Effects And Mediated Pathway Of Stimulations Of Area Postrema On Gastric Acid Secretion In Rats

The dorsal vagal complex (DVC) is composed of the dorsal motor nucleus of vagus (DMV), the nucleus of solitary tract (NTS) and the area postrema (AP). It is a parasympathetic preganglionic centre of gastric function. Other laboratories and our laboratory have reported the effects of stimulation of DMV and NTS on the gastric function in rats. But the effects of excitation of AP on gastric acid secretion have not been reported so far. In this study, we observed the effects of electrical stimulation and chemical stimulation of AP on gastric acid secretion and the action mechanism was probed.In the electrical stimulation experiments, BL-420 Biological Experimental System was used to give electrical stimulus. The stimulation parameters were: serial single stimulation, 30 Hz, 0.15 mA, 0.3 ms. The stimulation lasted for 5 min. After an interval of 5 min, the second stimulation was performed. The method of pylorus ligation was used to collect gastric juice. The pH value of the collected juice were measured by precision pH meter. The ECG and respiratory chart were recorded in the experiment. The results were as follows. Electrical stimulation of AP had no effects on the volumes of gastric juice, but gastric acidity had a marked increase. Electrical stimulation of AP increased respiration rate and inhibited heart rate.In the chemical stimulation experiments, 0.1μL of 0.01 mol/L, 0.1 mol/L and 1 mol/L L-Glutamine solutions were respectively microinjected into AP. 0.1μL of physiological saline was microinjected in the control group. The method of pylorus ligation and esophagus perfusion were used to collect gastric juice. The pH value of the collected juice were measured by precision pH meter. The ECG and respiratory chart were recorded in the experiment. The results were as follows. Chemical stimulation of AP had no effects on the volumes of gastric juice, but gastric acidity had a marked increase and L-Glu possessed dose-effect relationship on the promotion of acid secretion. Chemical stimulation of AP had no effects on both respiration rate and heart rate.The results mentioned above suggested that the excitation of AP promoted gastric acid secretion.The gastric acid secretion has significant decrease during chemical stimulation of AP after the vagus nerves beneath diaphragma were cut. The results showed that the promotive effects of AP on gastric acid secretion were withdrawn by the vagus nerves vagotomy beneath diaphragma. The results indicate that the efferent nerve pathway of AP promoting gastric acid secretion is vagus in rats.D-AP-5 is a NMDA receptor antagonist, pre-microinjection of D-AP-5 to AP effectively blocked the L-Glu response.The results suggest that L-Glu activation of area postrema neurons involves activation of NMDA receptors.