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Abstract
The expression of circadian clock genes was investigated inthe suprachiasmatic nuclei (SCN) of young adult and old laboratory mice. Sampleswere taken at two time points, which corresponded to the expected maximum(circadian time 7 [CT7]) or minimum (CT21) of mPermRNA expression. Whereas the young mice had a stable and well-synchronizedcircadian activity/rest cycle, the rhythms of old animals were less stableand were phase advanced. The expression of mPer1mRNA and mPer2 mRNA was rhythmic in bothgroups, with peak values at CT7. The levels of mClockand mCry1 mRNA were not different dependingon the time of day and did not vary with age. In contrast, an age-dependentdifference was found in the case of mPer2(but not mPer1) mRNA expression, with themaximum at CT7 significantly lower in old mice. The decreased expression of mPer2 may be relevant for the observed differencesin the overt activity rhythm of aged mice. (ChronobiologyInternational, 18(3), 559–565, 2001)