Links for Keyword: Biological Rhythms

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By C. CLAIBORNE RAY Q. Why do I wake up at exactly the same time every night, without any stimulus? It has happened all my life, and it doesn’t even matter what time I went to bed. A. What you are experiencing is probably a normal period of relative alertness that happens in the middle of the night, said Dr. Carl W. Bazil, director of the division of epilepsy and sleep at NewYork-Presbyterian/Columbia University Medical Center. “Most people realize that there is a natural drowsiness midday, usually around lunchtime,” Dr. Bazil said. “This is why many fortunate cultures developed the siesta.” But the reverse normally happens at night. The two interludes are both part of the body’s circadian rhythm, which he said is “controlled by an internal clock but of course influenced by lots of external things,” like caffeine, light, exercise and stress. Dr. Bazil said it might also help those who wake up midsleep to know that “before the advent of electrical lighting, it was normal for people to go to bed at sundown, sleep for about four hours and arise during that natural alertness for a few hours before returning for a ‘second sleep.’ ” © 2014 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: 19124 - Posted: 01.14.2014

by Simon Makin Sometimes wacky-sounding ideas aren't so crazy after all. If your body clock is all at sea after a long flight or a night shift, the way to reset it may be to scramble your timekeeping neurons even further. The body's master clock resides in a region of the brain called the suprachiasmatic nucleus. Each neuron in the SCN keeps its own time, but the neurons can synchronise their clocks by sending and receiving signals using a hormone called vasoactive intestinal polypeptide (VIP). When Erik Herzog at Washington University in St Louis, Missouri, and colleagues probed the hormone's effects, they discovered that a glut of VIP caused the neurons to lose the ability to synchronise. Herzog's team wondered whether this might have a beneficial effect. "If the cell rhythms are messed up and out of phase, the system may be more sensitive to environmental cues than it would be if all the cells were in sync," he says, allowing the body clock to adjust more readily. The VIP treatment To test the idea, they gave some mice an injection of VIP into the brain before fast-forwarding the light/dark cycle in their cages by 8 hours. The mice that received the hormone adjusted in 4.5 days on average, whereas untreated mice needed nearly eight days – gauging by how active the animals were when the lights were off. © 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: 18855 - Posted: 10.30.2013

Maggie Fox NBC News Every cell in your body has a little clock ticking away in it, researchers reported on Sunday. And while most of you is aging in a coordinated way, odd anomalies that have the researchers curious: Your heart may be “younger” than the rest of your tissues, and a woman’s breasts are older. Tumors are the oldest of all, a finding reported in the journal Genome Biology that might help scientists better understand cancer, explain why breast cancer is so common and help researchers find better ways to prevent it. Less surprising, but intriguing: embryonic stem cells, the body’s master cells, look just like newborns with a biological age of zero. The new measurements might be useful in the search for drugs or other treatments that can turn back the clock on aging tissue and perhaps treating or preventing diseases of aging, such as heart disease and cancer, says Steve Horvath, a professor of genetics at the David Geffen School of Medicine at UCLA. “The big question is whether the biological clock controls a process that leads to aging,” Horvath said. Horvath looked at a genetic process called methylation. It’s a kind of chemical reaction that turns on or off stretches of DNA. All cells have the entire genetic map inside; methylation helps determine which bits of the map the cells use to perform specific functions.

