Indoleamine 2,3-dioxygenase mediates anhedonia and anxiety-like behaviors caused by peripheral lipopolysaccharide immune challenge

Abstract

Upregulation of indoleamine 2,3-dioxygenase (IDO) by proinflammatory cytokines has been implicated as a biological mediator of inflammation-related mood disorders. Clinical reports on this neuro-immune interaction remain correlative, while mechanism-centered preclinical experiments have focused on a relatively narrow, and somewhat controversial, survey of depression-like behaviors that include the forced swim and tail suspension tests. Here, we sought to determine whether peripheral immune challenge with Escherichia coli, lipopolysaccharides (LPS) precipitates the development of translationally relevant depression-like behaviors and to investigate the role of IDO in mediating these LPS-induced behaviors. Intraperitoneal injection of C57BL/6J mice with LPS resulted in a robust, but transient, reduction in exploratory locomotor activity (eLMA) that returned to near baseline levels by 24h. Sucrose preference, a preclinical correlate of anhedonia, was diminished by more than 20% in LPS-treated compared to saline-treated control mice, and LPS induced a significant increase in anxiety-like behavior at 24h that was independent eLMA. Pretreatment of mice with an IDO inhibitor, 1-methyltryptophan (1MT), ablated the anxiogenic effects of LPS, while having no impact on sickness associated changes in body weight or eLMA. Additionally, 1MT pretreatment attenuated the LPS-induced reduction in sucrose preference, which was also confirmed in IDO-1 null mice. Interestingly, acute systemic administration of l-kynurenine, the enzymatic product of IDO, precipitated an anhedonic and anxiogenic effect in naïve mice without effect on eLMA. In a preclinical model, these data implicate IDO as a pivotal mediator of LPS-induced depression- and anxiety-like behavior.

Figure 1

Peripheral LPS challenge precipitated anxiety-like behavior in the open field test. Mice were observed in the testing chambers during a 5 minute session at the indicated times. (A) General dimensions and scoring zones for the open field test. (B) Intraperitoneal LPS injection causes a transient reduction in exploratory locomotor activity, and LPS-challenged mice exhibit (C) a reduced time spent in the central area of the arena and an (D) increase in the amount of time spent in close proximity to the arena walls (thigmotaxis). Correlation analysis indicates that treatment-induced changes in (E) central area time or (F) thigmotaxis are not merely a consequence of fluctuations in 24h locomotor activity. Data represent group means ± SEM, n=19–20 mice per group in at least two independent experimental replications. *p<0.05 versus control.

Figure 1

Peripheral LPS challenge precipitated anxiety-like behavior in the open field test. Mice were observed in the testing chambers during a 5 minute session at the indicated times. (A) General dimensions and scoring zones for the open field test. (B) Intraperitoneal LPS injection causes a transient reduction in exploratory locomotor activity, and LPS-challenged mice exhibit (C) a reduced time spent in the central area of the arena and an (D) increase in the amount of time spent in close proximity to the arena walls (thigmotaxis). Correlation analysis indicates that treatment-induced changes in (E) central area time or (F) thigmotaxis are not merely a consequence of fluctuations in 24h locomotor activity. Data represent group means ± SEM, n=19–20 mice per group in at least two independent experimental replications. *p<0.05 versus control.

Figure 1

Peripheral LPS challenge precipitated anxiety-like behavior in the open field test. Mice were observed in the testing chambers during a 5 minute session at the indicated times. (A) General dimensions and scoring zones for the open field test. (B) Intraperitoneal LPS injection causes a transient reduction in exploratory locomotor activity, and LPS-challenged mice exhibit (C) a reduced time spent in the central area of the arena and an (D) increase in the amount of time spent in close proximity to the arena walls (thigmotaxis). Correlation analysis indicates that treatment-induced changes in (E) central area time or (F) thigmotaxis are not merely a consequence of fluctuations in 24h locomotor activity. Data represent group means ± SEM, n=19–20 mice per group in at least two independent experimental replications. *p<0.05 versus control.

