Distinct Defects in Synaptic Differentiation of Neocortical Neurons in Response to Prenatal Valproate Exposure

Autism spectrum disorders (ASDs) are a heterogeneous group of neurodevelopmental disorders characterized by impairments in social interactions and stereotyped behaviors. Valproic acid (VPA) is frequently used to treat epilepsy and bipolar disorders. When taken during pregnancy, VPA increases the risk of the unborn child to develop an ASD. In rodents, in utero VPA exposure can precipitate behavioral phenotypes related to ASD in the offspring. Therefore, such rodent models may allow for identification of synaptic pathophysiology underlying ASD risk. Here, we systematically probed alterations in synaptic proteins that might contribute to autism-related behavior in the offspring of in utero VPA-exposed mice. Moreover, we tested whether direct VPA exposure of cultured neocortical neurons may recapitulate the molecular alterations seen in vivo. VPA-exposed neurons in culture exhibit a significant increase in the number of glutamatergic synapses accompanied by a significant decrease in the number of GABAergic synapses. This shift in excitatory/inhibitory balance results in substantially increased spontaneous activity in neuronal networks arising from VPA-exposed neurons. Pharmacological experiments demonstrate that the alterations in GABAergic and glutamatergic synaptic proteins and structures are largely caused by inhibition of histone deacetylases. Therefore, our study highlights an epigenetic mechanism underlying the synaptic pathophysiology in this ASD model.