Maternal phase control of fetal circadian oscillation during pregnancy.

Mother-pups interaction is essential for the normal development of individuals during ontogeny. In this review, the emphasis was on a special function in a special stage of development, i.e., fetal entrainment to pregnant mother of the circadian rhythm which is one of the fundamental autonomic functions in the organism. To this end, the basic assumptions and problems were introduced and the validity of the assumption was defended. Based on this, the various factors of postnatal life which might affect the phase angle of overt hormone rhythm were experimentally evaluated. Finally, by introducing experimental designs which were to exclude disturbing effects of the nursing mother, we found that the fetal oscillation was possibly entrainable by pregnant mother as early as in the middle of gestation. Possible mechanism of the entrainment and adaptive implications of the findings were discussed.