Neuronal ablation of p-Akt at Ser473 leads to altered 5-HT_1A/2A receptor function

The serotonergic system regulates a wide range of behavior, including mood and impulsivity, and its dysregulation has been associated with mood disorders, autism spectrum disorder, and addiction. Diabetes is a risk factor for these conditions. Insulin resistance in the brain is specifically associated with susceptibility to psychostimulant abuse. Here, we examined whether phosphorylation of Akt, a key regulator of the insulin signaling pathway, controls serotonin (5-HT) signaling. To explore how impairment in Akt function regulates 5-HT homeostasis, we used a brain-specific rictor knockout (KO) mouse model of impaired neuronal phosphorylation of Akt at Ser473. Cortical 5-HT _1A and 5-HT_2A receptor binding was significantly elevated in rictor KO mice. Concomitant with this elevated receptor expression, the 5-HT_1A receptor agonist 8-Hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) led to an increased hypothermic response in rictor KO mice. The increased cortical 5-HT_1A receptor density was associated with higher 5-HT_1A receptor levels on the cortical cell surface. In contrast, rictor KO mice displayed significantly reduced head-twitch response (HTR) to the 5-HT_2A/C agonist 2,5-dimethoxy-4-iodoamphetamine (DOI), with evidence of impaired 5-HT_2A/C receptor signaling. In vitro, pharmacological inhibition of Akt significantly increased 5-HT_1A receptor expression and attenuated DOI-induced 5-HT_2A receptor signaling, thereby lending credence to the observed in vivo cross-talk between neuronal Akt signaling and 5-HT receptor regulation. These data reveal that defective central Akt function alters 5-HT signaling as well as 5-HT-associated behaviors, demonstrating a novel role for Akt in maintaining neuronal 5-HT receptor function.