Site-specific changes in brain extra-SCN oscillators during early pregnancy in the rat

The influence of circadian timekeeping systems on behavior and physiology can change substantially as female mammals undergo the transition from a nonpregnant to a pregnant state. Here, we examined the possibility that site-specific changes in extra-SCN oscillators and in local rhythms might coincide with the emergence of new patterns of temporal organization among various behavioral and physiological rhythms. Specifically, we compared daily patterns of immunoreactive FOS and PER2 in 3 brain regions of pregnant and diestrous rats. We found that, in the oval nucleus of the bed nucleus of the stria terminalis (BnST-ov), the peak of the PER2 rhythm occurred approximately 12 hours out of phase in pregnant and diestrous females. In contrast, the phase of the rhythm in FOS was the same, but pregnant rats expressed more FOS in the BnST-ov than diestrous ones. In the central amygdala (CEA) of diestrous females, PER2 expression was arrhythmic, but Fos expression was elevated at night. No rhythms were seen in this region of pregnant females, nor were any rhythms seen in the basolateral amygdala of either group. Overall, the patterns in the BnST-ov and the CEA were consistent with the hypothesis that differential changes in daily rhythms within some extra-SCN brain regions might mediate the changes in the temporal organization of several behavioral and endocrine functions that occur during the transition from a nonpregnant to a pregnant state.