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Central administration of lipopolysaccharide induces depressive-like behavior in vivo and activates brain indoleamine 2,3 dioxygenase in murine organotypic hippocampal slice cultures.

Fu X, Zunich SM, O'Connor JC, Kavelaars A, Dantzer R, Kelley KW - J Neuroinflammation (2010)

Bottom Line: In accordance with the in vivo data, addition of LPS (10 ng/ml) to the medium of OHSCs induced steady-state expression of mRNA transcripts for IDO that peaked at 6 h and translated into increased IDO enzymatic activity within 8 h post-LPS.This activation of IDO by direct application of LPS was preceded by synthesis and secretion of TNFalpha and IL-6 protein and activation of iNOS while IFN gamma expression was undetectable.Targeting IDO itself may provide a novel therapy for inflammation-associated depression.

View Article: PubMed Central - HTML - PubMed

Affiliation: Integrative Immunology and Behavior Program, Department of Animal Sciences, College of ACES, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.

ABSTRACT

Background: Transient stimulation of the innate immune system by an intraperitoneal injection of lipopolysaccharide (LPS) activates peripheral and central expression of the tryptophan degrading enzyme indoleamine 2,3 dioxygenase (IDO) which mediates depressive-like behavior. It is unknown whether direct activation of the brain with LPS is sufficient to activate IDO and induce depressive-like behavior.

Methods: Sickness and depressive-like behavior in C57BL/6J mice were assessed by social exploration and the forced swim test, respectively. Expression of cytokines and IDO mRNA was measured by real-time RT-PCR and cytokine protein was measured by enzyme-linked immunosorbent assays (ELISAs). Enzymatic activity of IDO was estimated as the amount of kynurenine produced from tryptophan as determined by high pressure liquid chromatography (HPLC) with electrochemical detection.

Results: Intracerebroventricular (i.c.v.) administration of LPS (100 ng) increased steady-state transcripts of TNFalpha, IL-6 and the inducible isoform of nitric oxide synthase (iNOS) in the hippocampus in the absence of any change in IFN gamma mRNA. LPS also increased IDO expression and induced depressive-like behavior, as measured by increased duration of immobility in the forced swim test. The regulation of IDO expression was investigated using in situ organotypic hippocampal slice cultures (OHSCs) derived from brains of newborn C57BL/6J mice. In accordance with the in vivo data, addition of LPS (10 ng/ml) to the medium of OHSCs induced steady-state expression of mRNA transcripts for IDO that peaked at 6 h and translated into increased IDO enzymatic activity within 8 h post-LPS. This activation of IDO by direct application of LPS was preceded by synthesis and secretion of TNFalpha and IL-6 protein and activation of iNOS while IFN gamma expression was undetectable.

Conclusion: These data establish that activation of the innate immune system in the brain is sufficient to activate IDO and induce depressive-like behavior in the absence of detectable IFN gamma. Targeting IDO itself may provide a novel therapy for inflammation-associated depression.

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Central administration of LPS induces (A) IDO, (B) TNF╬▒, (C) IL-6 and (D) iNOS mRNA upregulation in the hippocampus. Mice were injected i.c.v. with either saline or LPS (100 ng) and the hippocampi were collected 6 h later. Steady-state expression of mRNA transcripts was measured by real-time RT-PCR. Average Ct values for LPS-treated mice were as follows: IDO = 33.0 ┬▒ 0.4; TNF╬▒ = 23.3 ┬▒ 0.4; IL-6 = 24.2 ┬▒ 0.4; iNOS = 28.0 ┬▒ 0.3. Data represent mean ┬▒ SEM (n = 4-5 mice/group). * p < 0.05, ** p < 0.01 compared to saline.
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Figure 2: Central administration of LPS induces (A) IDO, (B) TNF╬▒, (C) IL-6 and (D) iNOS mRNA upregulation in the hippocampus. Mice were injected i.c.v. with either saline or LPS (100 ng) and the hippocampi were collected 6 h later. Steady-state expression of mRNA transcripts was measured by real-time RT-PCR. Average Ct values for LPS-treated mice were as follows: IDO = 33.0 ┬▒ 0.4; TNF╬▒ = 23.3 ┬▒ 0.4; IL-6 = 24.2 ┬▒ 0.4; iNOS = 28.0 ┬▒ 0.3. Data represent mean ┬▒ SEM (n = 4-5 mice/group). * p < 0.05, ** p < 0.01 compared to saline.

Mentions: We have established that IDO and cytokine expression in the hippocampus of mice injected i.p. with LPS peaks within 6 h [29]. Therefore, the hippocampus was collected at the 6 h time point to determine the effects of LPS injected i.c.v. on the brain. Although IDO mRNA was undetectable in saline-treated mice, its expression increased significantly following central injection of LPS (p < 0.05) (Fig. 2A). LPS also increased TNF╬▒ (p < 0.01; Fig. 2B), IL-6 (p < 0.01; Fig. 2C), and iNOS (p < 0.05; Fig. 2D) mRNA expression compared to saline-injected controls. LPS did not cause a statistically significant increase in IFN╬│ mRNA expression (data not shown). These results indicate that centrally administered LPS activates brain cytokine signaling and increases brain IDO expression.