Figure 1

Peripheral LPS challenge precipitated anxiety-like behavior in the open field test. Mice were observed in the testing chambers during a 5 minute session at the indicated times. (A) General dimensions and scoring zones for the open field test. (B) Intraperitoneal LPS injection causes a transient reduction in exploratory locomotor activity, and LPS-challenged mice exhibit (C) a reduced time spent in the central area of the arena and an (D) increase in the amount of time spent in close proximity to the arena walls (thigmotaxis). Correlation analysis indicates that treatment-induced changes in (E) central area time or (F) thigmotaxis are not merely a consequence of fluctuations in 24h locomotor activity. Data represent group means ± SEM, n=19–20 mice per group in at least two independent experimental replications. *p<0.05 versus control.

Figure 1

Peripheral LPS challenge precipitated anxiety-like behavior in the open field test. Mice were observed in the testing chambers during a 5 minute session at the indicated times. (A) General dimensions and scoring zones for the open field test. (B) Intraperitoneal LPS injection causes a transient reduction in exploratory locomotor activity, and LPS-challenged mice exhibit (C) a reduced time spent in the central area of the arena and an (D) increase in the amount of time spent in close proximity to the arena walls (thigmotaxis). Correlation analysis indicates that treatment-induced changes in (E) central area time or (F) thigmotaxis are not merely a consequence of fluctuations in 24h locomotor activity. Data represent group means ± SEM, n=19–20 mice per group in at least two independent experimental replications. *p<0.05 versus control.

Figure 2

Anxiety-like behavior in the Light-Dark Box is increased by peripheral LPS challenge. (A) General dimensions of the light-dark box test chamber. (B) The duration of time spent exploring the illuminated side of the light-dark box is reduced by LPS. Data represent group means ± SEM, n=17–18 mice per group in at least two independent experimental replications. *p<0.05 versus control.

Figure 2

Anxiety-like behavior in the Light-Dark Box is increased by peripheral LPS challenge. (A) General dimensions of the light-dark box test chamber. (B) The duration of time spent exploring the illuminated side of the light-dark box is reduced by LPS. Data represent group means ± SEM, n=17–18 mice per group in at least two independent experimental replications. *p<0.05 versus control.

Figure 3

Indoleamine 2,3-dioxygenase mediates LPS-induced anxiety-like behavior in the open field test. After pretreatment with either vehicle or 1-methyltryptophan, the effects of LPS on (A) body weight and (B) locomotor activity over a 24h interval. (C) The duration of time spent within the central area or (D) in close proximity to the chamber walls was measured in the open field test at 24h post-LPS challenge. (F) The duration of time spent exploring the illuminated side of a light-dark box was also measured in different mice 24h post-LPS. Data represent group means ± SEM, n=7–12 mice per group in at least two independent experimental replications. *p<0.05 versus same pretreatment saline control, #p<0.05 versus 1MT/LPS.

Figure 3

Indoleamine 2,3-dioxygenase mediates LPS-induced anxiety-like behavior in the open field test. After pretreatment with either vehicle or 1-methyltryptophan, the effects of LPS on (A) body weight and (B) locomotor activity over a 24h interval. (C) The duration of time spent within the central area or (D) in close proximity to the chamber walls was measured in the open field test at 24h post-LPS challenge. (F) The duration of time spent exploring the illuminated side of a light-dark box was also measured in different mice 24h post-LPS. Data represent group means ± SEM, n=7–12 mice per group in at least two independent experimental replications. *p<0.05 versus same pretreatment saline control, #p<0.05 versus 1MT/LPS.

Figure 3

Indoleamine 2,3-dioxygenase mediates LPS-induced anxiety-like behavior in the open field test. After pretreatment with either vehicle or 1-methyltryptophan, the effects of LPS on (A) body weight and (B) locomotor activity over a 24h interval. (C) The duration of time spent within the central area or (D) in close proximity to the chamber walls was measured in the open field test at 24h post-LPS challenge. (F) The duration of time spent exploring the illuminated side of a light-dark box was also measured in different mice 24h post-LPS. Data represent group means ± SEM, n=7–12 mice per group in at least two independent experimental replications. *p<0.05 versus same pretreatment saline control, #p<0.05 versus 1MT/LPS.

