Changes in brain clock proteins over time and location during shifts in daily rhythm

During the delay zone of the phase response curve, a light pulse increases mPER1 and mPER2 protein levels despite their natural decline.

• Light pulses reset the circadian clock through the induction of Per gene expression.
• In the delay zone, light pulses elevate mPER1 and mPER2 proteins while their natural levels are decreasing.
• In the advance zone, light pulses further increase mPER1 protein levels, but do not affect mPER2.
• The distribution of mPER1 and mPER2 proteins in the suprachiasmatic nuclei corresponds with their mRNA levels.
• mPER1 expression in the shell region of the suprachiasmatic nuclei is associated with phase advances, whereas mPER2 is linked to phase delays.

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