Host resets phase of grafted SCN: influence of implant site, tissue specificity and pineal secretion

The suprachiasmatic nuclei (SCN) have daily fluctuations in energy consumption with glucose utilization high in the day, and low at night. In a previous study, we used [14C]2-deoxyglucose (2-DG) uptake to index the phase of the SCN, and found that in intact hamsters bearing SCN grafts in the third ventricle (3V), the native and grafted SCN, which were initially 12 h out of phase, became synchronized to the phase of the host clock [32]. In the present study, adult males (host animals) and pregnant females (source of donor tissue) were housed in opposite light-dark cycles. Host animals were sacrificed 14 days after implantation with either (1) SCN grafts into the lateral ventricle (LV), or (2) cortical grafts into 3V, or (3) SCN grafts in 3V of pinealectomized hamster. The results indicate that rhythms of 2-DG uptake are not induced in cortical tissue grafts, that the host SCN does not entrain SCN grafts located in the LV, and that entrainment of the grafted SCN (located in 3V) by the host circadian system occurs in the absence of pineal secretions.