Canine oesophageal mechanoreceptors.

The properties of slowly adapting oesophageal mechanoreceptors were determined in anaesthetized dogs in which the oesophagus had been isolated surgically. Changes in oesophageal pressure resulted in reproducible changes in oesophageal volume. Action potentials were recorded from thirty-three oesophageal afferent nerve fibres in the cervical vagus. All the receptors were located in the thoracic oesophagus. The conduction velocities of the afferent fibres ranged from 9.3 to 27.7 m/s (mean, 17.2; S.D., 4.1). The receptors were of the 'in series' type. In the pressure range of 0-1 mmHg, 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 oesophagus. The adapted discharge rate of eight units reached a maximum of 23-44 Hz (mean, 35; S.D., 8) at an oesophageal pressure of 8-15 mmHg (mean, 11; S.D., 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 fibres 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 out of thirty-three units showed a 'burst' response. The conduction velocities of these six units ranged from 18.7 to 23.5 m/s. Slowly adapting oesophageal mechanoreceptors could be subdivided functionally into two 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.