In the general population, less than 1% of children develop seizures, whereas over 30% of children with autism spectrum disorder (ASD) do so by adolescence. Maternal infection during pregnancy is a risk factor for both ASD and epilepsy, however we have limited understanding of how early-life immune insults alter neural circuitry implicated in both disorders. The medial prefrontal cortex (mPFC) is a brain region important for regulating diverse cognitive and emotional behaviors altered in ASD. We have obtained pilot data supporting altered mPFC circuit function after gestational exposure to a viral mimetic polyinosinic:polycytidylic acid (poly(I:C)). Using a high-throughput multisite field potential recording approach in acute mPFC brain slices, our preliminary results indicate that maternal immune activation (MIA) leads to persistent alterations in mPFC activity, at both presynaptic and postsynaptic loci, and an increased susceptibility to generation of epileptic activities in vitro. The proposed experiments will elucidate the precise cell type- and lamina-specific alterations underlying changes in network excitability.
Aim 1 of this proposal will identify changes to functional intracortical connectivity within the mPFC. Pregnant dams will be treated with saline or poly(I:C) to mount an acute antiviral inflammatory response. Acute brain slices containing mPFC will be prepared from adult offspring at three to four months of age. Laser scanning photostimulation based on patterned glutamate uncaging will be used to map excitatory synaptic connectivity within the mPFC between photo-excited presynaptic neurons and individual postsynaptic pyramidal and interneurons. Changes to laminar-specific inputs to excitatory and inhibitory cells types following MIA will be assessed by intracellular voltage-clamp recordings of synaptic activity. Immunohistochemical methods will confirm cell type, location and morphology and will be used to identify structural defects in lamination.
Aim 2 will evaluate alterations in the recruitment of distal inputs to the mPFC from two regions highly implicated in the initiation and spread of limbic seizures, the basolateral amygdala (BLA) and ventral hippocampus (vHC). AAV-CamKII?-ChR2/eYFP will be used to target expression of channelrhodopsin-eYFP or eYFP alone to excitatory neurons in these extra-prefrontal structures. Postsynaptic currents in mPFC in L2/3 and L5 neurons will be measured in response to optogenetic activation of BLA and vHC terminals, respectively, and changes in excitatory and inhibitory components assessed. Together these aims address circuit intrinsic and extrinsic changes that may contribute to the shared pathogenesis of ASD and epilepsy. Information gained from the interrogation of mPFC circuitry in an established MIA model will identify neuropathological alterations that might be targeted for therapies.
The proposed research will reveal neural circuit mechanisms underlying the role of prenatal exposure to maternal infection in the shared pathogenesis of autism spectrum disorder (ASD) and epilepsy, which have remarkably high rates of comorbidity in children and adolescents. Unlike genetic risk factors, maternal environmental factors are preventable and could therefore lead to improved strategies for decreasing risk and for intervention.