Dissecting the Role of Subtypes of Gastrointestinal Vagal Afferents.

Yoko B Wang,Guillaume De Lartigue,Amanda J Page

doi:10.3389/fphys.2020.00643

Abstract

Gastrointestinal (GI) vagal afferents convey sensory signals from the GI tract to the brain. Numerous subtypes of GI vagal afferent have been identified but their individual roles in gut function and feeding regulation are unclear. In the past decade, technical approaches to selectively target vagal afferent subtypes and to assess their function has significantly progressed. This review examines the classification of GI vagal afferent subtypes and discusses the current available techniques to study vagal afferents. Investigating the distribution of GI vagal afferent subtypes and understanding how to access and modulate individual populations are essential to dissect their fundamental roles in the gut-brain axis.

Highlights

The vagus nerve provides bidirectional communication between the gut and the brain
The lower GI tract is densely innervated by spinal afferents whose cell bodies lie in the dorsal root ganglia (DRG) (Spencer et al, 2016b)
This study suggests that vagal ganglia consist of 85% of nodose neurons and 15% of jugular neurons, of which eighteen subtypes of nodose neuron and six subtypes of jugular neuron have been identified (Kupari et al, 2019)

Summary

INTRODUCTION

The vagus nerve provides bidirectional communication between the gut and the brain. The vagus nerve comprises of both sensory and motor neurons with the number of afferent fibres outnumbering the efferent fibres by about 9 to 1 (Agostoni et al, 1957). Gene expression profiles (Egerod et al, 2018; Kupari et al, 2019) and neural circuits (Williams et al, 2016; Han et al, 2018; Kaelberer et al, 2018) have been introduced as new ways to categorise vagal afferent subtypes (Figure 2) All of these approaches aim to associate GI vagal afferents to their physiological and behavioural function, each classification has limitations when it comes to in vivo studies. A more specific vagal afferent classification has been made based on morphological specialisation of vagal afferent endings in the gut wall This approach distinguishes vagal afferent populations into three subtypes, namely the intraganglionic laminar endings (IGLEs), intramuscular arrays (IMAs) and mucosal afferents (Berthoud and Powley, 1992).

Limitations

Findings

CONCLUSION