Evidence for swallowing reflexes evoked by acid and mechanical stimulation of the vagal afferent nerves innervating the larynx in anesthetized guinea pigs

Abstract

PurposeSwallowing protects the lungs from aspiration and is evoked from the upper airways (UA) by activation of pharyngeal afferent nerves. We have tested the hypothesis that laryngeal (LX) afferent nerve activation may also evoke swallowing.MethodsSternohyoid muscle EMGs and UA airflow were used to detect swallows in anesthetized guinea pigs (GPs). Citric acid (CA; 0.01M, 50μL), applied topically to the LX mucosa, and UA pressure distensions, both applied 5× repetitively in 5 min intervals and delivered rostrally via the trachea, were used to evoke swallows.ResultsRepetitive LX CA challenge evoked swallowing (13±5 swallows; n=7). Severing both the recurrent (RLN) and superior (SLN) laryngeal nerves nearly abolished LX CA evoked swallows (0.3±0.3; n=4). Severing just the RLNs also nearly abolished the LX acid‐evoked swallows (1.3±0.9; n=4). By contrast, swallows evoked by 30sec pressure distensions of the UA were not prevented by RLN transection, with all intact (50±5; n=4) and RLN transected (26±3; n=4) GPs swallowing in response to each of 5 distensions. RLN transection did, however, delay the onset of UA distension evoked swallows (4.0±1.3s and 13.6±1.4s in intact and RLN transected GPs; n=4 each). A single, subsequent LX CA challenge evoked swallows in all 4 of these control GPs (4±1) but in none of the GPs with RLNs cut (0±0).ConclusionsLaryngeal vagal afferent nerve activation initiates swallowing.