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A The.Si.M.Bio.Sys. Group study reveals un precedented data on circadian rhythms
6/5/2009
Fluctuations in light intensity allow restoring the regularity of circadian rhythms. This is the main conclusion of the work carried out by Javier Buceta, group leader of (Theoretical and In Silico Modelling of Biological Systems) from the Co.S.Mo Lab –based at the Barcelona Science Park– and Antoni Díez-Noguera, dean at the Faculty of Pharmacy of the University of Barcelona and group leader of Chronobiology at the Department of Physiology of the said faculty. Ekkehard Ullner and J. García Ojalvo, from the Polytechnic University of Catalonia (UPC) have also participated in the work. The study, that has been published today, 6th of May, in Biophysical Journal, under the title “Noise-induced coherence in multicellular circadian clocks” () appears on the front page of this journal.
In higher organisms, such as mammals, biological or circadian rhythms are generated by a multicellular genetic clock which is located in two regions of the hypothalamus that are connected to each other known as suprachiasmatic nuclei (SCN), containing about 10,000 neurons each. In order to generate and regulate circadian rhythms, our biological clock needs to use the “cooperative cell behaviour” of SCN neurones. These neurons generate self-sustained, coherent oscillations and interact in a coupled manner –through a genetic circuit- forming a single unique rhythm (circadian rhythm) that is very efficiently modulated by the light-darkness alternance cycle in the 24 hours of a day. Up until now, several studies had established that arrhythmia was associated with a lack of coordination among the periodic expression of SCN neurone proteins: in arrhythmic animals, the expression of SCN neurone proteins is desynchronised. It was also known that constant light is one of the triggers of arrhythmia. Neurons are only capable of generating self-sustained and coherent oscillations (biological rhythm) if the illumination is sufficiently low. However, when intensity is increased, this coherent behaviour is lost and the biological rhythm is distorted: animals become arrhythmic.

The researchers of the study looked at the possibility to restore rhythmicity in the animals under these conditions by means of fluctuations in light intensity and decided to use mathematical modelling techniques to simulate the genetic and cell interactions of the neuro-physiological system that regulates the biological clock. This in silico experiment is of extraordinary interest because it has enabled researchers to find out that light intensity fluctuations help restore rhythmicity and coherence of circadian rhythms, and not the contrary, that is, their distortion, as could be intuitively deduced.

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