Prolonged therapy with antidepressants increases hippocampal level of kynurenic acid and expression of Kat1 and Kat2 genes.

Abstract

Accumulating data suggest an important role of disturbed kynurenine pathway and altered glutamatergic transmission in the pathogenesis of depression. In here, we focused on detailed analyses of kynurenic acid (KYNA) status in vivo following single and 14-day administration of selected tricyclic antidepressant drugs (TCAs) and serotonin selective reuptake inhibitors (SSRIs) in rats. The effect of antidepressants on serum and brain KYNA levels, as well as on the activity of kynurenine aminotransferases (KATs I and II) and expression of Kat1 and Kat2 genes mRNA was studied in three brain regions. Chronic, but not acute, application of antidepressants invariably stimulated KYNA production in hippocampus (amitriptyline, imipramine, fluoxetine and citalopram) and sporadically in cortex (amitriptyline, fluoxetine), whereas no change in KYNA level was observed in striatum. Cortical and hippocampal expression of Kat1 and Kat2 genes was increased after chronic, but not single administration of all studied antidepressants. The activity of semi-purified enzymatic proteins, KAT I and II, was not paralleling changes of Kat1 and Kat2 genes. Our data indicate that prolonged administration of antidepressants targets expression of KYNA biosynthetic enzymes. Furthermore, post-translational modulation of KATs seems to play an important role in tuning of KYNA synthesis within brain structures. We suggest that consistent increase of hippocampal KYNA levels may represent hallmark of antidepressant activity. Mechanisms governing region- and drug-selective action of antidepressants require further investigations.