FIGURE 2.

Schematic summary of in vivo and in vitro circadian synchronization. In vivo, the photic zeitgeber mainly entrains the central clock, which regulates the peripheral clocks through the internal timing cues including autonomic innervations, endocrine signaling and body temperature; the non-photic zeitgebers including arousal stimuli, temperature and food mainly entrain the peripheral clocks. In vitro, the circadian oscillations of cells or explants can be synchronized by temperature cycles, chemical factors (such as Dex, Fsk, or horse serum) and mechanical stimuli.