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Brain Behav Immun. 2015 Feb;44:106-20. doi: 10.1016/j.bbi.2014.08.011. Epub 2014 Sep 11.

Synergistic effects of NOD1 or NOD2 and TLR4 activation on mouse sickness behavior in relation to immune and brain activity markers.

Author information

1
Research Unit of Translational Neurogastroenterology, Institute of Experimental and Clinical Pharmacology, Medical University of Graz, Universitätsplatz 4, 8010 Graz, Austria. Electronic address: aitak.farzi@medunigraz.at.
2
Research Unit of Translational Neurogastroenterology, Institute of Experimental and Clinical Pharmacology, Medical University of Graz, Universitätsplatz 4, 8010 Graz, Austria.
3
Clinical Institute of Medical and Chemical Laboratory Diagnostics, Medical University of Graz, Auenbruggerplatz 15, 8036 Graz, Austria.
4
Core Facility Molecular Biology, Center for Medical Research, Medical University of Graz, Stiftingtalstrasse 24/1, 8010 Graz, Austria.
5
Core Facility Flow Cytometry, Center for Medical Research, Medical University of Graz, Stiftingtalstrasse 24/1, 8010 Graz, Austria.

Abstract

Toll-like receptors (TLRs) and nuclear-binding domain (NOD)-like receptors (NLRs) are sensors of bacterial cell wall components to trigger an immune response. The TLR4 agonist lipopolysaccharide (LPS) is a strong immune activator leading to sickness and depressed mood. NOD agonists are less active but can prime immune cells to augment LPS-induced cytokine production. Since the impact of NOD and TLR co-activation in vivo has been little studied, the effects of the NOD1 agonist FK565 and the NOD2 agonist muramyl dipeptide (MDP), alone and in combination with LPS, on immune activation, brain function and sickness behavior were investigated in male C57BL/6N mice. Intraperitoneal injection of FK565 (0.001 or 0.003mg/kg) or MDP (1 or 3mg/kg) 4h before LPS (0.1 or 0.83mg/kg) significantly aggravated and prolonged the LPS-evoked sickness behavior as deduced from a decrease in locomotion, exploration, food intake and temperature. When given alone, FK565 and MDP had only minor effects. The exacerbation of sickness behavior induced by FK565 or MDP in combination with LPS was paralleled by enhanced plasma protein and cerebral mRNA levels of proinflammatory cytokines (IFN-γ, IL-1β, IL-6, TNF-α) as well as enhanced plasma levels of kynurenine. Immunohistochemical visualization of c-Fos in the brain revealed that NOD2 synergism with TLR4 resulted in increased activation of cerebral nuclei relevant to sickness. These data show that NOD1 or NOD2 synergizes with TLR4 in exacerbating the immune, sickness and brain responses to peripheral immune stimulation. Our findings demonstrate that the known interactions of NLRs and TLRs at the immune cell level extend to interactions affecting brain function and behavior.

KEYWORDS:

Anxiety; Corticosterone; FK565; Food intake; Kynurenine; Lipopolysaccharide; Locomotion; Muramyl dipeptide; Proinflammatory cytokines; c-Fos

PMID:
25218901
PMCID:
PMC4295938
DOI:
10.1016/j.bbi.2014.08.011
[Indexed for MEDLINE]
Free PMC Article

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