A brief period of enriched caregiving during the first four days of life selectively enhances adult social investigation and increases neuropeptide receptor gene expression in female mice, according to a study published in Frontiers in Neuroscience by researchers Camilla Mancini, Lucy Babicola, Carlo Cifani, and Rossella Ventura. The investigation focused on whether providing an extra non-lactating female caregiver from postnatal day one to four could shape long-term social phenotypes and modify the mesocorticolimbic system in inbred DBA/2J female mice. By focusing on a narrow developmental window known to be critical for caregiver-infant attachment bond formation, the researchers sought to understand how non-nutritional social stimulation influences early developmental trajectories and adult behavioral outcomes. Their findings demonstrate that animals receiving extra nurturing care in early infancy exhibited a specific preference for direct social contact in adulthood, accompanied by elevated levels of oxytocin and vasopressin receptor messenger RNA within the nucleus accumbens, without displaying alterations in body weight, baseline anxiety, or motor activity.
The early postnatal period represents a highly sensitive developmental window during which heightened neural plasticity renders the mammalian brain exceptionally receptive to environmental cues. During this stage, neural circuits that regulate emotional processing, stress responsiveness, and social motivation, including the mesocorticolimbic pathway, undergo substantial maturation under the guidance of caregiver interactions. Extensive scientific research has established that early-life adversity, such as prolonged maternal separation, neglect, or fragmented parental care, can severely impair neurodevelopmental trajectories and increase adult vulnerability to psychiatric disorders. Conversely, considerably less scientific attention has been directed toward determining how positive early social enrichment, particularly when strictly confined to the earliest postnatal days, influences healthy neurodevelopment. Previous experiments conducted by the research team showed that disrupting the maternal-pup relationship between postnatal days one and four via repeated cross-fostering induced persistent depressive-like behavior and impaired social recognition in adult female mice, while the temporary presence of an alternative caregiver successfully prevented these behavioral deficits.
Building on those prior observations, the investigators designed an experimental model to evaluate whether augmenting caregiving availability during that identical sensitive period would produce beneficial or selective behavioral adaptations under otherwise undisturbed conditions. The research team utilized six- to eight-week-old male and female DBA/2J mice housed under strictly regulated environmental conditions with standardized ambient temperature, controlled relative humidity, and consistent twelve-hour light-dark schedules. Breeding trios consisting of two females and one male were mated at twelve weeks of age, after which pregnant females were assigned either to a standard control rearing protocol or to an early social enrichment condition. In the enrichment paradigm, a virgin, non-lactating adult female was introduced into the cage alongside the pregnant dam fifteen days after mating. Following delivery, both adult females were left undisturbed with the offspring until postnatal day four, allowing the virgin female to provide tactile stimulation, grooming, and continuous contact without supplying supplemental nutrition.
To quantify the behavioral interactions occurring within the nests, maternal behavior was observed systematically across the first seven postnatal days using instantaneous sampling sessions conducted twice daily. Trained observers recorded nursing, licking, grooming, and non-pup-directed activities displayed by the biological mothers and the additional caregiver. The quantitative behavioral records showed that pups reared in the early social enrichment condition received significantly more total nurturing care from postnatal day one to four than control litters, yielding a robust statistical effect. Crucially, the biological mothers in the enriched cages did not decrease their own maternal investment, confirming that the presence of the additional female created a genuine net increase in caregiving rather than triggering a compensatory decline in maternal engagement. In addition, physical growth assessments conducted at postnatal days five, eight, and ninety revealed identical developmental weight trajectories across both cohorts, confirming that the supplementary caregiving exerted its effects entirely independently of nutritional availability.
The researchers next investigated whether this brief neonatal social enrichment modified early attachment-related emotional reactivity by recording separation-induced ultrasonic vocalizations at postnatal day eight. Infant mice emit characteristic high-frequency distress calls when isolated from their mother and home nest, providing a validated metric of early affective state and attachment behavior. Individual pups were placed in an experimental chamber containing clean bedding, familiar home-cage bedding, or bedding carrying the scent of the additional caregiver. While exposure to familiar home-cage bedding elicited a statistically significant reduction in ultrasonic vocalization rates compared to clean bedding across all litters, the researchers found no significant differences between the enriched and control groups in total call numbers or mean call durations. This outcome demonstrated that the brief caregiving manipulation did not diminish normal attachment-related responsiveness to familiar olfactory cues, nor did it induce a generalized change in neonatal separation distress.
