Beginning to See the Light: Lessons Learned From the Development of the Circadian System for Optimizing Light Conditions in the Neonatal Intensive Care Unit.

Esther M Hazelhoff,Johanna H Meijer,Jeroen Dudink,Laura Kervezee

doi:10.3389/fnins.2021.634034

Esther M Hazelhoff, Johanna H Meijer + Show 2 more

Open Access

https://doi.org/10.3389/fnins.2021.634034

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Abstract

The circadian timing system optimizes health by temporally coordinating behavior and physiology. During mammalian gestation, fetal circadian rhythms are synchronized by the daily fluctuations in maternal body temperature, hormones and nutrients. Circadian disruption during pregnancy is associated with negative effects on developmental outcomes in the offspring, highlighting the importance of regular and robust 24-h rhythms over gestation. In the case of preterm birth (before 37 weeks of gestation), maternal cues no longer synchronize the neonate’s circadian system, which may adversely affect the neonate. There is increasing evidence that introducing robust light-dark cycles in the Neonatal Intensive Care Unit has beneficial effects on clinical outcomes in preterm infants, such as weight gain and hospitalization time, compared to infants exposed to constant light or constant near-darkness. However, the biological basis for these effects and the relationship with the functional and anatomical development of the circadian system is not fully understood. In this review, we provide a concise overview of the effects of light-dark cycles on clinical outcomes of preterm neonates in the NICU and its alignment with the development of the circadian system.

Highlights

During pregnancy, a highly controlled uterine environment provides the best possible conditions for optimal fetal development in preparation for a successful transition to postnatal life
As exposure to a bright day and dark night seems to positively influence weight gain, duration of hospital stay, and other clinically relevant measures, cycled light appears to be beneficial for the development of preterm babies
As the structures of the circadian system appear to be formed at 24 weeks, it is conceivable that the positive effects of cycled light are mediated through these structures

Summary

Introduction

A highly controlled uterine environment provides the best possible conditions for optimal fetal development in preparation for a successful transition to postnatal life. The mother supplies oxygen, hormones, and nutrients via the placenta In addition to these substrates, the mother conveys circadian timing cues to the fetus through her own daily rhythms in body temperature, physical activity, feeding behavior, and hormonal levels (Serón-Ferré et al, 2001, 2012; Bates and Herzog, 2020). Research in animal models supports these findings, showing that environmental disruption of circadian rhythms during pregnancy leads to adverse pregnancy outcomes (Summa et al, 2012) as well as to negative effects in the offspring later in life, such as altered adrenal function, impaired adaptive immune system, social avoidance and depressive like behavior (Borniger et al, 2014; Cissé et al, 2017a,b; Man et al, 2017; Smarr et al, 2017; Salazar et al, 2018)

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