and peripheral tissues could result in desynchronization of peripheral clocks.

scholarly journals The Hepatic Monocarboxylate Transporter 1 (MCT1) Contributes to the Regulation of Food Anticipation in Mice

2021 ◽  
Vol 12 ◽  
Author(s):  
Tomaz Martini ◽  
Jürgen A. Ripperger ◽  
Rohit Chavan ◽  
Michael Stumpe ◽  
Citlalli Netzahualcoyotzi ◽  
...  
Keyword(s):  
Food Restriction ◽  
Ketone Bodies ◽  
Cell Types ◽  
Time Of Day ◽  
Monocarboxylate Transporter ◽  
Monocarboxylate Transporter 1 ◽  
Circadian Timing System ◽  
Peripheral Clocks ◽  
Anticipatory Activity ◽  
Central Pacemaker

Daily recurring events can be predicted by animals based on their internal circadian timing system. However, independently from the suprachiasmatic nuclei (SCN), the central pacemaker of the circadian system in mammals, restriction of food access to a particular time of day elicits food anticipatory activity (FAA). This suggests an involvement of other central and/or peripheral clocks as well as metabolic signals in this behavior. One of the metabolic signals that is important for FAA under combined caloric and temporal food restriction is β-hydroxybutyrate (βOHB). Here we show that the monocarboxylate transporter 1 (Mct1), which transports ketone bodies such as βOHB across membranes of various cell types, is involved in FAA. In particular, we show that lack of the Mct1 gene in the liver, but not in neuronal or glial cells, reduces FAA in mice. This is associated with a reduction of βOHB levels in the blood. Our observations suggest an important role of ketone bodies and its transporter Mct1 in FAA under caloric and temporal food restriction.

scholarly journals Impact of nutrients on circadian rhythmicity

2015 ◽  
Vol 308 (5) ◽  
pp. R337-R350 ◽  
Author(s):  
Johanneke E. Oosterman ◽  
Andries Kalsbeek ◽  
Susanne E. la Fleur ◽  
Denise D. Belsham
Keyword(s):  
Circadian Rhythms ◽  
Circadian Clock ◽  
The Body ◽  
Circadian Rhythmicity ◽  
Energy Status ◽  
Peripheral Oscillators ◽  
Peripheral Clocks ◽  
Central Pacemaker ◽  
Almost All ◽  
The Impact

The suprachiasmatic nucleus (SCN) in the mammalian hypothalamus functions as an endogenous pacemaker that generates and maintains circadian rhythms throughout the body. Next to this central clock, peripheral oscillators exist in almost all mammalian tissues. Whereas the SCN is mainly entrained to the environment by light, peripheral clocks are entrained by various factors, of which feeding/fasting is the most important. Desynchronization between the central and peripheral clocks by, for instance, altered timing of food intake can lead to uncoupling of peripheral clocks from the central pacemaker and is, in humans, related to the development of metabolic disorders, including obesity and Type 2 diabetes. Diets high in fat or sugar have been shown to alter circadian clock function. This review discusses the recent findings concerning the influence of nutrients, in particular fatty acids and glucose, on behavioral and molecular circadian rhythms and will summarize critical studies describing putative mechanisms by which these nutrients are able to alter normal circadian rhythmicity, in the SCN, in non-SCN brain areas, as well as in peripheral organs. As the effects of fat and sugar on the clock could be through alterations in energy status, the role of specific nutrient sensors will be outlined, as well as the molecular studies linking these components to metabolism. Understanding the impact of specific macronutrients on the circadian clock will allow for guidance toward the composition and timing of meals optimal for physiological health, as well as putative therapeutic targets to regulate the molecular clock.

Mammalian clock output mechanisms

2011 ◽  
Vol 49 ◽  
pp. 137-151 ◽  
Author(s):  
Andries Kalsbeek ◽  
Chun-Xia Yi ◽  
Cathy Cailotto ◽  
Susanne E. la Fleur ◽  
Eric Fliers ◽  
...  
Keyword(s):  
Biological Clock ◽  
Endocrine System ◽  
Plasma Corticosterone ◽  
The Body ◽  
Hormone Release ◽  
Corticosterone Concentration ◽  
Timing System ◽  
Endogenous Rhythmicity ◽  
Peripheral Clocks ◽  
Specialized Organization

In mammals many behaviours (e.g. sleep–wake, feeding) as well as physiological (e.g. body temperature, blood pressure) and endocrine (e.g. plasma corticosterone concentration) events display a 24 h rhythmicity. These 24 h rhythms are induced by a timing system that is composed of central and peripheral clocks. The highly co-ordinated output of the hypothalamic biological clock not only controls the daily rhythm in sleep–wake (or feeding–fasting) behaviour, but also exerts a direct control over many aspects of hormone release and energy metabolism. First, we present the anatomical connections used by the mammalian biological clock to enforce its endogenous rhythmicity on the rest of the body, especially the neuro-endocrine and energy homoeostatic systems. Subsequently, we review a number of physiological experiments investigating the functional significance of this neuro-anatomical substrate. Together, this overview of experimental data reveals a highly specialized organization of connections between the hypothalamic pacemaker and neuro-endocrine system as well as the pre-sympathetic and pre-parasympathetic branches of the autonomic nervous system.

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