Sex-specific effects of prenatal valproic acid exposure on sociability and neuroinflammation: Relevance for susceptibility and resilience in autism

Autism spectrum disorder (ASD) is a group of neurodevelopmental disorders with an incidence four times higher in boys than in girls. By analyzing the effect of sex in a mouse model of ASD, we were able to identify immune alterations that could underlie this sex bias. Pregnant mice were injected subcutaneously with 600 mg/kg of valproic acid (VPA) or saline at gestational day 12.5. Their male and female offspring were evaluated in a social interaction test at adulthood, and only male VPA mice showed reduced sociability levels and a lack of preference for the social stimulus over a novel object. We then analyzed the corticosterone (CORT) response to an inflammatory stimulus, as a measure of the hypothalamus-pituitary-adrenal (HPA) function, and the neuroinflammatory state in adult and young animals. Adult VPA males exhibited increased basal CORT levels, while VPA females showed levels comparable to controls. As male mice showed a blunted CORT response at PD21 when compared to female mice, we propose that this early dimorphism could explain the different effects of VPA on HPA function. In addition, prenatal VPA exposure resulted in altered astroglial and microglial cell density levels in the cerebellum and dentate gyrus of adult mice. These neuroinflammatory effects were more pronounced in females than males, and appeared at early developmental stages. Hence, these postnatal glial density differences could underlie the behavioral alterations observed in adulthood, when only males show a social deficit. Our work contributes to the understanding of biological mechanisms affected by VPA on male and female rodents and shed light on the study of possible resilience mechanisms in the female population and/or susceptibility to ASD in boys.