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Programming of mice circadian photic responses by postnatal light environment
Elisabeth Brooks1, Dhruval Patel1, Maria Mercè Canal1
1Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom.
Insights
Early life light exposure programs the mammalian circadian system, influencing behavior and peripheral clocks. This research clarifies that perinatal light primarily affects adaptive responses, not retinal function or intrinsic molecular clock mechanisms.
Area of Science:
- Chronobiology
- Neuroscience
- Developmental Biology
Background:
- Early life experiences significantly impact long-term health.
- Perinatal light exposure is a novel factor influencing the developing circadian system.
- The suprachiasmatic nucleus (SCN) is the master circadian clock in mammals, but the precise impact of early light on its function is unclear.
Purpose of the Study:
- To investigate whether early light exposure imprints intrinsic molecular clock mechanisms or alters photic input processing.
- To systematically probe the mouse circadian system at multiple levels to understand the effects of postnatal light.
Main Methods:
- Electroretinography, pupillometry, and histology to assess retinal function and morphology.
- Circadian activity monitoring to evaluate behavioral responses to light and darkness.
- Real-time PER2::LUC rhythm recordings to measure clock gene expression in the SCN and peripheral tissues.
Main Results:
- Adult retinal function and morphology were largely unaffected by postnatal light.
- Behavioral responses to chronic light, but not constant darkness or acute light stimuli, depended on early light exposure.
- Long-term changes in clock gene expression were observed in the SCN and peripheral organs (heart, lung, spleen).
Conclusions:
- Perinatal light primarily programs the long-term adaptive responses of the circadian clock to environmental light.
- Early light exposure does not fundamentally alter retinal processing or intrinsic molecular clock mechanisms.
- Postnatal light has lasting effects on peripheral circadian clocks, indicating broad physiological consequences.
Abstract:
Early life programming has important consequences for future health and wellbeing. A key new aspect is the impact of perinatal light on the circadian system. Postnatal light environment will program circadian behavior, together with cell morphology and clock gene function within the suprachiasmatic nucleus (SCN) of the hypothalamus, the principal circadian clock in mammals. Nevertheless, it is still not clear whether the observed changes reflect a processing of an altered photic input from the retina, rather than an imprinting of the intrinsic molecular clock mechanisms. Here, we addressed the issue by systematically probing the mouse circadian system at various levels. Firstly, we used electroretinography, pupillometry and histology protocols to show that gross retinal function and morphology in the adult are largely independent of postnatal light experiences that modulate circadian photosensitivity. Secondly, we used circadian activity protocols to show that only the animal's behavioral responses to chronic light exposure, but not to constant darkness or the acute responses to a light stimulus depend on postnatal light experience. Thirdly, we used real-time PER2::LUC rhythm recording to show long-term changes in clock gene expression in the SCN, but also heart, lung and spleen. The data showed that perinatal light mainly targets the long-term adaptive responses of the circadian clock to environmental light, rather than the retina or intrinsic clock mechanisms. Finally, we found long-term effects on circadian peripheral clocks, suggesting far-reaching consequences for the animal's overall physiology.