Uncovering the female phenotype in the VPA autism model: Brain-region specific synaptic pattern, microglial priming and behavioral singularity

Abstract

Neurodevelopmental disorders, such as autism spectrum disorders (ASD), exhibit a poorly understood male bias. While sex differences may provide key insights into ASD etiology and treatment, the female side of animal models, such as prenatal valproic acid (VPA) exposure, remains incompletely characterized. Here, we evaluated the behavioral, synaptic, and microglial profiles of female VPA rats. Female VPA animals exhibited social deficits, including a decreased sociability index in the three-chamber test and reduced play and social-recognition behaviors in a peer-interaction test, while exploratory and repetitive activities were preserved. At the synaptic level, the medial prefrontal cortex (mPFC) showed increased synaptophysin (SYN) immunostaining, whereas the hippocampal subfield CA3, displayed reduced SYN. Additionally, CA3 neurons exhibited increased neuronal cell adhesion molecule (NCAM) immunostaining, while the mPFC showed increased levels of its polysialylated form (PSA-NCAM), resulting in distinct NCAM/PSA-NCAM ratio shifts in each region. In vitro, hippocampal and cortical neurons from female VPA animals exhibited preserved synaptic puncta number and dendritic tree length and responded to glutamate-induced remodeling similarly to controls, suggesting no intrinsic neuronal alterations. Microglia from the mPFC and the hippocampus exhibited a less ramified morphology, with increased cell numbers in the mPFC. Isolated and cultured microglia retained this reactive phenotype, yet they responded to the exposure to synaptic terminals similarly to controls. Our findings indicate that female VPA rats display a distinctive social deficit linked to brain-area-specific synaptic remodeling impairment and microglial reactivity. Sex-differences in the VPA model could provide valuable insights into neuron-glia interactions underlying autism.