A DIFFUSIBLE COUPLING SIGNAL FROM THE TRANSPLANTED SUPRACHIASMATIC NUCLEUS CONTROLLING CIRCADIAN LOCOMOTOR RHYTHMS

THE mammalian suprachiasmatic nuclei (SCN) transmit signals to the res t of the brain, organizing circadian rhythms throughout the body(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 signa l from the grafted SCN to the host brain is not known, although it has been presumed that functional recovery requires re-establishment of a ppropriate synaptic connections. We have isolated SCN tissue from hams ters 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 pacemaker s of Drosophila(10) and silkmoths(11), can sustain circadian activity rhythms by means of a diffusible signal.