Lateralized decrease of parvalbumin+ cells in the somatosensory cortex of ASD models is correlatedwith unilateral tactile hypersensitivity

Abstract

Inhibitory control of excitatory networks contributes to cortical functions. Increasing evidence indicates that parvalbumin expressing (PV+) basket cells (BC) are a major player in maintaining the balance between excitation (E) and inhibition (I) in the cortex. Disruption of E/I balance in cortical networks is believed to be a hallmark of autism spectrum disorders (ASD) and may contribute to sensory alterations seen in ASD. Here, we report a lateralized decrease in the number of PV+ BCs in L2/3 of the somatosensory cortex in the dominant hemisphere of adult Shank3-/- and Cntnap2-/- mouse models of ASD. The dominant hemisphere was identified during a reaching task to establish each animals dominant forepaw. Double labeling with anti-PV antibody and a biotinylated lectin (i.e., VVA) showed that the number of BCs was not different but rather, some BCs did not express detectable levels of PV (PV-), resulting in an elevated number of PV- VVA+ basket cells. This lateralized reduction was not observed in the number of interneurons from the other two major groups that express somatostatin or the serotonergic receptor 5HT3a. Finally, we showed that dominant hind paws had higher mechanical sensitivity (i.e., lower mechanical thresholds measured with von Frey test) but no difference in thermal sensitivity (measured with Hargreaves test) when compared to the other hind paw. This mechanical hypersensitivity in the dominant paw correlated with the decrease in the number of PV+ interneurons and reduced PV expression in the corresponding cortex. Together, these results suggest that the sensory hypersensitivity in ASD could be due to decreased inhibitory inputs to the dominant somatosensory cortex.