Endogenous clock gene expression in the suprachiasmatic nuclei of previsual newborn rabbits is entrained by nursing

Nov 22, 2008Developmental neurobiology

Natural body clock gene activity in the brain's daily rhythm center of newborn rabbits is influenced by nursing

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Abstract

Newborn rabbit pups demonstrate endogenous 24-hour rhythms in clock gene expression linked to nursing times.

The suprachiasmatic nuclei in newborn pups show daily changes in the expression of clock genes Per1, Per2, and Bmal1.
Pups nursed normally from postnatal days 1 to 7 exhibit similar rhythms in clock gene expression to those that were fasted.
Nursing has a significant role in entraining these circadian rhythms, as shown by changes in gene expression patterns when nursing times are shifted.
Pups with different nursing schedules display distinct daily patterns of body temperature, indicating synchronization with their nursing times.
Further investigation is needed to clarify the specific nonphotic cues that influence clock gene expression in these pups.

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The rabbit is particularly suitable for investigating the development of mammalian circadian function. Blind at birth, the pups are only visited by the mother to be nursed once every 24 h for about 3 min and so can be studied largely without maternal interference. They anticipate the mother's visit with increased behavioral arousal and with a rise in body temperature, both of which represent endogenous circadian rhythms. We now report that in newborn pups the suprachiasmatic nuclei of the hypothalamus (SCN; the main circadian pacemaker in mammals) show endogenous 24-h rhythmicity in the expression of the clock genes Per1, Per2, and Bmal1. Pups nursed from postnatal days 1 to 7 and fasted to day 9 showed the same rhythms of clock gene expression as normally nursed controls. We also report that these rhythms are entrained by nursing. Pups killed on postnatal days 3-4 showed the same rhythms in gene expression as pups in the previous experiment, whereas littermates subsequently nursed from postnatal days 4 to 7 with nursing delayed 6 h showed a corresponding shift in the diurnal pattern of clock gene expression. Consistent with this, two groups of pups implanted with telemetric thermal sensors and nursed 6 h apart had daily patterns in body temperature synchronized with the two different nursing times. We conclude that the expression of clock genes associated with the newborn rabbit's circadian system is entrained by nonphotic cues accompanying nursing, the exact nature of which now needs to be clarified.

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Endogenous clock gene expression in the suprachiasmatic nuclei of previsual newborn rabbits is entrained by nursing

Abstract

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