NEWBORN PRIMATE INFANTS ARE ENTRAINED BY LOW-INTENSITY LIGHTING

At the present time we do not know when the circadian timing system of human infants becomes responsive to light. Because of human study lim itations, it is not currently possible to address this issue in clinic al studies. Therefore, to provide insights into when the circadian sys tem of humans becomes responsive to light, baboons were studied. We fi rst 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 a nd 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 suffi cient to entrain circadian phase. However, low intensity lighting was not sufficient to induce changes in SCN metabolic activity or c-fos mR NA expression. Phase-response studies indicated that light exposure (2 00 lux) before the onset of activity most effectively shifted circadia n phase. These data provide direct evidence that the SCN are responsiv e to visually mediated light information in a primate at birth. Furthe r consideration of lighting conditions that infants are exposed to is therefore warranted.