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep
Link ID: 18816 - Posted: 10.21.2013

By GRETCHEN REYNOLDS If you consider yourself to be a born morning person or an inveterate night owl, there is new research that supports your desire to wake up early or stay up late. Each of us has a personal “chronotype,” or unique circadian rhythm, says Till Roenneberg, a professor of chronobiology at Ludwig Maximilian University in Munich and one of the world’s experts on sleep. In broad strokes, these chronotypes are usually characterized as early, intermediate or late, corresponding to people who voluntarily go to bed and wake early, at a moderate hour or vampirishly late. If you are forced to wake up earlier than your body naturally would, you suffer from what Roenneberg calls “social jet lag.” People with an early chronotype may do well with a 7 a.m. workday rising time, but others do not. Sleeping out of sync with your innate preferences can be detrimental to your health, especially for late chronotypes, who tend to be the most at odds with typical work schedules. A study conducted by the National Institutes of Health and published in March in PLOS ONE found that obese adults with late chronotypes tended to eat larger meals, develop more sleep apnea and have higher levels of stress hormones and lower levels of HDL, or “good,” cholesterol than obese people with other chronotypes. Their chronotype may also have contributed to weight gain in the first place, Roenneberg says. Research has shown that a single hour of social jet lag, the mismatch between your chronotype and your schedule, increases your risk for obesity by about 33 percent. In a study published in June in Chronobiology International, late-night chronotypes gained more weight during their freshman years at college than other new students did, even though college is one of the best fits for night owls. Copyright 2013 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: 18815 - Posted: 10.21.2013

by Ed Yong I’ve just arrived home from 14 hours of flying. The clocks on my phone and laptop have been ticking away the whole time, and it takes a few seconds to reset them to British time. The clocks in my body are more difficult. We run on a daily 24-hour body clock, which controls everything from our blood pressure to our temperature to how hungry we feel. It runs on proteins rather than gears. Once they’re built, these proteins stop their own manufacture after a slight delay, meaning that their levels rise and fall with a regular rhythm. These timers tick away inside almost all of our cells, and they’re synchronised by a tiny collection of 10,000 neurons at the bottom of our brain. It’s called the suprachiasmatic nucleus (SCN). It’s the master clock. It’s the conductor that keeps the orchestra in sync. The SCN is also sensitive to light. It gets signals from our eyes, which allows it to synchronise its ticking with the 24-hour cycle of day and night outside. The SCN is what connects the rhythms of our bodies with those of the planet. But when we travel far and fast, and suddenly land in a new time zone, the SCN becomes misaligned with the environment. It takes time to re-adjust, typically one day for every time zone crossed. In the meantime, our sleep is disrupted and our physiology goes weird. In other words: jet lag. But at Kyoto University, Yoshiaki Yamaguchi and Toru Suzuki have engineered mice that break this rule. They are, with apologies for the awful word, unjetlaggable. If you change the light in their cages to mimic an 8-hour time difference, they readjust almost immediately. Put them on a red-eye flight from San Francisco to London and they’d be fine.

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: 18745 - Posted: 10.05.2013

by Linda Geddes They say the early bird catches the worm, but night owls may be missing far more than just a tasty snack. Researchers have discovered the first physical evidence of structural brain differences that distinguish early risers from people who like to stay up late. The differences might help to explain why night owls seem to be at greater risk of depression. Around 10 per cent of people qualify as morning people or larks, and a further 20 per cent are night owls – with the rest of us falling somewhere in between. Your lark or night owl status is called your chronotype. Previous studies have suggested that night owls experience worse sleep, more tiredness during the day and consume greater amounts of tobacco and alcohol. This has prompted some to suggest that they are suffering from a form of chronic jet lag. To investigate further, Jessica Rosenberg at RWTH Aachen University in Germany and colleagues used diffusion tensor imaging to scan the brains of 16 larks, 23 night owls and 20 intermediate chronotypes. They found a reduction in the integrity of night owls' white matter – brain tissue largely comprised of fatty insulating material that speeds up the transmission of nerve signals – in areas associated with depression. "We think this could be caused by the fact that late chronotypes suffer from this permanent jet lag," says Rosenberg, although she cautions that further studies are needed to confirm cause and effect. © 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: 18731 - Posted: 10.01.2013

