Aging of the Mammalian Circadian System

Abstract

Numerous studies have demonstrated that as animals reach advanced age for the species, there are pronounced changes in the expression of diverse circadian rhythms. Many of the observed changes may reflect an overall deterioration of the health of the organism. On the other hand, changes in the circadian system may not simply reflect such deterioration, but may represent one of the underlying causes for the negative health effects associated with advanced age. Most studies of the effects of advanced age on the circadian system have been carried out on rodents and humans. Since Chapter 22 of this volume reviews the literature on the effects of aging on the human circadian system, this chapter will focus primarily on studies of rodents, particularly the best-studied animals in this regard: laboratory rats, mice, and golden (Syrian) hamsters. After first describing the multitude of changes that have been observed in the aging circadian system of rodents, this review will [1] examine the underlying physiologic mechanisms that lead to these changes, [2] provide an overview of attempts to attenuate or reverse age-related effects on circadian rhythmicity, and [3] speculate on the functional significance of such changes.