Expiratory-modulated laryngeal motoneurons exhibit a hyperpolarization preceding depolarization during superior laryngeal nerve stimulation in the in vivo adult rat

Swallowing requires the sequential activation of tongue, pharyngeal and esophageal muscles to propel the food bolus towards the stomach. Aspiration during swallow is prevented by adduction of the vocal cords during the oropharyngeal phase. Expiratory-modulated laryngeal motoneurons (ELM) exhibit a burst of action potentials during swallows elicited by electrical stimulation of the superior laryngeal nerve (SLN). Here we sought to investigate changes in membrane potential in ELM during superior laryngeal nerve stimulation in the anaesthetised, in vivo adult rat preparation. Intracellular recordings of ELM in the caudal nucleus ambiguus (identified by antidromic activation from the recurrent laryngeal nerve) demonstrated that ELM bursting activity following SLN stimulation is associated with a depolarization that is preceded by a small hyperpolarization. During spontaneous ELM bursts, the preceding hyperpolarization separated the bursting activity from its usual post-inspiratory activity. These findings demonstrate that the in vivo adult rat preparation is suitable for the study of swallow-related activity in laryngeal motoneurons.