Estricted Access to Food, but Not Sucrose, Saccharine, R Salt, Synchronizes the Expression of Period2 Protein N the Limbic Forebrain

bstract—Restricted feeding schedules (RF) in which daily ccess to food is limited to a few hours each day can entrain he rhythms of expression of circadian clock genes in the rain and periphery in rodents. The critical factors mediating he effect of RF on rhythms of clock gene expression are nknown. Previously, we demonstrated that daytime RF hifts the phase of expression of the clock protein, Period2 PER2) in the oval nucleus of the bed nucleus of the stria erminalis in rats kept on a 12-h light/dark cycle, and restored he rhythm of PER2 expression in rats housed in constant ight. We now report that RF also modifies the rhythms of ER2 expression in the central and basolateral nuclei of the mygdala and in the dentate gyrus, such that all three areas ecome synchronized, peaking 12 h after the time of food resentation. Daily limited access to sucrose or saccharine in reely fed rats or scheduled access to saline in sodiumeprived rats had no effect on these PER2 rhythms. Thus, it ould appear that the rhythms of PER2 in limbic forebrain tructures are sensitive to signals that arise from the allevition of a negative metabolic state associated with scheduled eeding and that access to rewarding substances in the abence of food deprivation or metabolic challenges, per se, is not ufficient to alter the rhythms of PER2 expression in these egions. © 2006 IBRO. Published by Elsevier Ltd. All rights eserved.