Abstract
In mammals, the master clock is located in the suprachiasmatic nucleus (SCN), which is composed of about 20 000 nonidentical neuronal oscillators expressing different intrinsic periods. These neurons are coupled through neurotransmitters to form a network consisting of two subgroups, i.e., a ventrolateral (VL) subgroup and a dorsomedial (DM) subgroup. The VL contains about 25% SCN neurons that receive photic input from the retina, and the DM comprises the remaining 75% SCN neurons which are coupled to the VL. The synapses from the VL to the DM are evidently denser than that from the DM to the VL, in which the VL dominates the DM. Therefore, the SCN is a heterogeneous network where the neurons of the VL are linked with a large number of SCN neurons. In the present study, we mimicked the SCN network based on Goodwin model considering four types of networks including an all-to-all network, a Newman-Watts (NW) small world network, an Erdös-Rényi (ER) random network, and a Barabási-Albert (BA) scale free network. We found that the circadian rhythm was induced in the BA, ER, and NW networks, while the circadian rhythm was absent in the all-to-all network with weak cellular coupling, where the amplitude of the circadian rhythm is largest in the BA network which is most heterogeneous in the network structure. Our finding provides an alternative explanation for the induction or enhancement of circadian rhythm by the heterogeneity of the network structure.
Highlights
The circadian rhythms of physiological and behavioral activity are universal in living things, reflecting the period of the earth’s axial rotation
We found that the circadian rhythm was induced in the BA, ER, and NW networks, while the circadian rhythm was absent in the all-to-all network with weak cellular coupling, where the amplitude of the circadian rhythm is largest in the BA network which is most heterogeneous in the network structure
We found that the heterogeneous network structure induces the circadian rhythm of the suprachiasmatic nucleus (SCN) in the case of weak cellular coupling where the rhythm is absent in the all-to-all network structure
Summary
The circadian rhythms of physiological and behavioral activity are universal in living things, reflecting the period of the earth’s axial rotation. SCN network output is dependent on environmental clues. It can be divided into two functional distinct subgroups, including a ventrolateral part (VL) and a dorsomedial part (DM).. The VL contains about 25% SCN neurons which receive photic input from the retina, and the DM comprises the remaining 75% SCN neurons. Both subgroups take part in the regulation of overt circadian rhythms. The periods vary in different regions of the SCN, with the DM running faster than the VL.. The SCN neurons are coupled through peptide neurotransmitters which differ between the VL and the DM. The detailed network structure of the SCN has not been discovered
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