Figure 3

Indoleamine 2,3-dioxygenase mediates LPS-induced anxiety-like behavior in the open field test. After pretreatment with either vehicle or 1-methyltryptophan, the effects of LPS on (A) body weight and (B) locomotor activity over a 24h interval. (C) The duration of time spent within the central area or (D) in close proximity to the chamber walls was measured in the open field test at 24h post-LPS challenge. (F) The duration of time spent exploring the illuminated side of a light-dark box was also measured in different mice 24h post-LPS. Data represent group means ± SEM, n=7–12 mice per group in at least two independent experimental replications. *p<0.05 versus same pretreatment saline control, #p<0.05 versus 1MT/LPS.

Figure 3

Indoleamine 2,3-dioxygenase mediates LPS-induced anxiety-like behavior in the open field test. After pretreatment with either vehicle or 1-methyltryptophan, the effects of LPS on (A) body weight and (B) locomotor activity over a 24h interval. (C) The duration of time spent within the central area or (D) in close proximity to the chamber walls was measured in the open field test at 24h post-LPS challenge. (F) The duration of time spent exploring the illuminated side of a light-dark box was also measured in different mice 24h post-LPS. Data represent group means ± SEM, n=7–12 mice per group in at least two independent experimental replications. *p<0.05 versus same pretreatment saline control, #p<0.05 versus 1MT/LPS.

Figure 4

Peripheral administration of L-kynurenine dose-dependently precipitates anxiety-like behavior in the open field test. Mice were injected subcutaneously with the indicated doses of L-kynurenine. Two hours later, (A) exploratory locomotor activity, (B) time spent in the central area and (C) time spent in close proximity to the chamber wall was measured in the open field test. Data represent group means ± SEM, n=6–7 mice per group in at least two independent experimental replications. *p<0.05 and **p<0.01 versus all other treatment groups.

Figure 4

Peripheral administration of L-kynurenine dose-dependently precipitates anxiety-like behavior in the open field test. Mice were injected subcutaneously with the indicated doses of L-kynurenine. Two hours later, (A) exploratory locomotor activity, (B) time spent in the central area and (C) time spent in close proximity to the chamber wall was measured in the open field test. Data represent group means ± SEM, n=6–7 mice per group in at least two independent experimental replications. *p<0.05 and **p<0.01 versus all other treatment groups.

Figure 4

Peripheral administration of L-kynurenine dose-dependently precipitates anxiety-like behavior in the open field test. Mice were injected subcutaneously with the indicated doses of L-kynurenine. Two hours later, (A) exploratory locomotor activity, (B) time spent in the central area and (C) time spent in close proximity to the chamber wall was measured in the open field test. Data represent group means ± SEM, n=6–7 mice per group in at least two independent experimental replications. *p<0.05 and **p<0.01 versus all other treatment groups.

Figure 5

Indoleamine 2,3-dioxygenase mediates LPS-induced anhedonia. The effect of LPS challenge on sucrose preference was measured over the 24h post-LPS interval in (A) mice that had been pretreated with either vehicle or 1-methyltryptophan (n=6 mice per group) or (B) in WT or IDO null mice (n=8–11 mice per group). (C) Sucrose preference was determined in WT mice that were subcutaneously administered the indicated doses of L-kynurenine (n=11 mice per group). Data represent group means ± SEM, in at least two independent experimental replications. *p<0.05 versus the indicated groups in A and B, *p<0.05 versus control group in C.

Figure 5

Indoleamine 2,3-dioxygenase mediates LPS-induced anhedonia. The effect of LPS challenge on sucrose preference was measured over the 24h post-LPS interval in (A) mice that had been pretreated with either vehicle or 1-methyltryptophan (n=6 mice per group) or (B) in WT or IDO null mice (n=8–11 mice per group). (C) Sucrose preference was determined in WT mice that were subcutaneously administered the indicated doses of L-kynurenine (n=11 mice per group). Data represent group means ± SEM, in at least two independent experimental replications. *p<0.05 versus the indicated groups in A and B, *p<0.05 versus control group in C.