ANXIOGENIC EFFECT OF SUBCLINICAL BACTERIAL-INFECTION IN MICE IN THE ABSENCE OF OVERT IMMUNE ACTIVATION

Challenge of animals with infectious microorganisms is well documented to affect a number of behavioral measures through activation of immun e-neural mechanisms. In the present study, the ability of an infectiou s microorganism to directly alter behavioral responses in the absence of an overt immunologic response was examined. Eight-week-old CF-1 mal e mice were infected orally with the Gram-negative pathogen Campylobac ter jejuni in order to establish a subclinical infection that did not result in immune activation. Microbiological examination of cecal cont ents revealed the presence of C. jejuni in all infected, but not contr ol, animals 1 and 2 days post-oral challenge. Measurement of interleuk in-6 (IL-6) levels and peripheral blood leukocyte populations did not reveal the activation of an overt immune response in 1 or 2 day infect ed animals as compared to controls. Infected mice demonstrated altered levels of anxiety-like behaviors on the elevated plus-maze as compare d to controls on Day 2, but not Day 1, as reflected by a significant d ecrease in exploratory and an increase in nonexploratory behaviors. Th e anxiogenic effect of a subclinical infection in the absence of an ov ert immunologic response suggests that the direct activation of neural pathways by microorganisms may play a role in behavior. (C) 1998 Else vier Science Inc.