chronobiology
clock | October 24, 2007I am sure I have ranted about the negative effects of DST here and back on Circadiana, but the latest study - The Human Circadian Clock's Seasonal Adjustment Is Disrupted by Daylight Saving Time (pdf) (press releases: ScienceDaily, EurekAlert) by Thomas Kantermann, Myriam Juda, Martha Merrow and Till Roenneberg shows that the effects are much more long-lasting and serious than previously thought. It is not "just one hour" and "you get used to it in a couple of days". Apparently it takes weeks for the circadian system to adjust, and in some people it never does. In this day and age of…
clock | September 27, 2007
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…
clock | September 20, 2007A post-doctoral position is available in the laboratory of Dr. Tosini to investigate the cellular and molecular mechanisms that control circadian rhythms in the mammalian retina [Tosini et al., (2007) Faseb J.; Sakamoto et al., (2004). J. Neuroscience 24: 9693-9697; Fukuhara et al., (2004) J. Neuroscience 24:1803-1811; Tosini G., Menaker, M. (1996) Science, 272: 419-421).The position is funded by a grant from the National Institute of Health.
The work will focus on the characterization of newly developed transgenic mice using physiological (ERG), molecular (Q-PCR and Laser Capture…
clock | September 19, 2007Circadian clocks: regulators of endocrine and metabolic rhythms by Michael Hastings, John S O'Neill and Elizabeth S Maywood is a new and excellent review of the interaction between the clocks and hormones in mammals, focusing at the molecular level. The pre-print PDF of the article is freely available on the Journal of Endocrinology site.
clock | August 12, 2007NBM found an excellent online article (which I have seen before but I forgot) depicting Phase-Response Curves (PRC) to injections of melatonin in humans, rodents and lizards.
Note how the shape is roughly opposite to that of a PRC to light pulses, i.e., at phases at which light elicits phase-delays, melatonin produces advances and vice versa:
The lizard PRC was actually constructed in our lab, about ten years before I joined. The article, though, gives the wrong reference to this:
Underwood, H. and M. Harless (1985). "Entrainment of the circadian activity rhythm of a lizard to melatonin…
clock | August 10, 2007Sometimes a metaphor used in science is useful for research but not so useful when it comes to popular perceptions. And sometimes even scientists come under the spell of the metaphor. One of those unfortunate two-faced metaphors is the metaphor of the Biological Clock.
First of all, there are at least three common meanings of the term - it is used to describe circadian rhythms, to describe the rate of sequence change in the DNA over geological time, and to describe the reaching of a certain age at which human fertility drops off ("my clock is ticking").
I prefer the Rube-Goldberg Machine…
clock | August 3, 2007This post from March 27, 2006 starts with some of my old research and poses a new hypothesis.
The question of animal models
There are some very good reasons why much of biology is performed in just a handful of model organisms. Techniques get refined and the knowledge can grow incrementally until we can know quite a lot of nitty-gritty details about a lot of bioloigcal processes. One need not start from Square One with every new experiment with every new species. One should, of course, occasionally test how generalizable such findings are to other organisms, but the value of models is hard…
clock | August 3, 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 | August 2, 2007This 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.
III. Whence Clocks?
Origin, Evolution, and Adaptive Function of Biological ClocksThe old saw about the early bird just goes to show that the worm should have stayed in bed. (Heinlein 1973)Now darkness falls.
Quail chirps.
What use Hawk eyes?
(Basho)
Local/temporary and global/universal environments. In the study of adaptive functions, usually the question is…
clock | August 1, 2007This post, originally published on January 16, 2005, was modified from one of my written prelims questions from early 2000.
