Activity of respiratory laryngeal motoneurons during fictive coughing and swallowing

Membrane potential changes and discharges from 28 laryngeal motoneurons wer e recorded intracellularly in the caudal nucleus ambiguus of decerebrate, p aralyzed and ventilated cats. Electrical activities were recorded from 17 e xpiratory laryngeal motoneurons (ELMs) with maximal depolarizing membrane p otential in early expiration, and from 11 inspiratory laryngeal motoneurons (ILMs) with maximal depolarizing membrane potential in inspiration. Activi ties during breathing were compared with those observed during fictive coug hing and swallowing evoked by electrical stimulation of the superior laryng eal nerves. These non-respiratory behaviors were evidenced in paralyzed ani mals by characteristic discharge patterns of the phrenic, abdominal nerves and pharyngeal branch of the vagus nerve. We recorded the activity of 11 EL Ms and 5 ILMs during coughing in which ELMs, but not ILMs, exhibited increa sed membrane depolarization and discharge frequencies. Membrane depolarizat ion and discharge frequencies of all ELMs were also significantly increased during swallowing. In addition, membrane depolarization of most ELMs (15/1 7) was preceded by a short-lasting hyperpolarization due to chloride-depend ent inhibitory mechanisms occurring at the onset of swallowing. Out of 10 I LMs tested during swallowing, 7 exhibited membrane depolarization, preceded in 5 cases by a short-lasting hyperpolarization. Discharge frequencies of ILMs were significantly reduced during swallowing. The same pattern of phas ic activities of ILMs and ELMs was observed during coughing and breathing, suggesting the involvement of similar excitatory pathways in both behaviors . These results imply that the duration of activation and the discharge fre quency of neurons of the central generator for breathing that drive larynge al motoneurons are enhanced during coughing. During swallowing, in addition to central excitatory mechanisms, laryngeal motoneurons are subjected to a n initial inhibition of unknown origin. This inhibition probably contribute s to the temporal organization of the swallowing motor sequence.