No effect of C1473G polymorphism in the tryptophan hydroxylase 2 gene on the response of the brain serotonin system to chronic fluoxetine treatment in mice

Selective serotonin reuptake inhibitors (SSRIs) are antidepressants that block serotonin transporter (SERT) and increase serotonin (5-HT) level in the synaptic cleft. The interaction between SERT and the key enzyme of 5-HT synthesis in the brain, tryptophan hydroxylase 2 (TPH2), is essential to maintain the brain 5-HT level. The G allele of C1473G polymorphism in Tph2 gene decreases enzyme activity by half in mouse brain. Here we studied effect of C1473G polymorphism on the reaction of brain 5-HT system to chronic fluoxetine treatment (120 mg/l in drinking water, for 3 weeks) in adult males of the congenic B6-1473C and B6-1473G mouse lines with high and low enzyme activity, respectively. The polymorphism did not affect the levels of 5-HT, its metabolite, 5-hydroxyindoleacetic acid (5-HIAA) and Tph2 gene mRNA in the brain. Fluoxetine significantly attenuated 5-HT levels in the cortex and striatum, 5-HIAA concentrations in the cortex, hippocampus, striatum and midbrain, and Tph2 gene expression in the midbrain. However, we did not observed any effect of the genotype x treatment interaction on these neurochemical characteristics. Therefore, C1473G polymorphism does not seem to play an essential role in the reaction of the brain 5-HT system to chronic fluoxetine treatment.