Journal of Applied Physiology, Vol 78, Issue 6 2070-2078, Copyright © 1995 by American Physiological Society

ARTICLES

Role of vagal afferents in the acute ventilatory responses to inhaled wood smoke in rats

Y. R. Kou, C. Y. Wang and C. J. Lai
Institute of Physiology, School of Medicine and Life Science, National Yang-Ming University, Taipei, Taiwan, Republic of China.

Spontaneous inhalation of wood smoke (approximately 6 ml) via tracheostomy immediately evoked either a slowing of respiration (SR) or an augmented inspiration (AI) in each of the 76 anesthetized Sprague-Dawley rats studied. The SR was abolished after perineural capsaicin treatment of both cervical vagi (PCT; n = 20) but persisted during cooling of both vagi to 6.7 degrees C (VGC, n = 12); PCT selectively blocked the conduction of unmyelinated C fibers, whereas VGC differentially blocked the conduction of myelinated fibers. In contrast, the AI was eliminated during VGC (n = 10) but was unaffected by PCT (n = 5). Furthermore, after the SR was abolished in rats with PCT, an AI became the dominant immediate response to inhaled wood smoke. Conversely, after the AI was eliminated in rats receiving VGC, a SR was instantly evoked by inhaled wood smoke. Removal of smoke particulates did not affect the SR (n = 17) but did prevent the AI in 5 of the 12 rats studied. These results suggest the following: 1) the SR is a reflex resulting from stimulation of bronchopulmonary C-fiber nerve endings by the gas-phase smoke; 2) the AI results from excitation of lung irritant receptors by the gas-phase and/or smoke particulates; and 3) in intact animals, both types of vagal bronchopulmonary afferents are probably activated by inhaled wood smoke.

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