title: Altered energy intake and the amplitude of the body temperature rhythm are associated with changes in phase, but not amplitude, of clock gene expression in the rat suprachiasmatic nucleus in vivo.
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.
authors.affiliation: a School of Anatomy, Physiology, and Human Biology, The University of Western Australia , Crawley , Australia.
authors.forename: Grace H
authors.initials: GH
authors.lastname: Goh
authors.affiliation: a School of Anatomy, Physiology, and Human Biology, The University of Western Australia , Crawley , Australia.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Mark
authors.affiliation: a School of Anatomy, Physiology, and Human Biology, The University of Western Australia , Crawley , Australia.
authors.forename: Shane K
authors.initials: SK
authors.lastname: Maloney
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D001683:Biological Clocks; D001831:Body Temperature / Q000502:physiology*; D056926:CLOCK Proteins / Q000235:genetics* / Q000378:metabolism; D002940:Circadian Rhythm / Q000502:physiology*; D002149:Energy Intake / Q000502:physiology*; D015870:Gene Expression / Q000502:physiology*; D008297:Male; D017208:Rats, Wistar; D013493:Suprachiasmatic Nucleus / Q000502:physiology*
chemical_list: D056926:CLOCK Proteins
keywords: Circadian clocks; body temperature; cafeteria feeding; calorie restriction; entrainment