Specific effects of thoracic vagotomy on the electrical activity of the gastric antrum and pylorus in rabbits.

The electrical activity of the antrum and the pylorus was recorded in rabbits, with chronically implanted electrodes. Effects of food intake were studied before and after bilateral vagotomy (b.v.), ventral vagotomy (v.v.) or dorsal vagotomy (d.v.) performed just above the diaphragm. In fasted animals, the electrical activity was characterized by bursts of potentials at a frequency of 1.93 +/- 0.09/min, initiated 45 mm or 20 mm from the pylorus in the greater and the lesser curvature respectively. The velocity of propagation of the bursts increased from 5-6 mm/s in the proximal antrum to 12-25 mm/s in the last 10 mm of the antrum along the greater curvature and from 2-4 mm/s to 5-15 mm/s along the lesser curvature. Feeding led to a rapid increase in the frequency of both antral and pyloric bursts up to 4.01 +/- 0.10/min, lasting 30-60 min after a large meal but only 15 min when the amount of food was restricted. The behaviour of the rabbits was not significantly affected by bilateral or ventral vagotomy. In contrast, dorsal vagotomy resulted in a drastic decrease of food intake. The mean frequency (fo) of bursts before meals was significantly reduced after vagotomy in v.v. animals (1.49 +/- 0.11/min, P less than 0.02) and in d.v. animals (1.34 +/- 0.08/min, P less than 0.001) but not in b.v. or sham-operated rabbits. For the first 3 d after surgery, the frequency (f) of bursts during the 30 min after the beginning of meals was significantly different from fo and reduced relative to f before nerve sections (1.9 +/- 0.11/min and 2.32 +/- 0.20/min respectively in b.v. and v.v. animals). In sham-operated animals, the value of f was closely similar to f before surgery. The effects of meals on the frequency of bursts were again similar to the effects in intact animals within 4-6 d for v.v. animals and 6-9 d for b.v. animals. In the pylorus, a different pattern for electrical activity, which consisted of trains of spikes at a frequency of 0.3/s, was superimposed on the bursts and was most marked in d.v. animals. The spiking activity was not affected by atropine, phentolamine or propranolol. The role of the vagus nerve in the motile responses of the antrum to food intake is discussed. These results indicate the existence of a non-cholinergic, non-adrenergic innervation of the pylorus which is involved in the opening of the sphincter and appears to be mediated by the dorsal vagal trunk.