Effects of stimulation of nucleus ambiguus complex on gastroduodenal function

We investigated the effects of stimulation of the nucleus ambiguus (NA) complex on gastroduodenal motility and gastric secretion in alpha-chloralose-anesthetized cats. Motility was measured by use of extraluminal force transducers sutured to the body, antrum, pylorus, and duodenum. Secretion was measured by determining changes in gastric pH, titratable acidity, and pepsinogen activity. Stimulation of the NA complex (right NA in 11 animals and left NA in 8 animals) elicited contractions of the antrum, pylorus, and duodenum, as well as sinus bradycardia and hypotension using stimulus parameters of 133 microA, 50 Hz, and 0.2-ms pulse duration. Both the motility and cardiovascular responses evoked by electrical stimulation of the NA complex were prevented by ipsilateral vagotomy. The optimum stimulus frequency for eliciting increases in gastroduodenal motility was 50 Hz. Frequencies higher than 50 Hz resulted in attenuated motility responses. This was not true of the heart rate response, as sinus bradycardia was maximal at 10 Hz and was maintained to 100 Hz. Electrical stimulation of the NA complex (8 animals) had no effect on pepsinogen secretion or titratable acidity, but produced a small (0.21 pH units) but significant increase in gastric pH. These results indicate that 1) stimulation of the NA complex results in pronounced increases in motility mediated by the ipsilateral vagus nerve, and 2) the pathways mediating these motility responses appear to involve more synapses than the pathways mediating the motor responses to the heart.