Vagal motor neurons in rats respond to noxious and physiological gastrointestinal distention differentially

Low-pressure gastrointestinal distention modulates gastrointestinal function by a vago-vagal reflex. Noxious visceral distention, as seen in an obstruction of the gastrointestinal tract, causes abdominal pain, vomiting and affective changes. Using single neuron recording and intracellular injection techniques, we characterized the neuronal responses of neurons in the dorsal motor nucleus of the vagus (DMNV) to low- and high-pressure distensions of stomach and duodenum. Low-pressure gastric distention inhibited the mean activity of the DMNV neurons whereas high-pressure gastric distention excited many neurons. Of 47 DMNV neurons, low-pressure gastric distention inhibited 39, excited four, and did not affect four neurons. High-pressure gastric distention inhibited 26, excited 20, and left one unaffected. Thirteen of the 39 DMNV neurons inhibited by low-pressure distention of the stomach reversed their response to excitation during high-pressure gastric distention. Among 47 DMNV neurons, low-pressure duodenal distention inhibited 30, excited 10, and did not affect the remaining seven neurons. High-pressure distention of the duodenum inhibited 25 and excited 22 neurons. Eight DMNV neurons inhibited by low-pressure duodenal distention were excited in early response to high-pressure distention of the duodenum. High-pressure duodenal distention caused an early excitation and late inhibition in the mean activity of the DMNV neurons while low-pressure duodenal distention only produced late inhibition. These results suggest that different reflexes are present between physiological distention and noxious stimulation of gastrointestinal tract.