Monosynaptic inhibition of phrenic motoneurons: a long descending projection from Bötzinger neurons

Synaptic connections between medullary expiratory neurons and phrenic motoneurons were studied in anesthetized cats using spike-triggered averaging of synaptic noise in phrenic motoneurons. Monosynaptic inhibition of phrenic motoneurons originating from the rostral medullary expiratory neurons of the Bötzinger complex was revealed. Neither mono- nor disynaptic inhibition from expiratory neurons of the nucleus retroambigualis was found. It was concluded that Bötzinger complex expiratory neurons make long descending inhibitory connections with phrenic motoneurons: the expiratory neurons of the nucleus retroambigualis do not appear to make synaptic connections with phrenic motoneurons.