chronobiology
clock | May 2, 2008You and I, as well as all of our mammalian brethren, have just a few photopigments, i.e., colored molecules that change shape when exposed to light and subsequently trigger cascades of biochemical reactions leading to changes in electrical properties of sensory neurons, which lead to modulation of neurotransmitter release, which propagates the information from one neuron to the next until it is integrated and interpreted somewhere in the brain - we see the light!
More under the fold....
Mammals have rhodopsin (in rod-shaped photoreceptor cells in the retina of the eye), three or four color-…
clock | May 1, 2008
If 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 | April 25, 2008Since 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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Clocks, Migration and the Effects of Global Warming (December 23, 2005)
Circadian…
clock | April 23, 2008From January 20, 2006, on the need to check the model-derived findings in non-model organisms.
There are pros and cons to the prevalent use of just a dozen or so species as standard laboratory models. On one hand, when a large chunk of the scientific community focuses its energies on a single animal, techniques get standardized, suppliers produce affordable equipment and reagents, experiments are more likely to get replicated by other labs, it is much easier to get funding, and the result is speedy increase in knowledge.
On the other hand, there are drawbacks. One is narrow focus which can…
clock | April 21, 2008This 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…
clock | April 20, 2008One 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.
In the case of mammals, the two pacemakers are the left and the right suprachiasmatic nucleus (SCN). The tow nuclei are anatomically close to each other and have direct nerve connections between them, so it is not difficult to imagine how the two clocks manage to remain continuously coupled (syncronized) to each other and, together, produce a single output, thus synchronizing all the rhythms in the body.
In the…
clock | April 19, 2008One 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 multicelular 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 perpheral clocks generate…
clock | April 18, 2008How birds know when and where to migrate (from April 03, 2006)
I've never ever expected to see the word "Zugunruhe" in New York Times! But here it is. It is one of my most favourite words of all times (right after "elusive"), and is even described pretty accurately:
Zugunruhe brooks no confusion. It has a Germanic certainty, and there can be no doubt what it means, once you know what it means. I confess that I only learned the word this week. If I understand the paper about it by Barbara Helm of the Max Planck Institute for Ornithology in Andechs, Germany, and the late Eberhard Gwinner in…
clock | April 17, 2008
A 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 | April 17, 2008As traveling is not conducive to vigorous blogging (apart from posting travelogue pictures), I have asked a couple of friends to write guest posts here. The first to step up to the plate is Anne Marie who put together her passion for bats and my passion for biological clocks and wrote this fascinating post:
Casinos on the infamous Vegas "strip" spare no expenses when it comes to extravagant decorations and architecture. You can find everything from indoor gondola rides to full-sized pirate ships that are sunk in mock-battles multiple times each day. One thing that you might notice,…
clock | April 14, 2008
This 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 | April 12, 2008Being 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 | April 10, 2008From the Harvard Division of Sleep Medicine:
To honor the distinguished career of Professor Richard Kronauer, we will again award the Richard E Kronauer Prize for Excellence in Biomathematical Modeling. This is presented to a graduate student or post-doctoral fellow who has made significant contributions to Modeling Circadian Rhythmicity, Sleep Regulation or Neurobehavioral Function. If you would like to be considered for this prize or would like to nominate someone, please send a recent abstract or paper as well as a current C.V. to ebklerman@hms.harvard.edu before April 27 2008.
The award…
clock | April 7, 2008
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.…
clock | March 5, 2008It has been almost three years since I promised to write a post detailing the photoperiodic response in mammals. (Birds are more complicated).
Now Shelley gives a good example - the snowshoe hare which changes color annually: it is dark in summer and white in winter. It is pretty easy to remember - it's all the Mel-something molecules involved. So, here is a very simplified, but essentially correct description of how this happens:
Light is detected by the photo-pigment melanopsin in the retinal ganglion cells of the eye. The cells send a signal to the clock (in the suprachiasmatic nucleus…
clock | March 2, 2008
The 11th Biennial Meeting of the Society for Research on Biological Rhythms will be held in Sandestin, FL on May 17th-21st, 2008. And I'll be there. This meeting occurs every two years (on even-numbered years, the International Congress and the Gordon Conference are in odd-numbered years). I attended three or four of these when it was down on Amelia Island, FL. Then I skipped the one in Whistler, Canada, four years ago as I had no money to go, and the one in Sandestin two years ago as I was out of science. But I'll be going back - with a mission: to explain Open Access to my colleagues…
clock | February 14, 2008I found two articles interesting to me in today's issue of PLoS Computational Biology - the first one about becoming a good scientist, the other on circadian rhythms:
On the Process of Becoming a Great Scientist:
In the vein of promoting further debate and discussion, I provide here a different and perhaps deeper look at what makes a successful scientist. While I can't claim to have the reputation of Hamming, I grew up in a family of well-known scientists, and have had plenty of chances to observe the trajectories of scientific careers over my lifetime. Based on that experience, I propose the…
clock | January 28, 2008Keystone sleep/circadian meeting. Jay Dunlap, Emmanuel Mignot and Amita Seghal are organizing a Keystone meeting on Genetics and Biochemistry of Sleep in Lake Tahoe, March 7-12 (click here to see large):
clock | January 7, 2008
I had no time to read this in detail and write a really decent overview here, perhaps I will do it later, but for now, here are the links and key excerpts from a pair of exciting new papers in PLoS Biology and PLoS ONE, which describe the patterns of expression of a second type of cryptochrome gene in Monarch butterflies.
This cryptochrome (Cry) is more similar to the vertebrate Cry than the insect Cry, also present in this butterfly. The temporal and spatial patterns of expression of the two types of Cry suggest that they may be involved in the transfer of time-information from the…
clock | December 22, 2007On Pilobolous:
When I first wrote my post on Pilobolus (here and here) I really wanted to do something extra, which I could not do at the time. If you scroll down that post, you will see I reprinted the Figure 1 from the Uebelmesser paper. What I wanted to do was find (and I asked around for something like that) the exact times of dawn and dusk at the site where Uebelmesser did her work and thus be able to figure out the dates when the tests were done and the exact phase-relationship between the dawn and the time when Pilobolus shoots its spores.
Now, I see that such a chart exists (via) and…