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By Nicholette Zeliadt Our sleep patterns, eating habits, body temperature and hormone levels are driven by the rhythmic activity of body's circadian clock. Travel across time zones or shift work can knock those rhythms out of whack, possibly leading to sleep problems, bipolar disorder, metabolic syndrome and even cancer. The lack of convenient and reliable methods to monitor the internal clock's activity has severely limited the study of circadian-related disease, but now, scientists report that they can easily track the circadian rhythms by analyzing a person's plucked hairs. The finding could one day help doctors diagnose and treat patients suffering from circadian dysfunction. The body's master clock, located in the brain region called the hypothalamus, is set by light, which activates clock genes that are responsible for keeping this timekeeper ticking correctly. Within the past decade, scientists have discovered that organs outside the brain (such as the skin, liver and pancreas) also keep track of time with 24-hour fluctuations in clock gene expression. Previous studies have attempted to monitor molecular timekeeping in blood cells or in cells lining the mouth, but these approaches are technically challenging. In an attempt to develop a simpler, noninvasive method to clock circadian rhythms, researchers led by Makoto Akashi of the Research Institute for Time Studies at Yamaguchi University in Japan obtained hairs plucked from volunteers' heads or chins and analyzed clock gene expression in hair follicle cells. They report online this week in the Proceedings of the National Academy of Sciences that the patterns of circadian gene expression in the hair follicle cells accurately reflected the subjects' behavioral rhythms, "demonstrating that this strategy is appropriate for evaluating the human peripheral circadian clock." © 2010 Scientific American

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep
Link ID: 14391 - Posted: 08.24.2010

By Katherine Harmon Having a mixed up body clock has been linked to a vast array of ailments, including obesity and bipolar disorder. And researchers are still trying to understand just how these cyclical signals influence aspects of our cellular and organ system activity. Now, a study published online August 3 in Cell Metabolism shows that in mice, a disrupted circadian rhythm spurs an increase in triglycerides—heightened levels of which have been linked to heart disease and metabolic syndrome in humans. To find this link, researchers compared normal lab mice to those bred to have dysfunctional sleep-wake cycles. As nocturnal animals, the control mice had the lowest levels of triglycerides at night, when they were most active, and higher levels during the daytime rest period. The mice with out-of-whack cycles kept confused hours, fed longer and were less active overall. These mutant mice also had far less fluctuation in their triglyceride levels. "We show that the normal up and down [of triglycerides] is lost in clock mutants," M. Mahmood Hussain, of the Department of Cell Biology and Pediatrics at the State University of New York Downstate Medical Center in Brooklyn and coauthor of the paper, said in a prepared statement. The mutant mice had "high triglycerides all the time," he noted. © 2010 Scientific American,

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming; Chapter 13: Homeostasis: Active Regulation of the Internal Environment
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep; Chapter 9: Homeostasis: Active Regulation of the Internal Environment
Link ID: 14322 - Posted: 08.05.2010

by Sujata Gupta WHAT happens when you take blind mice and see how they run? It turns out they can identify objects using receptors in the eye that were previously thought to have no role in forming images. Since humans possess the same receptors, the finding could point the way to giving blind people some ability to see. Mice, and humans, have three types of light-detecting receptor in the eye. Rods and cones detect light, darkness, shape and colour, and make normal sight possible. Receptors of the third type, the melanopsin-containing ganglion cells (MCGCs), were until now thought only to respond to light over longer periods of time, to help moderate patterns of sleep and wakefulness. To investigate their role in vision, Samer Hattar of the Krieger School of Arts and Sciences at Johns Hopkins University in Baltimore, Maryland, and colleagues engineered mice to lack rods and cones. When these mice were placed in a maze, they were able to identify a lever with a visible pattern on it which allowed them to escape. Mice that lacked rods, cones and MCGCs could not find the lever. In another task, the team found that the MCGC mice could follow the movement of a rotating drum (Neuron, DOI: 10.1016/j.neuron.2010.05.023). This suggests MCGCs can form "low-acuity yet measurable images", Hatter says. Tom Cronin at the University of Maryland notes that the mice in the experiment behave like people with "blindsight", who can navigate round objects without consciously perceiving them. "It's mind-boggling but I suspect that the mice are doing something like that," he says. © Copyright Reed Business Information Ltd.

