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Encyclopedia > Circadian rhythm

A circadian rhythm is an approximate daily periodicity, a roughly-24-hour cycle in the biochemical, physiological or behavioral processes of living beings, including plants, animals, fungi and cyanobacteria. The term "circadian", coined by Franz Halberg,[1] comes from the Latin circa, "around", and diem or dies, "day", meaning literally "approximately one day." The formal study of biological temporal rhythms such as daily, tidal, weekly, seasonal, and annual rhythms, is called chronobiology. For other uses, see Plant (disambiguation). ... For other uses, see Animal (disambiguation). ... Divisions Chytridiomycota Zygomycota Ascomycota Basidiomycota The Fungi (singular: fungus) are a large group of organisms ranked as a kingdom within the Domain Eukaryota. ... Orders The taxonomy is currently under revision. ... Franz Halberg is a scientist and the founder of modern chronobiology. ... For other uses, see Latins and Latin (disambiguation). ... Look up Circa on Wiktionary, the free dictionary The Latin word circa, literally meaning about, is often used to describe various dates (often birth and death dates) that are uncertain. ... This article is about tides in the Earths oceans. ... Chronobiology is a field of science that examines periodic (cyclic) phenomena in living organisms. ...


In a strict sense, circadian rhythms are endogenously generated, although they can be modulated by external cues, primarily daylight. They allow organisms to anticipate and prepare for precise and regular environmental changes. Look up Endogenous in Wiktionary, the free dictionary. ... Look up daylight in Wiktionary, the free dictionary. ...

Contents

History

The first endogenous circadian oscillation was observed in the 1700s by the French scientist Jean-Jacques d'Ortous de Mairan who noticed that 24-hour patterns in the movement of the leaves of the plant Mimosa pudica continued even when the plants were isolated from external stimuli. Jean-Jacques dOrtous de Mairan (November 26, 1678 – February 20, 1771) was a French geophysicist. ... Binomial name L. The Sensitive plant (Mimosa pudica L.) is a creeping annual or perennial herb often grown for its curiosity value: the compound leaves fold inward and droop when touched, re-opening within minutes. ...


In 1918 J. S. Szymanski showed that animals are capable of maintaining 24-hour activity patterns in the absence of external cues such as light and changes in temperature.[2]


The earliest known account of a circadian rhythm dates from the fourth century BC, when Androsthenes, in descriptions of the marches of Alexander the Great, described diurnal leaf movements of the tamarind tree. Diurnal may mean: in biology, a diurnal animal is an animal that is active in the daytime. ...


Criteria

Three general criteria of circadian rhythms are necessary to differentiate genuinely endogenous rhythms from coincidental or apparent ones: the rhythms persist in the absence of cues, they can be brought to match the local time, and will do so in a precise manner over a range of temperatures.

  • The rhythm persists in constant conditions (for example, constant dark) with a period of about 24 hours. The rationale for this criterion is to distinguish circadian rhythms from those "apparent" rhythms which merely are responses to external periodic cues. A rhythm cannot be declared to be endogenous unless it has been tested in conditions without external periodic input.
  • The rhythm is temperature-compensated, i.e. it maintains the same period over a range of temperatures. The rationale for this criterion is to distinguish circadian rhythms from other biological rhythms arising due to the circular nature of a reaction pathway. At a low enough or high enough temperature, the period of a circular reaction may reach 24 hours, but it will be merely coincidental.
  • The rhythm can be reset by exposure to an external stimulus. The rationale for this criterion is to distinguish circadian rhythms from other imaginable endogenous 24-hour rhythms that are immune to resetting by external cues and hence do not serve the purpose of estimating the local time. Travel across time zones illustrates the necessity of the ability to adjust the biological clock so that it can reflect the local time and anticipate what will happen next.

Timezone and TimeZone redirect here. ...

