Table 3.

Studies of kynurenine pathway metabolites in mood disorders.

	Location	Main finding
Major Depressive Disorder	Peripheral system	Tryptophan↓, Kynurenine↓, Kynurenic acid↓ (53–55), Kynurenic acid/Kynurenine↓ (56), Kynurenine/Tryptophan↑ (57, 58)
	Central system	Ventral prefrontal cortex kynurenic acid↓ (67) Anterior cingulate cortex, premedial cingulate cortex kynurenic acid↑ (68)
Bipolar Disorder	Peripheral system	Tryptophan↓, Kynurenine↓, Kynurenic acid↓ (71, 75), Kynurenine/Tryptophan↓ (73) 3-hydroxykynurenine↑ (71), Kynurenic acid/Kynurenine↑ (73)

↑ means the level of the metabolite was higher than healthy controls. ↓ means that the level of the metabolite was lower than healthy controls.