Effects of caffeine on circadian phase, amplitude and period evaluated in cells in vitro and peripheral organs in vivo in PER2::LUCIFERASE mice

Background and Purpose Caffeine is one of the most commonly used psychoactive substances. Circadian rhythms consist of the main suprachiasmatic nucleus (SCN) clocks and peripheral clocks. Although caffeine lengthens circadian rhythms and modifies phase changes in SCN-operated rhythms, the effects on caffeine on the phase, period and amplitude of peripheral organ clocks are not known. In addition, the role of cAMP/Ca2+ signalling in effects of caffeine on rhythm has not been fully elucidated.