Congenital brain serotonin deficiency leads to reduced ethanol sensitivity and increased ethanol consumption in mice

Serotonergic dysfunction has been hypothesized to play an important role in the pathophysiology of alcoholism. However, whether congenital serotonin (5-HT) deficiency leads to increased alcohol consumption or affects ethanol-related behaviors has not been established. Here, we use a transgenic mouse line that expresses a hypofunctional variant of the 5-HT synthesis enzyme, tryptophan hydroxylase 2, to examine the impact of 5-HT deficiency on responses to alcohol. We demonstrate that these 5-HT-deficient transgenic animals (Tph2KI mice) recover their righting reflex more rapidly than wild-type controls following a high dose of ethanol and exhibit blunted locomotor retardation in response to repeated ethanol administration. In addition, compared to WT controls, 5-HT-deficient animals consume significantly more ethanol and exhibit increased preference for ethanol in two-bottle choice tests. Our data also suggest that 5-HT plays a critical role in mediating the effects of ethanol on Akt/GSK3β signaling in the nucleus accumbens. Overall, our results corroborate previous theories regarding the importance of brain 5-HT levels in mediating responsiveness to alcohol and demonstrate, for the first time, that congenital 5-HT deficiency leads to increased ethanol consumption and decreased sensitivity to the sedative-like effects of ethanol, perhaps in part through modulating Akt/GSK3β signaling.