Reflex apneic response evoked by laryngeal exposure to wood smoke in rats: neural and chemical mechanisms.
We investigated the neural and chemical mechanisms contributing to the immediate ventilatory responses to laryngeal exposure to wood smoke in anesthetized Sprague-Dawley rats. Five milliliters of wood smoke were delivered into a functionally isolated larynx at a constant flow rate of 1.4 ml/s while the animals breathed spontaneously. Within 1 s after exposure, laryngeal wood smoke consistently triggered an apnea in each of the 42 rats tested. The apneic duration reached 1,636.4 +/- 105.4 (SE) % (n = 42) of the baseline expiratory duration. This apneic response was not affected by denervation of recurrent laryngeal nerves (n = 6) or by removal of smoke particulates (n = 14), but it was totally eliminated by topical application of an anesthetic (n = 8; lidocaine hydrochloride, 8%) to the laryngeal mucosa or by sectioning of the superior laryngeal nerves (n = 42). Furthermore, laryngeal application of a hydroxyl radical scavenger (dimethylthiourea; 500 mg/ml; n = 8) greatly diminished or abolished the smoke-induced apneic response, but it did not affect the apneic response evoked by laryngeal exposure to air saturated with 6% ammonia. These results suggest that the immediate apneic response to laryngeal wood smoke is a reflex resulting from the stimulation of the superior laryngeal afferents by the gas phase of wood smoke and that the stimulation is mediated through a hydroxyl radical mechanism.
Lin
Y S
YS
Institute of Physiology, School of Medicine and Life Science, National Yang-Ming University, Taipei, Taiwan 11221, Republic of China.
Kou
Y R
YR
D000641:Ammonia / Q000633:toxicity; D000758:Anesthesia; D000818:Animals; D016166:Free Radical Scavengers / Q000494:pharmacology; D007823:Laryngeal Nerves / Q000503:physiopathology; D007830:Larynx / Q000187:drug effects / Q000503:physiopathology*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D012009:Recurrent Laryngeal Nerve / Q000503:physiopathology; D012018:Reflex / Q000187:drug effects / Q000502:physiology*; D012891:Sleep Apnea Syndromes / Q000139:chemically induced / Q000503:physiopathology*; D012906:Smoke / Q000032:analysis*; D015208:Smoke Inhalation Injury / Q000473:pathology / Q000503:physiopathology*; D013890:Thiourea / Q000031:analogs & derivatives / Q000494:pharmacology; D014934:Wood
D016166:Free Radical Scavengers; D012906:Smoke; D000641:Ammonia; C038983:1,3-dimethylthiourea; D013890:Thiourea