Origin

Photosensitive proteins and circadian rhythms are believed to have originated in the earliest cells, with the purpose of protecting the replicating of DNA from high ultraviolet radiation during the daytime. As a result, replication was relegated to the dark. The fungus Neurospora, which exists today, retains this clock-regulated mechanism. Rhythmicity appears to be as important in regulating cyclic biochemical processes within an individual, as in coordinating with the environment. This is suggested by the maintenance (heritability) of circadian rhythms in fruit flies after several hundred generations in constant laboratory conditions (Sheeba et al. 1999), as well as the experimental elimination of behavioral but not physiological circadian rhythms in quail (Guyomarc'h et al. 1998, Zivkovic et al. 1999). For other uses, see Ultraviolet (disambiguation). ... Species N. crassa N. intermedia N. sitophila N. tetrasperma Neurospora is a genus of fungi. ...


The simplest known circadian clock is that of the prokaryotic cyanobacteria. Recent research has demonstrated that the circadian clock of Synechococcus elongatus can be reconstituted in vitro with just the three proteins of their central oscillator. This clock has been shown to sustain a 22-hour rhythm over several days upon the addition of ATP. Previous explanations of the prokaryotic circadian timekeeper were dependent upon a DNA transcription / translation feedback mechanism. It is an outstanding question whether circadian clocks in eukaryotic organisms require translation/transcription-derived oscillations. For although the circadian systems of eukaryotes and prokaryotes have the same basic architecture: input - central oscillator - output, they do not share any homology. This implies probable independent origins. Orders The taxonomy is currently under revision. ... Adenosine 5-triphosphate (ATP) is a multifunctional nucleotide that is most important as a molecular currency of intracellular energy transfer. ... Prokaryotes are unicellular (in rare cases, multicellular) organisms without a nucleus. ...


In 1971, Konopka and Benzer first identified a genetic component of the biological clock using the fruit fly as a model system. Three mutant lines of flies displayed aberrant behavior - one had a shorter period, another had a longer one and the third had none. All three mutations mapped to the same gene, which was named period.[3] The same gene was identified to be defective in the sleep disorder FASPS (Familial Advanced Sleep Phase Syndrome) in human beings thirty years later - underscoring the conserved nature of the molecular circadian clock through evolution. We now know many more genetic components of the biological clock. Their interactions result in an interlocked feedback loop of gene products resulting in periodic fluctuations that the cells of the body interpret as a specific time of the day.


A great deal of research on biological clocks was done in the last half of the 20th century. It is now known that the molecular circadian clock can function within a single cell; i.e., it is cell-autonomous.[4] At the same time, different cells may communicate with each other resulting in a synchronized output of electrical signaling. These may interface with endocrine glands of the brain to result in periodic release of hormones. The receptors for these hormones may be located far across the body and synchronize the peripheral clocks of various organs. Thus, the information of the time of the day as relayed by the eyes travels to the clock in the brain, and, through that, clocks in the rest of the body may be synchronized. This is how the timing of, for example, sleep/wake, body temperature, thirst, and appetite are coordinately controlled by the biological clock. For other uses, see Eye (disambiguation). ...


Importance in animals

Circadian rhythms are important in determining the sleeping and feeding patterns of all animals, including human beings. There are clear patterns of core body temperature, brain wave activity, hormone production, cell regeneration and other biological activities linked to this daily cycle. In addition, photoperiodism, the physiological reaction of organisms to the length of day or night, is vital to both plants and animals, and the circadian system plays a role in the measurement and interpretation of daylength. For other uses, see Sleep (disambiguation). ... Electroencephalography is the neurophysiologic exploration of the electrical activity of the brain by the application of electrodes to the scalp. ... For other uses, see Hormone (disambiguation). ... Photoperiodicity is the physiological reaction of organisms to the length of day or night. ...