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming; Chapter 10: Vision: From Eye to Brain
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep; Chapter 7: Vision: From Eye to Brain
Link ID: 14284 - Posted: 07.24.2010

By Lindsey Tanner Want happier, more alert teenagers? Let them sleep in a little. A new study reveals that delaying the school day by 30 minutes results in teens who are less sleepy and depressed. Scientists say that teens tend to be in their deepest sleep around dawn, when they typically need to arise for school. Interrupting that sleep can leave them groggy. Giving teens 30 extra minutes to start their school day leads to more alertness in class, better moods, less tardiness, and even healthier breakfasts, a small study found. "The results were stunning. There's no other word to use," said Patricia Moss, academic dean at the Rhode Island boarding school where the study was done. "We didn't think we'd get that much bang for the buck." The results appear in July's Archives of Pediatrics & Adolescent Medicine. The results mirror those at a few schools that have delayed starting times more than half an hour. Researchers say there's a reason why even 30 minutes can make a big difference. Teens tend to be in their deepest sleep around dawn -- when they typically need to arise for school. Interrupting that sleep can leave them groggy, especially since they also tend to have trouble falling asleep before 11 p.m. © 2010 Associated Press/AP Online

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming; Chapter 7: Life-Span Development of the Brain and Behavior
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep; Chapter 13: Memory, Learning, and Development
Link ID: 14240 - Posted: 07.08.2010

by Andy Coghlan A FAULTY internal clock in the cells in the pancreas that produce insulin could be behind type 2 diabetes - a condition in which the body is unable to produce or use insulin properly. The finding suggests that disruption of natural night and day cycles through artificial lighting may be a factor in the emergence of type 2 diabetes in adults. It also fits with studies showing that shift workers are unusually prone to the condition. Insulin is produced by beta cells to control glucose levels in the blood. Joseph Bass of Northwestern University in Evanston, Illinois, and colleagues grew mouse beta cells in the lab to monitor insulin secretion. They found that beta cells lacking circadian "clock" genes produced 50 per cent less insulin, showing that these genes are essential for normal insulin production (Nature, DOI: 10.1038/nature09253). Likewise, live mice with disrupted clock genes rapidly developed type 2 diabetes. The next step, says Bass, is to identify the "switch" in beta cells that responds to the clock, and use it to develop a treatment. "The key thing the researchers have shown is that disruption of this internal clock causes a defect in insulin secretion," says Noel Morgan of the Peninsula Medical School in Exeter, UK, who studies type 1 diabetes, in which the body's own immune system destroys its beta cells. © Copyright Reed Business Information Ltd.

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming; Chapter 13: Homeostasis: Active Regulation of the Internal Environment
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep; Chapter 9: Homeostasis: Active Regulation of the Internal Environment
Link ID: 14199 - Posted: 06.24.2010

By ANDREW POLLACK It seemed like the offer of a lifetime — earn $2,500 by flying to France aboard a private luxury jet. Even if it wins Food and Drug Administration approval, Nuvigil would have to compete with cheap jet-lag treatments like coffee. But as the fine print made clear, there would be no Eiffel Tower or chateaux, no foie gras or Bordeaux. Travelers were confined to a laboratory in either Toulouse or Rouffach with electrodes attached to their heads, testing whether a drug could keep their jet-lagged bodies awake. That drug, Nuvigil from Cephalon, could become the first medicine specifically approved by the Food and Drug Administration to combat jet lag. A jet-lag antidote might seem to be the latest lifestyle drug, a further step in the “medicalization” of something that is not an illness. But sleep specialists, who call the affliction “jet lag disorder,” say that while not exactly a disease, it is a condition that can be dangerous — as when someone tries to drive a car right after arriving in a distant time zone. For Cephalon, a company in Frazer, Pa., whose business tactics have attracted federal attention, the approval for jet lag is part of a plan to extend patent protection for its core franchise in stay-awake drugs. Copyright 2010 The New York Times Company

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep
Link ID: 13643 - Posted: 06.24.2010

