Regional circadian period difference in the suprachiasmatic nucleus of the mammalian circadian center

<jats:title>Abstract</jats:title><jats:p>The suprachiasmatic nucleus (<jats:styled-content style="fixed-case">SCN</jats:styled-content>) is the mammalian circadian rhythm center. Individual oscillating neurons have different endogenous circadian periods, but they are usually synchronized by an intercellular coupling mechanism. The differences in the period of each oscillating neuron have been extensively studied; however, the clustering of oscillators with similar periods has not been reported. In the present study, we artificially disrupted the intercellular coupling among oscillating neurons in the <jats:styled-content style="fixed-case">SCN</jats:styled-content> and observed regional differences in the periods of the oscillating small‐latticed regions of the <jats:styled-content style="fixed-case">SCN</jats:styled-content> using a transgenic rat carrying a luciferase reporter gene driven by regulatory elements from a <jats:italic>per2</jats:italic> clock gene (<jats:italic>Per2</jats:italic>::dluc rat). The analysis divided the <jats:styled-content style="fixed-case">SCN</jats:styled-content> into two regions – a region with periods shorter than 24 h (short‐period region, <jats:styled-content style="fixed-case">SPR</jats:styled-content>) and another with periods longer than 24 h (long‐period region, <jats:styled-content style="fixed-case">LPR</jats:styled-content>). The <jats:styled-content style="fixed-case">SPR</jats:styled-content> was located in the smaller medial region of the dorsal <jats:styled-content style="fixed-case">SCN</jats:styled-content>, whereas the <jats:styled-content style="fixed-case">LPR</jats:styled-content> occupied the remaining larger region. We also found that slices containing the medial region of the <jats:styled-content style="fixed-case">SCN</jats:styled-content> generated shorter circadian periods than slices that contained the lateral region of the <jats:styled-content style="fixed-case">SCN</jats:styled-content>. Interestingly, the <jats:styled-content style="fixed-case">SPR</jats:styled-content> corresponded well with the region where the <jats:styled-content style="fixed-case">SCN</jats:styled-content> phase wave is generated. We numerically simulated the relationship between the <jats:styled-content style="fixed-case">SPR</jats:styled-content> and a large <jats:styled-content style="fixed-case">LPR</jats:styled-content>. A mathematical model of the <jats:styled-content style="fixed-case">SCN</jats:styled-content> based on our findings faithfully reproduced the kinetics of the oscillators in the <jats:styled-content style="fixed-case">SCN</jats:styled-content> in synchronized conditions, assuming the existence of clustered short‐period oscillators.</jats:p>