Category Archives: Clock Tutorials

Persistence In Perfusion

Blogging on Peer-Reviewed Research

Persistence In PerfusionThis post, from January 25, 2006, describes part of the Doctoral work of my lab-buddy Chris.

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Phase-Response Curve and T-Cycles: Clocks and Photoperiodism in Quail

Phase-Response Curve and T-Cycles: Clocks and Photoperiodism in QuailThis is a summary of my 1999 paper, following in the footsteps of the work I described here two days ago. The work described in that earlier post was done surprisingly quickly – in about a year – so I decided to do some more for my Masters Thesis.
The obvious next thing to do was to expose the quail to T-cycles, i.e., non-24h cycles. This is some arcane circadiana, so please refer to the series of posts on entrainment from yesterday and the two posts on seasonality and photoperiodism posted this morning so you can follow the discussion below:
There were three big reasons for me to attempt the T-cycle experiment at that time:

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How eyes talk to each other?

How eyes talk to each other?One of the important questions in the study of circadian organization is the way multiple clocks in the body communicate with each other in order to produce unified rhythmic output.

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Quail: How many clocks?

Quail:  How many clocks?One of the assumptions in the study of circadian organization is that, at the level of molecules and cells, all vertebrate (and perhaps all animal) clocks work in roughly the same way. The diversity of circadian properties is understood to be a higher-level property of interacting multicellular and multi-organ circadian systems: how the clocks receive environmental information, how the multiple pacemakers communicate and synchronize with each other, how they convey the temporal information to the peripheral clocks in all the other cells in the body, and how peripheral clocks generate observable rhythms in biochemistry, physiology and behavior.

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Chossat’s Effect in humans and other animals

Chossat's Effect in humans and other animalsThis April 09, 2006 post places another paper of ours (Reference #17) within a broader context of physiology, behavior, ecology and evolution.
The paper was a result of a “communal” experiment in the lab, i.e., it was not included in anyone’s Thesis. My advisor designed it and started the experiment with the first couple of birds. When I joined the lab, I did the experiment in an additional number of animals. When Chris joined the lab, he took over the project and did the rest of the lab work, including bringing in the idea for an additional experiment that was included, and some of the analysis. We all talked about it in our lab meetings for a long time. In the end, the boss did most of the analysis and all of the writing, so the order of authors faithfully reflects the relative contributions to the work.
What is not mentioned in the post below is an additional observation – that return of the food after the fasting period induced a phase-shift of the circadian system, so we also generated a Phase-Response Curve, suggesting that food-entrainable pacemaker in quail is, unlike in mammals, not separate from the light-entrainable system.
Finally, at the end of the post, I show some unpublished data – a rare event in science blogging.

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Clock Tutorial #16: Photoperiodism – Models and Experimental Approaches

Clock Tutorial #16:  Photoperiodism - Models and Experimental ApproachesThis post (written on August 13, 2005) describes the basic theory behind photoperiodism and some experimental protocols developed to test the theory.

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Does circadian clock regulate clutch-size in birds? A question of appropriateness of the model animal.

 Does circadian clock regulate clutch-size in birds? A question of appropriateness of the model animal.This post from March 27, 2006 starts with some of my old research and poses a new hypothesis.

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Clock Tutorial #15: Seasonality

Clock Tutorial #15:  SeasonalityThis post (click on the icon) was originally written on May 07, 2005, introducing the topic of neuroendocrine control of seasonal changes in physiology and behavior.

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How Global Warming Disrupts Biological Communities – a Chronobiological Perspective

Clocks, Migration and the Effects of Global WarmingSince this is another one of the recurring themes on my blog, I decided to republish all of my old posts on the topic together under the fold. Since my move here to the new blog, I have continued to write about this, e.g., in the following posts:
Preserving species diversity – long-term thinking
Hot boiled wine in the middle of the winter is tasty….
Global Warming disrupts the timing of flowers and pollinators
Global Warming Remodelling Ecosystems in Alaska

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Clock Tutorial #14: Interpreting The Phase Response Curve

Clock Tutorial #14:  Interpreting The Phase Response CurveThis is the sixth post in a series about mechanism of entrainment, running all day today on this blog. In order to understand the content of this post, you need to read the previous five installments. The original of this post was first written on April 12, 2005.

