284 MATERNAL-FETAL COORDINATION OF CIRCADIAN RHYTHMICITY IN THE RAT

Abstract

Maternal coordination of the fetal biological clock was examined. Pregnant rats were housed in diurnal lighting (LD 12:12) from mating until 2 d prior to birth when they were transferred to darkness and the pups were born and reared in darkness. Circadian output was monitored in 10-d-old pups by measuring the rhythm in pineal N-acetyltransferase (NAT) activity. Analysis of NAT in the pups revealed a large daily rhythm in activity (0.1 nmol/g/h to 20 nmol/g/h) which was coordinated by the light-dark cycle during pregnancy. To determine whether the fetus could directly perceive alterations in lighting, 2 groups of pregnant rats were raised in diurnal lighting until day 7 of pregnancy. At that time one group was blinded and both groups were subjected to a phase shift in lighting until a reversed lighting cycle (DL 12:12) was attained. All were maintained in reversed lighting from day 14 of pregnancy until 2 d prior to birth when all were placed in darkness. Analysis of NAT activity in 10-d-old pups showed that the pups from both groups of mothers exhibited a clear daily rhythm but the phase of the rhythm was 10 hrs out of phase when one group was compared to the other; the NAT rhythm for pups reared by intact mothers was synchronized by the reversed lighting cycle whereas the rhythm of the pups born to blind mothers was synchronized by the maternal lighting cycle prior to blinding. Thus, mother is essential for transmitting lighting information to the fetal biological clock. Maternal coordination appears to have evolved for the purpose of preparing the immature mammal for entry into the environment.