[Activity of vagal efferent fibres innervating the smooth muscle of the dog's cardia].

Our experiments were performed on dogs in which the central end of the left thoracic vagus had been sutured to the peripheral end of the left phrenic nerve. In such preparations, the activity of motor units of the re-innervated left hemidiaphragm indicated the activity of the vagal efferent fibres. After the left hemidiaphragm had been transformed into subcutaneous muscle, we studied, (using electromyography in the unanesthetized dog), the discharge of vagal fibres which originally supplied the lower oesophageal sphincter (cardia). The present paper only deals with fibres showing low frequency tonic discharge. 1. For some fibres (VIC type ; N = 42), the spontaneous firing rate (1.5 less than f less than 4.5 spikes/s) is suddenly enhanced just after the buccopharyngeal stage of swallowing (12 less than f less than 16 spikes/s). The this discharge stops abruptly just before the end of oesophageal peristalsis and starts again 2 to 3 seconds later at a low frequency (15 less than f less than 4.5 spikes/s). 2. Other fibres (VEC ; N = 18), which also have a slow discharge frequency (1 less than f less than 3 spikes/s) stop firing soon after the onset of swallowing and remain silent until the end of oesophageal peristalsis. At this time, i.e. when the bolus enters the stomach, the discharge starts again with an increased frequency (5 less than mean frequency less than 9 spikes/s). 3. The behaviour of the tonic vagal fibres during swallowing, as well as their low discharge frequency, strongly suggest that these fibres originally controlled the smooth muscle of the lower oesophageal sphincter and excited either an inhibitory (VIC = vagal inhibitory fibres of cardia) or an excitatory control (VEC = vagal excitatory fibres of cardia) upon this area.