Electrophysiological and pharmacological properties of inhibitory postsynaptic potentials evoked in laryngeal motoneurons in decerebrate cats

Abstract

Electrophysiological and pharmacological properties of inhibitory postsynaptic potentials (IPSPs) induced in respiratory laryngeal motoneurons (LMNs) by electrical stimulation of the superior laryngeal nerve were investigated in decerebrate, paralyzed, vagotomized and artificially ventilated cats. In the inspiratory phase, a single pulse stimulation caused a short latency excitation followed by long-lasting inhibition of phrenic nerve discharge. A long latency wave of IPSPs occurred in inspiratory LMNs. In the expiratory phase, the same stimulation provoked a transient excitation in the phrenic nerve. An IPSP wave of long latency was induced in post-inspiratory LMNs. The time course of each long latency IPSP wave corresponded to that of either inspiratory inhibition of expiratory excitation of the phrenic discharge. These IPSP waves induced in both types of LMNs were decreased in amplitude by iontophoresed bicuculline but not by strychnine. These results suggest that laryngeally evoked IPSP waves in inspiratory and post-inspiratory LMNs are mediated through poly-synaptic pathways within the central respiratory network and the GABA(A)-receptors are involved in their final pathway.