Conference Agenda

Atypical sensory processing is a proposed etiological factor underlying the development of behavioral deficits in autism spectrum disorder (ASD). Patients with Phelan-McDermid Syndrome (PMS) often show somatosensory processing dysfunction, including altered sensitivity to touch and tactile defensiveness. Mice mutants of the Shank3 gene are generally considered a reliable model for studying ASD-like symptoms relevant to PMS. Specifically, Shank3B mutant mice display aberrant whisker-independent texture discrimination and reactivity to tactile stimuli. While behavioral deficits have been extensively described, the neural substrates of tactile sensory processing deficits in PMS are still poorly understood.

We posited that 1) the cortical somatosensory response is affected in Shank3 haploinsufficient (Shank3B^+/-) mice and contributes to the altered responsiveness of the behavioral phenotype; 2) focal inhibition of cortical activity can modulate the sensitivity to peripheral stimulation in Shank3B^+/- mice.

Preliminary results show that the spatiotemporal features of the sensory-evoked cortical response are substantially different in Shank3B^+/- compared to WT mice at post-natal day 60. Alterations of the sensory-evoked response involve most cortical regions including the barrel field and associative areas like the retrosplenial cortex. Specifically, the secondary response to the stimulus is the most affected, leading to a stronger and widespread late activation. Since the secondary response is associated with the perception of sensory stimuli, this aberrant and enduring activation suggests that perception of the stimulus is altered in Shank3B^+/- mice. Finally, results show that the aberrant processing of sensory stimuli leads to modifications on the functional connectivity (FC) of the barrel field with many other regions. Interestingly, the FC differences between mutated and wild type mice are brain-state dependent, i.e. strong in wakefulness and absent in deeper anesthesia.

Haploinsufficiency of the SH3 and multiple ankyrin repeat domains (Shank) 3 gene is associated with Phelan-McDermid Syndrome, a rare genetic disorder included in the Autism Spectrum Disorder (ASD), as well as idiopathic ASD forms. Shank3 is a multi-domain protein playing a crucial scaffolding role at the excitatory postsynaptic site. Shank3 KO mice exhibit social deficit and obsessive self-injurious grooming, associated with cortico-striatal synaptic defects. Evidence from this and other ASD models points to the synapse as a key element in ASD pathophysiology, therefore, functional synaptic rescue could represent an effective therapeutic strategy. In this respect, strong dendritogenic and synaptogenic activity are exhibited by a group of chemically heterogeneous compounds sharing psychedelic properties, which include the dissociative anesthetic ketamine and 5HT2A receptor agonists 2,5-Dimethoxy-4-iodoamphetamine (DOI) and N, N-dimethyltryptamine (DMT). We extended the characterization of the neurological phenotype of Shank3B +/- mice to probe the post-acute (24 hours) effects of a single sub-anesthetic dose of ketamine (10 mg/kg, i.p.) using behavioral tests, in vivo mesoscale imaging of excitatory neurons expressing the calcium indicator GCaMP7f during whisker stimulation, ex vivo slice electrophysiology and post-recording morphometric analysis of Layer V pyramidal neurons of the Barrel Field (BF). We found that ketamine ameliorates social deficit and partially rescues the alterations in sensory-evoked cortical functional connectivity observed in Shank3B +/- mice. In ex vivo electrophysiological recordings, intrinsic excitability and synaptic activity of BF Layer V pyramidal neurons are not affected by Shank3 haploinsufficiency or post-acute ketamine. In conclusion, we used a combination of functional and anatomical assays to probe the interaction between gene haploinsufficiency and the effects of post-acute ketamine on Shank3 +/- mice. The phenotypes under examination are closely linked to the genetics underlying Shank3-related disorders and thus highly predictive in drug discovery studies seeking to develop novel therapeutics.

Brain imaging studies in autistic individuals have revealed highly heterogenous patterns of atypical or disrupted functional connectivity as measured with fMRI. However, the origin and significance of these heterogeneous findings remain unclear. Leveraging the translatability of fMRI across species, here we clustered functional connectivity alterations in 20 etiologically-distinct mouse models of autism, and successfully decoded the observed dominant patterns of dysconnectivity in fMRI scans of autistic individuals. We also probed the neural bases of the observed fMRI dysconnectivity using mechanistically-relevant chemogenetic manipulations in the mouse.

We found that patterns of fMRI connectivity mapped in a large mouse database (n = 286 mutant mice, 209 control littermates) could be clustered into two dominant hypo- and hyperconnectivity subtypes. These subtypes were functionally dissociable andassociated with distinct signalling pathways involving synaptic signalling, or transcriptional and immune mechanisms, respectively.

Region-specific decoding of these fMRI connectivity patterns in autistic people (n=945 autistic individuals and n=1044 controls from ABIDE-1, 2 and an in house dataset) revealed two groups of individuals (N=166 and n=79, respectively) recapitulating the hyper- and hypo-connectivity patterns identified in rodents. These two subtypes were stable in cross-validation, encompassed dissociable network structure and symptom severity, and were spatially enriched for molecular pathways initially modelled in mice (hypoconnected, synaptic-signalling; hyperconnected, immune mechanisms). Corroborating a synaptic origin for the hypoconnected subtype, chemogenetics studies showed that fMRI hypoconnectivity can be the result of excitatory-inhibitory imbalance during early developmental windows.

Our data show that heterogenous fMRI connectivity in autism encodes for biologically-relevant information, and delineate two reproducible patterns of dysconnectivity underpinned by biologically-distinct etiological mechanisms.

Introduction

Despite extensive research utilizing brain magnetic resonance imaging that has revealed abnormal neuroanatomical characteristics in individuals with autism spectrum disorder (ASD), the extent and selectivity of these neuroanatomical abnormalities within the ASD spectrum remain unclear. Moreover, the shared neuroanatomical features among multiple brain disorders further complicate the translation of neuroimaging findings into practical clinical applications, posing an ongoing challenge in this field.

Objectives

We utilized a data-driven, coordinate-based, and reverse inference approach, specifically Bayes fACtor mOdeliNg (BACON), in a meta-analytical investigation of the selective neuroanatomical alteration profile of the autistic brain.

Methods

Voxel-based morphometry (VBM) data meeting eligibility criteria were extracted through a standardized search of BrainMap and MEDLINE databases, encompassing 849 published peer-reviewed experiments, 131 brain disorders, 22,747 clinical subjects, and 16,572 x-y-z coordinates. Two distinct datasets were created: the ASD dataset, consisting of VBM data related to the autistic spectrum, and the non-ASD dataset, comprising VBM data from other clinical conditions. Using activation likelihood estimation (ALE) maps from these datasets, BACON analysis was performed. This allowed us to obtain posterior probability distributions assessing the selectivity of brain alterations in ASD.

Results

Our findings demonstrated selective neuroanatomical alterations in both cortical and cerebellar regions in ASD. Specifically, eight clusters were identified with a selectivity value ≥ 90%, including the bilateral precuneus, right inferior occipital gyrus, left lobule IX, left Crus II, right Crus I, and right lobule VIIIA.

Conclusions

The identification of this distinctive neuroanatomical pattern sheds new light on the intricate pathophysiology of ASD, offering promising prospects for potential neuroimaging-based interventions in the future.