Exposure of Pregnant Rats to Restricted Feeding Schedule Synchronizes the SCN Clocks of Their Fetuses under Constant Light but Not under a Light-Dark Regime

Sep 30, 2010Journal of biological rhythms

Pregnant rats’ limited feeding schedule aligns their fetuses’ internal clocks in constant light but not in normal day-night cycles

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Abstract

Restricted feeding in pregnant rats under constant light restored circadian rhythmicity in the SCN of their newborn pups.

The circadian clock in the suprachiasmatic nucleus (SCN) develops gradually during the prenatal and early postnatal period in rats.
Nonphotic maternal cues primarily entrain the circadian system of fetuses and newborn pups during early development.
In conditions of constant light, pups born to mothers with ad libitum feeding did not show circadian rhythms in gene expression.
Restricted feeding during pregnancy under constant light led to synchronized circadian rhythms in the gene expression of their pups.
Fetal SCN clocks may be influenced by maternal rhythmic signals, with regular food intake potentially playing a crucial role in synchronization.

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The circadian clock in the suprachiasmatic nucleus (SCN) develops gradually during the prenatal and early postnatal period. In the rat, this period lasts from around the 15th day of gestation until the 10th day of postnatal development. The circadian system of fetuses and newborn pups is entrained mostly by nonphotic maternal cues during prenatal and early postnatal development. The aim of the present study was to ascertain whether exposure of pregnant rats to a restricted feeding (RF) regime was able to entrain the circadian clock in the SCN of their fetuses during the prenatal period. The potency of RF as an entraining cue was tested under conditions when pregnant rats were entrained to an external light/dark (LD) cycle as well as under conditions when the external timing signal was lacking, i.e., under constant light (LL). The control groups were fed ad libitum and the experimental groups had restricted access to food for 6 h during their resting time throughout pregnancy. Daily profiles of Avp and c-fos gene expression were examined by in situ hybridization in the SCN of 1-day-old pups. The data demonstrated that RF in pregnant rats kept under LD cycle did not notably affect the daily rhythms of c-fos and Avp expression in the SCN of pups. The SCN profiles of Avp and c-fos gene expression did not exhibit circadian rhythms in pups born to mothers maintained in LL and fed ad libitum, likely due to desynchrony among the pups within a litter. However, RF in the pregnant rats kept under LL restored the circadian rhythmicity of c-fos and Avp expression in the SCN of their newborn pups. The results suggest that the fetal SCN clock is dominantly entrained by rhythmic signals from the maternal SCN. However, under conditions when the rhythmic signaling might be lacking, such as LL, regular food intake of the mothers may also play an important role in synchronization of the fetal SCN clock during prenatal ontogenesis.

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Exposure of Pregnant Rats to Restricted Feeding Schedule Synchronizes the SCN Clocks of Their Fetuses under Constant Light but Not under a Light-Dark Regime

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