Some cuantifying measures for the circadian activity in the mammalian SCN

ROMÁN M; NIETO PS; GARBARINO PICO E; TAMARIT FA

Congreso; Giambiagi Winter School: 'Information Processing in Biological Systems, From Cells to Equations and Back; 2013

Virtually all living organisms exhibit circadian rhythms: variations in their biological processes with a period of about 24 hours. In the last decades clock genes were found in diverse organisms, which are fundamental for the establishment of circadian rhythms at the cellular level. In mammals, these clock genes are expressed in cells throughout the whole body and their activity is orchestrated from within the brain, in a tiny structure in the hypothalamus known as the suprachiasmatic nuclei (SCN). The braincells comprising such tissue are diverse and function in a coordinate fashion in order to drive physiological and behavioral rhythms, as they are able to communicate with each other, sync their activity and hence become -as a whole- a biological clock both precise and robust. But although the SCN cells function in a unified manner when coupled, they are not perfectly synchronous. In fact, the expression of clock genes within a slice displays a consistent (non-random) spatio-temporal pattern, that emerges as a consequence of the precise interactions between the SCN cells. The mechanisms by which these phase relationships are established are not well understood, but certainly depend on the integration of multiple intercellular signals present in the SCN,which ultimately defines its underlying functional connectivity. The physical sciences has to offer an ample repertoire of tools that could aid the process of quantifying these biological processes and hence clarify the inner mechanisms of the SCN. In particular, knowledge related to synchronization of complex networks can be used to gain understanding of the functional organization within the SCN. In this regard, the general aim of this work is to use theoretical tools in order to model the dynamical behavior observed in slices and to shed light on the SCN underlying connectivity involved in the emergence of such complex dynamics. In this work we use a model of circadian cellular oscillators coupled through different network architectures, in order to simulate the dynamical behavior observed in SCN slices. Some cuantifying measures, such as the ?phase locking? and the ?angular order parameter?, are proposed to characterize the emerging dynamical behavior in the model. We observe that, when these metrics are taken in consideration regarding the euclidean distance between network nodes, they reflect different profiles, having their origin in the underlying network topology. We posit that these metrics can be applied to experimental time-series from SCN slices in order to quantitatively characterize their spatio-temporal organization and potentially can be used as a tool for dilucidate the functional connectivity.