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Foster mother rat entrains circadian adrenocortical rhythm in blinded pups
Insights
Mothers predominantly entrain the corticosterone rhythm in blinded pups. This maternal influence overrides the light-dark cycle, establishing the pup's hormonal rhythm.
Area of Science:
- Endocrinology
- Chronobiology
- Developmental Biology
Background:
- Circadian rhythms, regulated by the light-dark cycle, are crucial for physiological processes.
- Corticosterone, a key stress hormone, exhibits a daily rhythm.
- Early life experiences can significantly impact the development of circadian rhythms.
Purpose of the Study:
- To investigate the primary entrainer of blood corticosterone rhythm in early postnatal development.
- To determine if maternal influence or the light-dark cycle is more critical for entraining corticosterone rhythms in blinded pups.
Main Methods:
- Optically enucleated (blinded) pups were studied from postnatal weeks 4–8.
- Pups were raised by natural mothers, foster mothers with different light-dark cycle alignments, or blinded mothers.
- Blood corticosterone levels were monitored to assess rhythm patterns.
Main Results:
- Blinded pups raised by intact mothers exhibited corticosterone rhythms entrained to maternal patterns, near light-dark transitions.
- When raised by foster mothers with reversed light-dark cycles, blinded pups' rhythms aligned with the foster mothers'.
- Blinded pups raised by blinded mothers showed rhythms synchronized with their mothers, irrespective of the external lighting cycle.
Conclusions:
- The nursing mother is the predominant entrainer of corticosterone rhythm in blinded pups.
- Maternal entrainment overrides the influence of the ambient light-dark cycle in early development.
- This highlights the critical role of maternal care in programming the endocrine system of offspring.
Abstract:
Free-running patterns of blood corticosterone rhythm were examined between the fourth and eighth postnatal week in blinded pups optically enucleated on day 1. When blinded pups were raised by intact natural mothers, the peak time of corticosterone rhythm appeared near the time of light-dark (LD) transition, which was close to that of mothers, and then free-ran. This phase relation between mothers and pups showed that mothers entrained pups' corticosterone rhythm. When blinded pups born of LD (or DL) mothers were raised by DL (or LD) foster mothers, the corticosterone rhythm in blinded pups was close to that of foster mothers at 4 wk of age, indicating that a foster mother plays a predominant role in entraining the pups' rhythm. When blinded pups were raised by blinded mothers whose rhythm was out of phase of the lighting cycle, pups' rhythm was in phase with that of mothers, showing that lighting cycle did not affect the pups' rhythm. These facts indicate that the mother nursing pups acts as the most predominant entrainer of corticosterone rhythm of the blinded pups.