| Histogenesis defined that the nucleus ambiguus (NA) and the dorsal motor nucleus of vagus (DMV) were located together in the embryo and took apart with the generation development in the vertebrate. NA and DMV are both the important visceral motor nucleus, and morphologic studies show that the fibers that sending from NA and DMV are located in the stomach, the heart and other viscera. Then, what differences are there in the physiological functions of NA and DMV? Comparatively, we investigated the effects of electrical stimulation of NA and DMV on gastric acid secretion, bicarbonate secretion, respiration and heart rate in urethane-anesthetized male rats.1. Studies on the NA. The rats were placed in a Jiangwan Type I stereotaxic apparatus. The dorsal surface of the brain stem was exposed by limited occipital craniotomy. According to the coordination of the NA as defined by the atlas of Paxinos and Watson, an electrode, whose diameter is 40-60 u m, was inserted vertically into the right or left side of the brain stem at a level 12.7 mm caudal to Bregma and 2.0 mm lateral to the midline, and to a depth of 9.6 mm below the dorsal surface. Stimulus parameters were 0.1 mA, 40 Hz, 0.3 ms and the stimulus duration was 10 min. The ECG and respiratory chart were recorded in the experiment. Gastric contents were collected with two methods, pylorus ligation and esophagus perfusion. Secretion was measured by determining changes in gastric volumes, titratable acidity, acid concentration and total bicarbonate. At the end of the experiments, the brain was stimulated by 1 mA direct current for 15 s. 0.9% sodium chloride and 1% potassium ferrocyanide were injected respectively into the aorta and then outflowed from the right atrium to identify the isolated iron ion coming from the top of electrode. And the brain was removed and fixed in a 10% Formalin solution for 2-3 days. Then the brains were sectioned at 40 u m on a freezing microtome, and stained with neutral red. Histological sections were examined microscopically. The site of the stimulus was blue and marked on plates represented from the atlas of Paxinos and Matson. Only the results that the tips of the . stimulus electrode were within the NA were used for statistical analysis.2. Studies on the DMV. In order to compare the functions of NA with those of DMV, we also studied the effects of electrical stimulation of DMV on gastric acid secretion, bicarbonate secretion, respiration and heart rate in urethane-anesthetized male rats. All the conditions were the same as the above, except that the electrode was inserted vertically into the right or left side of the brain stem at a level 13.8 mm caudal to Bregma and 0.7 mm lateral to the midline, and to a depth of 8.3 mm below the dorsal surface, and the method of pylorus ligation was used.The results were as follows. Electrical stimulation of NA had no effects on gastric volumes, titratable acidity, acid concentration, but elicited a badly pronounced increase in the total bicarbonate, as well as restraining of respiration and inducing sinus bradycardia. But electrical stimulation of DMV produced a badly significant increase in titratable acidity, and pronounced an evident increases in gastric volumes and acid concentration, as well as restraining respiration and inducing sinus bradycardia. These results indicate that (1) stimulation of NA results in a pronounced increase in the total bicarbonate secretion, comparatively, no change in gastric acid secretion, and (2) stimulation of DMV produced a significant increase in gastric acid secretion, but no change in total bicarbonate secretion, and (3) the fibers that send from NA and DMV and are located in the stomach innervate different cells, NA innervate the nonacid-secreting cells and DMV innervate the acid-secreting cells, that is the perietal cells, and (4) the parasympathetic preganglionic neurons coming from both NA and DMV innervate the heart, and respiratory organs, whose excitation inhibits the heart rate and respiratory frequency. These studies play an important role in e...
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