Upregulated 5-HT receptor-mediated currents in the prefrontal cortex layer 5 neurons in the 15q11-13 duplication mouse model of autism.

Serotonin (5-HT) is a well-known modulator of behavioral, physiological, and emotional functions of the forebrain region. We recently discovered alterations of serotonergic synaptic modulations in both, the prefrontal cortex (PFC) and the somatosensory cortex, in the 15q dup mouse model of autism spectrum disorder (ASD). To further understand the roles of the 5-HT system implicated in developmental disorders such as ASD, comparison with model animals exhibiting different phenotypes may be useful. In this study, we investigated the relationship between sociability and the magnitude of 5-HT receptor (5-HTR) activation-induced outward currents from layer 5 pyramidal neurons in the PFC, because a mouse model of Williams-Beuren syndrome (WBS; another developmental disorder exhibiting low innate anxiety and high sociability) reportedly showed larger 5-HT-induced currents. To investigate whether the 5-HTR activation-induced outward currents are involved in the endophenotype determination of social behavior, we examined 15q dup mice with a phenotype opposite to WBS. We found 5-HT elicited significantly larger outward currents in 15q dup mice than in WT controls, regardless of sociability. In contrast, baclofen-induced GABA receptor-mediated outward currents were not significantly different between genotypes, although GABA receptor was coupled to G as well as 5-HT. Further, we found the larger 5-HTR-mediated currents in 15q dup mice did not affect the magnitude of inhibitory action of NMDA receptor functions. Taken together, our results provide a potential physiological hallmark for developmental disorders that may involve the imbalance of the neuronal circuity in the PFC.