Functional connectivity among ventrolateral medullary respiratory neuronesand responses during fictive cough in the cat

1. This study tested predictions from a network model of ventrolateral medu llary respiratory neurone interactions for the generation of the cough moto r pattern observed in inspiratory and expiratory pump muscles. 2. Data were from 34 mid-collicularly decerebrated, paralysed, artificially ventilated cats. Cough-like patterns (fictive cough) in efferent phrenic a nd lumbar nerve activities were elicited by mechanical stimulation of the i ntrathoracic trachea. Neurones in the ventral respiratory group, including the Botzinger and pre-Botzinger complexes, were monitored simultaneously wi th microelectrode arrays. Spike trains were analysed for evidence of functi onal connectivity and responses during fictive cough with cycle-triggered h istograms, autocorrelograms, cross-correlograms, and spike-triggered averag es of phrenic and recurrent laryngeal nerve activities. 3. Significant cross-correlogram features were detected in 151 of 1988 pair s of respiratory modulated neurones. There were 59 central peaks, 5 central troughs, 11 offset peaks and 2 offset troughs among inspiratory neurone pa irs. Among expiratory neurones there were 23 central peaks, 8 offset peaks and 4 offset troughs. Correlations between inspiratory and expiratory neuro nes included 20 central peaks, 10 central troughs and 9 offset troughs. Spi ke- triggered averages of phrenic motoneurone activity had 51 offset peaks and 5 offset troughs. 4. The concurrent responses and multiple short time scale correlations supp ort parallel and serial network interactions proposed in our model for the generation of the cough motor pattern in the respiratory pump muscles. Infe rred associations included the following. (a) Excitation of augmenting insp iratory (I-Aug) neurones and phrenic motoneurones by I-Aug neurones. (b) In hibition of augmenting expiratory (E-Aug) neurones blv decrementing inspira tory (I-Dec) neurones. (c) Inhibition of I-Aug, I-Dec and E-Aug neurones by E-Dec neurones. (d) Inhibition of I-Aug and I-Dec neurones and phrenic mot oneurones by E-Aug neurones. The data also confirm previous results and sup port hypotheses in current network models for the generation of the eupnoei c pattern.