Diffusible and Driving Signals of The Biological Clock

摘要

While it is well established that the SCN is the site of an endogenous circadianpacemaker that drives many behavioral and physiological rhythms, the output or coupling mechanisms(s) for signaling the brain and the rest of the body is not known. We used an encapsulation technique to physically isolate the grafted neurons from the host brain. Because the donor period (about 24 hours) is easily distinguishable from the freerunning period (about 20 hours) of the host hamster, restored rhythms can be attributed unambiguously to the SCN of the donor tissue. Encapsulated SCN grafts (=4) implanted into the 3 rd ventricle of SCN-lesioned hamsters rescues wild-type locomotor behavior in (and only in) animals in which tissue survives within the capsule. This provides definitive evidence of diffusible output signals from the SCN in controlling locomotor rhythmicity.