Effects of antitussive drugs on the activity of the recurrent laryngeal nerve in cats.

Reflex responses in the recurrent laryngeal (RL) nerve to stimulation of superior laryngeal (SL) nerve and the effects of antitussive drugs on these reflex responses were studied in order to elucidate the site of action of these drugs in encéphale isolé cats. The RL nerve fibers were classified into four types by discharge patterns in respect to phases of artificial ventilation; type I: no spontaneous discharges, type II: discharges in phase with inflation of the lung, type III: discharges in phase with deflation of the lung, type IV: tonic discharges. Repetitive stimulation of the SL nerve elicited tonic burst discharges or short burst discharges in all types of RL nerve elicited tonic burst discharges or short burts discharges in all types of RL nerve, while the same procedure inhibited ongoing discharges of the type III and IV fibers only. The inhibited fibers tended to have slow conduction velocities (20-80 m/sec). Administration of antitussive drugs such as codeine, dextro methorphan and oxymetebanol as well as pentobarbital decreased the frequency of the after spike discharges in the RL nerves evoked following repetitive shocks to the SL nerve, but had no effects on the inhibition of RL nerve discharges evoked by the stimulation of the same nerve. The neuropharmacological implication of these findings as related to the cough reflex are discussed.