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The Mighty Ant-Lion

The Mighty Ant-LionFirst written on March 04, 2005 for Science And Politics, then reposted on February 27, 2006 on Circadiana, a post about a childrens’ book and what I learned about it since.

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Clock Tutorial #13: Using The Phase Response Curve

Clock Tutorial #13:  Using The Phase Response CurveThis is the fifth post in a series about mechanism of entrainment. Originally written on April 11, 2005.

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Friday Weird Sex Blogging – Postscript to Pittendrigh’s Pet Project – Phototaxis, Photoperiodism and Precise Projectile Parabolas of Pilobolus on Pasture Poop

Postscript to Pittendrigh's Pet Project - Phototaxis, Photoperiodism and Precise Projectile Parabolas of Pilobolus on Pasture PoopWe have recently covered interesting reproductive adaptations in mammals, birds, insects, flatworms, plants and protists. For the time being (until I lose inspiration) I’ll try to leave cephalopod sex to the experts and the pretty flower sex to the chimp crew.
In the meantime, I want to cover another Kingdom – the mysterious world of Fungi. And what follows is not just a cute example of a wonderfully evolved reproductive strategy, and not just a way to couple together my two passions – clocks and sex – but also (at the very end), an opportunity to post some of my own hypotheses online.

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Clock Tutorial #12: Constructing the Phase Response Curve

Clock Tutorial #12:  Constructing the Phase Response CurveThe fourth post in the series on entrainment, originally written on April 10, 2005, explains the step-by-step method of constructing a PRC.

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Some hypotheses about a possible connection between malaria and jet-lag

Some hypotheses about a possible connection between malaria and jet-lagHypotheses leading to more hypotheses (from March 19, 2006 – the Malaria Day):

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Clock Tutorial #11: Phase-Shifting Effects Of Light

Clock Tutorial #11: Phase-Shifting Effects Of LightThe third post in the series on entrainment, first written on April 10, 2005, starts slowly to get into the meat of things…As always, clicking on the spider-clock icon will take you to the site of the original post.

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Everything You Always Wanted To Know About Sleep (But Were Too Afraid To Ask)

ClockWeb%20logo2.JPG
This post is perhaps not my best post, but is, by far, my most popular ever. Sick and tired of politics after the 2004 election I decided to start a science-only blog – Circadiana. After a couple of days of fiddling with the templae, on January 8, 2005, I posted the very first post, this one, at 2:53 AM and went to bed. When I woke up I was astonished as the Sitemeter was going wild! This post was linked by BoingBoing and later that day, by Andrew Sullivan. It has been linked by people ever since, as recently as a couple of days ago, although the post is a year and a half old. Interestingly, it is not linked so much by science or medical bloggers, but much more by people who write about gizmos and gadgets or popular culture on LiveJournal, Xanga and MySpace, as well as people putting the link on their del.icio.us and stumbleupon lists. In order to redirect traffic away from Circadiana and to here, I am reposting it today, under the fold.

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Clock Tutorial #10: Entrainment

Clock Tutorial #10: EntrainmentThis is the second in a series of posts on the analysis of entrainment, originally written on April 10, 2005.

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Circadian Rhythms, or Not, in Arctic Reindeer

Blogging on Peer-Reviewed Research

Circadian Rhythms, or Not, in Arctic ReindeerA January 20, 2006 post placing a cool physiological/behavioral study into an evolutionary context.

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Clock Tutorial #9: Circadian Organization In Japanese Quail

Circadian Organization In Japanese QuailGoing into more and more detail, here is a February 11, 2005 post about the current knowledge about the circadian organization in my favourite animal – the Japanese quail.

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Seasonal Affective Disorder – The Basics

Seasonal Affective Disorder - The BasicsThis is an appropriate time of year for this post (February 05, 2006)…

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Clock Tutorial #8: Circadian Organization In Non-Mammalian Vertebrates

Circadian Organization In Non-Mammalian Vertebrates This post was originally written on February 11, 2005. Moving from relatively simple mammalian model to more complex systems.

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Oxytocin and Childbirth. Or not.