Central administration of lipopolysaccharide induces depressive-like behavior in vivo and activates brain indoleamine 2,3 dioxygenase in murine organotypic hippocampal slice cultures.

Fu X, Zunich SM, O'Connor JC, Kavelaars A, Dantzer R, Kelley KW - J Neuroinflammation (2010)

Central administration of LPS induces (A) IDO, (B) TNF╬▒, (C) IL-6 and (D) iNOS mRNA upregulation in the hippocampus. Mice were injected i.c.v. with either saline or LPS (100 ng) and the hippocampi were collected 6 h later. Steady-state expression of mRNA transcripts was measured by real-time RT-PCR. Average Ct values for LPS-treated mice were as follows: IDO = 33.0 ┬▒ 0.4; TNF╬▒ = 23.3 ┬▒ 0.4; IL-6 = 24.2 ┬▒ 0.4; iNOS = 28.0 ┬▒ 0.3. Data represent mean ┬▒ SEM (n = 4-5 mice/group). * p < 0.05, ** p < 0.01 compared to saline.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC2921406&req=5

Figure 2: Central administration of LPS induces (A) IDO, (B) TNF╬▒, (C) IL-6 and (D) iNOS mRNA upregulation in the hippocampus. Mice were injected i.c.v. with either saline or LPS (100 ng) and the hippocampi were collected 6 h later. Steady-state expression of mRNA transcripts was measured by real-time RT-PCR. Average Ct values for LPS-treated mice were as follows: IDO = 33.0 ┬▒ 0.4; TNF╬▒ = 23.3 ┬▒ 0.4; IL-6 = 24.2 ┬▒ 0.4; iNOS = 28.0 ┬▒ 0.3. Data represent mean ┬▒ SEM (n = 4-5 mice/group). * p < 0.05, ** p < 0.01 compared to saline.
Mentions: We have established that IDO and cytokine expression in the hippocampus of mice injected i.p. with LPS peaks within 6 h [29]. Therefore, the hippocampus was collected at the 6 h time point to determine the effects of LPS injected i.c.v. on the brain. Although IDO mRNA was undetectable in saline-treated mice, its expression increased significantly following central injection of LPS (p < 0.05) (Fig. 2A). LPS also increased TNF╬▒ (p < 0.01; Fig. 2B), IL-6 (p < 0.01; Fig. 2C), and iNOS (p < 0.05; Fig. 2D) mRNA expression compared to saline-injected controls. LPS did not cause a statistically significant increase in IFN╬│ mRNA expression (data not shown). These results indicate that centrally administered LPS activates brain cytokine signaling and increases brain IDO expression.

Bottom Line: In accordance with the in vivo data, addition of LPS (10 ng/ml) to the medium of OHSCs induced steady-state expression of mRNA transcripts for IDO that peaked at 6 h and translated into increased IDO enzymatic activity within 8 h post-LPS.This activation of IDO by direct application of LPS was preceded by synthesis and secretion of TNFalpha and IL-6 protein and activation of iNOS while IFN gamma expression was undetectable.Targeting IDO itself may provide a novel therapy for inflammation-associated depression.

View Article: PubMed Central - HTML - PubMed

Affiliation: Integrative Immunology and Behavior Program, Department of Animal Sciences, College of ACES, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.

ABSTRACT

Background: Transient stimulation of the innate immune system by an intraperitoneal injection of lipopolysaccharide (LPS) activates peripheral and central expression of the tryptophan degrading enzyme indoleamine 2,3 dioxygenase (IDO) which mediates depressive-like behavior. It is unknown whether direct activation of the brain with LPS is sufficient to activate IDO and induce depressive-like behavior.

Methods: Sickness and depressive-like behavior in C57BL/6J mice were assessed by social exploration and the forced swim test, respectively. Expression of cytokines and IDO mRNA was measured by real-time RT-PCR and cytokine protein was measured by enzyme-linked immunosorbent assays (ELISAs). Enzymatic activity of IDO was estimated as the amount of kynurenine produced from tryptophan as determined by high pressure liquid chromatography (HPLC) with electrochemical detection.

Results: Intracerebroventricular (i.c.v.) administration of LPS (100 ng) increased steady-state transcripts of TNFalpha, IL-6 and the inducible isoform of nitric oxide synthase (iNOS) in the hippocampus in the absence of any change in IFN gamma mRNA. LPS also increased IDO expression and induced depressive-like behavior, as measured by increased duration of immobility in the forced swim test. The regulation of IDO expression was investigated using in situ organotypic hippocampal slice cultures (OHSCs) derived from brains of newborn C57BL/6J mice. In accordance with the in vivo data, addition of LPS (10 ng/ml) to the medium of OHSCs induced steady-state expression of mRNA transcripts for IDO that peaked at 6 h and translated into increased IDO enzymatic activity within 8 h post-LPS. This activation of IDO by direct application of LPS was preceded by synthesis and secretion of TNFalpha and IL-6 protein and activation of iNOS while IFN gamma expression was undetectable.

Conclusion: These data establish that activation of the innate immune system in the brain is sufficient to activate IDO and induce depressive-like behavior in the absence of detectable IFN gamma. Targeting IDO itself may provide a novel therapy for inflammation-associated depression.

Show MeSH
Related in: MedlinePlus