Lipopolysaccharide-induced depressive-like behavior is mediated by indoleamine 2,3-dioxygenase activation in mice

Mol Psychiatry. 2009 May;14(5):511-22. doi: 10.1038/ Epub 2008 Jan 15.


Although elevated activity of the tryptophan-degrading enzyme indoleamine 2,3-dioxygenase (IDO) has been proposed to mediate comorbid depression in inflammatory disorders, its causative role has never been tested. We report that peripheral administration of lipopolysaccharide (LPS) activates IDO and culminates in a distinct depressive-like behavioral syndrome, measured by increased duration of immobility in both the forced-swim and tail suspension tests. Blockade of IDO activation either indirectly with the anti-inflammatory tetracycline derivative minocycline, that attenuates LPS-induced expression of proinflammatory cytokines, or directly with the IDO antagonist 1-methyltryptophan (1-MT), prevents development of depressive-like behavior. Both minocycline and 1-MT normalize the kynurenine/tryptophan ratio in the plasma and brain of LPS-treated mice without changing the LPS-induced increase in turnover of brain serotonin. Administration of L-kynurenine, a metabolite of tryptophan that is generated by IDO, to naive mice dose dependently induces depressive-like behavior. These results implicate IDO as a critical molecular mediator of inflammation-induced depressive-like behavior, probably through the catabolism of tryptophan along the kynurenine pathway.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Behavior, Animal / drug effects
  • Chromatography, High Pressure Liquid
  • Cytokinins / metabolism
  • Depression / blood
  • Depression / chemically induced*
  • Disease Models, Animal
  • Dose-Response Relationship, Drug
  • Enzyme Activation / drug effects
  • Enzyme Inhibitors / pharmacology
  • Enzyme Inhibitors / therapeutic use
  • Gene Expression Regulation / drug effects*
  • Hindlimb Suspension / methods
  • Indoleamine-Pyrrole 2,3,-Dioxygenase / antagonists & inhibitors
  • Indoleamine-Pyrrole 2,3,-Dioxygenase / genetics
  • Indoleamine-Pyrrole 2,3,-Dioxygenase / metabolism*
  • Kynurenine / adverse effects
  • Kynurenine / blood
  • Lipopolysaccharides / pharmacology*
  • Male
  • Mice
  • Mice, Inbred ICR
  • Minocycline / pharmacology
  • Minocycline / therapeutic use
  • Motor Activity / drug effects
  • Swimming
  • Time Factors
  • Tryptophan / analogs & derivatives
  • Tryptophan / blood
  • Tryptophan / pharmacology
  • Tryptophan / therapeutic use


  • Cytokinins
  • Enzyme Inhibitors
  • Indoleamine-Pyrrole 2,3,-Dioxygenase
  • Lipopolysaccharides
  • Kynurenine
  • Tryptophan
  • Minocycline
  • 1-methyltryptophan