Mild perinatal hypoxia uncouples excitatory-inhibitory circuit maturation and reprograms neocortical organization

Perinatal hypoxia is a major contributor to neurodevelopmental disorders; however, the consequences of mild-to-moderate perinatal hypoxia (MPH) remain insufficiently characterized. Here, we investigated cortical plasticity following MPH using a multimodal approach that combines behavioral assessment, histological analysis, and in vivo magnetic resonance imaging (MRI). Fifty-six Wistar Han rats were exposed to hypoxia or normoxia at postnatal day 1 (P1). Neurodevelopmental assessment from P3 to P14 revealed impaired rooting and vibrissae-placing reflexes in hypoxic rats. Histological analysis demonstrated: altered expression of microtubule-associated protein-2, apical dendrite bundling, reduced neurofilament-H expression, and decreased dendritic arbor complexity in large pyramidal neurons, indicating disrupted maturation of excitatory circuits. Increased parvalbumin expression, higher interneuron density, and its enhanced neurite elaboration indicated precocious development of inhibitory circuits, consistent with a compensatory response. MRI at P15, combined with whole-brain voxel-wise analysis, revealed a significant increase in fractional anisotropy in the anterior cingulate cortex (ACC). Convergent behavioral, histological, and imaging findings identified the ACC as the most vulnerable region following MPH, followed by the somatosensory cortex. These findings reveal early cytoarchitectural and MRI detectable correlates of a single episode of MPH, which, together with previous findings from this model, support the neurodevelopmental origin of persistent alterations in cortical structure and circuit function, characterized by an excitatory-inhibitory imbalance. The study identifies and defines a framework for understanding region-specific vulnerability and plasticity in the immature brain, with implications for improving the early detection of subtle perinatal brain injury, as a prerequisite for timely therapeutic intervention.