in the Regulation of Circadian Locomotor Activity

In most species, 24-h rhythms of physiology and activity are regulated by endogenous circadian clocks. In mammals, the circadian pacemaker located in the suprachiasmatic nuclei (SCN) of the hypothalamus (Moore and Eichler, 1972; Schibler and Sassone-Corsi, 2002; Stephan and Zucker, 1972) shows electrical activity rhythms of approximately 24 h under free-running conditions (Inouye and Kawamura, 1979). Therefore, to keep in synchrony with external time, the SCN have to be reset each day by environmental zeitgebers in a process termed entrainment. The predominant zeitgeber of the mammalian system is light that reaches the SCN via the retino-hypothalamic tract (Moore and Lenn, 1972). From the SCN, time information is transferred by various means to peripheral circadian oscillator