By Tina Hesman Saey The sun exerts hegemony over biological rhythms of nearly every organism on Earth. But two studies now show the moon is no slouch. It controls the cadence of at least two different biological clocks: one set by tides and the other by moonlight. The clocks, both discovered in sea creatures, work independently of the circadian clock, which synchronizes daily rhythms with the sun. The studies demonstrate that the moon’s light and its gravitational pull, which creates tides, can affect the behavior of animals. “The moon has an influence, definitely,” says Steven Reppert, a neurobiologist at the University of Massachusetts Medical School in Worcester, who was not involved with either study. “Clearly for these marine organisms, it’s very powerful and important.” Scientists established decades ago that circadian clocks govern people’s daily cycles of such things as hormone levels, blood pressure and body temperature. Nearly every organism, including single-celled creatures, has some version. Circadian clocks are composed of protein gears. In a loop that takes roughly 24 hours, levels of some proteins rise and then fall, while others fall and then rise. Sunlight sets the clocks, but once a clock is set it will keep running, even when scientists keep organisms in constant darkness. © Society for Science & the Public 2000 - 2013

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep
Link ID: 18714 - Posted: 09.28.2013

Charlie Cooper Scientists have moved a step closer to creating a specialist pill for jet lag, after research in mice revealed a possible mechanism for speeding up the body's natural response to moving across time zones. Researchers at the University of Oxford found they could improve the recovery time of mice exposed to irregular patterns of light and dark by blocking a particular gene in the brain, responsible for regulating the body's internal clock. Nearly all living things have an internal, subcellular mechanism - known as the circadian clock - that synchronises a variety of bodily functions to the 24-hour rhythm of the Earth's rotation. The circadian clock is regulated by a number of stimuli - chief among them light detected by the eye. But when daily patterns of light and dark are disrupted - as when we travel across several time-zones - the body clock falls out of synch, resulting in several days of fatigue and discomfort as our cells adjust to new daily patterns - experienced by long-haul fliers as jet lag. The body takes about one day to adjust for every time zone crossed. To understand the effect this has on the brain, researchers at the University of Oxford exposed mice to irregular patterns of light and dark to simulate moving across time zones. They monitored the activity of genes in the part of the brain responsible for setting the circadian clock - the suprachiasmatic nuclei (SCN) and observed that hundreds of genes were activated by light detected from the eye, all of which helped the body adjust to a new day-night rhythm. © independent.co.uk

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep
Link ID: 18590 - Posted: 08.31.2013

NICHOLAS SPITZER is a professor of neuroscience at the University of California. His research concentrates on the ways in which neurons take on specialised functions to enable signalling in the brain. He is editor-in-chief of BrainFacts.org, a public information service about the brain and nervous system, and is instrumental in the BRAIN Initiative, a research project backed by the White House to advance new technologies to help map the brain. What do you know about the brain that the rest of us don’t? The structure and function of the brain are determined by genes and environment. We think we know this—it’s nature and nurture—but what many don’t realise is that this remains true throughout life. People think the brain is malleable only when we’re young. But that’s just not true. The forms of plasticity we see in the young brain are sustained in the mature brain. By plasticity I mean the ability of the brain to change its structure and function in response to changes in the environment. In addition to the classical ways the brain changes (the strength of the connections, synapses and neurons) we now understand a third kind of brain plasticity in which the neurotransmitter molecules—the signals from one neuron to another—can actually switch. What does this mean for human development? Our experiments have mainly been done on adult rats. A finding that is directly related to the human condition is that putting the animals on different photoperiods [day and night cycles] changes the neurotransmitter identity in the hypothalamus [a part of the brain] and this changes the animal’s behaviour. When animals are on a short day (rats are nocturnal so a short day is good) they make dopamine, the reward chemical. On the long day the neurons switch from dopamine to somatostatin, which retards growth. © The Economist Newspaper Limited 2013.

