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

• Published in: The European journal of neuroscience 2015-12, Vol.42 (12), p.3128-3137
• Main Authors: Ono, Daisuke, Honma, Sato, Honma, Ken-ichi
• Format: Article
• Language: English
• Subjects: Animals; behaviour; bioluminescence; Circadian Clocks - physiology; Circadian Rhythm - physiology; Female; in vivo recording; Male; Mice, Inbred C57BL; Mice, Knockout; Motor Activity - physiology; Olfactory Bulb - physiology; optical fibre; Optogenetics; Period Circadian Proteins - metabolism; Receptors, Vasoactive Intestinal Peptide, Type II - genetics; Receptors, Vasoactive Intestinal Peptide, Type II - metabolism; Suprachiasmatic Nucleus - physiology; Suprachiasmatic Nucleus - physiopathology; Tissue Culture Techniques; vasoactive intestinal peptide; Wavelet Analysis
• ISSN: 0953-816X; 1460-9568
• DOI: 10.1111/ejn.13111

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. Circadian rhythms of clock gene Per2 product (PER2) were continuously monitored in the olfactory bulb (OB) of freely moving mice by means of a luciferase reporter and an optical fiber implantation. The suprachiasmatic nucleus (SCN) lesions disorganized circadian PER2 rhythms in the OB, whereas robust rhythms were detected in mice lacking the VIP receptor despite of destructed behavioural rhythms. The findings suggest the dependence of the OB circadian system on the SCN but not on behaviour rhythm.