Suppression of the Swallowing Reflex during Rhythmic Jaw Movements Induced by Repetitive Electrical Stimulation of the Dorsomedial Part of the Central Amygdaloid Nucleus in Rats.

Kojun Tsuji,Yoshihide Satoh

doi:10.3390/life10090190

Abstract

A previous study indicated that the swallowing reflex is inhibited during rhythmic jaw movements induced by electrical stimulation of the anterior cortical masticatory area. Rhythmic jaw movements were induced by electrical stimulation of the central amygdaloid nucleus (CeA). The swallowing central pattern generator is the nucleus of the solitary tract (NTS) and the lateral reticular formation in the medulla. Morphological studies have reported that the CeA projects to the NTS and the lateral reticular formation. It is therefore likely that the CeA is related to the control of the swallowing reflex. The purpose of this study was to determine if rhythmic jaw movements driven by CeA had inhibitory roles in the swallowing reflex induced by electrical stimulation of the superior laryngeal nerve (SLN). Rats were anesthetised with urethane. The SLN was solely stimulated for 10 s, and the swallowing reflex was recorded (SLN stimulation before SLN + CeA stimulation). Next, the SLN and the CeA were electrically stimulated at the same time for 10 s, and the swallowing reflex was recorded during rhythmic jaw movements (SLN + CeA stimulation). Finally, the SLN was solely stimulated (SLN stimulation following SLN + CeA stimulation). The number of swallows was reduced during rhythmic jaw movements. The onset latency of the first swallow was significantly longer in the SLN + CeA stimulation than in the SLN stimulation before SLN + CeA stimulation and SLN stimulation following SLN + CeA stimulation. These results support the idea that the coordination of swallowing reflex with rhythmic jaw movements could be regulated by the CeA.

Highlights

Rhythmic jaw movements were induced by repetitive electrical stimulation of the anterior and posterior cortical masticatory areas (CMA) in rats
The superior laryngeal nerve (SLN) and the central amygdaloid nucleus (CeA) were electrically stimulated at the same time for 10 s, and the swallowing reflex was recorded during rhythmic jaw movements (SLN + CeA stimulation)
The stimulation sites that induced rhythmic jaw movements are located in the dorsomedial part of the CeA (CeADM); stimulation of the ventrolateral part of the CeA or the other areas in the amygdala did not induce rhythmic jaw movements

Summary

Introduction

Rhythmic jaw movements were induced by repetitive electrical stimulation of the anterior and posterior cortical masticatory areas (CMA) in rats. The anterior area is the orofacial motor cortex, and the posterior area is the insular cortex [1,2,3]. Detailed analyses have been made of rhythmic jaw movements induced by stimulation of the CMA. The reciprocal connection between the anterior area and the posterior area of CMA is weak, and they work independently of each other [1,3]. Rhythmic jaw movements have been thought to be programmed by the masticatory central pattern generator (CPG) in the brainstem [4,5]. When a food bolus is accumulated in the oropharynx, swallowing reflex is induced

Objectives

Methods

Results

Conclusion