Blogging on Peer-Reviewed Research

From the Archives

Blogging on Peer-Reviewed Research

When teaching human or animal physiology, it is very easy to come up with examples of ubiqutous negative feedback loops. On the other hand, there are very few physiological processes that can serve as examples of positive feedback. These include opening of the ion channels during the action potential, the blood clotting cascade, emptying of the urinary bladder, copulation, breastfeeding and childbirth. The last two (and perhaps the last three!) involve the hormone oxytocin. The childbirth, at least in humans, is a canonical example and the standard story goes roughly like this:

When the baby is ready to go out (and there’s no stopping it at this point!), it releases a hormone that triggers the first contraction of the uterus. The contraction of the uterus pushes the baby out a little. That movement of the baby stretches the wall of the uterus. The wall of the uterus contains stretch receptors which send signals to the brain. In response to the signal, the brain (actually the posterior portion of the pituitary gland, which is an outgrowth of the brain) releases hormone oxytocin. Oxytocin gets into the bloodstream and reaches the uterus triggering the next contraction which, in turn, moves the baby which further stretches the wall of the uterus, which results in more release of oxytocin…and so on, until the baby is expelled, when everything returns to normal.

As usual, introductory textbook material lags by a few years (or decades) behind the current state of scientific understanding. And a brand new paper just added a new monkeywrench into the story. Oxytocin in the Circadian Timing of Birth by Jeffrey Roizen, Christina E. Luedke, Erik D. Herzog and Louis J. Muglia was published last Tuesday night and I have been poring over it since then. It is a very short paper, yet there is so much there to think about! Oh, and of course I was going to comment on a paper by Erik Herzog – you knew that was coming! Not just that he is my friend, but he also tends to ask all the questions I consider interesting in my field, including questions I wanted to answer myself while I was still in the lab (so I live vicariously though his papers and blog about every one of them).
Unfortunately, I have not found time yet to write a Clock Tutorial on the fascinating topic of embryonic development of the circadian system in mammals and the transfer of circadian time from mother to fetus – a link to it would have worked wonderfully here – so I’ll have to make shortcuts, but I hope that the gist of the paper will be clear anyway.

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Clock Tutorial #7: Circadian Organization in Mammals

Circadian Organization in Mammals This February 06, 2005 post describes the basic elements of the circadian system in mammals.

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A Huge New Circadian Pacemaker Found In The Mammalian Brain

Blogging on Peer-Reviewed Research

A Huge New Circadian Pacemaker Found In The Mammalian BrainIf 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.

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Clock Tutorial #6: To Entrain Or Not To Entrain, That Is The Question

 Clock Tutorial #6: To Entrain Or Not To Entrain, That Is The QuestionThis post from February 03, 2005 covers the basic concepts and terms on entrainment. This is also the only blog post to date that I am aware of that was cited in a scientific paper.

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Lithium, Circadian Clocks and Bipolar Disorder

Lithium, Circadian Clocks and Bipolar DisorderYou probably realize by now that my expertise is in clocks and calendars of birds, but blogging audience forces me to occasionally look into human clocks from a medical perspective. Reprinted below the fold are three old Circadiana posts about the connection between circadian clocks and the bipolar disorder, the third one being the longest and most involved. Here are the links to the original posts if you want to check the comments (especially the first comment on the third post):
January 18, 2005: Clocks and Bipolar Disorder
August 16, 2005: Bipolar? Avoid night shift
February 19, 2006: Lithium, Circadian Clocks and Bipolar Disorder

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ClockTutorial #5: Circadian Organization

ClockTutorial #5: Circadian Organization
I wrote this post back on February 02, 2005 in order to drive home the point that the circadian clock is not a single organ, but an organ system comprised of all cells in the body linked in a hierarchical manner:

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Flirting under Moonlight on a Hot Summer Night, or, The Secret Night-Life of Fruitflies

