Acute Psychological Stress Modulates the Expression of Enzymes Involved in the Kynurenine Pathway throughout Corticolimbic Circuits in Adult Male Rats

Figure 1

Schematic representation of tryptophan metabolism and its influence by stress. This figure shows the multiple ways that tryptophan can be metabolized. The classic, well-known pathway is its conversion to serotonin (purple). The primary pathway of tryptophan metabolism, however, is the kynurenine pathway (black), by which tryptophan is converted to kynurenine via tryptophan 2,3-dioxygenase (TDO) or indoleamine 2,3-dioxygenase 1 (IDO1). From there, it can be converted into the neuroprotective kynurenic acid (KNYA) via kynurenine aminotransferase (KAT1) or to quinolinic acid (QUIN) via a multistep process involving the enzymes kynurenine 3-monooxygenase (KMO), kynureninase (KYNU), and 3-hydroxyanthranilate 3,4-dioxygenase (3-HOA). An analysis of mRNA expression levels of tryptophan 2,3-dioxygenase (Tdo), indoleamine 2,3-dioxygenase 1 (Ido1), kynurenine aminotransferase (Kat1), kynurenine 3-monooxygenase (Kmo), kynureninase (Kynu), and 3-hydroxyanthranilate 3,4-dioxygenase (Haao) revealed increases in Ido1, Kmo, and Kynu mRNA expression in the amygdala (blue), decreases in Tdo mRNA expression in the hippocampus (green), an upregulation of Tdo, and downregulation of Haao mRNA expression in the hypothalamus (red) and a downregulation of Kynu mRNA expression in the medial prefrontal cortex (pink) (solid lines indicate significant changes, while dashed lines indicate trending changes). This figure summates the regional and temporal effects of acute stress on the mRNA expression of kynurenine pathway enzymes.