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep
Link ID: 18516 - Posted: 08.17.2013

Some colors humans are exposed to late at night could cause symptoms of clinical depression. That is the conclusion of a study that builds on previous findings that individuals exposed to dim levels of light overnight, such as from a glowing television set, can develop signs of clinical depression. Investigators, curious as to whether the color of light contributed to depressive symptoms in humans, designed an experiment that exposed hamsters to different colors. They chose hamsters because they are nocturnal, meaning they sleep during the day and are active at night. One group of hamsters was kept in the dark during their nighttime period. Another group of rodents was exposed to blue light and a third group slept in the presence of white light. A fourth group of hamsters was exposed to glowing red light. After four weeks, researchers noted how much sugary water the hamsters drank. The more depressed rodents consumed the least amount of water. Randy Nelson, chair of Ohio State University’s Department of Neuroscience and co-author of the study, said animals that slept in blue and white light appeared to be the most depressed. “What we saw is these animals didn’t show any sleep disruptions at all but they did have mucked up circadian clock genes and they did show depressive phenotypes whereas if they were in the dim red light, they did not,” Nelson said. Nelson explained that photosensitive cells in the retina, which don’t have much to do with vision, detect light and transmit signals to the master circadian clock in the brain that controls the natural sleep-wake cycle.

Related chapters from BP7e: Chapter 16: Psychopathology: Biological Basis of Behavior Disorders; Chapter 14: Biological Rhythms, Sleep, and Dreaming
Related chapters from MM:Chapter 12: Psychopathology: Biological Basis of Behavioral Disorders; Chapter 10: Biological Rhythms and Sleep
Link ID: 18483 - Posted: 08.10.2013

By Bora Zivkovic Sharks are not known for being good at running in running wheels. Or hopping from one perch to the other in a birdcage. Which is why, unlike hamsters or sparrows, sharks were never a very popular laboratory model for circadian research. The study of fish came late into the field of chronobiology due to technical difficulties of monitoring rhythms, at the time when comparative tradition was starting to make way to the more focused approach on choice model organisms – in this case, the zebrafish. But the comparative tradition was always very strong in the field. Reading the old papers (especially review papers and loooong theoretical papers) by the pioneers like Jurgen Asschoff and Colin Pittendrigh, it seems like researchers at the time were just going around and saying “let me try this species…and this one…and this one…”. And there were good reasons for this early approach. At the time, it was not yet known how widespread circadian rhythms were – it is this early research that showed they are ubiqutous in all organisms that live at or close to the surface of the earth or ocean. Another reason for such broad approach to testing many species was to find generalities – the empirical generalizations (e.g,. the Aschoff’s Rules) that allowed the field to get established, and that provided a template for the entire research program, including refining the proper experimental designs. © 2013 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: 18474 - Posted: 08.08.2013

By Meghan Rosen A short camping trip could help people rise and shine. After a week living in tents in Colorado’s Rockies, volunteers’ internal clocks shifted about two hours earlier, transforming night owls into early birds, researchers report August 1 in Current Biology. “It’s a clever study, and it makes a dramatic point,” says Katherine Sharkey, a sleep researcher and physician at Brown University. People get much more light outside than they do indoors, and that can reset their internal clocks, she says. A master clock in the brain controls the release of melatonin, a hormone that prepares the body for sleep. Melatonin levels rise in the early evening and then taper off in the morning before a person wakes up. But because so many people spend their days indoors and their nights bathed in the glow of electric lights, the body’s clock can get out of sync. Melatonin levels ramp up later in the evening and ebb later in the morning — often after a person has woken up. The lingering sleep hormone can make people groggy. Kenneth Wright Jr., a sleep researcher at the University of Colorado Boulder, and colleagues whisked eight volunteers away from artificial lights for a summer camping trip. After nightfall, the campers used only campfires for illumination — no flashlights (or cellphones) allowed. © Society for Science & the Public 2000 - 2013