EVOLUTIONARY PHYSIOLOGY OF BIOLOGICAL CLOCKS
"Circadian clocks allow organisms to predict, instead of merely react to, cyclic (predictable) changes in the environment". A sentence similar to this one is the opening phrase of many a paper in the field of chronobiology. Besides becoming a truth by virtue of frequent repetition, such a statement appeals to common sense. It is difficult to imagine a universe in which it was not true. Yet, the data supporting the above…
clock | July 31, 2007
If you are one of the few of my readers who actually slogged through my Clock Tutorials, especially the difficult series on Entrainment and Phase Response Curves, you got to appreciate the usefulness of the oscillator theory from physics in its application to the study of biological clocks. Use of physics models in the study of biological rhythms, pioneered by Colin Pittendrigh, is an immensely useful tool in the understanding of the process of entrainment to environmental cycles.
Yet, as I warned several times, a Clock is a metaphor and, as such, has to be treated with thought and caution…
clock | July 30, 2007This post, from January 25, 2006, describes part of the Doctoral work of my lab-buddy Chris.
Mammals have only one circadian pacemaker - the suprachiasmatic nucleus (SCN). Apparently all the other cells in the body contain circadian clocks, too, but only the SCN drives all the overt rhythms. Without the SCN, there are no rhythms - the peripheral clocks either get out of phase with each other, or their clocks stop ticking altogether.
If you place various tissues in a dish, the SCN cycles indefinitely. All other tissues are capable of only a few oscillations in the absence of a daily signal…
clock | July 29, 2007First 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.
When I was a kid I absolutely loved a book called "Il Ciondolino" by Ricardo Vamba - a book in two slim volumes for kids (how times change - try to publish a 200+ page book of dense text for children today!). I later found out that it was translated into English under the title The Prince And His Ants in 1910 (Luigi BERTELLI (M: 1858 or 1860 - 1920) (&ps: VAMBA) The Prince And His Ants [It-?]. Holt.(tr S F WOODRUFF) […
clock | July 28, 2007Being out of the lab, out of science, and out of funding for a while also means that I have not been at a scientific conference for a few years now, not even my favourite meeting of the Society for Research on Biological Rhythms. I have missed the last two meetings (and I really miss them - they are a blast!).
But it is funny how, many years later, one still remembers some posters from poster sessions. What makes a poster so memorable?
I guess it has something to do with one's interests - there is just not enough time during a session to check out every single one out of hundreds (or…
clock | July 26, 2007Hypotheses leading to more hypotheses (from March 19, 2006 - the Malaria Day):
I have written a little bit about malaria before, e.g, here and here, but this is my special Malaria Action Day post, inspired by a paper [1] that Tara sent me some weeks ago and I never got to write about it till now.
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In a journal called "Medical Hypotheses" Kumar and Sharma [1] propose that jet-lagged travellers may be more susceptible to getting infected with malaria. They write:
Rapid travel across several time zones leads to…
clock | July 24, 2007This 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…
clock | July 22, 2007This is an appropriate time of year for this post (February 05, 2006)...
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So, why do I say that it is not surprising the exposure to bright light alleviates both seasonal depression and other kinds of depression, and that different mechanisms may be involved?
In mammals, apart from visual photoreception (that is, image formation), there is also non-visual photoreception. The receptors of the former are the rods and cones that you all learned about in middle school. The receptors for the latter are a couple of thousand Retinal Ganglion…
clock | July 21, 2007A January 20, 2006 post placing a cool physiological/behavioral study into an evolutionary context.
There are two main hypotheses - not mutually exclusive - for the adaptive value of having a circadian clock. One is the Internal Synchronization hypothesis, stating that the circadian clock serves to synchronize biochemical and physiological processes within the body. The second is the External Synchronization hypothesis, stating that the circadian clock serves to syncronize the physiology and behavior to the natural environment.
The prediction from the Internal Hypothesis is that circadian…
clock | July 21, 2007Well, it's Thanksgiving tomorrow night so it's time to republish this post from last year, just in time for the ageless debate: does eating turkey meat make you sleepy? Some people say Yes, some people say No, and the debate can escalate into a big fight. The truth is - we do not know.
But for this hypothesis to be true, several things need to happen. In this post I look at the evidence for each of the those several things. Unfortunately, nobody has put all the elements together yet, and certainly not in a human. I am wondering...is there a simple easily-controlled experiment that…
clock | July 14, 2007You 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:…