Effects of Elimination of Maternal Circadian Rhythms during Pregnancy on the Postnatal Development of Circadian Corticosterone Rhythm in Blinded Infantile Rats*

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Abstract
The influence of maternal circadian rhythms on fetal circadian oscillations during pregnancy was examined. Circadian rhythms of spontaneous locomotor activity and plasma corticosterone level in pregnant rats were eliminated by bilateral lesions of the suprachiasmatic nuclei (SCN) at different stages of gestation and the postnatal manifestation of the circadian corticosterone rhythm was examined in individual pups. Effective lesions of SCN at day 3 of gestation resulted in an abortion in all rats examined. Rats whose SCN were lesioned at day 10 or 17 of gestation maintained their pregnancies. At term, pups were removed by cesarean operation and immediately blinded by bilateral ocular enucleation; they were reared by unoperated foster mother afterwards. All pups from SCN lesioned mothers showed a clear free running circadian of plasma corticosterone levels after the 4th wk of postnatal life. The circadian rhythm that developed in pups from SCN-lesioned mother at day 10 of gestation (G10 pups) was always phase-delayed .apprx. 4 h as compared with that in pups from mothers whose SCN were lesioned at day 17 of gestation (G17 pups) and in pups from sham-operated mothers (S pups). The circadian hormone rhythmicity develops in normal fashion postnatally when the maternal SCN are effectively lesioned after day 10 of gestation. The phase-angle difference in the circadian rhythm between G10 pups and G17 or S pups suggests that fetal circadian oscillation is entrainable at least after day 10 of gestation.

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