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep
Link ID: 18445 - Posted: 08.03.2013

by Kelly Servick It almost seems like a mystical correlation. Babies conceived at certain times of the year appear healthier than those conceived during other times. Now, scientists have shown that the bizarre phenomenon is actually true—and they think they may know why it happens. The work is "a really long-overdue analysis," says economist Douglas Almond of Columbia University, who was not involved in the study. "This is maybe not quite a smoking gun," he says, "but it's much stronger than the previous evidence." As early as the 1930s, researchers noticed that children born in winter were more prone to health problems later in life: slower growth, mental illness, and even early death. Among the proposed explanations were diseases, harsh temperatures, and higher pollution levels associated with winter, when those expectant mothers and near-term fetuses might be most vulnerable. But recently, as economists looked at demographics, the picture got more complicated. Mothers who are nonwhite, unmarried, or lack a college education are more likely to have children with health and developmental problems. They are also more likely to conceive in the first half of the year. That made it hard to tease out the socioeconomic effects from the seasonal ones. Economists Janet Currie and Hannes Schwandt of Princeton University took a new approach to resolving this long-standing question, using data from the vital statistics offices in New Jersey, New York, and Pennsylvania about births between 1994 and 2006. To control for socioeconomic status, their study looked only at siblings born to the same mother. And lo and behold, seasonal patterns persist, they report online today in the Proceedings of the National Academy of Sciences. © 2010 American Association for the Advancement of Science

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: 18363 - Posted: 07.09.2013

By Susan Milius After 17 years underground, throngs of ruby-eyed cicadas clawed up through the soil this year to partake in a once-in-a-lifetime, synchronized mating frenzy. Except it wasn’t one big insect orgy: It was three. The insects that unearthed themselves to breed in 2013 belong to three distinct species. You need only flip them over to see some differences, written in the varieties of their orange markings. You can hear the differences too, says Chris Simon of the University of Connecticut in Storrs. The tymbals on either side of a male’s abdomen vibrate to make the racket for which cicadas are famous. A chorus of courting Magicicada cassini males sounds like an electric carving knife revving up. M. septendecula coughs out a series of rasps. And M. septendecim serenades with the whistling drone of a B-movie spaceship. The various thrums and buzzings may mingle in the same neighborhood, but the last time ancestors of these species mated with each other was almost 4 million years ago, Simon says. That’s the conclusion of the most detailed genetic studies yet of periodical cicada evolutionary history, which Simon and colleagues published in April in the Proceedings of the National Academy of Sciences. With DNA plus episodic field observations, the scientists are getting an idea about the odd family tree of periodical cicadas, how the insects synchronize their life cycles and why they breed side-by-side with others unsuitable for mating. © Society for Science & the Public 2000 - 2013

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming; Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep
Link ID: 18321 - Posted: 06.29.2013

Matt Kaplan Just as city slickers have faster-paced lives than country folk, so too do urban birds, compared with their forest-dwelling cousins. The reason, researchers report today, is that urban noise and light have altered the city birds’ biological clocks1. The finding helps to explain prior reports that urban songbirds adopt more nocturnal lifestyles2–4 — data that prompted Davide Dominoni, an ecologist at the Max Planck Institute for Ornithology in Radolfzell, Germany, to investigate whether the birds’ activity patterns were merely behavioural responses to busy cities or were caused by an actual shift in the animals' body clocks. For the study, published in Proceedings of the Royal Society B, Dominoni and his colleagues set up an experiment with European blackbirds (Turdus merula). The scientists attached tiny 2.2-gram radio-pulse transmitters to blackbirds living in Munich, Germany, as well as to those living in a nearby forest. The transmitters monitored the birds’ activity for three weeks. Dominoni found that whereas forest birds started their activity at dawn, city birds began 29 minutes earlier, on average, and remained active for 6 minutes longer in the evening. Keen to determine these differences were due to physiological changes, Dominoni collected blackbirds from both locations and placed them into light- and sound-proof enclosures. For ten days these enclosures were illuminated with a constant, dim light so the birds had no idea what time of day it was, and their activity patterns were monitored. © 2013 Nature Publishing Group,

