Estradiol and parental experience, but not prolactin are necessary for ultrasound recognition and pup-retrieving in the mouse.

The effects of estradiol, prolactin and experience with pups on pup-retrieving and on the recognition of ultrasonic distress calls of the young by adult ovariectomized female mice were studied. Treatment with estradiol benzoate or experience with pups (for 5 days) induced pup-retrieving in 40% and 60% of the animals, respectively, as compared to 0% in inexperienced ovariectomized females. However, if pup-experience was achieved in the presence of estradiol, retrieving was shown by 90.5% of the animals. In addition, in this case models of the ultrasonic distress calls of the pups were significantly preferred ("recognized") in a discrimination task by the females. These females also showed a sharp increase in serum prolactin concentrations. Depleting prolactin from the blood by cysteamine, however, neither reduced the retrieving score nor disturbed ultrasound recognition. Thus prolactin is dispensable for maintaining maternal pup-retrieving and ultrasound recognition. The process of achieving pup-experience is enhanced by the presence of estradiol. Possible actions of estradiol in the brain are discussed.