«Timely prediction of seasonal periods of weather conditions, food availability or predator activity is crucial for survival of many species. Although not the only parameter, the changing length of the photoperiod ('daylength') is the most predictive environmental cue for the seasonal timing of physiology and behavior, most notably for timing of migration, hibernation and reproduction.»[5]

Impact of light-dark cycle

The rhythm is linked to the light-dark cycle. Animals, including humans, kept in total darkness for extended periods eventually function with a freerunning rhythm. Each "day," their sleep cycle is pushed back or forward, depending on whether their endogenous period is shorter or longer than 24 hours. The environmental cues that each day reset the rhythms are called Zeitgebers (from the German, Time Givers).[6] It is interesting to note that totally-blind subterranean mammals (e.g., blind mole rat Spalax sp.) are able to maintain their endogenous clocks in the apparent absence of external stimuli. Free-running sleep is sleep that is not artificially regulated. ... Zeitgebers are environmental cues that usually help keep the circadian cycle. ...


Freerunning organisms that normally have one consolidated sleep episode will still have it when in an environment shielded from external cues, but the rhythm is, of course, not entrained to the 24-hour light/dark cycle in nature. The sleep/wake rhythm may, in these circumstances, become out of phase with other circadian or ultradian rhythms such as temperature and digestion.[citation needed] Recent research has influenced the design of spacecraft environments, as systems that mimic the light/dark cycle have been found to be highly beneficial to astronauts. Ultradians are the regular recurrence in cycles of less than 24 hours from one stated point to another, as certain biologic activities which occur at such intervals, regardless of conditions of illumination. ... For other uses, see Temperature (disambiguation). ... For the industrial process, see anaerobic digestion. ... Edward White on a spacewalk during the Gemini 4 mission. ...


Arctic animals

Norwegian researchers at the University of Tromsø have shown that some Arctic animals (ptarmigan, reindeer) show circadian rhythms only in the parts of the year that have daily sunrises and sunsets. In one study of reindeer, animals at 70 degrees North showed circadian rhythms in the autumn, winter, and spring, but not in the summer. Reindeer at 78 degrees North showed such rhythms only autumn and spring. The researchers suspect that other Arctic animals as well may not show circadian rhythms in the constant light of summer and the constant dark of winter.[7][8] The University of Tromsø (Universitetet i Tromsø) is the worlds northernmost university. ... Binomial name Lagopus mutus (Montin, 1781) The Ptarmigan (Lagopus mutus) is a small (31-35 cm) bird in the grouse family. ... Caribou redirects here. ...


However, another study in northern Alaska found that ground squirrels and porcupines strictly maintained their circadian rhythms through 82 days and nights of sunshine. The researchers speculate that these two small mammals see that the apparent distance between the sun and the horizon is shortest once a day, and, thus, a sufficient signal to adjust by.[9] Genera Ammospermophilus Spermophilus Cynomys Marmota Tamias Sciurotamias The ground squirrels are all members of the Sciuridae most closely related to the genus Marmota and included in the tribe Marmotini. ... This article is about the rodent mammal. ...


The biological clock

The primary circadian "clock" in mammals is located in the suprachiasmatic nucleus (or nuclei) (SCN), a pair of distinct groups of cells located in the hypothalamus. Destruction of the SCN results in the complete absence of a regular sleep/wake rhythm. The SCN receives information about illumination through the eyes. The retina of the eyes contains not only "classical" photoreceptors but also photoresponsive retinal ganglion cells. These cells, which contain a photo pigment called melanopsin, follow a pathway called the retinohypothalamic tract, leading to the SCN. If cells from the SCN are removed and cultured, they maintain their own rhythm in the absence of external cues. Subclasses & Infraclasses Subclass †Allotheria* Subclass Prototheria Subclass Theria Infraclass †Trituberculata Infraclass Metatheria Infraclass Eutheria For the folk-rock band see The Mammals. ... The suprachiasmatic nucleus (SCN) is a region of the brain, located in the hypothalamus, that is responsible for controlling endogenous circadian rhythms. ... Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the... The hypothalamus links the nervous system to the endocrine system via the pituitary gland (hypophysis). ... Human eye cross-sectional view. ... A photoreceptor, or photoreceptor cell, is a specialized type of neuron found in the eyes retina that is capable of phototransduction. ... A Ganglion Cell (or sometimes called a gangliocyte) is a type of Neuron located in the retina that receives visual information from bipolar cells; its axons give rise to the optic nerve. ... Melanopsin is a photopigment found in specialized ganglion cells of the retina that are involved in the regulation of circadian rhythms and pupillary reflex. ... The Retinohypothalamic tract (RHT) is a photic input pathway involved in circadian rhythms. ...