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep
Link ID: 18233 - Posted: 06.05.2013

by Jennifer Viegas Roosters are genetically programmed to crow with the dawn, finds a new study that could also help to explain why dogs bark and cats meow. Previously it was unknown if crowing roosters were simply reacting to their environment. “‘Cock-a-doodle-doo’ symbolizes the break of dawn in many countries,” Takashi Yoshimura of Nagoya University, who worked on the study, was quoted as saying in a press release. “But it wasn’t clear whether crowing is under the control of a biological clock or is simply a response to external stimuli.” That’s because things like a car’s headlights can set a rooster off too, as anyone who has lived near these birds knows. To solve the mystery, Yoshimura and colleagues kept roosters under round-the-clock dim lighting. This didn’t deter the roosters. No matter what, they kept crowing each morning just before dawn. The researchers say this is proof that the vocalizing is entrained to a circadian rhythm. In short, the roosters are genetically programmed to crow at a certain time. At some point, the rising sun set the roosters’ internal clock, so now they crow every 24 hours. Most animals, and plants too, have such an internalized timing mechanism. That’s why we tend to eat, sleep, exercise and more at around the same times. By consciously being aware of the schedule, our body has a chance to adapt to it, so well-functioning circadian rhythms are often tied to good health. © 2013 Discovery Communications, LLC.

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep
Link ID: 17919 - Posted: 03.19.2013

US researchers have found a link between working night shifts and the risk of ovarian cancer. A study of more than 3,000 women suggested that working overnight increased the risk of early-stage cancer by 49% compared with doing normal office hours. One possible explanation was disruption of the sleep hormone melatonin, the researchers said. But experts warned more work was needed and there might be other explanations. It does however follow an earlier association made between shift work and breast cancer. The International Agency for Cancer Research has previously identified working shift patterns that disrupt the body's natural "clock" as a probable cause of cancer. In the latest investigation, researchers looked at 1,101 women with advanced ovarian cancer, 389 with borderline or early disease and 1,832 women without the condition. Overall, a quarter with advanced cancer said they had worked night shifts, compared with a third of those with borderline disease and one in five of the control group. Analysis of the data showed a 24% increased risk of advanced cancer and 49% increased risk of early-stage disease for night workers compared with those who worked during the day. But the results were only significant for women over the age of 50, the researchers reported in Occupational and Environmental Medicine. And the risk did not seem to increase for those who had worked night shifts for the longest. BBC © 2013

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming; Chapter 15: Emotions, Aggression, and Stress
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep; Chapter 11: Emotions, Aggression, and Stress
Link ID: 17913 - Posted: 03.18.2013

By Tina Hesman Saey Like the sun, insulin levels rise and fall in a daily rhythm. Disrupting that cycle may contribute to obesity and diabetes, a new study suggests. Many body systems follow a daily clock known as a circadian rhythm. Body temperature, blood pressure and the release of many hormones are on circadian timers. But until now, no one had shown that insulin — a hormone that helps control how the body uses sugars for energy — also has a daily cycle. Working with mice, researchers at Vanderbilt University in Nashville have found that rodents are more sensitive to insulin’s effects at certain times of day. Disrupting the animals’ circadian timers interferes with the hormone’s daily rise and fall and makes mice prone to obesity. If the findings hold up in humans, they could help explain why people who work night shifts tend to be overweight and suffer health problems. The discovery may also tie the obesity epidemic in part to staying up late and eating at the wrong time. Many people had thought that it was best for the body to maintain insulin at a relatively constant level, says Carl Johnson, a circadian biologist who led the new study. “But that’s not how organisms have adapted,” he says. Since the environment cycles through light and dark, body processes often coordinate with that rhythm. To uncover insulin’s natural rhythm, Johnson and his colleagues performed an “insulin clamp” procedure on mice. The clamp infuses glucose or insulin around the clock into mice that are moving freely in their cages. Measuring how much insulin or glucose the mice need to maintain constant blood sugar levels tells the researchers how responsive the animals are to the hormone at any given time of day. © Society for Science & the Public 2000 - 2013

