Neurogenesis and ontogeny of specific cell phenotypes within the hamster suprachiasmatic nucleus.
During late fetal and early neonatal life, the maternal circadian system coordinates the timing of a circadian clock in the hypothalamic suprachiasmatic nuclei (SCN) to the prevailing light-dark cycle. The role of the maternal SCN in the process of maternal coordination was investigated in rats. Complete lesions of the maternal SCN on day 7 of gestation disrupted rhythms of SCN glucose utilization in fetuses and pineal N-acetyltransferase activity in 10-d-old pups. This disruption was probably due to the desynchronization of individually oscillating fetal SCN, because individual pups born to and reared by SCN-lesioned dams under constant conditions exhibited normal circadian rhythms in drinking behavior. Cross-foster studies showed that the maternal circadian system can coordinate developing circadian rhythmicity during either the pre- or postnatal period. The results indicate that the maternal SCN are a necessary component of the mechanism of maternal coordination during both the pre- and postnatal periods.