Daytime light changes daily clock gene activity in the brain’s time-keeping center of mice

30-minute light pulses during the subjective day generally increased levels of Per1 and Per2 mRNA in the suprachiasmatic nuclei of mice.

• Light exposure during the day affects Per1 and Per2 gene expression in nocturnal rodents.
• More pronounced increases in Per1 and Per2 expression were observed in the morning compared to other times.
• A transient decrease in Per2 expression occurred after a short light pulse applied at midday.
• Prolonged light exposure starting at midday significantly increased Per2 expression but not Per1.
• Mice exposed to a light-dark cycle showed greater daily variations in Per levels compared to those in constant darkness.
• Mice synchronized to a skeleton photoperiod exhibited reduced amplitude in daily variations of Per levels compared to those in a light-dark cycle.

Simplified