Undergraduate Honors Theses

Thesis Defended

Spring 2018

Document Type


Type of Thesis

Departmental Honors


Integrative Physiology

First Advisor

Christopher Lowry

Second Advisor

Alena Grabowski

Third Advisor

Randolf DiDomenico

Fourth Advisor

Thomas LaRocca


Disorders associated with inflammation, including allergy and allergic asthma, are increasing in modern urban societies. The hygiene, or “Old Friends,” hypothesis attributes this escalation to the decreased exposure to immunoregulatory microorganisms. Evidence suggests that inflammation is also a risk factor for trauma- and stressor-related disorders including posttraumatic stress disorder (PTSD). PTSD can be characterized by exaggerated fear and startle and the inability to extinguish fear. Mycobacterium vaccae is a microorganism found in the soil that has immunoregulatory and anti-inflammatory properties; recent studies suggest that M. vaccae enhances fear extinction in rodent models, potentially through actions on brain serotonergic systems. The current study determined the effects of preimmunization with M. vaccae, or vehicle, on rats subsequently exposed to the fear-potentiated startle paradigm, when compared to home cage control rats. Immunization with M. vaccae enhanced between-session and within-session fear extinction. Changes in expression of htr1a mRNA were observed in this study, namely in the dorsomedial, rostral, and caudal parts of the dorsal raphe nucleus (DRN). These data are consistent with the hypothesis that M. vaccae may play a useful role in the prevention of disorders related to fear and serotonergic dysregulation.

Available for download on Thursday, April 09, 2020