Reflex apneic response evoked by laryngeal exposure to wood smoke in rats: neural and chemical mechanisms

J Appl Physiol (1985). 1997 Sep;83(3):723-30. doi: 10.1152/jappl.1997.83.3.723.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Ammonia / toxicity
  • Anesthesia
  • Animals
  • Free Radical Scavengers / pharmacology
  • Laryngeal Nerves / physiopathology
  • Larynx / drug effects
  • Larynx / physiopathology*
  • Male
  • Rats
  • Rats, Sprague-Dawley
  • Recurrent Laryngeal Nerve / physiopathology
  • Reflex / drug effects
  • Reflex / physiology*
  • Sleep Apnea Syndromes / chemically induced
  • Sleep Apnea Syndromes / physiopathology*
  • Smoke / analysis*
  • Smoke Inhalation Injury / pathology
  • Smoke Inhalation Injury / physiopathology*
  • Thiourea / analogs & derivatives
  • Thiourea / pharmacology
  • Wood


  • Free Radical Scavengers
  • Smoke
  • Ammonia
  • 1,3-dimethylthiourea
  • Thiourea