The Vagus Nerve at the Interface of the Microbiota-Gut-Brain Axis

Abstract

The microbiota, the gut, and the brain communicate through the microbiota-gut-brain axis in a bidirectional way that involves the autonomic nervous system. The vagus nerve (VN), the principal component of the parasympathetic nervous system, is a mixed nerve composed of 80% afferent and 20% efferent fibers. The VN, because of its role in interoceptive awareness, is able to sense the microbiota metabolites through its afferents, to transfer this gut information to the central nervous system where it is integrated in the central autonomic network, and then to generate an adapted or inappropriate response. A cholinergic anti-inflammatory pathway has been described through VN's fibers, which is able to dampen peripheral inflammation and to decrease intestinal permeability, thus very probably modulating microbiota composition. Stress inhibits the VN and has deleterious effects on the gastrointestinal tract and on the microbiota, and is involved in the pathophysiology of gastrointestinal disorders such as irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD) which are both characterized by a dysbiosis. A low vagal tone has been described in IBD and IBS patients thus favoring peripheral inflammation. Targeting the VN, for example through VN stimulation which has anti-inflammatory properties, would be of interest to restore homeostasis in the microbiota-gut-brain axis.

Traumatic stress and the autonomic brain‐gut connection in development: Polyvagal Theory as an integrative framework for psychosocial and gastrointestinal pathology

“…These effects are supported by animal studies indicating that maintained autonomic responses may be partly based on the interactions with immune function and microbiota (Mayer, Labus, Tillisch, Cole, & Baldi, ). The ANS via its parasympathetic branch is a central mediator of the microbiota‐gut‐brain axis, dysfunction of which is thought to underlie both functional and inflammatory GI disorders (Bonaz, Bazin, & Pellissier, ). GI inflammation has been linked to negative emotional states and autonomic reactivity in both animal models and human studies (Bonaz et al, ; Cielsielczyk, Furgała, Dobrek, Jusczak, & Thor, ; Ghia et al, ).…”

Connection between gut microbiome and brain development in preterm infants

“…There are several proposed mechanisms that could potentially be relevant to the preterm infants; however, few studies have been designed to explore the mechanisms by which the microbiome specifically affects preterm infant brain development. To date, immune system modulation (Berer et al, ; Erny et al, ; Honda & Takeda, ; Lee, Menezes, Umesaki, & Mazmanian, ; Sampson & Mazmanian, ), microbial metabolites (Bourassa, Alim, Bultman, & Ratan, ), and vagus nerve activation (Bonaz, Bazin, & Pellissier, ) are the most studied pathways linking gut microbiota and neurological development (summarized in Figure ).…”

“…Potential communication/connections between gut microbiota and brain that might have implications in preterm infant brain development include immune system modulation, neurotransmitters and/or neuromodulators produced by gut microbiota, alteration of systemic inflammation and neuroinflammation, signaling between central nerve system and vagus nerve, and regulation of intestinal and blood-brain barrier functions the microbiome specifically affects preterm infant brain development. To date, immune system modulation (Berer et al, 2011;Erny et al, 2015;Honda & Takeda, 2009;Lee, Menezes, Umesaki, & Mazmanian, 2011;Sampson & Mazmanian, 2015), microbial metabolites (Bourassa, Alim, Bultman, & Ratan, 2016), and vagus nerve activation (Bonaz, Bazin, & Pellissier, 2018) are the most studied pathways linking gut microbiota and neurological development (summarized in Figure 1).…”

Endocrine regulation of gut function – a role for glucagon‐like peptide‐1 in the pathophysiology of irritable bowel syndrome

“…Beneath the epithelial layer, intrinsic and extrinsic neurons relay neural information both within the GI tract and between the gut and the CNS. However, evidence that this communication system extends beyond the epithelial barrier to the microbially dominated environment of the gut lumen has resulted in it being referred to as the microbiota–gut–brain axis (Bonaz, Bazin, & Pellissier, ; Forsythe, Bienenstock, & Kunze, ; Martin et al., ).…”