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Published on: January 24, 2013
Darkness during early postnatal development is required for normal circadian patterns in the adult rat
T Cambras1, M M Canal, R Cernuda-Cernuda
1Departament de Fisiologia, Universitat de Barcelona , Barcelona , Spain .
Insights
Early life light exposure is crucial for developing a healthy circadian system. Lack of darkness during development disrupts the circadian rhythm, impacting locomotor activity and brain function.
Area of Science:
- Neuroscience
- Chronobiology
- Developmental Biology
Background:
- Early light exposure significantly impacts brain development and circadian system maturation.
- The precise roles of light quantity versus quality in perinatal development remain incompletely understood.
Purpose of the Study:
- To investigate how varying light conditions during early development affect the maturation of the circadian system in rats.
- To determine the influence of light quantity and the presence of darkness on the development of circadian rhythms and associated neural markers.
Main Methods:
- Rats were raised under six different light conditions from weaning until constant bright light exposure.
- Locomotor activity, circadian rhythmicity, vasointestinal polypeptide (VIP) immunoreactivity in the suprachiasmatic nucleus (SCN), and retinal melanopsin-expressing cells were assessed.
- Light conditions were manipulated post-weaning in some groups to observe subsequent rhythm entrainment.
Main Results:
- Rats deprived of darkness during suckling became arrhythmic under constant bright light post-weaning.
- Rats exposed to continuous light without darkness during suckling developed robust circadian rhythms, influenced by light quantity.
- Higher VIP immunoreactivity in the SCN correlated with weaker circadian rhythms; no differences were observed in melanopsin-expressing cells.
Conclusions:
- The quantity of light, particularly the presence of darkness, during early life is critical for normal circadian system development.
- Absence of darkness during early development impairs the ability to entrain circadian rhythms later in life.
- These findings highlight the necessity of natural light-dark cycles for proper circadian behavior development.
Abstract:
Early light experience influences the brain during development. Perinatal light exposure has an important effect on the development of the circadian system, although the role of quantity versus quality of light in this process is still unclear. We tested the development of the circadian rhythm of locomotor activity under constant bright light from the day of weaning, of six groups of rats raised under different light conditions during suckling. Results indicated that when rats received daily darkness during suckling (rats reared under constant darkness or light-dark cycles with dim or bright light) became arrhythmic when exposed to continuous bright light after weaning. However, those rats reared in the absence of darkness (constant dim or bright light, or alternating dim and bright light) developed a circadian rhythm, which was stronger and had a shorter period depending on the quantity of light received during suckling. Vasointestinal polypeptide immunoreactivity in the suprachiasmatic nucleus (SCN) was higher in those rats with weaker rhythms. However, no apparent differences among these groups were found in the melanopsin-expressing retinal ganglion cells, which provide the SCN with light input in the photoentrainment process. When bright light was shifted to dim light in three of the groups on day 57 after weaning, all of them generated a circadian rhythm with a longer period in those rats previously arrhythmic. Our results indicate the importance of the amount of light received at the early stages of life in the development of the circadian system and suggest that darkness is needed for the normal development of circadian behaviour.
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