Synaptic inhibition of phrenic motoneurones evoked by stimulation of the superior laryngeal nerve.

Synaptic responses evoked in phrenic motoneurones (PMNs) by stimulation of the superior laryngeal nerve (SLN) were analysed in anaesthetised cats. Stimulation of the SLN was followed by inhibition of ipsilateral phrenic nerve discharge with the latency of 9.5 +/- 2.3 ms (mean +/- S.D.) and hyperpolarizations of ipsilateral PMN membrane potentials (latency, 8.4 +/- 2.1 ms) which were observed after stimuli applied both during inspiration and expiration. During the injection of Cl ions, the hyperpolarizations were either reversed or flattened in all 28 tested PMNs, thus indicating a direct inhibition. The possibility that the inhibitory postsynaptic potentials are produced by segmental respiratory interneurones is discussed.