Two descending medullary inspiratory pathways to phrenic motoneurones

Synaptic connections of the medullary inspiratory neurones of the nucleus tractus solitarius (NTS) and nucleus retroambigualis (NRA) with phrenic motoneurones were studied using spike triggered averaging of the synaptic noise of phrenic motoneurones. More than 60% of NTS inspiratory neurones made monosynaptic connections with phrenic motoneurones, while similar connections between NRA and phrenic motoneurones could be shown in less than 7% of studied neuronal pairs. Relations between cross-correlations and observed synaptic connectivity of the phrenic motoneurones are also discussed.