It appears that the SCN takes the information on day length from the retina, interprets it, and passes it on to the pineal gland, a tiny structure shaped like a pine cone and located on the epithalamus. In response the pineal secretes the hormone melatonin. Secretion of melatonin peaks at night and ebbs during the day. The pineal gland (also called the pineal body or epiphysis) is a small endocrine gland in the brain. ... A cone (in formal botanical usage: strobilus, plural strobili) is an organ on plants in the division Pinophyta (conifers) that contains the reproductive structures. ... The epithalamus is a dorsal posterior segment of the diencephalon (a segment in the middle of the brain also containing the hypothalamus and the thalamus) which includes the habenula, the stria medullaris and the pineal body. ... Melatonin, 5-methoxy-N-acetyltryptamine, is a hormone found in all living creatures from algae[1] to humans, at levels that vary in a diurnal cycle. ...


The circadian rhythms of humans can be entrained to slightly shorter and longer periods than the earth's 24 hours. Researchers at Harvard have recently shown that human subjects can at least be entrained to a 23.5-hour cycle and a 24.65-hour cycle (the latter being the natural solar day-night cycle on the planet Mars).[10] Adjectives: Martian Atmosphere Surface pressure: 0. ...


Determining the human circadian rhythm

Overview of human circadian biological clock with some physiological parameters.
Overview of human circadian biological clock with some physiological parameters.

The classic phase markers for measuring the timing of a mammal's circadian rhythm are melatonin secretion by the pineal gland and core body temperature.


For temperature studies, people must remain awake but calm and semi-reclined in near darkness while their rectal temperatures are taken continuously. The average human adult's temperature reaches its minimum at about 05:00 (5 a.m.), about two hours before habitual wake time, though variation is great among normal chronotypes. Chronotype is an attribute of human beings reflecting whether they are alert and prefer to be active early or late in the day. ...


Melatonin is absent from the system or undetectably low during daytime. Its onset in dim light, dim-light melatonin onset (DLMO), at about 21:00 (9 p.m.) can be measured in the blood or the saliva. Both DLMO and the midpoint (in time) of the presence of the hormone in the blood or saliva have been used as circadian markers.


However, newer research indicates that the melatonin offset may be the most reliable marker. Benloucif et al in Chicago in 2005 found that melatonin phase markers were more stable and more highly correlated with the timing of sleep than the core temperature minimum. They found that both sleep offset and melatonin offset were more strongly correlated with the various phase markers than sleep onset. In addition, the declining phase of the melatonin levels was more reliable and stable than the termination of melatonin synthesis.[11]


One method used for measuring melatonin offset is to analyze a sequence of urine samples throughout the morning for the presence of the melatonin metabolite 6-sulphatoxymelatonin (aMT6s). Laberge et al in Quebec in 1997 used this method in a study which confirmed the frequently found delayed circadian phase in healthy adolescents.[12] A metabolite is the product of metabolism. ...


Outside the "master clock"

More-or-less independent circadian rhythms are found in many organs and cells in the body outside the suprachiasmatic nuclei (SCN), the "master clock." These clocks, called peripheral oscillators, are found in the esophagus, lung, liver, pancreas, spleen, thymus and the skin [13] . Though oscillators in the skin respond to light, a systemic influence has not been proven so far [14][15]. There is some evidence that also the olfactory bulb and prostate may experience oscillations when cultured, suggesting that also these structures may be weak oscillators.