Related chapters from BP7e: Chapter 13: Homeostasis: Active Regulation of the Internal Environment; Chapter 14: Biological Rhythms, Sleep, and Dreaming
Related chapters from MM:Chapter 9: Homeostasis: Active Regulation of the Internal Environment; Chapter 10: Biological Rhythms and Sleep
Link ID: 17831 - Posted: 02.23.2013

By Laura Hambleton, Winter often brings the flu, coughs, ski injuries and shoveling strains. Add to these ailments a more deadly one: heart attacks. A recent study has found that more fatal heart attacks and strokes occur during the winter than at other times of the year. And it doesn’t seem to matter if the winter is occurring in the warmer climes of Southern California or the frostier ones of Boston. After sifting through about 1.7 million death certificates filed between 2005 and 2008, cardiologists Bryan Schwartz of the University of New Mexico and Robert A. Kloner of the Heart Institute at the Good Samaritan Hospital in Los Angeles found a 26 to 36 percent greater death rate for heart attacks in winter than summer “despite different locations and climates,” Kloner says. The worst months are December, January, February and the beginning of March. The doctors analyzed the cause of death for people in Texas, Arizona, Georgia, Los Angeles, Washington state, Pennsylvania and Massachusetts. Of those who died of heart disease, the winter weather pattern was clear. In Los Angeles, for example, there were about 70 deaths per day from cardiac disease, Schwartz said. “In the summer, L.A. had an average circulatory death rate of about . . . 55 deaths per day.” The research uncovered patterns in cardiac deaths from “seven different climate patterns,” according to the study, and “death rates at all sites clustered closely together and no one site was statistically different from any other site.” An abstract of the study was published in the American Heart Association journal Circulation. © 1996-2013 The Washington Post

Related chapters from BP7e: Chapter 14: Biological Rhythms, Sleep, and Dreaming; Chapter 19: Language and Hemispheric Asymmetry
Related chapters from MM:Chapter 10: Biological Rhythms and Sleep; Chapter 15: Language and Our Divided Brain
Link ID: 17763 - Posted: 02.05.2013

By Stephani Sutherland If you have trouble sleeping, laptop or tablet use at bedtime might be to blame, new research suggests. Mariana Figueiro of the Lighting Research Center at Rensselaer Polytechnic Institute and her team showed that two hours of iPad use at maximum brightness was enough to suppress people's normal nighttime release of melatonin, a key hormone in the body's clock, or circadian system. Melatonin tells your body that it is night, helping to make you sleepy. If you delay that signal, Figueiro says, you could delay sleep. Other research indicates that “if you do that chronically, for many years, it can lead to disruption of the circadian system,” sometimes with serious health consequences, she explains. The dose of light is important, Figueiro says; the brightness and exposure time, as well as the wavelength, determine whether it affects melatonin. Light in the blue-and-white range emitted by today's tablets can do the trick—as can laptops and desktop computers, which emit even more of the disrupting light but are usually positioned farther from the eyes, which ameliorates the light's effects. The team designed light-detector goggles and had subjects wear them during late-evening tablet use. The light dose measurements from the goggles correlated with hampered melatonin production. On the bright side, a morning shot of screen time could be used as light therapy for seasonal affective disorder and other light-based problems. Figueiro hopes manufacturers will “get creative” with tomorrow's tablets, making them more “circadian friendly,” perhaps even switching to white text on a black screen at night to minimize the light dose. Until then, do your sleep schedule a favor and turn down the brightness of your glowing screens before bed—or switch back to good old-fashioned books. © 2013 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: 17743 - Posted: 02.02.2013