To assess whether the effects of early social enrichment endured into maturity, the female offspring underwent a battery of behavioral tests beginning at three months of age, ordered sequentially from least to most demanding to limit procedural carry-over. In the open field test administered at postnatal day ninety, automated video tracking revealed that adult female mice from both rearing backgrounds traveled equivalent total distances and spent comparable amounts of time exploring the arena perimeter. These metrics indicated that the early caregiving experience did not produce lasting modifications in baseline locomotion or generalized anxiety-like behavior. Similarly, when the animals were evaluated in the forced swimming test at postnatal days ninety-nine and one hundred, blind manual scoring of immobility and paddling behavior revealed no differences between the groups. These findings confirmed that early social enrichment did not alter passive stress-coping strategies or behavioral despair in adult female mice.
In sharp contrast to the absence of general emotional or locomotor differences, testing in the three-chamber apparatus revealed pronounced, domain-specific modifications in adult social behavior. When given free access to explore an arena containing an unfamiliar female mouse housed inside a perforated cylinder alongside an identical cylinder containing an inanimate object, both experimental groups exhibited a normal baseline preference by spending more time exploring the social chamber than the object chamber. However, a detailed analysis of direct physical interaction, quantified as the duration of active sniffing and close cylinder contact, revealed a significant interaction between rearing condition and stimulus type. Post-hoc testing demonstrated that adult female mice exposed to early social enrichment spent significantly more time engaged in direct investigation of the unfamiliar conspecific compared to control females, indicating an enhancement in direct social investigation rather than a generalized increase in exploratory activity.
To identify potential neurobiological correlates underlying this heightened adult social investigation, the researchers performed quantitative real-time polymerase chain reaction analyses on bilateral tissue punches harvested from the nucleus accumbens of behaviorally naive adult females. The molecular assays focused specifically on oxytocin receptor and vasopressin type 1a receptor gene expression, two highly conserved neuropeptide signaling systems that regulate affiliative behaviors, social recognition, and motivational processing. The analysis demonstrated that adult female mice that experienced early social enrichment exhibited significantly higher levels of oxytocin receptor messenger RNA and vasopressin 1a receptor messenger RNA in the nucleus accumbens compared to control animals. Given the established role of accumbal oxytocinergic and vasopressinergic pathways in modulating social reward and assigning salience to conspecific cues, the authors noted that this dual upregulation represents a plausible molecular correlate of the observed increase in adult social investigation.
The investigators also conducted developmental gene expression analyses on whole half-brain samples collected at postnatal day five, immediately following the conclusion of the enrichment protocol, to examine immediate transcriptional changes. At this neonatal stage, relative levels of oxytocin and vasopressin receptor transcripts did not differ significantly between enriched and control pups. The authors suggested that this temporal dissociation might indicate that the molecular phenotype emerges gradually across development through delayed transcriptional programming or experience-dependent circuit maturation, rather than via an immediate post-treatment surge. Nevertheless, the researchers cautioned that because the neonatal analysis was performed on entire half-brain extracts while the adult analysis utilized micro-punches restricted to the nucleus accumbens, the early whole-hemisphere screen could have lacked the anatomical sensitivity necessary to detect small, region-specific changes that may have already been localized within subcortical nuclei.
The researchers emphasized several important methodological limitations, noting that their molecular findings represent associative correlates rather than direct proof of a causal neurobiological mechanism. Because the study quantified messenger RNA expression rather than functional receptor protein abundance, ligand binding affinity, or local peptide release, targeted pharmacological and circuit-level interventions will be required to confirm whether accumbal receptor signaling directly drives the increased social investigation. Furthermore, the experiments evaluated only female mice belonging to the inbred DBA/2J strain, leaving unresolved whether these behavioral and transcriptional alterations generalize to males or other genetic backgrounds, and adult testing did not track estrous cycle stages. Despite these limitations, the authors concluded that brief caregiving enrichment during the first four postnatal days is sufficient to induce enduring, region-specific adaptations in social neuropeptide systems and selectively promote adult social investigation in female mice.
Subject of Research: Early-life social enrichment and adult neurobehavioral outcomes in female mice
Article Title: Early social enrichment enhances adult social investigation and increases oxytocin and vasopressin receptor mRNA expression in the nucleus accumbens of adult female mice
Article References: Mancini, C., Babicola, L., Cifani, C., & Ventura, R. (2026). Early social enrichment enhances adult social investigation and increases oxytocin and vasopressin receptor mRNA expression in the nucleus accumbens of adult female mice. Frontiers in Neuroscience, 20, Article 1962157. https://doi.org/10.3389/fnins.2026.1962157
Image Credits: AI Generated
DOI: 10.3389/fnins.2026.1962157
Keywords: neuroscience, maternal care, social behavior, oxytocin receptor, vasopressin receptor, nucleus accumbens, developmental plasticity, behavioral neuroscience, Early, social, enrichment, enhances
