Dissociation ofPer1andBmal1circadian rhythms in the suprachiasmatic nucleus in parallel with behavioral outputs

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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