Developmental analysis of visually evoked defensive behavior identifies age and sex-specific responses and underlying synaptic and glia changes.

Defensive behaviors such as freezing and escaping are crucial for survival, involving the complex integration of sensory and motor circuits. While instinctive, the ability to discern threat and adapt responsiveness is acquired through life experience, shaped by sensory maturation and emotional state. Disrupting these processes by sensory deprivation or chronic stress can induce disproportionate reactions, underscoring the need for a comprehensive understanding of age and sex-specific variations in defensive responses and adaptation. Here, we employed behavioral testing and immunohistochemistry to analyze visually evoked defensive responses and synaptic and glial development in the superficial superior colliculus (sSC) and dorsal periaqueductal gray (dPAG). Our findings demonstrate distinct age and sex-dependent behavioral profiles that are correlated with synaptic and glial changes in these brain regions. This study provides critical insights into the establishment and adaptation of visual threat responses and underlying circuits, laying the groundwork for future investigations into the cellular mechanisms governing defensive behaviors.