Circadian Rhythm Affected By The Difference In Sensitivity To Light-information And Coupling Intensity Of SCN Neurons

The suprachiasmatic nucleus(SCN)is an endogenous clock in mammalian brain.It is the main clock for regulating biological physiological and behavioral rhythms,and has two major functions:regulating entrainment range and maintaining free running period.Like other brain tissues,the SCN are composed of neurons,which contain about 20000 neurons.They are usually divided into two groups i.e.,the ventrolateral part(VL)and the dorsomedial part(DM).They are coupled by neurotransmitters to form a network and output a uniform periodic oscillation signal.It is found that the neuronal coupling intensity and light sensitivity intensity are different between different groups,and the influence of these differences on the entrainment range and free running period of SCN has not been known.Therefore,this paper mainly makes a specific study on this kind of influence.First of all,we analyze the content to be studied through the basic theory of complex network,so as to determine the basic structure of SCN network(in this paper,SCN network is regarded as a fully connected network,that is,all neurons in the network have connected edges).Then,the Poincare model describing the dynamic behavior of the oscillator is modified to increase the heterogeneity of light sensitive intensity q and coupling strength p and the light-darkness cycles signals.The model of SCN neuron network under light-darkness was constructed.Then,the model is used for numerical simulation to study the influence of the heterogeneity of light sensitive intensity(q)and coupling intensity(p)on SCN entrainment range.We found that the relationship of the entrainment range to the difference depends on the coupling between two groups.When the coupling strength is much smaller than the light intensity,the relationship is parabolic-like,and the maximum of the entrainment range is obtained with no difference of the sensitivity.When the coupling strength is much larger than the light intensity,the relationship is monotonically changed,and the maximum of the entrainment range is obtained when the difference is the largest.Next the numerical simulation results are analyzed qualitatively to verify the correctness of the simulation results.Finally,based on the entrainment range research,the SCN network model was modified to remove the light-darkness cycle signal and the coupling intensity heterogeneity,and add the continuous illumination item.In this model,we study the influence of the heterogeneity of light sensitivity(q)on SCN free running period.We found that,when the difference of light sensitivity is smaller(i.e.q from 0 or 2 to 1),the SCN self-oscillation period is smaller.When there is no difference in light sensitivity(i.e.q=1),then the SCN self-oscillation period is minimum.Our finding may provide an explanation for the exitance of the difference in the sensitivity to light-information as well as shed light on how to increase the flexibility of the SCN represented by widening the entrainment range,so that the organism can better adapt to the changes of the external environment.