Autism spectrum disorder (ASD) is a multifactorial disorder with characteristic synaptic and gene expression changes. Early intervention during childhood is thought to benefit prognosis. Here, we examined the changes in cortical synaptogenesis, synaptic function, and gene expression from birth to the juvenile stage in a marmoset model of ASD induced by valproic acid (VPA) treatment. Early postnatally, synaptogenesis was reduced in this model, while juvenile-age VPA-treated marmosets showed increased synaptogenesis, similar to observations in human tissue. During infancy, synaptic plasticity transiently increased and was associated with altered vocalization. Synaptogenesis-related genes were downregulated early postnatally. At three months of age, the differentially expressed genes were associated with circuit remodeling, similar to the expression changes observed in humans. In summary, we provide a functional and molecular characterization of a non-human primate model of ASD, highlighting its similarity to features observed in human ASD.
Humans and various nonhuman primates respond negatively to inequity not in their favor (i.e., inequity aversion), when inequity between two individuals is introduced. Common marmosets, a highly prosocial species, further discriminated between human actors who reciprocated in social exchanges, and those who did not. Conversely, marmoset models of autism, induced via prenatal exposure to valproic acid (VPA marmosets), did not discriminate. Interestingly, previous studies of inequity aversion in marmosets have produced negative results, or were limited to males. Recent studies suggest that inequity aversion is highly influenced by the tasks employed. Here we show inequity aversion in both male and female marmosets using a novel task which required a relatively long duration of response. Marmosets were required to hold a spoon for 2 s to receive a reward. Marmosets successfully performed the task when they observed an unfamiliar conspecific partner obtaining the same reward (equity test). However, when they witnessed the partner receiving a more attractive reward for equal effort (inequity test), unexposed marmosets, which were not exposed to either valproic acid or saline during the fetal period refused to respond. This inequity aversion was not observed in unexposed marmosets when the partner was absent. In contrast, marmosets with fetal exposure to valproic acid (VPA marmosets) successfully executed the task irrespective of their partners' reward conditions. As prenatal exposure to valproic acid is a well-known procedure to induce autism spectrum disorder (ASD)-like behaviors in rodents, we propose that VPA marmosets failed to show inequity aversion due to weak social motivation or interest towards others.
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