The effect of lipopolysaccharide (LPS) on inflammatory markers in blood and brain and on behavior in individually-housed pigs

• Published in: Physiology & behavior 2018-10, Vol.195, p.98-111
• Main Authors: Nordgreen, Janicke, Munsterhjelm, Camilla, Aae, Frida, Popova, Anastasija, Boysen, Preben, Ranheim, Birgit, Heinonen, Mari, Raszplewicz, Joanna, Piepponen, Petteri, Lervik, Andreas, Valros, Anna, Janczak, Andrew M.
• Format: Article
• Language: English
• Subjects: Inflammation; Lipopolysaccharide (LPS); Noradrenaline; Pig; Sickness behavior; Tail biting
• ISSN: 0031-9384; 1873-507X
• DOI: 10.1016/j.physbeh.2018.07.013

Most of us have experienced deterioration of mood while ill. In humans, immune activation is associated with lethargy and social withdrawal, irritability and aggression; changes in social motivation could, in theory, lead to less functional interactions. This might also be the case for animals housed in close confinement. Tail biting in pigs is an example of damaging social behavior, and sickness is thought to be a risk factor for tail biting outbreaks. One possible mechanism whereby sickness may influence behavior is through cytokines. To identify possible mediators between immune activation and behavioral change, we injected 16 gilts with lipopolysaccharide (LPS; O111:B4; 1.5 μg kg−1 IV through a permanent catheter). In LPS-treated pigs, a significant increase in cortisol, TNF-α, IL-1 receptor antagonist, IL-6, and IL-8 was observed alongside decreased activity within the first 6 h after the injection. CRP was elevated at 12 and 24 h after injection, and food intake was reduced for the first 24 h after injection. Three days post-injection, LPS pigs had lower levels of noradrenaline in their hypothalamus, hippocampus and frontal cortex compared to saline-injected pigs. Pigs injected with LPS also had higher levels of the pro-inflammatory cytokine IFN-γ in their frontal cortex compared to saline-injected pigs. Thus, a low dose of LPS can induce changes in brain cytokine levels and neurotransmitter levels that persist after inflammatory and stress markers in the periphery have returned to baseline levels. •Pigs injected with lipopolysaccharide (LPS) decreased activity and appetite during the first hours after injection.•Three days after injection, LPS treated pigs had lower levels of noradrenaline in several brain areas compared to controls.•Pigs injected with LPS also had higher levels of the cytokine IFN-γ in their frontal cortex compared to controls.•LPS can influence brain physiology even after inflammatory and stress markers in the periphery have returned to baseline.