Resetting central and peripheral circadian oscillators in transgenic rats

In multicellular organisms, circadian oscillators are organized into multit issue systems which function as biological clocks that regulate the activit ies of the organism in relation to environmental cycles and provide an inte rnal temporal framework. To investigate the organization of a mammalian cir cadian system, we constructed a transgenic rat Line in which luciferase is rhythmically expressed under the control of the mouse Per1 promoter. Light emission from cultured suprachiasmatic nuclei (SCN) of these rats was invar iably and robustly rhythmic and persisted for up to 32 days in vitro. Liver , Lung, and skeletal muscle also expressed circadian rhythms, which damped after two to seven cycles in vitro. In response to advances and delays of t he environmental Light cycle, the circadian rhythm of light emission from t he SCN shifted more rapidly than did the rhythm of locomotor behavior or th e rhythms in peripheral tissues. We hypothesize that a self-sustained circa dian pacemaker in the SCN entrains circadian oscillators in the periphery t o maintain adaptive phase control, which is temporarily Lost following Larg e, abrupt shifts in the environmental Light cycle.