Effect of cold air on laryngeal mechanoreceptors in the dog.

We have previously described laryngeal receptors specifically activated by cooling. The aim of this study is to determine the effect of cold air on laryngeal mechanoreceptors responding primarily to transmural pressure and respiratory movements of the larynx. We have recorded action potentials from 30 single fibers in the peripheral cut end of the internal branch of the superior laryngeal nerve of 11 anesthetized, spontaneously breathing dogs. Of 29 receptors studied with a constant flow of cold air through the isolated upper airway 13 showed a marked reduction in their discharge (0 to 15% of control), 10 showed a moderate decrease (16 to 84% of control) and the remaining 6 were minimally affected. Seven of the 29 receptors showed, prior to the inhibition, a transient initial stimulation. Transient state responses of the most affected receptors lagged behind laryngeal temperature. Three of the most affected endings were also studied during spontaneous breathing of cold air; to a progressive decrease in laryngeal temperature corresponded a progressive decrease in receptor activity. Susceptibility of the receptors to laryngeal cooling and topical anesthesia did not closely correlate. Our results indicate that in evaluating the reflex responses to upper airway cooling both excitation of cold receptors and inhibition of laryngeal mechanoreceptors should be taken into account.