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 LeuOXT found in most placental mammals, the Cebidae ProOXT and ValProOXT taxon-specific variants act as equi-efficacious agonists for the G-dependent pathway but are weaker agonists for the β-arrestin engagement and subsequent endocytosis toward the oxytocin receptor (OXTR). Upon interaction with the AVPR1a, ProOXT and the common LeuOXT yielded similar signaling profiles, being equally efficacious on G and β-arrestin, while ValProOXT showed reduced relative efficacy toward β-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 ValProOXT and ProOXT 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 .