A new study, done with mice and published in the Federation of the American Societies of Experimental Biology Journal, suggests that miscommunication between the immune system and brain may be to blame for extended sickness symptoms and other cognitive disorders in elderly people and animals with an infection.
"In the course of our other studies on inflammation and aging, we repeatedly saw that old animals suffered an exaggerated inflammatory response in the brain compared to younger adults when their peripheral immune system was experimentally activated," said Rodney W. Johnson, a professor of integrative immunology and behavior in the department of animal sciences. "Knowing the role of brain inflammation in behavioral deficits and neurodegenerative diseases, we felt this could be important, especially because immunity is often suppressed in the elderly, making them more susceptible to infections."
Johnson and his colleagues compared behavior in young adult and aged mice that were made temporarily ill by exposure to lipopolysaccharide (LPS), a molecule present on E. coli and other gram-negative bacteria that strongly activates the immune system.
"When a person or pet develops an infection, their behavior changes: They stop eating; they become lethargic; they have reduced cognitive abilities," Johnson said.
How do you know a mouse feels sick? Like unhealthy humans, mice show decreased appetite, weight loss and less social interaction, said Johnson, who likened his own lack of interest in getting up off the couch to greet visitors when he is sick to a mouse's lack of curiosity about new cage mates when it is sick.
LPS injections caused older mice to stop eating for a longer amount of time, lose more weight and show less social behavior
Contact: Molly McElroy, Univ. of Illinois News Bureau
University of Illinois at Urbana-Champaign