Breastmilk vesicles link maternal postnatal depression to offspring brain development

Postnatal depression and offspring neurodevelopment

Approximately 10–20% of women worldwide experience postnatal depression, a common mental health problem during the perinatal period. Epidemiological studies show that children of mothers with postnatal depression face greater challenges in cognitive and language development, behavioral regulation, and academic achievement, and have a higher risk of adolescent depression. Previous studies have largely explained this link through genetic susceptibility, the intrauterine environment, and postnatal care and parent–child interaction. Yet why the effects are so multifaceted and long-lasting, and through what molecular mechanisms and signaling pathways a mother's psychological state influences offspring development, have remained unclear.

The clue lies in breastmilk

Lactation is a key hub of mother–infant connection after birth. Beyond providing nutrition, breastmilk contains a variety of bioactive components. To clarify the role of the rearing environment, the team first conducted cross-fostering experiments in mice, in which healthy dams and depression-model dams exchanged pups. Pups born to healthy dams but nursed by depression-model dams showed more pronounced cognitive and emotional behavioral abnormalities than pups born to depression-model dams but nursed by healthy dams, indicating that the rearing environment strongly influences offspring neurodevelopment.

Analysis of multiple brain regions showed that pups nursed by depression-model dams had shorter dendrites and fewer branches in newborn neurons of the hippocampal dentate gyrus, along with elevated frequency of excitatory synaptic input. The abnormalities occurred mainly at the stage of neuronal maturation rather than reflecting reduced neural stem cell proliferation. These changes were detectable as early as postnatal day 21 and persisted at adult time points, indicating that the effects of the early rearing environment can extend into later developmental stages.

Breastmilk extracellular vesicles act as messengers delivering "depression signals" to the offspring brain

Breastmilk contains abundant microRNAs (miRNAs), a substantial proportion of which are encapsulated in small extracellular vesicles (sEVs) only 30–150 nm in diameter. The team found that the miRNA landscape in breastmilk vesicles from mothers with postnatal depression was markedly remodeled, with miR-15a-5p, miR-15b-5p, and miR-205-5p showing the most prominent upregulation; the mouse model reproduced the same changes. Using fluorescent reporter mice, the researchers observed that after only three days of nursing, fluorescent signals derived from breastmilk vesicles appeared in the pups' hippocampal, cortical, and hypothalamic neurons, indicating that maternal vesicles enter the offspring brain through lactation. Reporter gene experiments further showed that breastmilk miRNAs entering the offspring brain were "working efficiently," exerting significant regulatory effects on offspring brain genes. Administering breastmilk vesicles from mothers with postnatal depression to healthy pups was sufficient to induce cognitive impairment after weaning; breastmilk fractions depleted of vesicles had no such effect. When Rab27a, a key regulator of vesicle secretion, was specifically knocked out in the mammary glands of depressed dams, breastmilk vesicle secretion decreased by 58%, and the cognitive and neurodevelopmental deficits in pups nursed by these dams were markedly ameliorated.

mGluR8 in SuM excitatory neurons is a key target

Through single-cell transcriptomic analysis of the whole brain and hypothalamus, the team focused on excitatory neurons in the hypothalamic supramammillary nucleus (SuM). Tracing experiments showed that axons of these neurons project to the hippocampal dentate gyrus and form contacts with newborn granule cells. Further investigation revealed that expression of the metabotropic glutamate receptor mGluR8 in SuM neurons was affected. This receptor is located at the axon terminals of SuM neurons projecting to the dentate gyrus, where it helps regulate glutamate release and limit excessive excitatory input. Normally, mGluR8 expression in the mouse SuM rises gradually to adult levels during postnatal days 0–21. Under exposure to postnatal depression breastmilk vesicles, this upregulation was suppressed. Even after lactation-related exposure ended, expression levels remained low at adult time points.

To test the role of mGluR8, the team intervened specifically in SuM neurons projecting to the dentate gyrus. Reducing mGluR8 expression in pups nursed by healthy dams reproduced the relevant abnormalities, whereas increasing its expression in pups nursed by depression-model dams improved behavioral performance, neuronal morphology, and synaptic function. Inhibiting the relevant miRNAs in offspring SuM neurons also ameliorated the corresponding deficits. These results indicate that suppression of mGluR8 expression by breastmilk vesicle miRNAs is an important component of postnatal depression-related offspring neurodevelopmental abnormalities.

To further understand how these changes affect neuronal activity, the team used miniature head-mounted microscopes to record calcium activity in newborn granule cells of freely moving mice. During the inter-trial interval and memory retrieval phases, calcium activity frequency in these cells was elevated. However, cross-day tracking of the same neurons revealed that cells related to contextual memory showed reduced activity amplitude when reactivated. This "high-frequency, low-amplitude" activity pattern indicates that increased activity does not mean enhanced memory-related function. Overall activity became more frequent while memory-related responses weakened, providing a neural activity-level explanation for the cognitive abnormalities in mice.

Rethinking breastmilk, rethinking postnatal depression

First, breastmilk can directly participate in offspring brain development through bioactive components. miRNAs carried by breastmilk vesicles can enter the offspring brain and influence gene expression in specific neurons within specific time windows, thereby altering neural circuit activity and the maturation of newborn neurons. In healthy states, this may be one of the important molecular bases for the long-term cognitive benefits of breastfeeding; when mothers are depressed, changes in this pathway may contribute to offspring cognitive and emotional behavioral abnormalities. Future population follow-up studies could assess the relationship between breastmilk vesicle miRNAs in postnatal depression and long-term child development, clarifying their value for early risk assessment.

Second, a new maternal–infant molecular communication pathway. Previous studies have shown that sperm miRNAs can transmit paternal environmental experience information; this study shows that breastmilk vesicle miRNAs can serve as carriers of maternal environmental signals, filling an important gap in the picture of intergenerational epigenetic transmission. The "maternal depressive state–breastmilk vesicle miRNAs–offspring neurodevelopment" pathway provides a new theoretical framework for understanding how the early-life environment influences long-term brain health. More broadly, this study further reveals the biological link between postnatal depression and offspring developmental risk and identifies key intervenable steps in animal models, providing experimental evidence for exploring early intervention. Future work could continue to explore whether, while supporting breastfeeding, improving maternal depression or intervening in the relevant molecular pathways can improve offspring development.

Third, maternal mental health deserves full attention. According to current clinical guidance, mothers with postnatal depression can generally continue breastfeeding and should receive timely treatment and feeding support suited to their circumstances. The present findings are not yet sufficient to justify changing clinical feeding recommendations, but they strongly suggest that society, the healthcare system, and families should prioritize psychological support and care for pregnant and postpartum women, and that mothers should not bear the burden of illness and childcare alone.

Taken together, this study links "maternal emotion–breastmilk vesicle miRNAs–offspring neurodevelopment" into a testable and intervenable biological pathway: it expands the boundaries of breastmilk function, deepens understanding of the intergenerational effects of postnatal depression, and provides molecular targets and time windows for early screening, prevention, and intervention in perinatal mental health.