Flirting under Moonlight on a Hot Summer Night, or, The Secret Night-Life of FruitfliesAs we mentioned just the other day, studying animal behavior is tough as “animals do whatever they darned please“. Thus, making sure that everything is controlled for in an experimental setup is of paramount importance. Furthermore, for the studies to be replicable in other labs, it is always a good idea for experimental setups to be standardized. Even that is often not enough. I do not have access to Science but you may all recall a paper from several years ago in which two labs tried to simultaneously perform exactly the same experiment in mice, using all the standard equipment, exactly the same protocols, the same strain bought from the same supplier on the same date, the same mouse-feed, perhaps even the same colors of technicians’ uniforms and yet, they got some very different data!
The circadian behavior is, fortunately, not chaotic, but quite predictable, robust and easily replicable between labs in a number of standard model organisms. Part of the success of the Drosophila research program in chronobiology comes from the fact that for decades all the labs used exactly the same experimental apparatus, this one, produced by Trikinetics (Waltham, Massachusetts) and Carolina Biologicals (Burlington, North Carolina):
drosophila%20apparatus.jpg
This is a series of glass tubes, each containing a single insect. An infrared beam crosses the middle of each tube and each time the fly breaks the beam, by walking or flying up and down the tube, the computer registers one “pen deflection”. All of those are subsequently put together into a form of an actograph, which is the standard format for the visual presentation of chronobiological data, which can be further statistically analyzed.
The early fruitfly work was done mainly in Drosophila pseudoobscura. Most of the subsequent work on fruitfly genetics used D.melanogaster instead. Recently, some researchers started using the same setup to do comparative studies of other Drosophila species. Many fruitfly clock labs have hundreds, even thousands, of such setups, each contained inside a “black box” which is essentially an environmental chamber in which the temperature and pressure are kept constant, noise is kept low and constant (“white noise”), and the lights are carefully controlled – exact timing of lights-on and lights-off as well as the light intensity and spectrum.
In such a setup, with a square-wave profile of light (abrupt on and off switches), every decent D.melanogaster in the world shows this kind of activity profile:
fruitfly%20crepuscular.JPG
The activity is bimodal: there is a morning peak (thought to be associated with foraging in the wild) and an evening peak (thought to be associated with courtship and mating in the wild).
The importance of standardization is difficult to overemphasize – without it we would not be able to detect many of the subtler mutants, and all the data would be considered less trustworthy. Yet, there is something about standardization that is a negative – it is highly artificial. By controlling absolutely everything and making the setup as simple as possible, it becomes very un-representative of the natural environment of the animal. Thus, the measured behavior is also likely to be quite un-natural.
Unlike in the lab, the fruitflies out in nature do not live alone – they congregate with other members of the species. Unlike in a ‘black box’, the temperature fluctuates during the day and night in the real world. Also unlike the lab, the intensity and spectrum of light change gradually during the duration of the day while the nights are not pitch-black: there are stars and the Moon providing some low-level illumination as well. Thus, after decades of standardized work, it is ripe time to start investigating how the recorded behaviors match up with the reality of natural behavior in fruitflies.
Three recent papers address these questions by modifying the experimental conditions in one way or another, introducing additional environmental cues that are usually missing in the standard apparatus (and if you want to know what they found, follow me under the fold):

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Clock Tutorial #4: On Methodology

Clock Tutorial #4: On Methodology I wrote this post back on January 23, 2005. It explains how clock biologists think and how they design their experiments:

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The Lark-Mouse and the Prometheus-Mouse

Blogging on Peer-Reviewed Research

The Lark-Mouse and the Prometheus-MouseTwo interesting papers came out last week [from the Archives - click on the clock logo to see the original post], 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:

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Clock Tutorial #3c – Darwin On Time

Darwin On Time 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:

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A Pacemaker is a Network

A Pacemaker is a NetworkThis is going to be a challenging post to write for several reasons. How do I explain that a paper that does not show too much new stuff is actually a seminal paper? How do I condense a 12-page Cell paper describing a gazillion experiments without spending too much time on details of each experiment (as much as I’d love to do exactly that)? How do I review it calmly and critically without gushing all over it and waxing poetically about its authors? How do I put it in proper theoretical and historical perspective without unnecessarily insulting someone? I’ll give it a try and we’ll see how it turns out (if you follow me under the fold).
Clock Genes – a brief history of discovery
Late 1990s were a period of amazing activity and rate of discovery in chronobiology, specifically in molecular basis of circadian rhythms. Sure, a few mutations resulting in period changes or arrhythmicity were known before, notably period in fruitflies, frequency in the fungus Neurospora crassa, the tau mutation in hamsters and some unidentified mutations in a couple of Protista.
But in 1995, as the molecular techniques came of age, flood-gates opened and new clock genes were discovered almost every week (or so it appeared).

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ClockTutorial #3b – Whence Clocks?

