Laryngeal cold receptors.

We have previously demonstrated the presence of specific laryngeal 'flow' receptors activated independently of transmural pressure. This study considers the operational characteristics of these endings. In 15 anesthetized dogs we recorded single unit action potentials from the peripheral cut end of the internal branch of the superior laryngeal nerve. All the 30 laryngeal 'flow' receptors studied showed an inspiratory modulation when the dog was breathing room air at 26 degrees C and 55% relative humidity (laryngeal temperature approximately equal to 34 degrees C) through the upper airway. All the receptors became silent when the temperature of the inspired air was raised to 36-40 degrees C, 100% relative humidity (laryngeal temperature between 35 and 38 degrees C) and increased their activity when the temperature in the larynx was decreased either by lowering the temperature or the humidity of the inspired air. Fourteen laryngeal 'flow' receptors were tested with a steady flow of air, directed through the isolated in vivo larynx, at different temperatures and saturated with water vapor. Their discharge rate was found to be inversely related to laryngeal temperature (from 35 to 25 degrees C) and independent of airflow. Their rate of adaptation indicates a high dynamic sensitivity. In the isolated larynx preparation these receptors were activated by airflow in both inspiratory and expiratory directions provided that laryngeal temperature was lower than 35 degrees C. We conclude that the previously described laryngeal 'flow' receptors operate as thermoreceptors activated by cooling.