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Newborn primate infants are entrained by low intensity lighting
S A Rivkees1, P L Hofman, J Fortman
1Section of Pediatric Endocrinology, James Whitcomb Riley Hospital, Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis 46202, USA.
Insights
Human infants
Area of Science:
- Neuroscience
- Chronobiology
- Developmental Biology
Background:
- The timing of the human infant circadian system's responsiveness to light is unknown.
- Clinical studies are limited in investigating early light responses in infants.
Purpose of the Study:
- To determine when the human infant circadian system becomes responsive to light.
- To investigate the role of the suprachiasmatic nuclei (SCN) in mediating light responses at birth.
Main Methods:
- Assessed SCN metabolic activity and c-fos mRNA expression in newborn baboons and infants exposed to light.
- Examined photic entrainment of circadian rhythmicity using cycled lighting in infants.
- Conducted phase-response studies to determine optimal light exposure timing.
Main Results:
- Newborn baboons and infants show increased SCN metabolic activity and c-fos mRNA expression in response to bright light, indicating photic responsiveness at birth.
- Low-intensity cycled lighting (200 lux) can entrain circadian rhythmicity in infants.
- Light exposure before activity onset is most effective for shifting circadian phase.
Conclusions:
- The suprachiasmatic nuclei (SCN) are responsive to visually mediated light at birth in primates.
- Infant lighting conditions warrant further consideration for proper circadian system development.
Abstract:
At the present time we do not know when the circadian timing system of human infants becomes responsive to light. Because of human study limitations, it is not currently possible to address this issue in clinical studies. Therefore, to provide insights into when the circadian system of humans becomes responsive to light, baboons were studied. We first assessed if the biological clock located in suprachiasmatic nuclei (SCN) is responsive to light at birth. When term newborn infants were exposed to bright light at night (5000 lux), SCN metabolic activity and c-fos mRNA expression increased, indicating the presence of photic responsiveness. When photic entrainment of developing rhythmicity was examined in infants, low intensity (200 lux) cycled lighting was sufficient to entrain circadian phase. However, low intensity lighting was not sufficient to induce changes in SCN metabolic activity or c-fos mRNA expression. Phase-response studies indicated that light exposure (200 lux) before the onset of activity most effectively shifted circadian phase. These data provide direct evidence that the SCN are responsive to visually mediated light information in a primate at birth. Further consideration of lighting conditions that infants are exposed to is therefore warranted.