Developmental and Juvenile Ultrasonic Vocalizations in the Shank3 Mutant Rat Model of Phelan-Mcdermid Syndrome and Autism Spectrum Disorder

Background:  Mutations in the SHANK3 gene lead to autism spectrum disorder (ASD), Phelan-McDermid Syndrome (PMS), as well as intellectual disabilities (Betancur & Buxbaum, 2013; Gauthier et al., 2009; Leblond et al., 2014; Moessner et al., 2007). Reduced expression of SHANK3, which codes for a synaptic scaffolding protein, has been hypothesized to lead to impairments in key brain functions underlying social communication and cognition (Durand et al., 2007). Both mutant mouse and, more recently, rat models have been generated in an effort to assess the neurobiological and behavioral effects of mutations in Shank3 (Yang et al., 2012; Peca et al., 2011; Kouser et al., 2013; Harony-Nicholas et al., 2015; Jaramillo et al., 2016; Zhou et al., 2016).

Objectives:  The present experiments aimed to evaluate various aspects of social communication using the sophisticated tool of ultrasonic vocalizations, taking advantage of the only generated rat model of Shank3 mutations and carrying out studies across early life and during critical juvenile developmental windows in both haploinsufficient and null mutant animals.

Methods:  Isolation-induced ultrasonic vocalizations (USVs) were collected from newborn Sprague-Dawley rat pups on postnatal day (PND) 7, the peak day of calling (Wöhr et al., 2008). As juveniles (PND 26-29), a USV playback paradigm was executed by presenting individual rats with a natural 50-kHz USV versus an acoustic control stimulus, and comparing subsequent USV production and approach behavior toward the stimulus source. Juvenile sociability was also assessed via the three-chambered social approach assay in which rats could choose to interact with a novel object or a novel conspecific, a social novelty assay in which rats could choose to interact with a familiar or a novel conspecific, and a play-promoting reciprocal social interaction assay in which rats could freely engage with a novel wildtype (WT), sex-matched conspecific.

Results:  Male Shank3 heterozygous pups exhibited reduced USVs, emitting significantly fewer calls compared to male Shank3 WT pups. The USV playback assay revealed no genotype differences in locomotor response, as rats of all genotypes and sexes similarly approached the source of the 50-kHz USV and spent more time in close proximity to the source of the affiliative 50-kHz call than the control stimulus. Effects of genotype on USV emission during the playback assay are currently being analyzed. Preliminary data suggest normal sociability during the social approach assay but deficits in the preference for social novelty, as well as subtle genotype effects on some measures of the reciprocal social interaction assay. We are continuing the data analysis and reproducibility experiments at this time.

Conclusions:  This study led to the discovery of a novel phenotype, reduced pup call emissions, in the Shank3 rat model of PMS and ASD. The data presented here lend support for the important role of Shank3 in social communication and for the use of this rat model as a tool to study the neurobiology underlying the behavioral phenotypes of PMS and ASD. These findings will provide the basis for further investigations into both the behavioral and biological consequences of mutations in SHANK3.