By David Ropeik It’s that time of year, when crocuses bloom, the lawn starts to need mowing, and most Americans lose an hour’s sleep setting their clocks ahead. (Remember? Spring forward, fall back.) So here are answers to your questions about the time switch — and about sleep. Most Americans move their clocks ahead for daylight-saving time in the wee hours of the second Sunday in March. The day of the big switch used to be the first Sunday of April, but Congress put a new rule into effect last year as an energy-saving measure. What's the rationale behind the switchover? As the year progresses toward the June solstice, the Northern Hemisphere gets longer periods of sunlight. Timekeepers came up with daylight-saving time — or summer time, as it’s known in other parts of the world — to shift some of that extra sun time from the early morning (when timekeepers need their shut-eye) to the evening (when they play softball). The idea is that having the extra evening sunlight will cut down on the demand for lighting, and hence cut down on electricity consumption — and that few people will miss having it a little darker at, say, 6 o'clock in the morning. At least that's how the theory goes. © 2008 Microsoft

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep
Link ID: 11393 - Posted: 06.24.2010

Inside the bodies of animals from fruit flies to humans, internal clocks are constantly ticking, making sure activity levels and a host of physiological functions rise and fall in a 24-hour cycle. Inside cells, many of the proteins that keep the internal clocks ticking on time have their own cycles, accumulating when they are needed, then vanishing when their work is done for the day. A newly identified gene mutation in mice has now revealed how these molecular oscillations are kept on track. Howard Hughes Medical Institute investigator Joseph Takahashi and his colleagues discovered the gene's role in regulating circadian rhythms, which they reported in the journal Cell, published online as an immediate early publication on April 26 and published in print on June 1, 2007. Joint lead authors in Takahashi's Northwestern University laboratory were Sandra Siepka and Seung-Hee Yoo, and another co-author, Choogon Lee, is from Florida State University. The team named the mutated gene Overtime because it knocks the mouse's circadian clock out of whack, lengthening its sleep-wake cycle to 26 hours. Circadian rhythms, the activity patterns that occur on a 24-hour cycle, are important biological regulators in virtually every living creature. In humans and other animals, the brain's internal circadian clock regulates sleep and wake cycles, as well as body temperature, blood pressure, and the release of various endocrine hormones. © 2007 Howard Hughes Medical Institute

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep
Link ID: 10227 - Posted: 06.24.2010

Researchers from Brigham and Women’s Hospital (BWH) in Boston and Jefferson Medical College have found that the body’s natural biological clock is more sensitive to shorter wavelength blue light than it is to the longer wavelength green light, which is needed to see. The discovery proves what scientists have suspected over the last decade: a second, non-visual photoreceptor system drives the body’s internal clock, which sets sleep patterns and other physiological and behavioral functions. “This discovery will have an immediate impact on the therapeutic use of light for treating winter depression and circadian disorders,” says George Brainard, Ph.D., professor of neurology at Jefferson Medical College of Thomas Jefferson University in Philadelphia. “Some makers of light therapy equipment are developing prototypes with enhanced blue light stimuli.” ©2003 Thomas Jefferson University Hospital

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep
Link ID: 4245 - Posted: 06.24.2010

Discovery that clocks in organs use different genes could impact postgenomic research and circadian medicine BOSTON, MA –The daily rhythms of the body—once thought to be strictly governed by a master clock lodged in the brain—appear to be driven to a remarkable degree by tiny timepieces pocketed in organs all over the body. What‘s more, these peripheral timepieces appear to be strikingly idiosyncratic in appearance—more like Swatch watches than classic Timexes. Clocks located in the liver and heart appear to use very different sets of genes to perform essentially the same functions, researchers at Harvard Medical School and the Harvard School of Public Health report in the April 21 Nature online. The study, among the first to explore circadian time mechanisms outside the brain, could have a potentially broad impact on the burgeoning fields of circadian medicine and postgenomic science. Clinicians have known for years that organs function at different rates—the heart beats, kidneys transport ions and electrolytes, the liver metabolizes lipids, sugars, and amino acids differently over the course of the day—and have used this knowledge to design more effective drug regimens for patients. A better understanding of what drives those local rhythms, and how they go wrong, could aid physicians’ efforts.

