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Previous work has demonstrated that neuroimaging biomarkers which capture functional connectivity of the brain can be used to define a specific and robust endophenotype in Fmr1 -/y mice, a well-established animal model of human Fragile-X Syndrome (FXS). However, it is currently unknown whether this macroscopic measure of brain connectivity is sufficiently sensitive to reliably detect changes caused by pharmacological interventions. Here we inhibited the activity of the metabotropic glutamate receptor-5 (mGluR5) using AFQ056/Mavoglurant, a drug that is assumed to normalize excitatory/inhibitory neural signaling imbalances in FXS. We employed resting-state-fMRI (rs-fMRI) and diffusion-weighted imaging (DWI) to test whether Mavoglurant re-established brain connectivity - at least partly - within some of the affected circuits in Fmr1 -/y mice that are related to social behavior deficits. In line with previous findings, we observed that Fmr1 -/y mice exhibited impaired social interaction, reduced connectivity in three main functional networks and altered network topology. At the group level, Mavoglurant did neither rescue abnormal social behavioral nor white matter abnormalities; however, for some, but not all of these circuits Mavoglurant had a genotype-specific effect of restoring functional connectivity. These results show that rs-fMRI connectivity is sufficiently sensitive to pick up system-level changes after the pharmacological inhibition of mGluR5 activity. However, our results also show that the effects of Mavoglurant are confined to specific networks suggesting that behavioral benefits might be restricted to narrow functional domains., (Copyright © 2019 The Authors. Published by Elsevier Inc. All rights reserved.)

Autism spectrum disorders (ASD) are a set of complex neurodevelopmental disorders for which there is currently no targeted therapeutic approach. It is thought that alterations of genes regulating migration and synapse formation during development affect neural circuit formation and result in aberrant connectivity within distinct circuits that underlie abnormal behaviors. However, it is unknown whether deviant developmental trajectories are circuit-specific for a given autism risk-gene. We used MRI to probe changes in functional and structural connectivity from childhood to adulthood in Fragile-X (Fmr1-/y) and contactin-associated (CNTNAP2-/-) knockout mice. Young Fmr1-/y mice (30 days postnatal) presented with a robust hypoconnectivity phenotype in corticocortico and corticostriatal circuits in areas associated with sensory information processing, which was maintained until adulthood. Conversely, only small differences in hippocampal and striatal areas were present during early postnatal development in CNTNAP2-/- mice, while major connectivity deficits in prefrontal and limbic pathways developed between adolescence and adulthood. These findings are supported by viral tracing and electron micrograph approaches and define 2 clearly distinct connectivity endophenotypes within the autism spectrum. We conclude that the genetic background of ASD strongly influences which circuits are most affected, the nature of the phenotype, and the developmental time course of the associated changes.