LITHIUM LENGTHENS THE PERIOD OF CIRCADIAN-RHYTHMS IN LESIONED HAMSTERS BEARING SCN GRAFTS

Lithium lengthens the free-running period of circadian rhythms in a wide variety of organisms. The object of the present study was to examine the effects of lithium treatment on free-running activity rhythms in suprachiasmatic nuclei lesioned (SCN-X) hamsters that had recovered circadian rhythmicity following transplantation of fetal anterior hypothalamic grafts containing the suprachiasmatic nuclei (SCN). The animals were housed individually in cages equipped with running wheels, and locomotor activity was monitored using a computer-based data acquisition system. At the end of the behavioral tests, animals were anesthetized and perfused. Brain sections were immunostained for vasoactive intestinal peptide (VIP) and vasopressin-associated neurophysin (NP) to evaluate the extent of the lesion and the presence of afunctional graft. In both intact and in SCN-X grafted animals, lithium lengthened the period of free running activity without affecting the amount of activity or the precision of the rhythm.