Discharge of efferent vagal fibers supplying gastric antrum: indirect study by nerve suture technique.

Abstract

The unit activity of vagal efferent fibers suspected to be involved in the nervous control of gastric motility was studied on dogs in which the central end of the left vagus was sutured to the peripheral end of the left phrenic nerve. In such preparations, the activity of the motor units of the reinnervated diaphragm became an indicator of the activity of vagal efferent fibers. This activity was recorded using electromyography in unanesthetized dogs after part of the left diaphragm was transplanted to a subcutaneous site. These fibers fired spontaneously at low frequency (from 0.1 to 5 spikes/s). In the fasted dog, this discharge frequency fluctuated with the various phases of the migrating myoelectric complexes (MMC) occurring on the gastric antrum: mean frequencies of about 0.1-1.5 spikes/s during phase I; 1.5-5 spikes/s in phase III; intermediate values for phases II and IV. After feeding, the discharge frequency was as high as during phase III of a MMC, and this sustained activity lasted several hours. Vagal discharges were increased by distending the gastric walls and decreased by a slight general anesthesia or duodenal distension. Vagal fibers synapse with intramural neurons, which in turn excite smooth muscle of the gastric antrum.