Fos rhythms in the hypothalamus of Rattus and Arvicanthis that exhibit nocturnal and diurnal patterns of rhythmicity

This study compared patterns of Fos expression within the suprachiasmatic n ucleus (SCN), the region immediately dorsal to the SCN (the lower subparave ntricular zone, LSPV). and the supraoptic nucleus (SON) of grass rats (Arvi canthis niloticus) and lab rats (Rattus norvegicus). Among grass rats we al so compared individuals exhibiting nocturnal and diurnal patterns of wheel running. In the SCN of both groups of grass rats, as well as laboratory rat s, Fos was elevated during the light compared to the dark portions of the d ay, and was expressed in 7-12% of cells containing vasoactive intestinal po lypeptide (VIP). Fos was higher in the LSPV during the night compared to th e day in both forms of grass rats but not in laboratory rats. In the SON, F os rose from day to night in the diurnal grass rats and in laboratory rats, but not in nocturnal grass rats. These patterns are consistent with the hy pothesis that VIP cells in the SCN function similarly in nocturnal and diur nal rodents, but that the SON and the region dorsal to the SCN are associat ed with intra and interspecific differences in rhythmicity, respectively. ( C) 2001 Elsevier Science B.V. All rights reserved.