The effect of oestrogen and progesterone on maternal behaviour in rats

Treatment or implantation of oestrone, oestradiol or progesterone on the third day postpartum into the ventromedial-arcuate region of the hypothalamus produced a complex pattern of changes in established maternal behaviour in rats. Progesterone implanted into the ventromedial-arcuate region of the hypothalamus increased the time spent nursing. In contrast, it was shortened by oestradiol given subcutaneously or implanted hypothalamically or extrahypothalamically, or by oestrone implanted into the hypothalamus. Oestradiol by an route used oestrone implanted into the hypothalamus caused marked reduction of pup weight and retrieval frequency. Progesterone had no such effect. Maternal care involving retrieval, sniffing, licking and nursing, expressed in seconds care, declined after hypothalamic and systemic oestradiol treatment. However, oestrone implanted into the hypothalamus increased seconds of care on days 9 and 10. Progesterone did not affect this function.