Structural and functional differences in the barrel cortex of Mecp2 null mice

Functional deficits in sensory systems are commonly noted in neurodevelopmental disorders, such as the Rett syndrome (RTT). Defects in methyl CpG binding protein gene (MECP2) largely accounts for RTT. Manipulations of the Mecp2 gene in mice provide useful models to probe into various aspects of brain development associated with the RTT. In this study, we focused on the somatosensory cortical phenotype in the Bird mouse model of RTT. We used voltage-sensitive dye imaging to evaluate whisker sensory evoked activity in the barrel cortex of mice. We coupled this functional assay with morphological analyses in postnatal mice and investigated the dendritic differentiation of barrel neurons and individual thalamocortical axon (TCA) arbors that synapse with them. We show that in Mecp2-deficient male mice, whisker-evoked activity is roughly topographic but weak in the barrel cortex. At the morphological level, we find that TCA arbors fail to develop into discrete, concentrated patches in barrel hollows, and the complexity of the dendritic branches in layer IV spiny stellate neurons is reduced. Collectively, our results indicate significant structural and functional impairments in the barrel cortex of the Bird mouse line, a popular animal model for the RTT. Such structural and functional anomalies in the primary somatosensory cortex may underlie orofacial tactile sensitivity issues and sensorimotor stereotypies characteristic of RTT.