https://orcid.org/0000-0001-5431-9939
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ABSTRACT
Circadian rhythms in mammals are driven by a central clock in the suprachiasmatic nucleus (SCN). In vitro, temperature cycles within the physiological range can act as potent entraining cues for biological clocks. We altered the body temperature (Tc) rhythm in rats by manipulating energy intake (EI) to determine whether EI-induced changes in Tc oscillations are associated with changes in SCN clock gene rhythms in vivo. Male Wistar rats (n = 16 per diet) were maintained on either an ad libitum diet (CON), a high energy cafeteria diet (CAF), or a calorie restricted diet (CR), and Tc was recorded every 30 min for 6-7 weeks. SCN tissue was harvested from rats at zeitgeber time (ZT) 0, ZT6, ZT12, or ZT18. Expression of the clock genes Bmal1, Per2, Cry1, and Rev-erbα, the heat shock transcription factor Hsf1, and the heat shock protein Hsp90aa1, were determined using qPCR. The circadian profile of gene expression for each gene was characterized using cosinor analysis. Compared to the CON rats, the amplitude of Tc was decreased in CAF rats by 0.1 °C (p < 0.001), and increased in CR rats by 0.3 °C (p < 0.001). The amplitude of Hsp90aa1 expression was lowest in CAF rats and highest in CR rats (p = 0.045), but the amplitude of all of the clock genes and Hsf1 were unaffected by diet (p > 0.25). Compared to CON, phase advances of the Tc, Bmal1, and Per2 rhythms were observed with CR feeding (p < 0.05), but CAF feeding elicited no significant changes in phase. The present results indicate that in vivo, the SCN is largely resistant to entrainment by EI-induced changes in the Tc rhythm, although some phase entrainment may occur.
Acknowledgements
We thank Greg Cozens, Celeste Wale, Dr. Jeremy Smith, and Julie-Ann de Bond for technical assistance in the laboratory; the staff of the Pre-Clinical Facility in UWA for assistance with the animal experiments, and Dr. Chris Mayberry for advice on animal surgery.
Declaration of interest
The authors report no conflicts of interest, and declare that this work is original and has not been published elsewhere.
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Additional information
Notes on contributors
Grace H. Goh
Conception and design of research: Peter J. Mark, Shane K. Maloney, Grace H. Goh
Performed experiments: Grace H. Goh, Peter J. Mark, Shane K. Maloney
Analyzed data: Grace H. Goh, Peter J. Mark, Shane K. Maloney
Interpreted results of experiments: Grace H. Goh, Peter J. Mark, Shane K. Maloney
Prepared figures: Grace H. Goh
Drafted manuscript: Grace H. Goh
Edited and revised manuscript: Grace H. Goh, Peter J. Mark, Shane K. Maloney
Approved final version of manuscript: Grace H. Goh, Peter J. Mark, Shane K. Maloney
Peter J. Mark
Conception and design of research: Peter J. Mark, Shane K. Maloney, Grace H. Goh
Performed experiments: Grace H. Goh, Peter J. Mark, Shane K. Maloney
Analyzed data: Grace H. Goh, Peter J. Mark, Shane K. Maloney
Interpreted results of experiments: Grace H. Goh, Peter J. Mark, Shane K. Maloney
Prepared figures: Grace H. Goh
Drafted manuscript: Grace H. Goh
Edited and revised manuscript: Grace H. Goh, Peter J. Mark, Shane K. Maloney
Approved final version of manuscript: Grace H. Goh, Peter J. Mark, Shane K. Maloney
Shane K. Maloney
Conception and design of research: Peter J. Mark, Shane K. Maloney, Grace H. Goh
Performed experiments: Grace H. Goh, Peter J. Mark, Shane K. Maloney
Analyzed data: Grace H. Goh, Peter J. Mark, Shane K. Maloney
Interpreted results of experiments: Grace H. Goh, Peter J. Mark, Shane K. Maloney
Prepared figures: Grace H. Goh
Drafted manuscript: Grace H. Goh
Edited and revised manuscript: Grace H. Goh, Peter J. Mark, Shane K. Maloney
Approved final version of manuscript: Grace H. Goh, Peter J. Mark, Shane K. Maloney