Chronobiology

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Description


The variations of the timing and duration of biological activity in living organisms occur for many essential biological processes. These occur (a) in animals (eating, sleeping, mating, hibernating, migration, cellular regeneration, etc.), (b) in plants (leaf movements, photosynthetic reactions, etc.), and in microbial organisms such as fungi and protozoa. They have even been found in bacteria, especially among the cyanobacteria (aka blue-green algae, see bacterial circadian rhythms). The most important rhythm in chronobiology is the circadian rhythm, a roughly 24 hour-cycle shown by physiological processes in all these organisms. The term circadian comes from the Latin circa, meaning "around" and dies, "day", meaning "approximately a day."


The circadian rhythm can further be broken down into routine cycles during the day:
alphabet rubber stamp


Diurnal, which describes organisms active during the day
rubber stamp ink pad


Nocturnal, which describes organisms active in the night


Crepuscular, which describes animals primarily active during the dawn and dusk (ex: white-tailed deer)


Many other important cycles are also studied, including:


Infradian rhythms, which are cycles longer than a day, such as the annual migration or reproduction cycles found in certain animals or the human menstrual cycle.


Ultradian rhythms, which are cycles shorter than 24 hours, such as the 90-minute REM cycle, the 4-hour nasal cycle, or the 3-hour cycle of growth hormone production.


Tidal rhythms, commonly observed in marine life, which follow the roughly 12-hour transition from high to low tide and back.


Gene oscillations some genes are expressed more during certain hours of the day than during other hours.


History


A circadian cycle was first observed in the 18th century in the movement of plant leaves by the French scientist Jean-Jacques d'Ortous de Mairan (for a description of circadian rhythms in plants by de Mairan, Linnaeus, and Darwin see this page). In 1751 Swedish botanist and naturalist Carolus Linnaeus (Carl von Linn) designed a floral clock using certain species of flowering plants. By arranging the selected species in a circular pattern, he designed a clock that indicated the time of day by the flowers that were open at each given hour. For example, among members of the daisy family, he used the hawk's beard plant which opened its flowers at 6:30 AM and the hawkbit which did not open its flowers until 7 AM.


The 1960 symposium at Cold Spring Harbor Laboratory laid the groundwork for the field of chronobiology.


It was also in 1960 that Patricia DeCoursey invented the phase response curve, since one of the major tools used in the field.


Franz Halberg of the University of Minnesota, who coined the word circadian, is widely considered the "father of American chronobiology". However, it was Colin Pittendrigh and not Halberg who was elected to lead the Society for Research in Biological Rhythms in the 1970s. Halberg wanted more emphasis on the human and medical issues while Pittendrigh had his background more in evolution and ecology. With Pittendrigh as leader, the Society members did basic research on all types of organisms, plants as well as animals. More recently it has been difficult to get funding for such research on any other organisms than mice, rats, humans and fruit flies.


Recent developments


More recently, light therapy and melatonin administration have been explored by Dr. Alfred J. Lewy (OHSU), Dr. Josephine Arendt (University of Surrey, UK) and other researchers as a means to reset animal and human circadian rhythms. Humans can be morning people or evening people; these variations are called chronotypes for which there are various assessment tools and biological markers.


In the second half of 20th century, substantial contributions and formalizations have been made by Europeans such as Jrgen Aschoff and Colin Pittendrigh, who pursued different but complementary views on the phenomenon of entrainment of the circadian system by light (parametric, continuous, tonic, gradual vs. nonparametric, discrete, phasic, instantaneous, respectively; see this historical article, subscription required).


There is also a food-entrainable biological clock, which is not confined to the suprachiasmatic nucleus. The location of this clock has been disputed. Working with mice, however, Fuller et al. concluded that the food-entrainable clock seems to be located in the dorsomedial hypothalamus. During restricted feeding, it takes over control of such functions as activity timing, increasing the chances of the animal successfully locating food resources.


Other fields


Chronobiology is an interdisciplinary field of investigation. It interacts with medical and other research fields such as sleep medicine, endocrinology, geriatrics, sports medicine, space medicine and photoperiodism.


The unsubstantiated theory of biorhythms, which is said to describe a set of cyclic variations in human behaviour based on physiological and emotional cycles, is not a part of chronobiology.


