Role of nucleus retroambigualis in respiratory reflexes evoked by superior laryngeal and vestibular nerve afferents and in emesis

An ascending projection from the medullary nucleus retroambigualis (NRA) has recently been described as important for the control of the upper airway during vocalization. We evaluated the importance of this projection in other behaviors by making localized injections of the neurotoxin kainic acid in the NRA in decerebrate cats, most of which were paralyzed and artificially ventilated. In contrast to its importance for vocalization, the NRA is not essential for activation of upper airway musculature during respiration, swallowing, vomiting, or reflexes elicited by superior laryngeal or vestibular nerve afferents. However, kainic acid injections in the NRA and adjacent reticular formation prolonged the inhibitory phrenic motoneuronal response to superior laryngeal nerve stimulation and abolished or reduced abdominal motoneuronal responses during respiration, vomiting, and superior laryngeal nerve stimulation. Thus, of the behaviors we investigated, the importance of the ascending projection from the NRA appears to be limited to vocalization, while descending projections from the NRA region are important in a number of behaviors.