HEAVY-WATER LENGTHENS THE PERIOD OF FREE-RUNNING RHYTHMS IN LESIONED HAMSTERS BEARING SCN GRAFTS

Heavy water (D2O) lengthens the period of free-running circadian rhyth ms in most organisms. We compared the effect of D2O on freerunning loc omotor activity rhythms in intact and SCN-lesioned (SCN-X) hamsters th at had recovered circadian rhythmicity following implantation of SCN g rafts. The animals were housed individually in cages equipped with run ning wheels, and locomotor activity was monitored using a computer-bas ed data acquisition system. At the end of the behavioral tests, animal s were anesthetized and perfused. Brain sections were immunostained fo r vasoactive intestinal peptide (VIP) and vasopressin (VP) to evaluate the extent of the lesion and the presence of a functional graft. The D2O similarly lengthened the period of free-running activity without a ffecting amount of activity in both intact and in SCN-X grafted animal s. The results indicate that D2O acts directly on the SCN to lengthen the free-running period, and suggest that coupling between pacemakers within the grafted SCN is as efficient as in the intact SCN.