Effects of preimmunization with a heat-killed preparation of Mycobacterium vaccae on serotonin receptor subtype 1A expression: implications for stress resilience

Undergraduate Honors Thesis

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Citeable URL: https://scholar.colorado.edu/concern/undergraduate_honors_theses/70795813s

Abstract

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.

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