ABLATION OF THE MATERNAL SUPRACHIASMATIC NUCLEI DISRUPTS THE TIMING OF THE FETAL CIRCADIAN CLOCK

Abstract

We have proven in the rat that a functional circadian clock oscillates in the fetal suprachiasmatic nuclei (SCN) and that the maternal circadian system coordinates the phase of the fetal clocks to ambient lighting conditions (Science 220:969, 1983). As the first step towards elucidating the mechanism of maternal coordination, we examined the effects of maternal SCN ablation. The 14C-deoxyglucose (DG) method was used to monitor metabolic activity of the fetal SCN. Timed pregnant rats were exposed to diurnal lighting throughout pregnancy. On gestational day 7, dams either received bilateral electrolytic SCN lesions or sham lesions. On gestational day 18, all were placed in constant darkness; dams were injected i.v. with 145 μCi/kg DG during either mid-subjective day or mid-subjective night on gestational day 21. Autoradiographs of serial sections of fetal brains from sham-operated dams revealed that the fetal SCN were all metabolically active during subjective day (n=18) and all inactive during subjective night (n=18). In contrast, after histologically confirmed complete SCN ablation in the dam, there was no significant day-night variation of SCN metabolic activity in the fetuses; activity was scattered over the inactive to active range within each of the 3 litters studied (8-10 fetuses/litter) at each of the two injection times. The results indicate that the maternal SCN are essential for coordination of the fetal circadian clock. (Supported by PHS Grant HD14427)