| Restraint water-immersion stres(sRWIS; 21±1℃), considered to be a mixture of physical and psychological stressors, has very strong effect on body. It can induce lower body temperature, emotion change and gastric disfunction, which include vagally-mediated gastric hypercontractility, hypersecretion of gastric acid and acute gastric erosions.It is well known that stress can activate hypothalamus-pituitary-adrenocortical(HPA) axis,which change the functional state of organ system through a series of biological reactions,and keep steady-state. However, according to the former research, RWIS mainly induced the hyperactivity of the parasympathetic nervous system.Medulla is the primary centre of gastric function. The vagal parasympathetic neurons innervating the stomach are largely located in the dorsal motor nucleus of the vagus(DMV) and partly in the nucleus ambiguus(NA). The nucleus of solitary tract receive the sensory information from the stomach. Therefore, medulla is a nerve center which dominate gastrointestinal function directly. Hypothalamus is a higher nerve centre of gastric function. Research on morphology shows that Fos expression in medullary DMV, NTS and hypothalamic SON, PVN were enhanced markedly when stress ulcer were arisesed by RWIS. From above we see that enhanced activity of nerve centre of gastric function are closely associated with appearance of stress ulcer.Many studies show that there is a two-way connection of nerve fiber between PVN and DMV, so as PVN and NTS is similar. PVN and NTS are very important nuclei in preoptic region of hypothalamus.Magnocellular neurosecretory neurons distributed both in PVN and SON, and this kind of cell can secret vasopressin and oxytocin. The hormones released by PVN and SON were transported to neurohypophysis through paraventriculohypophyseal tract and supraopticohypophyseal tract respectively, and both of the two nuclei took part in the regulation of gastric function. Since PVN and medullary have close link, SON may have close fiber link with medullary. It has already been proved that there is nerve fiber contact between SON and NTS, but the situation is unhnow between SON and DMV.More and more studies show that stress can change the state of axonal transport and synapse, and in some cases, silent synapse can even be activated. While RWIS, as a powerful compound stress, whether has function to change neural pathway and leads to stress ulcer eventually?In the context of having solved the above problems and learned the effect of stress on neural pathway , we cut off the vagus nerve to block the feedback information of stress and dictate from nerve centre,then the approach to influence neural pathway of stress is decrease. under the state of RWIS,the Fos expression in medulla and hypothalamus is unknow.Aimed at the above questions, this research were divided into two parts。Part1:We applied retrograde tracing method of horse radish(HRP) to discuss two qustions. (1) If there is direct nerve fiber connection between SON and DMV? (2)If RWIS influence neural pathway in nerve centre of gastric function?Male Wistar rats were randomly divided into 2 groups designated according to suffering RWIS or not. In stress group, we inject HRP into DMV. After operation, rats were replaced in their home cages for 60 min before restraint water-immersion stress(RWIS)to recover consciousnes. Rats were then restrained and immersed in cold water(21±1℃) for 3 h. 48-60h after injection, the rat was anesthetized with pentobarbital sodium,and then was perfused quickly with buffer. Afterward, the brain was removed immediately and cryoprotected overnight in 20% sucrose in 0.1 mol/l PB at 4℃until sectioning. Histochemical detection of HRP were applied in sections. In control group, rats were operate in the same way as the above besides not suffering RWIS. We found: Cells labelled by HRP were found in SON; The number of cells labelled by HRP in stress group was more than that of control group(P <0.01);The amount of labelled cells in the PVN of the same side as jinjection site is larger than the opposite(P <0.01).These show that there is direct nerve fiber connection between SON and DMV; RWIS can change neural pathway between PVN and DMV; PVN have more nerve fiber project to the same side DMV.Part 2: In this part we applied immuno-histochemical methods to observe the Fos expression in medulla and hypothalamus under RWIS after bilateral subdiaphragamatic vagotomy. Since the operation can block the feedback information of stress, from Fos expression we can investigate the influence of this information on Information transfer across synapses. Male Wistar rats weighting 180-220 g were randomly divided into two groups: Operation group, Control group. Bilateral subdiaphragamatic vagotomy was performed in rats of operation group, the vagus were uncovered but were not cut off in control group. Six days after operation, rats were put into death after restraint water-immersion stress(3 h). The abdominal cavity temperature was measured, the gastric mucosal ulcer index was determined according to Guth criteria, and the immuno-histochemical methods were used to detect the Fos expression in medulla and hypothalamus. We found: Expression of Fos was decreased significantly in DMV, NTS and PVN after bilateral subdiaphragamatic vagotomy(P<0.05), and the decrease in AP was the most prominent (P<0.01); the abdominal cavity temperature was lower than that of the control group(P<0.05); the gastric mucosal ulcer index was reduced significantly(P<0.05). The results suggest that the feedback regulation information from the gastrointestinal tract, rather than lower body temperature and psychological stressor, play a dominant role in inducing the Fos expression in DMV, NTS, AP and PVN. Since Fos expression is a mark of neuronal excitability, combining the results of part 1,the results show that the transfer of information among medulla and hypothalamus tend to be weaker after the feedback information of stress were bated.
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