Immp2l knockdown increases stimulus-driven instrumental behaviour but does not alter goal-directed learning or neuron density in cortico-striatal circuits in a mouse model of Tourette syndrome and autism spectrum disorder

Abstract

AbstractCortico-striatal neurocircuits mediate goal-directed and habitual actions which are necessary for adaptive behaviour. It has recently been proposed that some of the core symptoms of autism spectrum disorder (ASD) and Gilles de la Tourette syndrome (GTS), such as tics and repetitive behaviours, may emerge because of imbalances in these neurocircuits. We have recently developed a model of ASD and GTS by knocking downImmp2l, a mitochondrial gene frequently associated with these disorders. The current study sought to determine whetherImmp2lknockdown (KD) in male mice alters flexible, goal- or cue-driven behaviour using procedures specifically designed to examine response-outcome and stimulus-response associations, which underlie goal-directed and habitual behaviour, respectively. WhetherImmp2lKD alters neuron density in cortico-striatal neurocircuits known to regulate these behaviours was also examined.Immp2lKD mice and wild type-like mice (WT) were trained on Pavlovian and instrumental learning procedures where auditory cues predicted food delivery and lever-press responses earned a food outcome. It was demonstrated that goal-directed learning was not changed forImmp2lKD mice compared to WT mice, as lever-press responses were sensitive to changes in the value of the food outcome, and to contingency reversal and degradation. There was also no difference in the capacity of KD mice to form habitual behaviours compared to WT mice following extending training of the instrumental action. However,Immp2lKD mice were more responsive to auditory stimuli paired with food as indicated by a non-specific increase in lever response rates during Pavlovian-to-instrumental transfer. Finally, there were no alterations to neuron density in striatum or any prefrontal cortex or limbic brain structures examined. Thus, the current study suggests that Immp2l is not necessary for learned maladaptive goal or stimulus driven behaviours in ASD or GTS, but that it may contribute to increased capacity for external stimuli to drive behaviour. Alterations to stimulus-driven behaviour could potentially influence the expression of tics and repetitive behaviours, suggesting that genetic alterations toImmp2lmay contribute to these core symptoms in ASD and GTS. Given that this is the first application of this battery of instrumental learning procedures to a mouse model of ASD or GTS, it is an important initial step in determining the contribution of known risk-genes to goal-directed versus habitual behaviours, which should be more broadly applied to other rodent models of ASD and GTS in the future.