Furthermore, liver cells, for example, appear to respond to feeding rather than to light. Cells from many parts of the body appear to have freerunning rhythms. The liver is the largest internal organ in the human body, and is an organ present in vertebrates and some other animals. ... For other uses, see Light (disambiguation). ...


Light and the biological clock

Light resets the biological clock in accordance with the phase response curve (PRC). Depending on the timing, light can advance or delay the circadian rhythm. Both the PRC and the required illuminance vary from species to species; much lower light levels are required to reset the clocks in nocturnal rodents than in humans. Phase response curve (PRC) illustrates the relationship between the timing of administration of a sleep phase affecting drug or treatment, and the effect on the sleep phase (a/k/a sleep timing). ... Illuminance is the total luminous flux incident per unit area. ...


In addition to light intensity, wavelength (or color) of light is an important factor in the degree to which the clock is reset. Melanopsin is most efficiently excited by blue light, 420-440 nm[16] according to some researchers while others have reported 470-485nm. Melanopsin is a photopigment found in specialized ganglion cells of the retina that are involved in the regulation of circadian rhythms and pupillary reflex. ...


The myth of the 25-hour day

Early investigators determined the human circadian period to be 25 hours or more. They went to great lengths to shield subjects from time cues and daylight, but they were not aware of the effects of indoor electric lights. The subjects were allowed to turn on light when they were awake and to turn it off when they wanted to sleep. Electric light in the evening delayed their circadian phase. These results became well known.[17]


The human circadian period

Modern research under very controlled conditions has shown the human period for adults to be just slightly longer than 24 hours on average. Czeisler et al at Harvard found the range for normal, healthy adults of all ages to be quite narrow: 24 hours and 11 minutes ± 16 minutes. The "clock" resets itself daily to the 24-hour cycle of the earth's rotation.[17]


Human health

There are many health problems associated with a disturbance in the human circadian rhythm, such as Seasonal Affective Disorder (SAD), delayed sleep phase syndrome (DSPS) and other circadian rhythm disorders.[18] Circadian rhythms also play a part in the reticular activating system which is crucial for maintaining a state of consciousness. Light therapy lamp for Seasonal Affective Disorder Seasonal affective disorder, also known as winter depression, is an affective, or mood, disorder. ... Delayed sleep-phase syndrome (DSPS) is a chronic disorder of sleep timing. ... The reticular activating system is the name given to part of the brain (the Reticular Formation and its connections) believed to be the centre of arousal and motivation in animals (including humans). ...


Disruption

Disruption to rhythms usually has a negative effect. Many travelers have experienced the condition known as jet lag, with its associated symptoms of fatigue, disorientation and insomnia. Jet lag (or jet-lag) is a physical condition caused by crossing multiple time zones during flight. ... The word fatigue is used in everyday living to describe a range of afflictions, varying from a general state of lethargy to a specific work induced burning sensation within muscle. ... This article is about the sleeping disorder. ...


A number of other disorders, for example bipolar disorder and some sleep disorders, are associated with irregular or pathological functioning of circadian rhythms. Recent research suggests that circadian rhythm disturbances found in bipolar disorder are positively influenced by lithium's effect on clock genes.[19] For other uses, see Bipolar. ... For other uses, see Bipolar. ... This article is about the chemical element. ...


Disruption to rhythms in the longer term is believed to have significant adverse health consequences on peripheral organs outside the brain, particularly in the development or exacerbation of cardiovascular disease. Timing of medical treatment in coordination with the body clock may significantly increase efficacy and reduce drug toxicity or adverse reactions. For example, appropriately timed treatment with angiotensin converting enzyme inhibitors (ACEi) may reduce nocturnal blood pressure and also benefit left ventricular (reverse) remodeling. Captopril, the first ACE inhibitor ACE inhibitors, or inhibitors of Angiotensin-Converting Enzyme, are a group of pharmaceuticals that are used primarily in treatment of hypertension and congestive heart failure, in most cases as the drugs of first choice. ... The left ventricle is one of four chambers (two atria and two ventricles) in the human heart. ...


