Sex-and age- dependent modulation of synaptic proteins and behavioral variability in a postnatal valproic acid model.

Valproic acid (VPA) exposure is widely used to model autism spectrum disorder (ASD)-like phenotypes; however, the developmental timing and sex-specific molecular consequences of postnatal exposure remain incompletely understood. Disruptions in synaptogenesis and synaptic protein dynamics are considered central to the neurobiological underpinnings of ASD. This study investigated age- and sex-dependent behavioral and synaptic alterations following postnatal VPA administration during a critical developmental window (P30-P60). C57BL/6 female and male mice were exposed to a single intraperitoneal dose of VPA on postnatal day 14. Behavioral assessments included social interaction, open field, olfactory preference, and Morris water maze tests. Molecular analyses focused on the postsynaptic proteins Neurogranin (Nrgn) and PSD-95 (Dlg4) across the hippocampus, prefrontal cortex, and olfactory bulb. Postnatal VPA exposure produced age- and sex-dependent behavioral variability rather than uniform deficits. Males exhibited more pronounced modulation in locomotor and social parameters, whereas females showed relative resilience in spatial learning measures. In the hippocampus, VPA induced a significant increase in Nrgn mRNA and PSD-95 protein in 1-month-old males, suggesting temporally restricted synaptic remodeling during early maturation. These molecular alterations were region-specific and interaction-driven, with limited treatment effects observed in the prefrontal cortex and olfactory bulb. Importantly, protein levels were primarily influenced by age and sex rather than treatment alone, indicating tightly regulated developmental modulation rather than sustained synaptic loss. Collectively, these findings demonstrate that postnatal VPA exposure perturbs the temporal dynamics of synaptic maturation in a sex- and region-dependent manner, highlighting hippocampal vulnerability during adolescence. The results emphasize the importance of incorporating developmental stage and biological sex in mechanistic studies of ASD-related neuroplasticity.