Swallow-related inhibition in laryngeal motoneurons.

Inhibitory postsynaptic potentials (IPSPs) of laryngeal motoneurons (LMs) are essential for narrowing the glottis at just the right time during swallowing, which prevents aspiration. To examine the property of IPSPs of LMs during swallowing, we monitored the effects of intracellular application of chloride ion and extracellular application of inhibitory neurotransmitter antagonists on the membrane potential trajectories of LMs during fictive swallowing in decerebrate, paralyzed cat. Adductor LMs hyperpolarized briefly at the beginning of the pharyngeal stage of swallowing (PS) and then depolarized explosively during the remaining part of the PS. Abductor LMs exhibited various patterns during swallowing; hyperpolarization during the PS followed by depolarization at the offset of the PS, slight depolarization, or plateau potentials. Chloride-dependent IPSPs were revealed during the initial part of PS in adductor LMs and during the whole PS in abductor LMs. The swallow-related IPSPs were depressed by iontophoretic extracellular application of bicuculline in both adductor and abductor LMs, but they were not modified by strychnine application. It is concluded that the swallow-related inhibition of both adductor and abductor LMs is chloride-dependent IPSPs mediated through GABA(A) receptors, not through glycine receptors.