Shift work, particularly the night shift, has in December 2007 been listed by the World Health Organization (WHO) as a "probable cause" of cancer.[20] Second shift redirects here. ... WHO redirects here. ...


Effects on cocaine sensitization in mice

Circadian rhythms and clock genes expressed in brain regions outside the SCN may significantly influence the effects produced by drugs such as cocaine.[21][22] Moreover, genetic manipulations of clock genes profoundly affect cocaine's actions.[23] For other uses, see Cocaine (disambiguation). ...


See also

Actigraphy is a method of study of circadian rhythm and wake-sleep patterns. ... Advanced sleep phase syndrome (ASPS) is a sleep disorder in which patients feel very sleepy early in the evening (e. ... RNA expression pattern Orthologs Human Mouse Entrez Ensembl Uniprot Refseq Location Pubmed search Aryl hydrocarbon receptor nuclear translocator-like, also known as ARNTL, Bmal1, or Mop3, is a gene. ... Chronobiology is a field of science that examines periodic (cyclic) phenomena in living organisms. ... Chronotype is an attribute of human beings reflecting whether they are alert and prefer to be active early or late in the day. ... Circadian rhythm sleep disorders are a family of sleep disorders affecting the timing of sleep. ... Cryptochrome is a name used historically for the blue light photoreceptors of plants. ... Expression pattern Orthologs Human Mouse Entrez Ensembl Uniprot Refseq Location Pubmed search Cryptochrome 1 (photolyase-like), also known as CRY1, is a human gene. ... RNA expression pattern Orthologs Human Mouse Entrez Ensembl Uniprot Refseq Location Pubmed search Cryptochrome 2 (photolyase-like), also known as CRY2, is a human gene. ... Jet lag (or jet-lag) is a physical condition caused by crossing multiple time zones during flight. ... RNA expression pattern Orthologs Human Mouse Entrez Ensembl Uniprot Refseq Location Pubmed search Period homolog 1 (Drosophila), also known as PER1, is a human gene. ... RNA expression pattern Orthologs Human Mouse Entrez Ensembl Uniprot Refseq Location Pubmed search Period homolog 2 (Drosophila), also known as PER2, is a human gene. ... RNA expression pattern Orthologs Human Mouse Entrez Ensembl Uniprot Refseq Location Pubmed search Period homolog 3 (Drosophila), also known as PER3, is a human gene. ...

