Liquid‐sensitive laryngeal receptors in the developing sheep, cat and monkey.

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Abstract
Action potentials were recorded from single afferent units of the superior laryngeal nerves in neonatal and adult sheep, cats and monkeys when liquids were passed over the laryngeal mucosa. Two types of mucosal receptors, sensitive to water but not to isotonic saline, were found in each species from birth. The most common type of unit responded after a short latency (< 1 s), discharged maximally in the first 1-3 s and became inactive when the stimulus was withdrawn. The other type responded only after several seconds, the discharges gradually increasing in frequency and continuing after removal of the stimulus. Reproducible responses were elicited by tactile stimulation of the laryngeal mucosa over the receptive field of each of the long-latency units. Fewer than 50% of the short-latency units were excited, the remainder responding only unreproducibly to firm pressure. Short-latency, but not long-latency, units responded to milk, gastric contents, saliva and isotonic solutions of sugars. The responses of long-latency units to water were often modified by, but rarely dependent on, reflexly evoked activity in laryngeal muscles. The conduction velocities of afferent fibers of water sensitive units ranged 22-49 m/s, and differed little from those of water-insensitive laryngeal mechanoreceptors. Histological examination of the laryngeal mucosa showed that taste buds were present in lambs from birth; they developed postnatally in kittens and monkeys. Taste buds were not associated with water-sensitive units.