Towards a molecular biology of the circadian clock and sleep of mammals

Abstract

Behavioral states of rest and activity are temporally organized. Since the beginning of life on Earth, plants and animals have been forced to adapt to the daily rhythm of the planet's rotation about its axis. In complex vertebrates (birds and mammals), rest and activity have evolved into the electrophysiologically and behaviorally distinct states of sleep and wakefulness. The evolutionary emergence of bouts of rapid eye movement (REM) sleep may be even more recent; the echidna, one of the earliest mammals, lacks this sleep stage (Siegel et al., 1994). The cycling of these behavioral states is under neural control, and much is known about their cellular basis, but the underlying events at the molecular level are virtually unknown. Here each of us highlights some of the new approaches for investigating the molecular substrate for behavioral state control of circadian rhythmicity (WJS) and sleep (PJS) in mammals.