Perseverative stereotypic behavior of Epac2 KO mice in a reward-based decision making task

Dynamic Foraging Behavior Performance Is Not Affected by Scn2a Haploinsufficiency

Dysfunction in the gene SCN2A, which encodes the voltage-gated sodium channel Nav1.2, is strongly associated with neurodevelopmental disorders including autism spectrum disorder and intellectual disability (ASD/ID). This dysfunction typically manifests in these disorders as a haploinsufficiency, where loss of one copy of a gene cannot be compensated for by the other allele. Scn2a haploinsufficiency affects a range of cells and circuits across the brain, including associative neocortical circuits that are important for cognitive flexibility and decision-making behaviors. Here, we tested whether Scn2a haploinsufficiency has any effect on a dynamic foraging task that engages such circuits. Scn2a +/- mice and wild-type (WT) littermates were trained on a choice behavior where the probability of reward between two options varied dynamically across trials and where the location of the high reward underwent uncued reversals. Despite impairments in Scn2a-related neuronal excitability, we found that both male and female Scn2a +/- mice performed these tasks as well as wild-type littermates, with no behavioral difference across genotypes in learning or performance parameters. Varying the number of trials between reversals or probabilities of receiving reward did not result in an observable behavioral difference, either. These data suggest that, despite heterozygous loss of Scn2a, mice can perform relatively complex foraging tasks that make use of higher-order neuronal circuits.

The Dopamine Hypothesis of Autism Spectrum Disorder Revisited: Current Status and Future Prospects

Autism spectrum disorder (ASD) comprises a group of neurodevelopmental disorders characterized by social deficits and stereotyped behaviors. Despite intensive research, its etiopathogenesis remains largely unclear. Although studies consistently reported dopaminergic anomalies, a coherent dopaminergic model of ASD was lacking until recently. In 2017, we provided a theoretical framework for a "dopamine hypothesis of ASD" which proposed that autistic behavior arises from a dysfunctional midbrain dopaminergic system. Namely, we hypothesized that malfunction of 2 critical circuits originating in the midbrain, that is, the mesocorticolimbic and nigrostriatal pathways, generates the core behavioral features of ASD. Moreover, we provided key predictions of our model along with testing means. Since then, a notable number of studies referenced our work and numerous others provided support for our model. To account for these developments, we review all these recent data and discuss their implications. Furthermore, in the light of these new insights, we further refine and reconceptualize our model, debating on the possibility that various etiologies of ASD converge upon a dysfunctional midbrain dopaminergic system. In addition, we discuss future prospects, providing new means of testing our hypothesis, as well as its limitations. Along these lines, we aimed to provide a model which, if confirmed, could provide a better understanding of the etiopathogenesis of ASD along with new therapeutic strategies.

Epac: new emerging cAMP-binding protein

The well-known second messenger cyclic adenosine monophosphate (cAMP) regulates the morphology and physiology of neurons and thus higher cognitive brain functions. The discovery of exchange protein activated by cAMP (Epac) as a guanine nucleotide exchange factor for Rap GTPases has shed light on protein kinase A (PKA)-independent functions of cAMP signaling in neural tissues. Studies of cAMP-Epac-mediated signaling in neurons under normal and disease conditions also revealed its diverse contributions to neurodevelopment, synaptic remodeling, and neurotransmitter release, as well as learning, memory, and emotion. In this mini-review, the various roles of Epac isoforms, including Epac1 and Epac2, highly expressed in neural tissues are summarized, and controversies or issues are highlighted that need to be resolved to uncover the critical functions of Epac in neural tissues and the potential for a new therapeutic target of mental disorders.