THE RESPIRATORY ACTIVITY OF THE SUPERIOR LARYNGEAL NERVE IN THE RAT

The aim of this study was to characterize the laryngeal afferent activity of the rat. The animals were anesthetized and breathing spontaneously. Laryngeal afferent activity was recorded from both the whole superior laryngeal nerve (SLN) and from single fibers isolated from this nerve. An overall inspiratory augmenting activity was observed in the whole SLN during tracheostomy breathing, tracheal occlusion and upper airway breathing, but an expiratory augmenting activity was present during upper airway occlusion. The inspiratory modulated activity was abolished by bilateral section of the hypoglossal nerves but not the recurrent laryngeal nerves. A great number of receptors (46/80, 58%) were identified as 'drive' receptors, and others as 'pressure' (22/80, 28%) and 'irritant' type receptors (9/80, 11%). Nineteen pressure receptors were stimulated by positive transmural pressure, while only three stimulated by negative pressure. Nine drive receptors were also stimulated by positive pressure and inhibited by negative pressure. Such response to pressure was further evaluated by applying maintained pressures to the functionally isolated upper airway. These results are essentially consistent with findings obtained in the rabbit, but differ from those reported for the dog.