Behaviors of bulbar respiratory interneurons during fictive swallowing and vomiting.

Behaviors of the same individual medullary respiratory interneurons were examined during both swallowing and vomiting. In 8 decerebrated and paralyzed cats, 18 neurons having either augmenting expiratory (E-AUG), decrementing expiratory (E-DEC), decrementing inspiratory (I-DEC), or constant inspiratory (I-CON) firing patterns were recorded near the most rostral part of the nucleus ambiguus. All neurons exhibited elementary reflexes to single-shock stimulation of the superior laryngeal nerve. During fictive swallowing elicited by superior laryngeal nerve stimulation, all neurons were basically inactive. During fictive vomiting induced by vagal stimulation and/or emetic drugs, all E-AUG and E-DEC neurons tested either were silent or fired weakly between successive retches, whereas I-DEC and I-CON neurons tested exhibited burst activity during the retching and early-expulsion phases. These results indicate that these bulbar respiratory neurons, which may be involved in respiratory rhythmogenesis, are multifunctional neurons that could also be involved in vomiting but not likely in swallowing.