Undergraduate Honors Theses

Thesis Defended

Spring 2016

Document Type


Type of Thesis

Departmental Honors


Integrative Physiology

First Advisor

Dr. Christopher Lowry

Second Advisor

Dr. David Sherwood

Third Advisor

Dr. Daniel Jones


The coevolution of microorganisms and their hosts have resulted in the formation of symbiotic relationships between both organisms. These formed associations have in turn benefited larger animals by enhancing their adaption towards external environments and protecting against pathogens. Recent studies have further highlighted the importance of microbial interactions by analyzing their role in proper immune regulation and their effect on behavior and health. Faulty immunoregulatory circuits have been implicated in the rapid rise of chronic inflammatory diseases and considered a risk factor for psychiatric diseases. Although studies have begun to understand the link between microbes and stress-related behaviors, few studies have focused on the potential influence of environmental bacteria on anxiety related disorders. In this study we show that rats that were subcutaneously immunized with heat–killed M. vaccae, a non-pathogenic environmental bacterium, expressed reduced levels of anxiety-related behaviors when tested in the elevated T-maze. As compared to the control group, M. vaccae-treated rats expressed significantly lower latencies when measuring inhibitory avoidance, a behavior related to generalized-anxiety. During the escape task, a behavior associated with panic behavior, M. vaccae treated rats had larger latencies to leave the open arm, but the differences between groups were not significant. The results of our studies suggest a beneficial effect of heat-killed M. vaccae on anxiety-related behaviors in the elevated T-maze. Our study supports the on-going hypothesis regarding the beneficial role of immunoregulatory environmental microbes in control of emotional behavior and emotional states.