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep
Link ID: 1932 - Posted: 06.24.2010

— Researchers have traced the light-sensing circuitry for a type of “second sight” that is distinct from the conventional visual system and seems to interact directly with the body’s internal clock. The researchers speculate that subtle genetic malfunctions of this machinery might underlie some sleep disorders. In an article published in the February 8, 2002, Science, a research team led by Howard Hughes Medical Institute investigator King-Wai Yau described the circuitry, which consists of a subset of nerve cells that carry visual signals from the eye to the brain. The scientists showed that circadian-pacemaker nerve cells almost certainly depend on a different light-sensing pigment, called melanopsin, than the conventional visual system, which relies on rod and cone photoreceptors arrayed across the retina. ©2002 Howard Hughes Medical Institute

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming; Chapter 10: Vision: From Eye to Brain
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep; Chapter 7: Vision: From Eye to Brain
Link ID: 1497 - Posted: 06.24.2010

Researchers in Sweden say there might be a link between constant summer sunlight and a high rate of suicide in Greenland, a finding that medical officials in northern Canada are watching. A team led by psychiatrist Karin Sparring Björkstn of the Karolinska Institutet looked at the seasonal variation of suicides throughout Greenland between 1968 and 2002. The team's findings, published in the journal BMC Psychiatry on Friday, found an increase in the number of suicides during the summer months in Greenland, with a peak in June. Björkstn told CBC News she was surprised by the findings, but believes the sunlight could be amplifying underlying mental health issues and other problems. "There are, of course, many reasons that people commit suicide. But in the summer, when you don't sleep for extended periods of time, or you sleep very little, you may lose judgment," she said. "Some people actually become manic or delirious and they really don't know what they are doing. Perhaps they didn't intend to commit suicide." In the north of the Arctic island, Björkstn said 82 per cent of suicides occurred during the long periods of 24-hour summer light. Björkstn's team also suggested that light-generated imbalances could lead to increased impulsiveness. © CBC 2009

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming; Chapter 16: Psychopathology: Biological Basis of Behavior Disorders
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep; Chapter 12: Psychopathology: Biological Basis of Behavioral Disorders
Link ID: 12837 - Posted: 06.24.2010

By Tina Hesman Saey Scientists are discovering how tiny clocks inside each cell can march to the beat of a master drummer in the brain. Chuwy/iStockphoto, illustration by T. Dube Timing is everything. Just ask a comedian, trapeze artist, Romeo and Juliet — or nearly any cell in your body. Ticking away inside almost all cells are tiny clocks composed of protein gears. Scientists have known that these molecular clocks govern the daily rhythms of life, from mealtimes and bedtimes to the rise and fall of hormone levels, body temperature and blood pressure. New research shows that circadian clocks, as the daily timekeepers are known, do more than just control day-to-day schedules. Such clocks, some scientists say, have the potential to play a role in nearly every biological function. Studies of bacteria, rodents and fruit flies suggest that circadian clocks may time processes as diverse as cellular division and aging. “When you start asking, ‘what does the clock control?’ you have to say, ‘everything,’” says Erik Herzog, a biologist at Washington University in St. Louis. Some of the new insights come from studying the brain’s master clock, a pair of structures known as the suprachiasmatic nucleus, or SCN, that set the body’s daily rhythms. Other work, meanwhile, suggests that the SCN is not a single monolithic clock but more a set of interrelated nodes that help coordinate clocks throughout the body. And still other researchers have found that the SCN may not even be the ultimate arbiter of the body’s time, and that other organs control biological rhythms on their own without much, if any, help from the SCN. © Society for Science & the Public 2000 - 2010

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep
Link ID: 13909 - Posted: 06.24.2010

