Regulation of circadian rhythmicity in mammals by a neural pacemaker, the suprachiasmatic nuclei (SCN), will be studied using a new transplant technique recently developed in our laboratory; neural transplants of 14-day embryonic SCN restore circadian rhythmicity in adult male hamster hosts previously rendered arrthymic by electrolyhtic SCN lesioning. The planned transplant experiments will address: specificity of SCN in restoring rhyhthmicity, role of age of fetal transplant tissue in graft survival and restoration of rhythmicity, effect of transplant location on restoration of rhythmicity, neural or humoral mode of SCN action, rate and pathway of SCN transplant re- enervation, and degree of optic nerve fiber re-enervation for photoentrainment. Locomotor activity will be used to monitor daily rhythmicity of intact hosts initially in constant conditions (DD), as well as after lesioning and transplantation and in a final light schedule of LD entrainment. Subsequently, animals will be sacrified, hypothalamic areas will be serially sectioned, and the tissue stained with histological and immunocytological methods to confirm viability of transplants, their normal neuropeptide expression, and completeness of host lesioning. SCN transplantation holds promise, in specific term, for elucidating SCN pacemaker mechanisms. More generally, the transplant paradigm may serve as a model for understanding neural mechanisms.
