Splitting of daily activity patterns in CS mice is linked to clock gene activity outside the brain's main time-keeping center

CS mice exhibit a spontaneous splitting in their circadian rhythm of locomotor activity under constant darkness.

• Two weakly coupled oscillators may regulate locomotor activity rhythm in CS mice.
• Circadian rhythms of mPer1 and mPer2 in the suprachiasmatic nucleus (SCN) show a single peak in both split and unsplit mice.
• During rhythm splitting, mPer1 and mPer2 rhythms are slightly phase delayed relative to the activity onset, but their phase relationship remains unchanged.
• In the cerebral cortex, mPer1 and mPer2 exhibit bimodal fluctuations corresponding to split activity components, while unsplit mice show a single peak.
• No differences in mPer3 rhythms were observed between split and unsplit mice in either the SCN or cerebral cortex.
• Circadian oscillations of mPer1, mPer2, and mPer3 in the SCN are not associated with the rhythm splitting in CS mice.

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