Suprachiasmatic nucleus lesions abolish and fetal grafts restore circadian gnawing rhythms in hamsters.

It is widely accepted that the suprachiasmatic nuclei (SCN) of the hypothalamus serve as biological pacemakers, organizing daily activities. However some circadian rhythms are controlled by extra-SCN structures. Transplantation of fetal donor SCN in SCN-lesioned rodents induces recovery of rhythmic locomotor and drinking activities. Such grafts do not however, restore appropriate gonadal responses to photoperiodic stimuli. It is not known whether other behavioral rhythms are restored by fetal tissue grafts, or whether various responses are restored simultaneously. In the present study, we established that circadian rhythms of gnawing behavior are abolished following SCN lesions. Next, we measured both gnawing and wheel-running activity in SCN-lesioned hamsters following transplantation of fetal hypothalamic grafts containing the SCN. The results indicate that such grafts restore circadian rhythms of gnawing behavior, and that gnawing and wheel-running rhythms re-emerge at about the same time.