The physiological activity and importance of the vagus nerve have let it into the spotlight as an alternative treatment for inflammatory bowel diseases. Indeed, the anatomical characteristics of this nerve can provide a multimodal capacity to relieve, control, and suppress the harmful effects of inflammatory bowel conditions. Furthermore, the unique mixed component of 80% afferent and 20% efferent fibers enables exceptional communication between the central nervous system and the gastrointestinal tract. As a result, bioelectric medicine modifying and improving the vagal nerve function has become an alternative treatment for anti-TNF-alpha drugs, known for unwanted side effects.

Vagus Nerve:

The vagus nerve is the longest in the body, and indeed, it extends from the medulla oblongata to the digestive tract. Also, it is known as the pneumogastric nerve since it innervates the pharynx, larynx, heart and lungs, and all the gastric system from the esophagus to the recto-colon.

As mentioned previously, it comprises 80% afferent and 20% efferent fibers, and it is a paired nerve, as it has a left and right VN. Furthermore, its anatomical and bidirectional communication characteristics make the VN a cornerstone of the brain-gut axis, promoting coordinated functioning. Ultimately, proper VN function reflects optimal motility, secretion, gut permeability, and immunity.

The digestive system function is not perceived, as it is often unconscious. However, in specific pathologies, the digestive process is sensed as painful. In turn, gastrointestinal therapies such as changes in nutritional patterns, drugs, and VN stimulation have been used as clinical management of gastrointestinal disorders.

Bioelectric medicine:

The use of neuromodulation in bioelectric medicine allows digestive function restoration, thus reflecting in less drug usage and reduced adherence issues. Furthermore, the efficacy of bioelectric therapy resides in the stimulation of VN’s anti-inflammatory role via afferent fibers and the release of glucocorticoids to stimulate the HPA axis. In addition, VN’s efferent fibers promote the cholinergic anti-inflammatory pathway.

Vagal afferent fibers: Anti-inflammatory agents.

Vagal afferent fibers originate from the different layers of the gut wall, such as the external muscle layers, myenteric plexus, and mucosal lamina propria. Furthermore, they can inform the functional state of the GI tract by carrying sensory signals as projections that then translate in the hypothalamus, amygdala, thalamus, hippocampus, and cerebral cortex.

In addition, these structures, as part of the CAN (cholinergic anti-inflammatory pathway), can modulate autonomic, behavioral, cognitive, and endocrine responses. Ultimately, this results in the balance of the autonomic nervous system (ANS).

Also, afferent fibers can detect the presence of nutrients, the food’s temperature, as they are mechanoreceptors and osmoreceptors. As a result, afferent fibers can carry the signal of pain and inflammatory processes to the CAN where the HPA axis can be modified and the ANS.

Nowadays, non-invasive neurostimulation is under clinical investigation on IBD and pediatric UC patients. Indeed, this therapeutic approach aims to decrease proinflammatory cytokines such as IL-6, IL-12, IL-23, and TNF-alpha. The applications are found, but the VN recruitment is still unknown, with variations in width, pulse, amplitude, and frequency. – Ana Paola Rodríguez Aricniega, MS.

Bibliography:

Bonaz, Bruno et al. “Therapeutic Potential of Vagus Nerve Stimulation for Inflammatory Bowel Diseases.” Frontiers in neuroscience vol. 15 650971. 22 Mar. 2021, doi:10.3389/fnins.2021.650971

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