Early-life maternal separation induces anxiety-like behavior in male mice associated with reduced dentate gyrus neurogenesis and hippocampal inflammatory remodeling

Early-life adversity increases vulnerability to affective disorders, but the neural alterations underlying sex-dependent susceptibility remain unclear. Here, C57BL/6J mouse pups underwent maternal separation (MS) for 3 h daily from postnatal day 1 to 10, and adult male and female offspring were assessed behaviorally. MS induced significant anxiety-like behavioral alterations in male offspring, whereas comparable anxiogenic changes were not detected in females. c-Fos-based regional screening identified the hippocampus as a candidate region. In males, the reduction in c-Fos-positive cells was further localized to the dorsal and ventral dentate gyrus (DG), whereas females showed no significant change in overall hippocampal c-Fos expression. Transcriptomic analysis of the hippocampus revealed enrichment of inflammation-related pathways and downregulation of neurogenesis-related signatures, whereas histological analyses demonstrated reduced adult DG neurogenesis, including decreased quiescent and activated neural stem cells and reduced DCX immunoreactivity. These neurogenic alterations were accompanied by microglial activation, increased hippocampal pro-inflammatory cytokine expression, reduced IL-10 expression, and increased microglia-neural stem cell proximity. Together, these findings indicate that early-life maternal separation is associated with anxiety-like behavioral alterations in male offspring accompanied by reduced DG neurogenesis and hippocampal inflammatory alterations.