Early social enrichment enhances adult social investigation and increases oxytocin and vasopressin receptor mRNA expression in the nucleus accumbens of adult female mice

Introduction The early postnatal period is a sensitive window for the development of social behavior, during which interactions with caregivers play a critical role in shaping brain circuits and neuropeptide systems involved in social interaction. Although the prolonged effects of early positive social experiences are well established, less is known about social enrichment restricted to the first postnatal days. Methods Here, we examined whether early social enrichment (ESE), provided by the presence of an additional non-lactating caregiving female from postnatal day (P) 1 to 4, during attachment bond formation, influences early attachment-related responses, adult social behavior, and oxytocin and vasopressin receptor expression within the mesocorticolimbic system in DBA/2J female mice. Results ESE pups received significantly more nurturing care, which did not affect physical development but induced selective long-lasting effects on social behavior, increasing preference for social investigation in adulthood. This behavioral modification was associated with the modulation of neuropeptide systems known to be involved in sociability. Adult ESE mice exhibited increased expression of oxytocin and vasopressin receptors specifically in the nucleus accumbens. Discussion These findings demonstrate that a brief social enrichment during the first postnatal days is sufficient to induce long-term and region-specific adaptations of the social neuropeptide systems and shape adult social behavior.