Prenatal reduction of E14.5 embryonically fate-mapped pyramidal neurons in a mouse model of autism.

Although several observations suggest that the constitutive biological, genetic or physiological changes leading to autism spectrum disorders (ASD) start in utero, their early impact on the number and density of neurons in the brain remains unknown. Using genetic fate mapping associated with the immunollabeling-enabled three-dimensional imaging of solvent-cleared organs (iDISCO) clearing method we identified and counted a selective population of neocortical and hippocampal pyramidal neurons in the in utero valproate (VPA) mouse model of autism. We report that 1 day before birth, the number of pyramidal neurons born at E14.5 in the neocortex and hippocampus of VPA mice is smaller than in age-matched controls. VPA also induced a reduction of the neocortical-but not hippocampal-volume 1 day before birth. Interestingly, VPA mice present an increase in both neocortical and hippocampal volumes 2 days after birth compared with controls. These results suggest that the VPA-exposed hippocampus and neocortex differ substantially from controls during the highly complex perinatal period, and specially 1 day before birth, reflecting the early pathogenesis of ASD.