A diffusible coupling signal from the transplanted suprachiasmatic nucleus controlling circadian locomotor rhythms.
Silver, Rae; LeSauter, Joseph; Tresco, Patrick A.; Lehman, Michael N.
[Letter] Nature. 382(6594):810-813, August 29, 1996.

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THE mammalian suprachiasmatic nuclei (SCN) transmit signals to the rest of the brain, organizing circadian rhythms throughout the body *RF 1-4*. Transplants of the SCN restore circadian activity rhythms to animals whose own SCN have been ablated [5-9]. The nature of the coupling signal from the grafted SCN to the host brain is not known, although it has been presumed that functional recovery requires re-establishment of appropriate synaptic connections. We have isolated SCN tissue from hamsters within a semipermeable polymeric capsule before transplantation, thereby preventing neural outgrowth but allowing diffusion of humoral signals. Here we show that the transplanted SCN, like neural pacemakers of Drosophila [10] and silkmoths [11], can sustain circadian activity rhythms by means of a diffusible signal.

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