Transplantation of the suprachiasmatic nucleus in the rat.

Restoration of the circadian rhythmicity in wheel-running activity was shown in rats with bilateral suprachiasmatic nuclei (SCN) lesions, after transplantation of the neonatal SCN into the wall of the third ventricle. Free-running circadian rhythms of the wheel-running activity were recorded in young adult rats at least for a month under constant dark condition. Then, bilateral SCNs were completely lesioned electrolytically under deep pentobarbital anaesthesia. After further recording for more than two months without obvious circadian rhythmicity in wheel-running activity, the animals were subjected to transplantation of the SCN. SCNs taken from day 1 neonatal rats were transplanted by injecting the grafts into the third ventricle of the host rat under pentobarbital anaesthesia. After recovery from the procedure, the rat was returned to a cage with a running wheel. Food and water were available at all times. Successful transplantation led to restoration of the circadian rhythmicity starting from two weeks and up to three months after the transplantation. To identify the SCN in the transplanted graft, we used an immunohistochemical staining method for the VIP (vasoactive intestinal polypeptide) and vasopressin. The VIP was located particularly in the ventral area of the SCN, whereas vasopressin was in the dorsal area. In most cases, where circadian rhythmicity was successfully restored, the graft was attached to the caudal wall of the third ventricle.