Effects of neonatal oxytocin manipulation on development of social behaviors in mice.

The oxytocin (OT) neural system is thought to be involved in the underlying mechanisms that guide the development of social behaviors. In the present study, we examined the effects of neonatal oxytocin manipulation in mice. Within 24 hours after birth, pups in the treatment group randomly received an intraperitoneal injection of OT or OT antagonist (OTA), and those in the control group received a saline injection or handling only. Some of these mice underwent a test that counted the number of isolation-induced ultrasound vocalizations they made on postnatal day 6, and they were further tested for sociability at 8-9 weeks of age and for neuroendocrine stress response to novel environments at 19-20 weeks of age. Another group of mice was tested for alloparental responsiveness at 13-15 weeks of age. The OT injection affected sociability and alloparental responsiveness. In an approach/avoidance test, most of the mice made a social approach to an unfamiliar conspecific of the same sex, but females that had received a neonatal injection of 3 μg of OTA did not show this response. The neonatal OTA treatment appeared to inhibit females' sociability in a dose-dependent fashion. In a retrieving test, females that had received a neonatal injection of 3 μg of OT retrieved significantly more pups than did those that had received 3 μg of OTA, although neither of the treatments caused the females to behave significantly differently from control group females. Meanwhile, a neonatal injection of 3 μg of OTA increased the latency to retrieve pups in males. These results suggested that neonatal OT action may positively regulate alloparental responsiveness in adulthood. Considering that the organizational effects of OT have also been shown in voles and rats, the mechanism by which neonatal OT modifies the development of social behaviors appears to be common to all rodents.