| We previously used the Restraint Water-Immersion Stress (RWIS)model in rats to study the neuronal pathways activated during the RWIS. After different durations of RWIS, neuronal activation, demonstrated by Fos-immunoreactivity (Fos-IR), was found significantly increased in specific brain areas, such as the medullary visceral zone [mainly dorsal motor nucleus of the vagus (DMV), nucleus of solitary tract (NTS), area postrema (AP), and nucleus ambiguus(NA)] and the hypothalamus [mainly supraoptic nucleus (SON) and paraventricular nucleus (PVN)]. Among which DMV and SON neuronal activities degree were the most. Whether the vasopressinergic pathway from the PVN/SON to the DMV plays a role in regulating the gastric function? To clarify the question, the aim of the present study was to investigate the effect of arginine-vasopressin (AVP) microinjected into the DMV on gastric motor and secretory functions.The study was divided into three parts.Experiment 1, to investigate the effect of AVP in DMV on gastric motility.(1) Two doses (0.018 nmol and 0.18 nmol) of AVP (0.2μL) were microinjected into the DMV to investigate the effect of AVP.(2) Control experiment. Normal saline (0.2μL ) was microinjected into the DMV .Experiment 2, to investigate the mechanism involved in the effect of AVP on regulating the gastric motility.Two groups of rats with six in each were pretreated with SR49059 (0.32 nmol in 0.2μL into DMV) 15min or hexamethonium (8μmol in 1ml,i.v. ) 30min before the AVP was administrated.Experiment 3, to investigate the effect of AVP in DMV on gastric acid secretion,.(1) AVP (0.18 nmol in 0.2μL) was microinjected into the DMV to investigate the effect of AVP .(2) Control experiment. Normal saline (0.2μL) was microinjected into the DMV. A latex balloon connected with a pressure transducer was inserted into the pylorus to record the gastric motility. Gastric acid output was collected every 20 min after saline flush with the method of esophageal perfusion, the pH value of the collected juice was measured by precision pH meter.The blood pressure, electrocardiogram and respiration of the rats were continuously monitored by the BL-420 Biological Experimental System.Microinjection of AVP (0.018nmol and 0.18nmol in 0.2μL) microinjected into right DMV significantly inhibited the gastric motility. The inhibitory motility effect of AVP (0.18μmol in 0.2μL) was completely blocked by SR49059 (0.32nmol in 0.2μL), the specific AVP V1a receptor antagonist, and abolished by hexamethonium (8μmol in 1ml, i.v.), the neuronal nicotinic cholinergic receptor antagonist.Conclusion: These results indicated that, AVP inhibited the gastric motility and excited the acid secretion by activating the specific V1a AVP receptors in DMV, and the cholinergic neuron pathway may be involved. |
