Laryngeal exposure to wood smoke in rats evokes a reflex apnea which is mediated through superior laryngeal afferents (J. Appl. Physiol. 83: 723-730, 1997). To study the role of laryngeal C-fiber afferents in eliciting this response, capsaicin aerosol (0.05 - 0.2 microg/ml) and 5 ml of wood smoke were delivered separately into a functionally isolated larynx of anesthetized Sprague-Dawley rats at a constant flow rate of 1.4 ml/s, while animals breathed spontaneously. Studies were repeated after either an intravenous injection of ruthenium red (2 mg/kg; n = 8), a perineural capsaicin treatment (200 microg/ml for 5 min; n = 8) of the superior laryngeal nerves, or a perineural sham treatment (n = 8); Ruthenium red inhibits the stimulation of afferent C-fiber nerve endings by capsaicin, whereas perineural capsaicin treatment selective blocks the conduction of C-fiber afferents. Either ruthenium red or perineural capsaicin treatment abolished the apneic response to laryngeal capsaicin, but did not significantly affect the apneic response to laryngeal wood smoke. Furthermore, the apneic responses to both types of irritants were not significantly altered by perineural sham treatment, yet were completely eliminated by a subsequent denervation of superior laryngeal nerves. Our results suggest that superior laryngeal C-fiber afferents are not involved in eliciting the reflex apneic response to laryngeal wood smoke in anesthetized rats. It is speculated that this response may result mainly from the stimulation of myelinated afferents, possibly laryngeal irritant receptors.
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机译：大鼠喉部暴露于木烟中会引起反射性呼吸暂停，这是通过上喉部传入神经介导的（J. Appl。Physiol。83：723-730，1997）。为了研究喉C纤维传入者在引起这种反应中的作用，将辣椒素气雾剂（0.05-0.2微克/毫升）和5毫升木烟以恒定流速分别输送到功能分离的麻醉的Sprague-Dawley大鼠喉中1.4 ml / s的速度，而动物自发呼吸。静脉注射钌红（2 mg / kg; n = 8），经神经上辣椒素治疗（200 microg / ml 5分钟; n = 8），喉上神经，或神经鞘内假治疗，然后重复研究。 （n = 8）;钌红抑制辣椒素对传入C纤维神经末梢的刺激，而神经周辣椒素治疗选择性地阻止了C纤维传入的传导。钌红或会阴部辣椒素治疗均消除了对喉辣椒素的呼吸暂停反应，但并未显着影响对喉木烟的呼吸暂停反应。此外，对两种刺激物的呼吸暂停反应并没有通过神经假手术得到显着改变，但随后的上喉神经神经支配却被完全消除。我们的研究结果表明，在麻醉的大鼠中，上咽喉C纤维传入并不参与引起对喉木烟的反射性呼吸暂停反应。据推测，这种反应可能主要是由于髓鞘传入的刺激，可能是喉刺激性受体的刺激。
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