LIGHT-INDUCED GENE-EXPRESSION IN THE SUPRACHIASMATIC NUCLEUS OF YOUNGAND AGING RATS

We investigated age-related changes in a molecular mechanism associate d with synchronization of circadian rhythms to the environment. In mam mals, the suprachiasmatic nucleus (SCN) of the hypothalamus contains a circadian pacemaker that regulates a variety of physiological and beh avioral rhythms. Recent studies have demonstrated photic induction of immediate early genes (IEGs) such as c-fos in the SCN in a circadian-p hase dependent manner, suggesting that IEGs may be part of the pathway for entrainment of circadian rhythms. We find that there is a decreas ed 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 i ndicated by IEGs may provide insights into the molecular machinery of the biological clock and ultimately elucidate mechanisms underlying th e age-dependent decay of circadian organization.