Notes

  1. ^ http://www.msi.umn.edu/~halberg Halberg Chronobiology Center
  2. ^ Danchin, Antoine. "Important dates 1900-1919". HKU-Pasteur Research Centre. 
  3. ^ Purves, Dale et al [2001]. "Molecular Mechanisms of Biological Clocks", NEUROSCIENCE (e-book), second edition, Sunderland, MA, U.S.A.: Sinauer Associates. ISBN 0-87893-742-0. Retrieved on 2008-05-30. 
  4. ^ Circadian gene expression in individual fibroblast...[Cell. 2004] - PubMed Result
  5. ^ Zivkovic, Bora "Coturnix" (August 13, 2005 / July 25, 2007). Clock Tutorial #16: Photoperiodism - Models and Experimental Approaches. A Blog Around the Clock. ScienceBlogs. Retrieved on 2007-12-09.
  6. ^ Circadian rhythms. Rapid eye movement (REM) sleep. Armenian Medical Network (2007). Retrieved on 2007-09-19.
  7. ^ Spilde, Ingrid. "Reinsdyr uten døgnrytme", forskning.no, December 2005. Retrieved on 2007-11-24. (Language: Norwegian, Bokmål) 
  8. ^ Zivkovic, Bora, aka Coturnix, chronobiologist. Circadian Rhythms, or Not, in Arctic Reindeer. A Blog around the Clock. ScienceBlogs.com. Retrieved on 2007-11-24.
  9. ^ Zivkovic, Bora, aka Coturnix, chronobiologist (February 11, 2007). Small Arctic Mammals Entrain to Something during the Long Summer Day. A Blog Around the Clock. ScienceBlogs.com. Retrieved on 2007-11-26.
  10. ^ Scheer, Frank A. J. L.; Kenneth P. Wright, Jr., Richard E. Kronauer, Charles A. Czeisler (2007-08-08). "Plasticity of the Intrinsic Period of the Human Circadian Timing System". PLoS ONE. 
  11. ^ Benloucif, S.; Guico, M.J.; Reid, K.J.; Wolfe, L.F.; L'Hermite-Baleriaux, M.; Zee, P.C. (2005). "Stability of melatonin and temperature as circadian phase markers and their relation to sleep times in humans.". J Biol Rhythms 20 (2): pages 178-88. Chicago, Illinois, USA: Center for Sleep and Circadian Biology, Departments of Neurology, Northwestern University Feinberg School of Medicine. 
  12. ^ Laberge, L.; Lesperance, P.; Tremblay, R.; Lambert, C.; Montplaisir, J. (1997). "Phase delay of 6-sulphatoxymelatonin in normal adolescents" (in English). Sleep Research 26: p. 727. Québec, Canada: Centre d'etude du Sommeil, Hopital du Sacre-Coeur, Département de Psychologie, Département de Pharmacologie, Departement de Psychiatrie, Université de Montréal. 
  13. ^ Zanello, S. et al., J. Inv. Dermatol. 2000, Vol. 115, 4 Oct.: Expression of the Circadian Clock Genes clock and period1 in Human Skin
  14. ^ Kawara, S. et al. J. Inv. Derm. 2002, Vol 119, 6 Dec.: Low-dose UVB Rays Alter the mRNA Expression of the Circadian Clock Genes in cultured Human Keratinocytes
  15. ^ Campbell, S. and Murphy, P, Science 1998, Vol 279, 16 Jan.: Extraocular Circadian Phototransduction in Humans
  16. ^ Newman LA, Walker MT, Brown RL, Cronin TW, Robinson PR: "Melanopsin forms a functional short-wavelength photopigment", Biochemistry. 2003 Nov 11;42(44):12734-8.
  17. ^ a b Human Biological Clock Set Back an Hour (1999). Retrieved on 2007-09-23.
  18. ^ Circadian Rhythms and Sleep. Circadian Rhythms and Sleep. Serendip (2007). Retrieved on 2007-09-19.
  19. ^ NIMH · Science News from 2006 · Lithium Blocks Enzyme To Help Cells’ Clocks Keep On Tickin’
  20. ^ IARC: Press Release Nr. 180 «Shiftwork that involves circadian disruption is “probably carcinogenic to humans”.»
  21. ^ Uz T, Akhisaroglu M, Ahmed R, Manev H (2003). "The pineal gland is critical for circadian Period1 expression in the striatum and for circadian cocaine sensitization in mice". Neuropsychopharmacology 28 (12): 2117-23. PMID 12865893. 
  22. ^ Kurtuncu M, Arslan A, Akhisaroglu M, Manev H, Uz T (2004). "Involvement of the pineal gland in diurnal cocaine reward in mice". Eur J Pharmacol 489 (3): 203-5. doi:10.1016/j.ejphar.2004.03.010. PMID 15087244. 
  23. ^ McClung C, Sidiropoulou K, Vitaterna M, Takahashi J, White F, Cooper D, Nestler E (2005). "Regulation of dopaminergic transmission and cocaine reward by the Clock gene". Proc Natl Acad Sci U S A 102 (26): 9377-81. PMID 15967985. 