ClockTutorial #3b - Whence Clocks?This post about the origin, evolution and adaptive fucntion of biological clocks originated as a paper for a class, in 1999 I believe. I reprinted it here in December 2004, as a third part of a four-part post. Later, I reposted it here.

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Everything Important Cycles

Everything Important CyclesMicroarrays have been used in the study of circadian expression of mammalian genes since 2002 and the consensus was built from those studies that approximately 15% of all the genes expressed in a cell are expressed in a circadian manner. I always felt it was more, much more.
I am no molecular biologist, but I have run a few gels in my life. The biggest problem was to find a control gene – one that does not cycle – to make the comparisons to. Actin, which is often used in such studies as control, cycled in our samples. In the end, we settled on one of the subunits of the ribosome as we could not detect a rhythm in its expression. The operative word is “could not detect”. My sampling rate was every 3 hours over a 24-hour period, so it is possible that we could have missed circadian expression of a gene that has multiple peaks, or a single very narrow peak, or a very low amplitude of cycling (it still worked as a control in our case, for different reasons). Thus, my feeling is that everything or almost everything that is expressed in a cell will be expressed in a rhythmic pattern.
If you have heard me talk about clocks (e.g., in the classroom), or have read some of my Clock Tutorials, you know that I tend to say something like “All the genes that code for proteins that are important for the core function of a cell type are expressed in a circadian fashion”. So, genes important for liver function will cycle in the liver cells, genes important for muscle function will cycle in muscle cells, etc.
But I omit to note that all such genes that are important for the function of the cell type are all the genes that are expressed in that cell. The genes not used by that cell are not expressed. But I could not go straight out and say “all the genes that are expressed in a cell are expressed in a circadian pattern”, because I had no data to support such a notion. Until yesterday.
What happened yesterday?

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ClockTutorial #3a – Clock Evolution

ClockTutorial #3a - Clock EvolutionThis post, originally published on January 16, 2005, was modified from one of my written prelims questions from early 2000.

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Clock Classics: It all started with the plants

From the ArchivesThis is a repost of a May 29, 2008 post:

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ClockTutorial #2a: Forty-Five Years of Pittendrigh’s Empirical Generalizations

From the Archives
This is the third in the series of posts designed to provide the basics of the field of Chronobiology. This post is interesting due to its analysis of history and sociology of the discipline, as well as a look at the changing nature of science. You can check out the rest of Clock Tutorials here.

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The Clock Metaphor

The Clock Metaphor
Chad wrote a neat history of (or should we say ‘evolution of’) clocks, as in “timekeeping instruments”. He points out the biological clocks are “…sort of messy application, from the standpoint of physics…” and he is right – for us biologists, messier the better. We wallow in mess, cherish ambiguity and relish in complexity. Anyway, he is talking about real clocks – things made by people to keep time. And he starts with a simple definition of what a clock is:

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ClockTutorial #2: Basic Concepts and Terms

From the Archives
This is the second in the series of posts designed to provide the basics of the field of Chronobiology. See the first part: ClockTutorial #1 – What Is Chronobiology and check out the rest of them here – they will all, over time, get moved to this blog.

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Basics: Biological Clock

Basics: Biological ClockConsidering 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:

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ClockTutorial #1 – What Is Chronobiology

ClockWeb%20logo2.JPG This is the first in a series of posts from Circadiana designed as ClockTutorials, covering the basics of the field of Chronobiology. It was first written on January 12, 2005:

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Chossat’s Effect in humans and other animals

Chossat's Effect in humans and other animalsThis April 09, 2006 post places another paper of ours (Reference #17) within a broader context of physiology, behavior, ecology and evolution.
The paper was a result of a “communal” experiment in the lab, i.e., it was not included in anyone’s Thesis. My advisor designed it and started the experiment with the first couple of birds. When I joined the lab, I did the experiment in an additional number of animals. When Chris joined the lab, he took over the project and did the rest of the lab work, including bringin in the idea for an additional experiment that was included, and some of the analysis. We all talked about it in our lab meetings for a long time. In the end, the boss did most of the analysis and all of the writing, so the order of authors faithfully reflects the relative contributions to the work.
What is not mentioned in the post below is an additional observation – that return of the food after the fasting period induced a phase-shift of the circadian system, so we also generated a Phase-Response Curve, suggesting that food-entrainable pacemaker in quail is, unlike in mammals, not separate from the light-entrainable system.
Finally, at the end of the post, I show some unpublished data – a rare event in science blogging.

