Anxiogenic effect of subclinical bacterial infection in mice in the absence of overt immune activation

Abstract

LYTE, M., J. J. VARCOE AND M. T. BAILEY. Anxiogenic effect of subclinical bacterial infection in mice in the absence of overt immune activation. PHYSIOL BEHAV 65(1) 63–68, 1998.—Challenge of animals with infectious microorganisms is well documented to affect a number of behavioral measures through activation of immune-neural mechanisms. In the present study, the ability of an infectious microorganism to directly alter behavioral responses in the absence of an overt immunologic response was examined. Eight-week-old CF-1 male mice were infected orally with the Gram-negative pathogen Campylobacter jejuni in order to establish a subclinical infection that did not result in immune activation. Microbiological examination of cecal contents revealed the presence of C. jejuni in all infected, but not control, animals 1 and 2 days post-oral challenge. Measurement of interleukin-6 (IL-6) levels and peripheral blood leukocyte populations did not reveal the activation of an overt immune response in 1 or 2 day infected animals as compared to controls. Infected mice demonstrated altered levels of anxiety-like behaviors on the elevated plus-maze as compared to controls on Day 2, but not Day 1, as reflected by a significant decrease in exploratory and an increase in nonexploratory behaviors. The anxiogenic effect of a subclinical infection in the absence of an overt immunologic response suggests that the direct activation of neural pathways by microorganisms may play a role in behavior.