Neuronal plasticity within the medullary dorsal horn: the nasopharyngeal response returns 3 days after bilateral sectioning of the anterior ethmoidal nerve (1130.19)

Stimulation of the nasal passages with ammonia vapors can reflexly produce bradycardia, apnea, and increased peripheral resistance. However, after acute bilateral sectioning of the anterior ethmoidal nerve (AEN), the nerve that innervates the nasal passages, this nasopharyngeal response consists of only a slight apnea and an increase in arterial pressure. In the present experiments, in urethane‐anesthetized Sprague‐Dawley rats, we recorded the cardiorespiratory responses to ammonia vapor stimulation of the nasal passages 3, 5, 7 and 9 days after bilateral sectioning of the AEN, and compared these responses to those from rats with sham and acute (0 day) AEN sectioning. After nasal stimulation, heart rate (HR) decreased 62% in Sham rats but only 12% in Acute rats. After waiting 3 days following AEN sectioning, HR decreased 26%, and when waiting 9 days by 32%. The re‐establishment of the cardiorespiratory responses to nasal stimulation after bilateral AEN sectioning suggests that other nerves that innervate the nasal passages are able to provide an afferent signal sufficient to initiate the nasopharyngeal reflex. Additionally, because the bradycardia is strongly attenuated after acute AEN sectioning, our research suggests that neuronal plasticity within the medullary dorsal horn, the brainstem termination site of the AEN, may be necessary before the re‐establishment of the nasopharyngeal response can occur. Grant Funding Source : Supported by MWU Office of Research and Sponsored Programs.