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Some hypotheses about a possible connection between malaria and jet-lag

Some hypotheses about a possible connection between malaria and jet-lagHypotheses leading to more hypotheses (from March 19, 2006 – the Malaria Day):

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Lithium, Circadian Clocks and Bipolar Disorder

Lithium, Circadian Clocks and Bipolar DisorderYou probably realize by now that my expertise is in clocks and calendars of birds, but blogging audience forces me to occasionally look into human clocks from a medical perspective. Reprinted below the fold are three old Circadiana posts about the connection between circadian clocks and the bipolar disorder, the third one being the longest and most involved. Here are the links to the original posts if you want to check the comments (especially the first comment on the third post):
January 18, 2005: Clocks and Bipolar Disorder
August 16, 2005: Bipolar? Avoid night shift
February 19, 2006: Lithium, Circadian Clocks and Bipolar Disorder

Continue reading

Everything Important Cycles

Everything Important CyclesMicroarrays have been used in the study of circadian expression of mammalian genes since 2002 and the consensus was built from those studies that approximately 15% of all the genes expressed in a cell are expressed in a circadian manner. I always felt it was more, much more.
I am no molecular biologist, but I have run a few gels in my life. The biggest problem was to find a control gene – one that does not cycle – to make the comparisons to. Actin, which is often used in such studies as control, cycled in our samples. In the end, we settled on one of the subunits of the ribosome as we could not detect a rhythm in its expression. The operative word is “could not detect”. My sampling rate was every 3 hours over a 24-hour period, so it is possible that we could have missed circadian expression of a gene that has multiple peaks, or a single very narrow peak, or a very low amplitude of cycling (it still worked as a control in our case, for different reasons). Thus, my feeling is that everything or almost everything that is expressed in a cell will be expressed in a rhythmic pattern.
If you have heard me talk about clocks (e.g., in the classroom), or have read some of my Clock Tutorials, you know that I tend to say something like “All the genes that code for proteins that are important for the core function of a cell type are expressed in a circadian fashion”. So, genes important for liver function will cycle in the liver cells, genes important for muscle function will cycle in muscle cells, etc.
But I omit to note that all such genes that are important for the function of the cell type are all the genes that are expressed in that cell. The genes not used by that cell are not expressed. But I could not go straight out and say “all the genes that are expressed in a cell are expressed in a circadian pattern”, because I had no data to support such a notion. Until yesterday.
What happened yesterday?

Continue reading

A Pacemaker is a Network

A Pacemaker is a NetworkThis is going to be a challenging post to write for several reasons. How do I explain that a paper that does not show too much new stuff is actually a seminal paper? How do I condense a 12-page Cell paper describing a gazillion experiments without spending too much time on details of each experiment (as much as I’d love to do exactly that)? How do I review it calmly and critically without gushing all over it and waxing poetically about its authors? How do I put it in proper theoretical and historical perspective without unnecessarily insulting someone? I’ll give it a try and we’ll see how it turns out (if you follow me under the fold).
Clock Genes – a brief history of discovery
Late 1990s were a period of amazing activity and rate of discovery in chronobiology, specifically in molecular basis of circadian rhythms. Sure, a few mutations resulting in period changes or arrhythmicity were known before, notably period in fruitflies, frequency in the fungus Neurospora crassa, the tau mutation in hamsters and some unidentified mutations in a couple of Protista.
But in 1995, as the molecular techniques came of age, flood-gates opened and new clock genes were discovered almost every week (or so it appeared).

Continue reading

The Clock Metaphor

The Clock Metaphor
Chad wrote a neat history of (or should we say ‘evolution of’) clocks, as in “timekeeping instruments”. He points out the biological clocks are “…sort of messy application, from the standpoint of physics…” and he is right – for us biologists, messier the better. We wallow in mess, cherish ambiguity and relish in complexity. Anyway, he is talking about real clocks – things made by people to keep time. And he starts with a simple definition of what a clock is:

Continue reading

Basics: Biological Clock

Basics: Biological ClockConsidering 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:

Continue reading

Seasonal Affective Disorder – The Basics

Seasonal Affective Disorder - The BasicsThis is an appropriate time of year for this post (February 05, 2006)…

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