The serotonin6 receptor (5-HT6R) is a promising target for treating cognitive deficits of schizophrenia often linked to alterations of neuronal development. This receptor controls neurodevelopmental processes, but the signaling mechanisms involved remain poorly understood. Using a proteomic strategy, we show that 5-HT6Rs constitutively interact with cyclin-dependent kinase 5 (Cdk5). Expression of 5-HT6Rs in NG108-15 cells induced neurite growth and expression of voltage-gated Ca(2+) channels, two hallmarks of neuronal differentiation. 5-HT6R-elicited neurite growth was agonist independent and prevented by the 5-HT6R antagonist SB258585, which behaved as an inverse agonist. Moreover, it required receptor phosphorylation at Ser350 by Cdk5 and Cdc42 activity. Supporting a role of native 5-HT6Rs in neuronal differentiation, neurite growth of primary neurons was reduced by SB258585, by silencing 5-HT6R expression or by mutating Ser350 into alanine. These results reveal a functional interplay between Cdk5 and a G protein-coupled receptor to control neuronal differentiation.

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Autism spectrum disorder (ASD) is a neurodevelopmental disorder that results from a complex interaction between genes and environment. Breastfeeding (BF) is thought to promote healthy cognitive development, and a body of research has suggested that it may also protect against ASD. Our objectives were to identify the relationship between the initiation and duration of BF and the severity of clinical presentation in ASD. Data were collected from 243 children with a confirmed diagnosis of ASD followed in the ELENA cohort. Clinical severity was measured according to multiple dimensions using standardised tools. The frequency of the initiation of BF was comparable to that of the general population and the rate of children still being breastfed at six months of age was higher. Our results did not indicate a contribution of initiation or duration of BF to the prevention of clinical severity of ASD. We discuss our results in the light of possible methodological limitations of previous reports of an association between BF and ASD.Clinical Trial Registration: NCT02625116.