On the nature of the circadian clock in mammals

Am J Physiol. 1993 May;264(5 Pt 2):R821-32. doi: 10.1152/ajpregu.1993.264.5.R821.


The evidence for the essential role of the suprachiasmatic nucleus (SCN) for the generation and maintenance of circadian rhythms in mammals is briefly reviewed. The pharmacology of the phase-response curve is considered and a new circadian measure, the phase-dose-response surface (PDRS), is introduced. The role of neurotransmission, ion fluxes, and non-neuronal cellular elements in the generation and maintenance of circadian rhythmicity is considered. Cell culture of the SCN is proposed as a tool for the functional analysis of clock mechanism. The critical contribution of coupling and synchronization of clock elements is reviewed in the context of the explicit predictions generated by a strong coupling model of the circadian clock. Finally, the nature of the circadian output signal is analyzed from a phylogenetic viewpoint.

Publication types

  • Editorial
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.
  • Review

MeSH terms

  • Animals
  • Biological Clocks*
  • Circadian Rhythm*
  • Humans
  • Ions
  • Mammals / physiology*
  • Suprachiasmatic Nucleus / physiology
  • Synaptic Transmission
  • Time Factors


  • Ions