Ewen Callaway You might call it our circadian eye. A handful of retina cells sense light, not for vision, but instead to reset our body clocks each day. Killing off these cells in mice leaves their sight unharmed, but throws their clocks out of whack, two new studies show. Jolting these cells back into action might offer salvation to insomniacs, whose circadian cycles are slightly off, says Satchidananda Panda, a molecular biologist at the Salk Institute in San Diego, who led one study. Natural degeneration of these cells could also explain why insomnia often strikes the elderly. "Maybe we can develop an eye drug to reset your clock," he says. Alternatively, triggering the cells with extra-pale blue light – the wavelengths they're most sensitive to – could do the same trick, says Samer Hattar, a neuroscientist at Johns Hopkins University in Baltimore. Hattar's team identified the same role for the cells, which produce a recently-discovered light sensor called melanopsin. The first evidence for our circadian eye came in the 1920s, when an American physician noticed that congenitally blind mice can still dilate their pupils – a sign of light detection – despite lacking rods and cones, the photosensors that transform light to vision. © Copyright Reed Business Information Ltd.

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming; Chapter 10: Vision: From Eye to Brain
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep; Chapter 7: Vision: From Eye to Brain
Link ID: 11703 - Posted: 06.24.2010

If your child is born in the winter or fall, it will have better long-range eyesight throughout its lifetime and less chance of requiring thick corrective glasses, predicts a Tel Aviv University investigation led by Dr. Yossi Mandel, a senior ophthalmologist in the Israel Defense Forces Medical Corps. Forming a large multi-center Israeli team, the scientists took data on Israeli youth aged 16-23 and retroactively correlated the incidence of myopia (short-sightedness) with their month of birth. The results were astonishing. Babies born in June and July had a 24% greater chance of becoming severely myopic than those born in December and January – the group with the least number of severely myopic individuals. The investigators say that this evidence is likely applicable to babies born anywhere in the world. The results of the study were published this month in the clinical eye journal Ophthalmology. The team interpolated data from a sample size of almost 300,000 young adults, making it one of the largest epidemiological surveys carried out in the world on any subject. Is this great disparity in eyesight related to one’s luck or astrological sign? “Nonsense,” balks study co-author Prof. Michael Belkin of Tel Aviv University’s Goldschleger Eye Research Institute, the most prominent eye research organization in Israel and the region. Belkin is also Incumbent to the Fox Chair of Ophthalmology and one of the founders and first director of the Goldschleger Institute, established more than 25 years ago at the Sheba Medical Center. In November Prof. Belkin will attend the annual American Academy of Ophthalmology conference in New Orleans, La. © PhysOrg.com 2003-2007

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming; Chapter 10: Vision: From Eye to Brain
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep; Chapter 7: Vision: From Eye to Brain
Link ID: 10652 - Posted: 06.24.2010

Roxanne Khamsi Mice with a gene mutation that disrupts their sleep cycles show signs of hyperactivity and addictive tendencies, a new study reveals. Researchers say that such "manic" behaviour displayed by the animals bolsters the theory that glitches in the body's internal clock can cause psychiatric illnesses such as bipolar disorder. Mice that received injections of DNA to compensate for the mutated gene regained regular sleep cycles and showed normal behaviour. This type of gene therapy will not work to treat people with bipolar disorder anytime soon, researchers stress, but they believe genetic experiments in rodents will reveal the potential targets for psychiatric drug treatments. Colleen McClung at the University of Texas Southwestern Medical Center in Dallas, US, and colleagues conducted experiments on mice with a mutation in their Clock gene. This gene normally activates other genes in the cell – with a certain regularity and on a daily basis. The human version is thought to be responsible for many of our circadian rhythms, including our wake/sleep cycle. Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0609625104) © Copyright Reed Business Information Ltd

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming; Chapter 16: Psychopathology: Biological Basis of Behavior Disorders
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep; Chapter 12: Psychopathology: Biological Basis of Behavioral Disorders
Link ID: 10107 - Posted: 06.24.2010

The first gene known to control the internal clock of humans and other mammals works much differently than previously believed, according to a study by Utah and Michigan researchers. The surprising discovery means scientists must change their approach to designing new drugs to treat jet lag, insomnia, some forms of depression, sleep problems in shift workers and other circadian rhythm disorders, according to researchers at the University of Utah's Huntsman Cancer Institute and the University of Michigan, Ann Arbor. The study – which involved the so-called tau mutation that causes hamsters to have a 20-hour day instead of a 24-hour day – will be published online the week of July 3 in the journal Proceedings of the National Academy of Sciences. The researchers discovered that what was previously believed about the tau mutation – that a decrease in gene activity sped up a mammal's internal clock – was incorrect. Instead, the mutation caused an increase in gene activity to speed up the clock, making the day two to four hours shorter for affected animals. Previous work had indicated that the tau mutation occurred in a gene called casein kinase 1 epsilon (CK1) and that the mutation caused an 85 percent loss of gene activity. This, it was thought, explained why the hamster had a short day. But as it turns out, this idea was wrong.

