chronobiology
clock | March 21, 2007A new paper just came out today on PLoS-Biology: Glucocorticoids Play a Key Role in Circadian Cell Cycle Rhythms. The paper is long and complicated, with many control experiments, etc, so I will just give you a very brief summary of the main finding.
One of the three major hypotheses for the origin of circadian clocks is the need to shield sensitive cellular processes - including cell division - from the effects of UV radiation by the sun, thus relegating it to night-time only:
The cyclic nature of energetic availability and cycles of potentially degrading effects of the sun's ultraviolet…
clock | March 20, 2007I have written about the relationship between circadian clocks and food numerous times (e.g., here, here and here). Feeding times affect the clock. Clock is related to hunger and obesity. Many intestinal peptides affect the clock as well.
There is a lot of research on food-entrainable oscillators, but almost nothing on the possibility that there is a separate circadian pacemaker in the intestine. It is usually treated as a peripheral clock, entirely under the influence of the SCN pacemaker in the brain, even when it shows oscillations in clock-gene expression for several days in a dish.…
clock | March 19, 2007It has been known for quite a while now that bipolar disorder is essentially a circadian clock disorder. However, there was a problem in that there was no known animal model for the bipolar disorder.
Apparently that has changed, if this report is to be believed:
"There's evidence suggesting that circadian genes may be involved in bipolar disorder," said Dr. Colleen McClung, assistant professor of psychiatry and the study's senior author. "What we've done is taken earlier findings a step further by engineering a mutant mouse model displaying an overall profile that is strikingly similar to…
clock | March 3, 2007This news just came in:
Charles F- Ehret died of natural causes on February 24th at his home in Grayslake, Illinois, a suburb of Chicago.
His Wikipedia entry is quote short:
Charles Frederick Ehret is a WWII veteran (Battle of the Bulge/Ardennes along the Siegfried Line) as well as a world renowned molecular biologist who worked at Argonne National Laboratory (ANL) in Lemont, Illinois, USA, for 40 years. Dr. Ehret researched the effects of electromagnetic radiation on bacillus megaterium with Dr. Edward Lawrence (Larry) Powers, as well as the effects of time shifts on paramecia, rats and…
clock | February 28, 2007This is a story about two mindsets - one scientific, one not - both concerned with the same idea but doing something very different with it. Interestingly, both arrived in my e-mail inbox on the same day, but this post had to wait until I got out of bed and started feeling a little bit better.
First, just a little bit of background:
Circadian oscillations are incredibly robust, i.e., resistant to perturbations and random noise from the environment. Ricardo Azevedo has described one model that accounts for such robustness in his two-part post here and here and others have used other methods…
clock | February 12, 2007 This post is a modification from two papers written for two different classes in History of Science, back in 1995 and 1998. It is a part of a four-post series on Darwin and clocks. I first posted it here on December 02, 2004 and then again here on January 06, 2005:
II. Darwin on Time
There is a season for everything
And a time for every purpose under the heaven:
A time to be born, and a time to die:
A time to plant and a time to reap.... (Ecclesiastes)
In this section I will attempt to evaluate from Darwin's writings what he thought about the selective role of environmental periodicities…
clock | February 10, 2007There are several journals dedicated to biological rhythms or sleep. Of those I regularly check only two or three of the best, so I often miss interesting papers that occur in lower-tier journals. Here is one from December 2006 that caught my eye the other day:
Mammalian activity - rest rhythms in Arctic continuous daylight:
Activity - rest (circadian) rhythms were studied in two species of Arctic mammals living in Arctic continuous daylight with all human-induced regular environmental cues (zeitgebers) removed. The two Arctic species (porcupine and ground squirrel) lived outdoors in large…
clock | February 5, 2007Two interesting papers came out last week, both using transgenic mice to ask important questions about circadian organization in mammals. Interestingly, in both cases the gene inserted into the mouse was a human gene, though the method was different and the question was different:
Turning a Mouse Into A Lark
The first paper (Y. Xu, K.L. Toh, C.R. Jones, J.-Y. Shin, Y.-H. Fu, and L.J. PtáÄekModeling of a Human Circadian Mutation Yields Insights into Clock Regulation by PER2. Cell, Vol 128, 59-70, 12 January 2007) is concerned with the human clock mutation that is responsible for FASBS (…
clock | January 31, 2007In light of my post earlier today about the discrepanices between 'real time' and 'clock time' (or 'social time'), it is heartening that the Parliament in the U.K. wisely decided not to switch their clocks to the time the rest of Europe observes. If they did, they would be seriously out of whack. After all, at Zero Meridian in Greenwich (yup, I stood astride it, of course), midnight is really midnight - it is the middle of the time zone. Resetting it by one hour would put the Brits at the far Western edge of another time zone and they would always experience true midnight a long time (60-…
clock | January 31, 2007While study of Time-Perception is, according to many, a sub-discipline of chronobiology, I personally know very little about it. Time perception is defined as interval timing, i.e., measuring duration of events (as opposed to counting, figuring which one of the two events happened first and which one second, or measuring time of day or year).
Still, since this blog is about all aspects of biological timing, I have to point you to a new paper in Neuron (press release) about a new computer model for human time-perception.