2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance with the Gregorian calendar. ... is the 150th day of the year (151st in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 343rd day of the year (344th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 262nd day of the year (263rd in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 328th day of the year (329th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 328th day of the year (329th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 330th day of the year (331st in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 266th day of the year (267th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 262nd day of the year (263rd in leap years) in the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ...

Further reading

  • Aschoff J (ed.) (1965) Circadian Clocks. North Holland Press, Amsterdam
  • Avivi A, Albrecht U, Oster H, Joel A, Beiles A, Nevo E. 2001. Biological clock in total darkness: the Clock/MOP3 circadian system of the blind subterranean mole rat. Proc Natl Acad Sci USA 98:13751- 13756.
  • Avivi A, Oster H, Joel A, Beiles A, Albrecht U, Nevo E. 2002. Circadian genes in a blind subterranean mammal II: conservation and uniqueness of the three Period homologs in the blind subterranean mole rat, Spalax ehrenbergi superspecies. Proc Natl Acad Sci USA 99:11718-11723.
  • Ditty JL, Williams SB, Golden SS (2003) A cyanobacterial circadian timing mechanism. Annu Rev Genet 37:513-543
  • Dunlap JC, Loros J, DeCoursey PJ (2003) Chronobiology: Biological Timekeeping. Sinauer, Sunderland
  • Dvornyk V, Vinogradova ON, Nevo E (2003) Origin and evolution of circadian clock genes in prokaryotes. Proc Natl Acad Sci USA 100:2495-2500
  • Koukkari WL, Sothern RB (2006) Introducing Biological Rhythms. Springer, New York
  • Martino T, Arab S, Straume M, Belsham DD, Tata N, Cai F, Liu P, Trivieri M, Ralph M, Sole MJ. Day/night rhythms in gene expression of the normal murine heart. J Mol Med. 2004 Apr;82(4):256-64. Epub 2004 Feb 24. PMID: 14985853
  • Refinetti R (2006) Circadian Physiology, 2nd ed. CRC Press, Boca Raton
  • Takahashi JS, Zatz M (1982) Regulation of circadian rhythmicity. Science 217:1104–1111
  • Tomita J, Nakajima M, Kondo T, Iwasaki H (2005) No transcription–translation feedback in circadian rhythm of KaiC phosphorylation. Science 307: 251–254

Moore-Ede, Martin C., Sulszman, Frank M., and Fuller, Charles A. (1982) "The Clocks that Time Us: Physiology of the Circadian Timing System." Harvard University Press, Cambridge, MA. ISBN 0-674-13581-4.


External links

The Open Directory Project (ODP), also known as dmoz (from , its original domain name), is a multilingual open content directory of World Wide Web links owned by Netscape that is constructed and maintained by a community of volunteer editors. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 18th day of the year in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 290th day of the year (291st in leap years) in the Gregorian calendar. ... The University of California, Irvine is a public coeducational research university situated in Irvine, California. ... Nature is a prominent scientific journal, first published on 4 November 1869. ...

  Results from FactBites:
 
Circadian Rhythm | Circadian Rhythms | Circadian Rhythm Sleep Disorders (497 words)
Circadian rhythm sleep disorders are disruptions of the natural biological cycles that control how people are attuned to night and day.
The circadian "clock" in humans is located mainly in the suprachiasmatic nucleus (SCN), which is a group of cells located in the hypothalamus (a portion of the brain).
Circadian rhythms are important in determining human sleeping patterns.
Circadian rhythm - Wikipedia, the free encyclopedia (1463 words)
Circadian rhythms are important in determining the sleeping and feeding patterns of all animals, including human beings.
Circadian rhythms are believed to have originated in the earliest cells to provide protection for replicating DNA, from high ultraviolet radiation during day-time.
The simplest known circadian clock is that of the prokaryotic cyanobacteria.
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