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep
Link ID: 9090 - Posted: 06.24.2010

PORTLAND, Ore. – Research conducted at Oregon Health & Science University suggests that contrary to popular belief, the body has more than one "body clock." The previously known master body clock resides in a part of the brain called the suprachiasmatic nucleus (SCN). Researchers at OHSU's Oregon National Primate Research Center (ONPRC) have now revealed the existence of a secondary clock-like mechanism associated with the adrenal gland. The research also suggests a high likelihood that additional clocks exist in the body. The study results are printed in the current edition of the journal Molecular Endocrinology. "We're all familiar with the idea that the body has a master clock that controls sleep-wake cycles. In fact, most of us have witnessed the impacts of this clock in the form of jet lag where it takes the body a number of days to adjust to a new time schedule following a long flight," explained Henryk Urbanski, Ph.D., senior author of the study and a senior scientist at ONPRC. "Our latest research suggests that a separate but likely related clock resides in the adrenal gland. The adrenal gland is involved in several important body functions, such as body temperature regulation, metabolism, mood, stress response and reproduction. The research also suggests that other peripheral clocks reside throughout the body and that these clocks are perhaps interconnected." To conduct the research, scientists studied adrenal gland function in rhesus macaque monkeys which is very similar to human adrenal gland function. Specifically, researchers measured gene expression in the adrenal gland of monkeys during a 24-hour period (six times a day, four-hour intervals).

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep
Link ID: 8948 - Posted: 06.24.2010

Gaia Vince Reindeer have a body clock that does not rely on a 24-hour day/night light cycle, according to Norwegian researchers. It may explain how they stay awake to carry out their Christmas duties. Instead, the herbivores’ stomachs seem to keep their body clocks ticking along. Karl-Arne Stokkan at the University of Troms, and colleagues, logged the festive animals’ movements every 10 minutes for a year using a radio transmitter device embedded in collars around the reindeers’ necks. The collars were placed on 12 reindeer – six who roamed a mountainous region of mainland Norway at a latitude of 70 North, and six found in the more-northerly Arctic archipelago of Svalbard (78 N). Winter in these regions is unyieldingly dark, while in summer the Sun does not set. Spring and autumn provide just a few weeks of night/day cycles. In the absence of light stimuli humans, like most mammals, naturally revert to a 6 to 8-hour sleep pattern due to an inbuilt circadian rhythm. © Copyright Reed Business Information Ltd

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep
Link ID: 8330 - Posted: 06.24.2010

Temperature triggers significant changes in the expression of specific clock genes. The biological clock controls the circadian rhythms of a wide range of physiological and behavioral processes, from fluctuating hormone levels to sleep–wake cycles and feeding patterns. While it's well known that circadian clock elements sense and respond to light cycles, much less is known about how daily temperature cycles affect the clock's timing mechanism in vertebrates. In the open-access journal PLoS Biology, Kajori Lahiri, Nicholas Foulkes, and their colleagues study temperature related responses at the genetic and molecular level in zebrafish. This genetically tractable model organism is especially suited to this task because adults, larvae, and even embryos can tolerate a wide range of core body temperatures (being cold-blooded animals) that can be manipulated simply by changing the water temperature. Temperature variations of as little as 2 C (35.6 F) can reset the zebrafish clock, Lahiri et al. show, and precise shifts in temperature trigger significant changes in the expression of specific clock genes. More explicitly, clock genes per4, cry2a, cry3, and clock1 showed rhythmic expression under temperature cycles when animals were raised in the dark, and the expression profiles during the high temperature phase matched those seen during a light phase when animals experienced light-dark cycles.

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep
Link ID: 7958 - Posted: 06.24.2010