rPer1 and rPer2 induction during phases of the circadian cycle critical for light resetting of the circadian clock

In a 24-hour light-dark cycle, Per1 showed strong induction in the rat circadian center during the early day.

• Light exposure activates the Per1 and Per2 genes, contributing to the resetting of the circadian clock.
• In a shorter 24-hour light-dark cycle, Per1 is predominantly induced in the ventrolateral region of the suprachiasmatic nucleus.
• In contrast, a longer 25-hour light-dark cycle results in strong induction of rPer2 at the end of the light phase and early dark periods.
• These findings indicate that Per1 and Per2 are differentially regulated in response to varying light-dark cycles.

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