See also


Bacterial circadian rhythms


Chronotype


Sense of time


Suprachiasmatic nucleus


Alexander Chizhevsky


References


^ a b Patricia J. DeCoursey, Jay C. Dunlap, Jennifer J. Loros (2003). Chronobiology. Sinauer Associates Inc. ISBN 978-0878931491. 


^ Nelson RJ. 2005. An Introduction to Behavioral Endocrinology. Sinauer Associates, Inc.,: Massachusetts. Pg587.


^ Nelson RJ. 2005. An Introduction to Behavioral Endocrinology. Sinauer Associates, Inc.,: Massachusetts. Pg587.


^ Nelson RJ. 2005. An Introduction to Behavioral Endocrinology. Sinauer Associates, Inc.,: Massachusetts. Pg587.


^ Leon Kreitzman; Russell G. Foster (2004). Rhythms of life: the biological clocks that control the daily lives of every living thing. New Haven, Conn: Yale University Press. ISBN 0-300-10969-5. 


^ Zivkovic, Bora (2006-07-03). "ClockTutorial #2a, Forty-Five Years of Pittendrigh's Empirical Generalizations". A Blog Around the Clock. ScienceBlogs. http://scienceblogs.com/clock/2006/07/clocktutorial_3_fortyfive_year.php. Retrieved 2007-12-23. 


^ Zivkovic, Bora (2006-05-17). "Clocks in Bacteria V". A Blog Around the Clock. ScienceBlogs. http://scienceblogs.com/clock/2006/09/clocks_in_bacteria_v_how_about.php. Retrieved 2007-12-23. 


^ Fuller, Patrick M.; Jun Lu, Clifford B. Saper (2008-05-23). "Differential Rescue of Light- and Food-Entrainable Circadian Rhythms" (free abstract). Science 320 (5879): 10741077. doi:10.1126/science.1153277. PMID 18497298. http://www.sciencemag.org/cgi/content/abstract/320/5879/1074. Retrieved 2008-05-30. 


^ Postolache, Teodor T. (2005). Sports Chronobiology, An Issue of Clinics in Sports Medicine. Saunders. ISBN 978-1416027690. 


^ Ernest Lawrence Rossi, David Lloyd (1992). Ultradian Rhythms in Life Processes: Inquiry into Fundamental Principles of Chronobiology and Psychobiology. Springer-Verlag Berlin and Heidelberg GmbH & Co. K. ISBN 978-3540197461. 


^ Hayes, D.K. (1990). Chronobiology: Its Role in Clinical Medicine, General Biology, and Agriculture. John Wiley & Sons. ISBN 978-0471568025. 


Further reading


Hastings, Michael, "The brain, circadian rhythms, and clock genes". Clinical review. BMJ 1998;317:1704-1707 19 December.


U.S. Congress, Office of Technology Assessment, "Biological Rhythms: Implications for the Worker". U.S. Government Printing Office, September 1991. Washington, DC. OTA-BA-463. NTIS PB92-117589


Ashikari, M., Higuchi, S., Ishikawa, F., and Tsunetsugu, Y., "Interdisciplinary Symposium on 'Human Beings and Environments': Approaches from Biological Anthropology, Social Anthropology and Developmental Psychology". Sunday, 25 August 2002


"Biorhythm experiment management plan", NASA, Ames Research Center. Moffett Field, 1983.


"Biological Rhythms and Human Adaptation to the Environment". US Army Medical Research and Materiel Command (AMRMC), US Army Research Institute of Environmental Medicine.


Ebert, D., K.P. Ebmeier, T. Rechlin, and W.P. Kaschka, "Biological Rhythms and Behavior", Advances in Biological Psychiatry. ISSN 0378-7354


Horne, J.A. (Jim) & stberg, Olov (1976). A Self-Assessment Questionnaire to determine Morningness-Eveningness in Human Circadian Rhythms. International Journal of Chronobiology, 4, 97-110.


External articles


Halberg Chronobiology Laboratory at the University of Minnesota, founded by Franz Halberg, the "Father of Chronobiology"


The University of Virginia offers an online tutorial on chronobiology.


See the Science Museum of Virginia publication Can plants tell time?


The University of Manchester has an informative Biological Clock Web Site


Cycles Research Institute includes an article on Alexander Chizhevsky.


S Ertel's analysis of Chizhevsky's work


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Categories: Biology | Circadian rhythms | Neuroscience