Medullary respiratory neurones and control of laryngeal motoneurones during fictive eupnoea and cough in the cat

1. This study addressed the hypothesis that ventrolateral medullary respira tory neurones participate, in the control of laryngeal motoneurones during both eupnoea and coughing. 2. Data were obtained from 28 mid-collicular decerebrated, artificially ven tilated cats. Cough-like motor patterns (fictive cough) in phrenic, lumbar and recurrent laryngeal nerves were elicited by mechanical stimulation of t he intrathoracic trachea. Microelectrode arrays were used to monitor simult aneously several neurones in the ventral respiratory group, including the B otzinger and pre-Botzinger complexes. Spike trains were evaluated for respo nses during fictive cough and evidence of functional connectivity with spik e-triggered averages of efferent recurrent laryngeal nerve activity. 3. Primary features were observed in averages triggered by 94 of 332 (28 %) neurones. An offset biphasic wave with a positive, time lag was present in the unrectified average for 10 inspiratory and 13 expiratory neurones. The se trigger neurones were respectively identified as inspiratory laryngeal m otoneurones with augmenting, decrementing, plateau and 'other' discharge pa tterns, and expiratory laryngeal motoneurones with decrementing firing patt erns, 4. Rectified averages triggered by inspiratory neurones included 37 offset peaks, 11 central peaks and one offset trough. Averages triggered by expira tory neurones had 12 offset peaks, six central peaks and four offset trough s. Relationships inferred from these features included premotor actions of inspiratory neurones with augmenting, decrementing, plateau and 'other' pat terns on inspiratory laryngeal motoneurones, and premotor actions of decrem enting and 'other' expiratory neurones on expiratory laryngeal motoneurones . Corresponding changes in neuronal firing patterns during fictive cough su pported these inferences. 5. The data confirm and extend previous results on the control of laryngeal motoneurones during eupnoea and support the hypothesis that the same premo tor neurones help to shape motoneurone firing patterns during both eupnoea and coughing.