Elsevier

Neuroscience

Volume 197, 1 December 2011, Pages 65-71
Neuroscience

Cellular and Molecular Neuroscience
Research Paper
Restricted feeding regime affects clock gene expression profiles in the suprachiasmatic nucleus of rats exposed to constant light

https://doi.org/10.1016/j.neuroscience.2011.09.028Get rights and content

Abstract

The master circadian clock located in the suprachiasmatic nuclei (SCN) is dominantly entrained by external light/dark cycle to run with a period of a solar day, that is, 24 h, and synchronizes various peripheral clocks located in the body's cells and tissues accordingly. A daily restricted normocaloric feeding regime synchronizes the peripheral clocks but has no effect on SCN rhythmicity. The aim of this study was to elucidate whether feeding regime may affect the molecular mechanism generating SCN rhythmicity under conditions in which the rhythmicity is disturbed, as occurs under constant light. The rats were maintained under constant light for 30 days and were either fed ad libitum during the whole period, or their access to food was restricted to only 6 h a day during the last 2 weeks in constant light. Locomotor activity was monitored during the whole experiment. On the last day in constant light, daily expression profiles of the clock genes Per1, Per2, Bmal1, and Rev-erbα were determined in the SCN of both groups by in situ hybridization. Due to their exposure to constant light, the rats fed ad libitum became completely arrhythmic, while those exposed to the restricted feeding were active mostly during the time of food availability. In the SCN of behaviorally arrhythmic rats, no oscillations in Rev-erbα and Bmal1 gene expression were detected, but very low amplitude, borderline significant, oscillations in Per1 and Per2 persisted. Restricted feeding induced significant circadian rhythms in Rev-erbα and Bmal1 gene expression, but did not affect the low amplitude oscillations of Per1 and Per2 expression. These findings demonstrate that, under specific conditions, when the rhythmicity of the SCN is disturbed and other temporal entraining cues are lacking, the SCN molecular clockwork may likely sense temporal signals from changes in metabolic state delivered by normocaloric food.

Highlights

▶Daily restricted normocaloric feeding regime has no effect on the SCN rhythmicity. ▶We examined whether the feeding regime may affect the SCN under constant light. ▶Under constant light, Per1 and Per2 mRNA exhibited low amplitude rhythms in the SCN. ▶The RF induced circadian rhythms in Rev-erbα and Bmal1 gene expression in the SCN. ▶The SCN molecular clockwork may likely sense signaling delivered by normocaloric food.

Section snippets

Experimental animals

Two-month-old male Wistar rats (Bio Test, Konarovice, Czech Republic) were maintained at a temperature of 21±2 °C under a regime of 12 h of light and 12 h of darkness per day. Light was provided by overhead 40-W fluorescent tubes, illumination was between 50 and 300 lux, depending on the cage position in the animal room. The animals had free access to food and water. On the day of the experiment, the animals were released into LL, that is, the light was not turned off at 18:00 h, the usual time

Effect of LL on locomotor activity

Releasing the rats into LL affected their locomotor activity, as previously demonstrated (Polidarová et al., 2011). The rats started to run with a period of 25.5±0.3 h during the first 14 days of LL (data not shown), and thereafter the rhythmicity gradually deteriorated. Finally, after 30 days in LL, rhythmicity was completely lost. All rats fed ad libitum became completely arrhythmic on the 30th day in LL, as confirmed by periodogram analysis (data demonstrated in the study by Polidarová et

Discussion

These data demonstrate that in the SCN of rats that are behaviorally completely arrhythmic due to 30-day-exposure to LL, not all rhythms in clock gene expression are completely abolished. Although the Bmal1 and Rev-erbα expression did not exhibit circadian rhythmicity, attenuated low amplitude rhythms of Per1 and Per2 expression were suggested. Exposing the rats maintained under LL to RF did not affect the weak rhythm of Per1 and Per2 expression, but affected significantly the rhythms of Bmal1

Conclusion

In conclusion, our data demonstrate that in the SCN of rats behaviorally arrhythmic due to prolonged exposure to LL, low amplitude oscillations in Per1 and Per2 gene expression may be detected. These rhythms, though only borderline significant, may reflect a persistence of synchrony among a small subpopulation of the SCN cells. Moreover, our data demonstrate for the first time that under conditions of prolonged exposure to LL, the RF may synchronize Rev-erbα and Bmal1 gene expression profiles

Acknowledgments

The authors gratefully acknowledge Eva Suchanová and Lenka Hummerová for their excellent technical assistance. The study was supported by grants Nos. 305/09/0321, P303/11/0668, 309/08/H079, LC554, and by Research Project AV0Z 50110509.

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