Repeated cross-fostering affects maternal behavior and olfactory preferences in rat pups.

Disturbances in early mother-infant relationships are strongly associated with changes in the development of a number of physiological and behavioral systems in the neonate that can create a complex change in patterns of vulnerability throughout life. Institutionalized children, despite receiving adequate care, display important behavioral changes in adult life, and such changes are strongly associated with a lack of selective and consistent attachment to the maternal figure in early life. It is not yet clear how human adoption processes alter the mother-infant relationship early in life. Here, to mimic the situation of human adoption and explore the impact on the formation of attachment between the infant and a caregiver, we use a repeated cross-fostering (RCF) model in rodents in two postnatal periods, postnatal days (PND) 1 to 3 (early RCF) and 9 to 11 (late RCF). Early exposure but not late exposure to RCF reduces the pups' preference for the odor of the mother figure. Moreover, early exposure and slightly later exposure to RCF reduce maternal care and motivation in collecting the pups and bringing them to the nest. The RCF protocol creates an unstable environment for mother-pup interaction, but it seems to affect learned attachment to the mother only when it occurs during the corresponding sensitive period of development.

Functional New World monkey oxytocin forms elicit an altered signaling profile and promotes parental care in rats.

The neurohormone oxytocin is a key player in the modulation of reproductive and social behavioral traits, such as parental care. Recently, a correlation between different forms of oxytocin and behavioral phenotypes has been described in the New World Monkeys (NWMs). Here, we demonstrate that, compared with the Leu8OXT found in most placental mammals, the Cebidae Pro8OXT and Saguinus Val3Pro8OXT taxon-specific variants act as equi-efficacious agonists for the Gq-dependent pathway but are weaker agonists for the ß-arrestin engagement and subsequent endocytosis toward the oxytocin receptor (OXTR). Upon interaction with the AVPR1a, Pro8OXT and the common Leu8OXT yielded similar signaling profiles, being equally efficacious on Gq and ß-arrestin, while Val3Pro8OXT showed reduced relative efficacy toward ß-arrestin. Intranasal treatment with either of the variants increased maternal behavior and also promoted unusual paternal care in rats, as measured by pup-retrieval tests. We therefore suggest that Val3Pro8OXT and Pro8OXT are functional variants, which might have been evolutionarily co-opted as an essential part of the adaptive genetic repertoire that allowed the emergence of taxon-specific complex social behaviors, such as intense parental care in the Cebidae and the genus Saguinus.