The emerging role of the gut microbiome in posttraumatic stress disorder

Abstract

Posttraumatic stress disorder (PTSD) occurs in some people following exposure to a terrifying or catastrophic event involving actual/threatened death, serious injury, or sexual violence. PTSD is a common and debilitating mental disorder that imposes a significant burden on individuals, their families, health services, and society. Moreover, PTSD is a risk factor for chronic diseases such as coronary heart disease, stroke, diabetes, as well as premature mortality. Furthermore, PTSD is associated with dysregulated immune function. Despite the high prevalence of PTSD, the mechanisms underlying its etiology and manifestations remain poorly understood. Compelling evidence indicates that the human gut microbiome, a complex community of microorganisms living in the gastrointestinal tract, plays a crucial role in the development and function of the host nervous system, complex behaviors, and brain circuits. The gut microbiome may contribute to PTSD by influencing inflammation, stress responses, and neurotransmitter signaling, while bidirectional communication between the gut and brain involves mechanisms such as microbial metabolites, immune system activation, and the vagus nerve. In this literature review, we summarize recent findings on the role of the gut microbiome in PTSD in both human and animal studies. We discuss the methodological limitations of existing studies and suggest future research directions to further understand the role of the gut microbiome in PTSD.

Keywords: Gut microbiome; Gut-microbiota-brain axis; Posttraumatic stress disorder; Trauma.

Figure 1:. The putative bidirectional communication system of the gut–microbiota–brain axis.

This system involves the endocrine, humoral, immune, and metabolic pathways. On the one hand, stress and emotions can affect the concentration of stress hormone (e.g., noradrenaline) and neurotransmitters in the gut lumen, and this might contribute to the changes in the composition and activity (e.g., microbial gene expression or signaling between taxa) of the gut microbial community. On the other hand, the microbiota can produce neuroactive compounds such as serotonin [5-hydroxytryptamine (5-HT)], gamma-aminobutyric acid (GABA), and microbial metabolites [short-chain fatty acids (SCFA)]. These metabolites can travel through portal circulation to interact with the host immune system, influence metabolism and/or affect local neuronal cells of the enteric nervous system and afferent pathways of the vagus nerve that signal directly to the brain. Altered composition of microbiota: it pertains to changes in response to stress and alterations in the microbiota composition, which subsequently influence emotional processing through the bidirectional communication in the gut-brain axis.