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 <i>in vivo</i>

<p>Circadian rhythms in mammals are driven by a central clock in the suprachiasmatic nucleus (SCN). <i>In vitro</i>, temperature cycles within the physiological range can act as potent entraining cues for biological clocks. We altered the body temperature (T<sub>c</sub>) rhythm in rats by manipulating energy intake (EI) to determine whether EI-induced changes in T<sub>c</sub> oscillations are associated with changes in SCN clock gene rhythms <i>in vivo</i>. Male Wistar rats (<i>n</i> = 16 per diet) were maintained on either an <i>ad libitum</i> diet (CON), a high energy cafeteria diet (CAF), or a calorie restricted diet (CR), and T<sub>c</sub> was recorded every 30 min for 6-7 weeks. SCN tissue was harvested from rats at <i>zeitgeber</i> time (ZT) 0, ZT6, ZT12, or ZT18. Expression of the clock genes <i>Bmal1, Per2, Cry1</i>, and <i>Rev-erbα</i>, the heat shock transcription factor <i>Hsf1</i>, and the heat shock protein <i>Hsp90aa1</i>, 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 T<sub>c</sub> was decreased in CAF rats by 0.1 °C (<i>p</i> < 0.001), and increased in CR rats by 0.3 °C (<i>p</i> < 0.001). The amplitude of <i>Hsp90aa1</i> expression was lowest in CAF rats and highest in CR rats (<i>p</i> = 0.045), but the amplitude of all of the clock genes and <i>Hsf1</i> were unaffected by diet (<i>p</i> > 0.25). Compared to CON, phase advances of the T<sub>c</sub>, <i>Bmal1</i>, and <i>Per2</i> rhythms were observed with CR feeding (<i>p</i> < 0.05), but CAF feeding elicited no significant changes in phase. The present results indicate that <i>in vivo</i>, the SCN is largely resistant to entrainment by EI-induced changes in the T<sub>c</sub> rhythm, although some phase entrainment may occur.</p>