Abstract
Autistic spectrum disorders (ASDs) are classified as pervasive developmental disorders characterized by abnormalities in various cognitive and behavioral functions. Although exact underlying causes are still unknown, autism is thought to be caused by a complex combination of genetic and/or environmental factors. Interestingly, nearly 30% of autistic patients show elevated blood levels of serotonin (5-HT) and, therefore, certain genetic and environmental factors that are known to elevate 5-HT levels may play a role in the development of autism. It has previously been shown that serotonergic manipulation during early brain development promotes brain abnormalities in areas associated with social and anxiety-related behaviors. However, due to the lack of an appropriate animal model, the effect of this serotonergic manipulation on pro-social and anxiety-related behaviors has yet to be investigated. In the present study, we used the prairie vole (Microtus ochrogaster) as an animal model system. The prairie vole is a socially monogamous rodent that forms long-term pair bonds after mating and demonstrates an array of affiliative behaviors towards conspecifics. In these experiments, it was found that perinatal treatment with 5-methoxytryptamine, a non-selective serotonin agonist, impairs social affiliation and may increase anxiety-related behavior. It was also found that these behavioral changes correlate with a decrease in the number of 5-HT neurons in the dorsal raphe nucleus as well as a decrease in 5-HT fiber optic densities within four distinct amygdalar nuclei. Collectively, these data demonstrate the effects of neonatal exposure to 5-HT on pro-social and anxiety-like behaviors and the possible involvement of 5-HT in the regulation of these behaviors. Ultimately, the data obtained from these experiments may help to establish the prairie vole as an animal model of autism and also help to facilitate our understanding of ASDs and the neurobiological abnormalities that underlie such a complex neuropsychiatric disorder.
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