Vagal tone: effects on sensitivity, motility, and inflammation

Abstract

The vagus nerve (VN) is a key element of the autonomic nervous system. As a mixed nerve, the VN contributes to the bidirectional interactions between the brain and the gut, i.e., the brain-gut axis. In particular, after integration in the central autonomic network of peripheral sensations such as inflammation and pain via vagal and spinal afferents, an efferent response through modulation of preganglionic parasympathetic neurons of the dorsal motor nucleus of the vagus and/or preganglionic sympathetic neurons of the spinal cord is able to modulate gastrointestinal nociception, motility, and inflammation. A low vagal tone, as assessed by heart rate variability, a marker of the sympatho-vagal balance, is observed in functional digestive disorders and inflammatory bowel diseases. To restore a normal vagal tone appears as a goal in such diseases. Among the therapeutic tools, such as drugs targeting the cholinergic system and/or complementary medicine (hypnosis, meditation…), deep breathing, physical exercise, VN stimulation (VNS), either invasive or non-invasive, appears as innovative. There is new evidence in the current issue of this Journal supporting the role of VNS in the modulation of gastrointestinal functions.

The Vagus Nerve in Appetite Regulation, Mood, and Intestinal Inflammation

“…There is however increasing indirect evidence, based on heart rate variability monitoring, to support an immune-modulatory role of the CAIP in humans (reviewed in 130,131 ). In healthy subjects, reduced heart rate variability indices (= low vagal tone) are independently associated with increased serum CRP and IL-6 levels and increased TNF and IL-6 production in endotoxin-stimulated whole blood.…”

Cholinergic modulation of the immune system presents new approaches for treating inflammation

“…Using this device, investigators have demonstrated efficacy at reducing sympathetic nerve activity in normal volunteers (Clancy et al, 2014). Another device, GammaCore (electroCore LLC, Basking Ridge, NJ) is hand-held and uses two disc electrodes for transcutaneous stimulation of the cervical vagus nerve (Bonaz et al, 2016c). Use of such non-invasive devices in treating chronic inflammatory diseases will need to consider patient compliance, which is also a concern with drug therapy (Bonaz et al, 2016c).…”

“…Another device, GammaCore (electroCore LLC, Basking Ridge, NJ) is hand-held and uses two disc electrodes for transcutaneous stimulation of the cervical vagus nerve (Bonaz et al, 2016c). Use of such non-invasive devices in treating chronic inflammatory diseases will need to consider patient compliance, which is also a concern with drug therapy (Bonaz et al, 2016c). The clinical efficacy of these approaches is currently under evaluation.…”

The shock tactics set to shake up immunology

“…The results of this trial were published last July in Proceedings of the National Academy of Sciences 11 . Findings from another vagal-stimulation trial were published around the same time 12 . Bruno Bonaz, a gastroenterologist at the University Hospital in Grenoble, France, implanted stimulators into seven people with Crohn's disease.…”