Impaired expression of the mPer2 circadian clock gene in the suprachiasmatic nuclei of aging mice.

The expression of circadian clock genes was investigated in the suprachiasmatic nuclei (SCN) of young adult and old laboratory mice. Samples were taken at two time points, which corresponded to the expected maximum (circadian time 7 [CT7]) or minimum (CT21) of mPer mRNA expression. Whereas the young mice had a stable and well-synchronized circadian activity/rest cycle, the rhythms of old animals were less stable and were phase advanced. The expression of mPerl mRNA and mPer2 mRNA was rhythmic in both groups, with peak values at CT7. The levels of mClock and mCry1 mRNA were not different depending on the time of day and did not vary with age. In contrast, an age-dependent difference was found in the case of mPer2 (but not mPerl) mRNA expression, with the maximum at CT7 significantly lower in old mice. The decreased expression of mPer2 may be relevant for the observed differences in the overt activity rhythm of aged mice.