Light-induced gene expression in the suprachiasmatic nucleus of young and aging rats.

We investigated age-related changes in a molecular mechanism associated with synchronization of circadian rhythms to the environment. In mammals, the suprachiasmatic nucleus (SCN) of the hypothalamus contains a circadian pacemaker that regulates a variety of physiological and behavioral rhythms. Recent studies have demonstrated photic induction of immediate early genes (IEGs) such as c-fos in the SCN in a circadian-phase dependent manner, suggesting that IEGs may be part of the pathway for entrainment of circadian rhythms. We find that there is a decreased response of the IEGs c-fos, and NGFI-A but not NGFI-B in the SCN of old animals after photic stimulation. Changes in gene transcription indicated by IEGs may provide insights into the molecular machinery of the biological clock and ultimately elucidate mechanisms underlying the age-dependent decay of circadian organization.