The biological clock of very premature primate infants is responsive to light

Abstract

Each year more than 250,000 infants in the United States are exposed to artificial lighting in hospital nurseries with little consideration given to environmental lighting cycles. Essential in determining whether environmental lighting cycles need to be considered in hospital nurseries is identifying when the infant's endogenous circadian clock becomes responsive to light. Using a non-human primate model of the developing human, we examined when the circadian clock, located in the hypothalamic suprachiasmatic nuclei (SCN), becomes responsive to light. Preterm infant baboons of different ages were exposed to light (5,000 lux) at night, and then changes in SCN metabolic activity and gene expression were assessed. After exposure to bright light at night, robust increases in SCN metabolic activity and gene expression were seen at ages that were equivalent to human infants at 24 weeks after conception. These data provide direct evidence that the biological clock of very premature primate infants is responsive to light.

Figure 1

Autoradiographic images of preterm baboon-brain sections showing SCN DG uptake after exposure to 5,000 lux of light at night. The infants shown are either 160 (Upper) or 125 (Lower) PC days of age and were either blindfolded (Right) or directly exposed (Left) during light exposure. The images are at mid-SCN levels. Arrows identify the SCN.

Figure 2

Relative OD values of individual animals generated from DG-uptake studies at PC days 160 (A) and 125 (B). Animals were exposed directly (dotted bars) or blindfolded (black bars) during exposure to 5,000 lux of light. Relative OD values are means ± SEM of three determinations at mid-SCN level per animal.

Figure 3

In situ hybridization images generated with ³⁵S-labeled cRNA probes showing c-fos (Upper) and per1 (Lower) mRNA expression at PC day 125 after exposure to light at night with (Right) or without (Left) blindfolds. Arrows identify the SCN.

Figure 4

Relative OD values of the SCN autoradiographic images generated from c-fos (A) and per1 (B) mRNA expression studies. Animals were studied either with (black bars) or without (dotted bars) blindfolds during 5,000 lux of light exposure. Relative OD values are means ± SEM of three determinations at mid-SCN level.