Inhibition of antral and pyloric electrical activity by vagal afferent stimulation in the rabbit.

The effects of stimulation of cervical vagal afferents on the electromyographic activity (e.m.g.) of the gastric antrum and pylorus have been studied both in conscious and decorticate, curarized rabbits. In the latter group, stimulation at 10-15 Hz (0.3-0.4 mA; 5-7 ms duration) inhibited both the antral and pyloric e.m.g. in 21 rabbits, elicited an excitatory response in two more but produced no change in the remaining 13 animals. The inhibitory response was not affected by guanethidine (1 mg/kg, i.v.), phentolamine (1 mg/kg, i.v.) or propranolol (0.1 mg/kg, i.v.) and persisted in rabbits in which the contralateral cervical vagus and both splanchnic nerves had been cut, the coeliac ganglia and both adrenal glands had been extirpated. It was only abolished by combined section of the spinal cord at the level of C1, C2 and the contralateral vagus in the neck. In conscious rabbits, vagal stimulation at 2-5 Hz (0.4 mA; 0.5-1.0 ms duration) consistently inhibited antral and pyloric e.m.g. This inhibitory response persisted in the presence of phentolamine, propranolol and naloxone (0.25-1.00 mg/kg), and in adrenalectomized rabbits with cut splanchnic nerves and extirpated coeliac ganglia. However, it was completely abolished by section of both vagi above the diaphragm. It is concluded that (1) the vagal afferents responsible for the inhibition of the gastric e.m.g. are already included in the abdominal vagus nerves, (2) this inhibition of gastric e.m.g. is mediated by non-adrenergic fibers, one group of them emerging from the thoracic spinal cord to join the thoracic vagi via the stellate ganglia.