PACEMAKER INTERACTIONS IN THE MAMMALIAN CIRCADIAN SYSTEM

Circadian rhythms in mammals are generated by pacemaker cells located in the suprachiasmatic nucleus (SCN) of the anterior hypothalamus. The identity of these cells,however,is not known, and little information exists regarding the mechanisms by which they communicate with each ot her and with the organism. None-theless, pacemaker interactions must o ccur to produce single, coherent rhythms of behavior and physiology. R ecently it has become possible to observe the result of these interact ions using circadian chimeras,animals with two clocks with distinct pe riods,that have been produced by SCN transplantation. Using the tau mu tation in golden hamsters,chimeras expressing two circadian rhythms of behavior simultaneously were created. The two rhythms exhibited compl ex interactions including cases of relative coordination. This basic r esult indicates that pacemaker interactions are rhythmic and phase dep endent. Further analysis should help to elucidate the nature of the co upling signal and the identity of the pacemaker cells.