Transplantation of the neonatal suprachiasmatic nuclei into rats with complete bilateral suprachiasmatic lesions.

The suprachiasmatic nuclei (SCN) obtained from neonatal day 1 rats were transplanted into the third ventricle of SCN lesioned rats which had shown circadian arrhythmicity in wheel-running activity for more than 2 months. In 8 out of 16 rats that received SCN transplantation, appearance of circadian rhythms in wheel-running activity was observed between 2 and 9 weeks after transplantation. Histological examination revealed ingrowth of the grafts into the periventricular zone, caudal from the lesioned SCN. These findings suggest that the recovery of circadian rhythmicity was the result of functional reinnervation of the periventricular zone by efferent fibers from the SCN.