Canine oesophageal mechanoreceptors.

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Abstract
The properties of slowly adapting esophageal mechanoreceptors were determined in anesthetized dogs in which the esophagus had been isolated surgically. Changes in esophageal pressure resulted in reproducible changes in esophageal volume. Action potentials were recorded from 33 esophageal afferent nerve fibers in the cervical vagus. All the receptors were located in the thoracic esophagus. The conduction velocities of the afferent fibers ranged from 9.3 to 27.7 m/s (mean, 17.2; SD, 4.1). The receptors were of the in series type. In the pressure range of 0-1 mm Hg, all units were tonically active with irregular firing rates that ranged from 0.2 to 13.0 Hz. Lung inflation altered the discharge rate in a variable manner depending upon the degree of distension of the esophagus. The adapted discharge rate of 8 units reached a maximum of 23-44 Hz (mean, 35; SD, 8) at an esophageal pressure of 8-15 mm Hg (mean, 11; SD, 3). The relationship between pressure and discharge rate was linear over a narrow pressure range. Ramps of similar gradient produced higher discharge rates in units whose afferent fibers had higher conduction velocities. In some units a large increase in firing rate occurred over a narrow pressure range and became more pronounced with ramps of increasing gradient. This increase in firing rate was called a burst. Six of 33 units showed a burst response. The conduction velocities of these 6 units ranged from 18.7 to 23.5 m/s. Slowly adapting esophageal mechanoreceptors could be subdivided functionally into 2 types. Their discharge pattern was dominated by a narrow response range. These properties may be significant in an organ that is normally empty and has a low residual volume.