Ontogeny of Circadian Corticosterone Rhythm in Female Rats: Effects of Periodic Maternal Deprivation and Food Restriction

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Abstract
The effects of maternal deprivation and food restriction on the ontogeny of the circadian blood corticosterone rhythm were studied. Control rats were normally mothered, weaned on day 23, and allowed to eat ad libitum. Experimental rats were subjected to 12 h of periodic maternal deprivation during either the day or night beginning on day 3. After weaning, they were either continued on food restriction or fed ad libitum. The daily corticosterone patterns were determined serially at 15, 20, 25, 30, and 35 days of age in individual rats. At 20 days of age, only maternally deprived rats showed corticosterone variations. Although peaks coinciding with the suckling period were observed in only half of the animals, all pups raised by the same mother showed similar corticosterone profiles. Late (day 16) onset of maternal deprivation or maternal deprivation in neonatally blinded pups did not cause such corticosterone fluctuations on day 20. In sighted rats raised by daytime suckling, nocturnal feeding appeared the day after weaning when fed ad libitum. Not only sighted animals but also neonatally blinded animals raised by periodic feeding established circadian corticosterone rhythms fully synchronized to their feeding patterns by day 25. The results indicate that 1) the feeding (but not suckling) rhythm is a more direct entrainer of corticosterone rhythm than is the light-dark cycle, 2) the emergence of lightdark entrainment of feeding and corticosterone rhythms in the sighted pups is highly self-programmed, and 3) some unknown factor(s), possibly related to mother-pup interactions, may trigger corticosterone variations before the feeding rhythm matures as a dominant synchronizer. (Endocrinology106: 636, 1980)