Circadian PER2::LUC rhythms in the olfactory bulb of freely moving mice depend on the suprachiasmatic nucleus but not on behaviour rhythms

Oct 23, 2015The European journal of neuroscience

Daily activity patterns in the smell-processing area of moving mice depend on the brain’s master clock but not on their behavior rhythms

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Abstract

Robust circadian rhythms were detected in the olfactory bulb and suprachiasmatic nucleus for up to 19 days in freely moving mice.

The relationship between the master circadian clock in the suprachiasmatic nucleus and the olfactory bulb's circadian clock was examined.
Bilateral lesions in the suprachiasmatic nucleus abolished circadian behavior rhythms and disrupted PER2 rhythms in the olfactory bulb.
The olfactory bulb exhibited multiple oscillatory components with similar circadian periods, indicating potential internal desynchronization.
Circadian rhythms in PER2 were present in mice lacking vasoactive intestinal peptide receptor 2, even as behavioral rhythms deteriorated.
The circadian rhythm in the cultured olfactory bulb was as robust as that in the cultured suprachiasmatic nucleus but was reset by slice preparation.

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The temporal order of physiology and behaviour in mammals is regulated by the coordination of the master circadian clock in the suprachiasmatic nucleus (SCN) and peripheral clocks in various tissues outside the SCN. Because the circadian oscillator(s) in the olfactory bulb (OB) is regarded as SCN independent, we examined the relationship between the SCN master clock and the circadian clock in the OB. We also examined the role of vasoactive intestinal peptide receptor 2 in the circadian organization of the OB. We continuously monitored the circadian rhythms of a clock gene product PER2 in the SCN and OB of freely moving mice by means of a bioluminescence reporter and an optical fibre implanted in the brain. Robust circadian rhythms were detected in the OB and SCN for up to 19 days. Bilateral SCN lesions abolished the circadian behaviour rhythms and disorganized the PER2 rhythms in the OB. The PER2 rhythms in the OB showed more than one oscillatory component of a similar circadian period, suggesting internal desynchronization of constituent oscillators. By contrast, significant circadian PER2 rhythms were detected in the vasoactive intestinal peptide receptor 2-deficient mice, despite the substantial deterioration or abolition of circadian behavioural rhythms. These findings indicate that the circadian clock in the OB of freely moving mice depends on the SCN master clock but not on the circadian behavioural rhythms. The circadian PER2::LUC rhythm in the cultured OB was as robust as that in the cultured SCN but reset by slice preparation, suggesting that culturing of the slice reinforces the circadian rhythm.

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Circadian PER2::LUC rhythms in the olfactory bulb of freely moving mice depend on the suprachiasmatic nucleus but not on behaviour rhythms

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