Inhibitory influence of lung vagal C-fiber afferents on the delayed ventilatory response to inhaled wood smoke in rats.
We studied the influences of lung vagal afferents on the delayed ventilatory response to inhaled wood smoke in 35 Sprague-Dawley rats. Wood smoke (approximately 6 ml) was inhaled via tracheostomy when animals breathed spontaneously. Immediately after inhalation, wood smoke evoked a slowing of respiration or an augmented inspiration, followed by a delayed tachypnea. Owing to the increase in respiratory frequency, the delayed ventilatory response usually resulted in an increase in minute ventilation (VI). The smoke-induced increase in VI was elevated after perineural capsaicin treatment of both cervical vagi (PCT, n = 12), but was unaltered during cooling of both vagi to 6.7 degrees C (VGC, n = 9); PCT selectively blocked the conduction of unmyelinated C-fibers, whereas VGC differentially blocked the conduction of myelinated fibers. Furthermore, the smoke-induced increase in VI after PCT was unaffected by an additional application of VGC (n = 12), whereas it was magnified by an additional application of PCT during VGC (n = 9). This magnification was not changed after a subsequent bilateral vagotomy (n = 21). Removal of smoke particulates did not affect the increase in VI evoked by smoke inhalation (n = 14). These results suggest that 1) the smoke-induced delayed ventilatory response is restrained by the inhibitory input from lung vagal C-fibers, whereas it was not influenced by the input from irritant receptors and 2) the gas phase of wood smoke is responsible for eliciting this delayed ventilatory response.
Wang
C Y
CY
Division of Basic Medical Science, Foo-Yin Junior College of Nursing and Medical Technology, Kaohsiung, Taiwan, R.O.C.
Lai
C J
CJ
Kou
Y R
YR
D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D002211:Capsaicin / Q000494:pharmacology; D005260:Female; D008297:Male; D009412:Nerve Fibers / Q000502:physiology*; D012123:Pulmonary Ventilation / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012906:Smoke; D014630:Vagus Nerve / Q000502:physiology*
D012906:Smoke; D002211:Capsaicin