Differential control of peripheral circadian rhythms by suprachiasmatic-dependent neural signals.

Although dependent on the integrity of a central pacemaker in the suprachiasmatic nucleus of the hypothalamus (SCN), endogenous daily (circadian) rhythms are expressed in a wide variety of peripheral organs. The pathways by which the pacemaker controls the periphery are unclear. Here, we used parabiosis between intact and SCN-lesioned mice to show that nonneural (behavioral or bloodborne) signals are adequate to maintain circadian rhythms of clock gene expression in liver and kidney, but not in heart, spleen, or skeletal muscle. These results indicate that the SCN regulates expression of circadian oscillations in different peripheral organs by diverse pathways.