Birth by Cesarean Section Remodels Neonatal Brain Barriers and Associated Immune and Metabolic Pathways in Mice

ABSTRACT Mode of delivery shapes early-life physiology through multiple pathways, including stress and hormonal signalling, neonatal oxygenation, and exposure to maternal microbes. Cesarean section (CS) bypasses several of these processes and has been associated with altered immune maturation and neurodevelopmental outcomes in humans and animal models. Given that CS is also known to disrupt gut barrier integrity and that gut and brain barriers operate as a coordinated network, we investigated whether CS-associated changes extend to early postnatal brain barriers. Using a mouse model, we compared CS-delivered pups with vaginally born (VB) controls at postnatal days 8-9. Brain barrier permeability and cellular architecture were assessed using tracer extravasation and vascular and tight junction analysis, choroid plexus immune populations were profiled, and metabolomic profiling was performed in cortex and plasma. Blood-brain barrier structural readouts in the medial prefrontal cortex were mostly preserved. In contrast, the blood-cerebrospinal fluid barrier (BCSFB) exhibited structural alterations in both its vascular and epithelial tight junction compartments. These barrier changes were accompanied by immune remodelling, including expansion of antigen-presenting border-associated macrophages and reduced parenchymal microglia density. CS delivery increased brain tracer accumulation, consistent with altered barrier function during this developmental window. Metabolomic profiling further identified lower levels of key brain metabolites, including N-acetylaspartate, a marker of neuronal metabolic state. Together, these findings demonstrate that CS delivery induces early alterations in brain barrier function, BCSFB structure, immune landscape, along with brain and plasma metabolic profiles in mice. This identifies delivery mode as a key perinatal variable shaping neonatal brain physiology and establishes a framework for dissecting how birth context may influence long-term neurodevelopmental trajectories.