Separate daily rhythms of Per1 and Bmal1 genes in the brain’s internal clock linked to behavior

The circadian rhythms of two key clock genes in the suprachiasmatic nucleus may adopt different phases and free-running periods relative to each other.

• Light pulses at subjective evening cause an immediate phase delay in one rhythm, while a gradual phase delay occurs in the other rhythm similar to activity offset.
• Cultured SCN slices from mice show that the two rhythms can have significantly different periods and are internally desynchronized over a three-week culture period.
• No regional specificity was found in the SCN regarding the periods of the two clock genes.
• The two rhythms do not synchronize with circadian intracellular calcium rhythms or with firing rhythms, despite some persistent coupling.
• The findings suggest a distinct regulatory mechanism for the expression of the clock genes associated with activity onset and offset.

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