"If you toss a pebble into a lake," he explained, "the ripples of water…
clock | January 31, 2007
If you really read this blog "for the articles", especially the chronobiology articles, you are aware that the light-dark cycle is the most powerful environmental cue entraining circadian clocks. But it is not the only one. Clocks can also be entrained by a host of other ("non-photic") cues, e.g., scheduled meals, scheduled exercise, daily dose of melatonin, etc.
Clocks in heterothermic ("cold-blooded") animals can also entrain to temperature cycles. Lizards can entrain to temperature cycles (pdf) in which the difference between nightime low and daytime high temperatures is as small as…
clock | January 29, 2007If you discover a brain chemical which, when missing or malfunctioning (due to a mutation in its receptor) abruptly puts people and animals to sleep when they don't want to - a condition called narcolepsy - then you can work on creating a drug that acts in the opposite way and induces sleep when you want to.
Apparently, that is what a Swiss team just did (Nature news report here and Nature blog commentary here). The drug, still without a sexy name, is known by its "code-name" ACT-078573.
The target of the drug is the orexin system. Orexins (also known as hypocretins - the discovery was…
clock | January 27, 2007Considering I've been writing textbook-like tutorials on chronobiology for quite a while now, trying always to write as simply and clearly as possible, and even wrote a Basic Concepts And Terms post, I am surprised that I never actually defined the term "biological clock" itself before, despite using it all the time.
Since the science bloggers started writing the 'basic concepts and terms' posts recently, I've been thinking about the best way to define 'biological clock' and it is not easy! Let me try, under the fold:
A biological clock is a structure that times regular re-occurence of…
clock | January 27, 2007The Merriam-Webster Word of the Day for January 27, 2007 is:
quotidian ⢠\kwoh-TID-ee-un\ ⢠adjective
1 : occurring every day
*2 : belonging to each day : everyday
3 : commonplace, ordinary
Example Sentence:
As an employee, Fiona is gifted at solving the difficult problems that arise from time to time, but she is often careless about the quotidian responsibilities of her job.Did you know?
In Shakespeare's play As You Like It, the character Rosalind observes that Orlando, who has been running about in the woods carving her name on trees and hanging love poems on branches, "…
clock | January 1, 2007 If you are interested in the background and recent history of the research on mammalian SCN in line of Erik Herzog's work I described in VIP synchronizes mammalian circadian pacemaker neurons and A Huge New Circadian Pacemaker Found In The Mammalian Brain, you may want to look at these old Circadiana posts as well:
-----------------------------Cutting Edge: Circadian Rhythm of Astrocytes (February 02, 2005):
Erik has done it again. He is not one to publish 30 papers per year, but whenever he publishes one, it always gives me the chills and thrills! What beautiful science:
Circadian Rhythm…
clock | December 20, 2006For science bloggers, a study older than a week is often too old to blog about. For scientists, last five years of literature are the most relevant (and many grad students, unfortunately, never read the older stuff). I thought that for journalists, 24-cycle was everything. Apparently not.
Northwest Explorer's 'Senior Life' columnist is having a Senior Moment, I guess. In this article about Seasonal Affective Disorder, he mentions a study that is several years old and, what's worse, has been shown to be wrong. No, the mammalian circadian clock CANNOT be reset by shining a light at the…
clock | December 20, 2006Here is the second guest-post by Heinrich (from March 20, 2005):
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Here is the #2 guest contribution by Heinrich (not Heindrocket) of She Flies With Her Own Wings (http://coeruleus.blogspot.com/):
Most of this post was inspired by a grand rounds / journal club given by David Dinges about two weeks ago based on years of his own research and large surveys. One line of argument in the presentation that I thought was particularly interesting - one that we as sleep researchers might want to remember when we write grants and perform our…
clock | December 20, 2006Memory Experts Show Sleeping Rats May Have Visual Dreams:
Matthew A. Wilson, professor of brain and cognitive sciences at MIT's Picower Institute for Learning and Memory, and postdoctoral associate Daoyun Ji looked at what happens in rats' brains when they dream about the mazes they ran while they were awake.
In a landmark 2001 study, Wilson showed that rats formed complex memories for sequences of events experienced while they were awake, and that these memories were replayed while they slept--perhaps reflecting the animal equivalent of dreaming.
Because these replayed memories were detected…
clock | December 19, 2006If you really read this blog 'for the articles', you know some of my recurrent themes, e.g., that almost every biological function exhibits cycles and that almost every cell in every organism contains a more-or-less functioning clock. Here is a new paper that combines both of those themes very nicely, but I'll start with a little bit of background first.
Daily Rhythms in Sensory Sensitivity
If almost every biochemical, physiological and behavioral function exhibits daily cycles, it is no surprise that such rhythms have been discovered in sensory sensitivity of many sensory modalities -…
clock | December 18, 2006Well, not me, but people who know what I know. Heinrich aka Sir Oolius explains how the US military uses the knowledge of circadian rhythms and sleep in applications to torture. Just place the prisoners in a state of perpetual jet-lag and no temporal cues, then interrogate them at the time where their circadian rhythm of cognitive performance is at its lowest.