Dexmedetomidine reduces lipopolysaccharide induced neuroinflammation, sickness behavior, and anhedonia

Abstract

Background: Peripheral innate immune response may induce sickness behavior through activating microglia, excessive cytokines production, and neuroinflammation. Dexmedetomidine (Dex) has anti-inflammatory effect. We investigated the effects of Dex on lipopolysaccharide (LPS)-induced neuroinflammation and sickness behavior in mice.

Materials and methods: BALB/c mice were intraperitoneally (i.p.) injected with Dex (50 ug/kg) or vehicle. One hour later, the mice were injected (i.p.) with Escherichia coli LPS (0.33 mg/kg) or saline (n = 6 in each group). We analyzed the food and water intake, body weight loss, and sucrose preference of the mice for 24h. We also determined microglia activation and cytokines expression in the brains of the mice. In vitro, we determine cytokines expression in LPS-treated BV-2 microglial cells with or without Dex treatment.

Results: In the Dex-pretreated mice, LPS-induced sickness behavior (anorexia, weight loss, and social withdrawal) were attenuated and microglial activation was lower than vehicle control. The mRNA expression of TNF-α, MCP-1, indoleamine 2, 3 dioxygenase (IDO), caspase-3, and iNOS were increased in the brain of LPS-challenged mice, which were reduced by Dex but not vehicle.

Conclusion: Dexmedetomidine diminished LPS-induced neuroinflammation in the mouse brain and modulated the cytokine-associated changes in sickness behavior.

Fig 1. Dexmedetomidine facilitates recovery from LPS-induced sickness behavior and inhibite LPS-associated anhedonia.

Mice were challenged with saline (control) or LPS or LPS combined with Dex or Dex+Yoh. (A) Social exploratory behavior was measured using line crossed percentage method before and 2, 4, 8, and 24 h after LPS injection. Data are mean ± SEM. All group n = 6. ** P < 0.005, compared with control group; # P < 0.05 compared with LPS group. (B) Line crossed percentage were measured in different groups of mice at 8 and 24 h after LPS injection. (C) Food intake and water intake were measured in 24 h after LPS injection. (D) The sucrose preference was determined at 31, 37, and 43 h after LPS injection. Data are mean ± SEM, n = 6. * P < 0.05; ** P < 0.005.

Fig 2. Dexmedetomidine decreased the microglia Iba-1 in the brain of LPS-challenged mice.

Mice were challenged with saline (control) or LPS or LPS combined with Dex or Dex+Yoh for 24 h. Immnuohistochemistry staining showed microglia Iba-1 expression in the (A) cortex and (B) hippocampus of the mice. Dex: dexmedetomidine; Yoh: yohimbine.

Fig 3. Dexmedetomidine decreased the microglia activation in BV-2 cells.

BV-2 cells were treated with PBS (control) or LPS or LPS+Dex for 8 h. Iba-1 expression in the cells was determined using western blot. The right panel shows the quantification of Iba-1 levels. Dex(1): dexmedetomidine 1 uM; Dex(10): dexmedetomidine 10 uM. Data are mean ± SEM, n = 3. * P < 0.05; ** P < 0.005.

Fig 4. Dexmedetomidine attenuates LPS-induced mRNA expressions of inflammatory cytokines, Caspase 3, iNOs and increased Bcl-2 expression in mice brain.

Mice were challenged with saline (control) or LPS or LPS combined with Dex or Dex+Yoh for 24 h. TNF-α, MCP-1, IDO1, iNOS, Bcl-2, and caspase-3 mRNA expression in (A) cortex and (B) hippocampus were determined using RT-PCR (left panel) and quantitative real-time PCR (right panel). Data are mean ± SEM, n = 6. * P < 0.05; ** P < 0.005.

Fig 5. Dexmedetomidine suppresses LPS-induced mRNA expressions of inflammation cytokines, Caspase 3, iNOS and increased Bcl-2 expression in BV-2 cells.

BV2 cells were challenged with PBS (control) or LPS or LPS combined with Dex or Dex+Yoh for 8 h. TNF-α, MCP-1, IDO1, Bcl-2, iNOS and caspase-3 mRNA expression were determined using RT-PCR (left panel) and quantitative real-time PCR (right panel). Data are mean ± SEM. All groups n = 3. * P < 0.05; ** P < 0.005.

Fig 6. Dexmedetomidine reduced apoptotic associated signals in the LPS-challenged mice brain and BV-2 cells.

Mice were challenged with saline (control) or LPS or LPS combined with Dex or Dex+Yoh for 24 h. Immnuohistochemistry staining showed cleaved caspase-3 expression (arrows) in the (A) cortex and (B) hippocampus of the mice. (C) BV-2 cells were treated with PBS (control) or LPS or LPS+Dex for 8 h. Expression of iNOS, Bcl-xL, and cleaved caspase-3 in the cells were analyzed using western blot. Dex(1): dexmedetomidine 1 uM; Dex(10): dexmedetomidine 10 uM. Data are mean ± SEM. All groups n = 3. * P < 0.05; ** P < 0.005.