Rimarystudyonthe Mechanism Of Acute Hypoxia Induced Inappetence In Rats

Many studies reported a loss of body mass during people from plain living migrated to plateau.Loss body mass during high-altitude sojours is largely caused by decreased food intake.Appetite and weight loss induced by migrating to plateau may weaken their working capacity.Hence,study on the mechanism of plateau environment induced appetite loss would help to explore effective solutions and improve the working efficiency of plateau people from plain living.Multiple neural circuits in the brain have evolved to process information about food intake,central nervous system(CNS)played the most important regulator role in the food intake behavior,it produced a sense of hunger based on the energy demand of body,meanwhile obtained the information about food availability and palatability is transmitted into the brain by taste,smell and visual through polymodal sensory pathways than stimulate feeding behavior.During food consumption,food components stimulates secretion of polypeptide hormones form gastrointestinal enteroendocrine cells,these hormones function as satiety signals to trigger satiation and stop to eat to keep the metabolism of energy balanced.Hypothalamus is the most key brain area that regulates food intake and body weight,moreover CNS is very sensitive to hypoxia,therefore we deduced that hypoxia inhibit the regulation of appetite by hypothalamus,and induced a poor appetite in altitude.The cannabinoid type 1 receptor(CB1)is widely expressed in the hypothalamus,associated with the regulation of appetite and body weight.The CB1 receptor is expressed on axon terminals of a variety of neural populations,activation of the CB1 receptor with endocannabinoid signaling results postsynaptic depolarization of neurons to regulate both excitatory and inhibitory transmitter including glutamatergic,GABArgic,and monoaminergic release.Activation of the CB1 receptors shows increases food intake.Blockade of CB1 receptor decreased ghrelin secretion by activating the mamamlian target of rapamycin(mTOR)pathway.mTOR is highly conserved serine/threonine protein kinase.mTOR signaling pathway thus functions as a checkpoint by which cells sense and decode change in energy status and substrate,which in turn determines the rate of protein biosynthesis.Study showed the activation of the mTOR pathway in arcuate nucleus(ARC)suppresses food intake.We speculate that hypoxia might directly or regulated by mTOR pathway inhibiting the CB1 receptor in the hypothalamus.This study assessed the affection of hypoxia on the food intake of rats by compare the food intake of rats in plain and plateau simulated environment.Observing the expression of CB1 receptor and mTOR of rats in plain and plateau simulated environment,which was the food intake metabolism related receptor in hypothalamus,to explore the mechanism of acute hypoxia induced appetite loss.MethodThe rats assigned into three groups by random number table: control group,rats were raised in plain environment;hypoxia 1-day group and hypoxia 7-days group,rats were raised in 5000 m hypobaric chamber for 1 day or 7days and All rats were raise according to laboratory principles separately.The weight of rats and intake food were recorded every day,and hypothalamus were collected on the terminated day of experiment.Western blot and immune-histochemical were used to analysis the protein expression of CB1 receptor and c-Fos.And assigned the rats into two groups by random number table: control group or hypoxia group,after both group rats were fasted 12 h in plain environment,control group exposed in plain environment and hypoxia group were exposed in 5000 m hypobaric chamber keep faseted for 24 h and than the rats were re-fed,animals were measures of food intake in 12 h.Repeat the assigned group,but the animals without the food,control group were sacrificed in plain environment,hypoxia 24 h group were sacrificed in 5000 m hypobaric chamber for 6h,hypothalamus were collected on the terminated time of experiment.Western blot were used to analysis the protein expression of mTOR and downstream target of mTOR action.And assigned the rats into two groups by random number table: hypoxia group and rapamycin group,both group rats were fasted 12 h in plain environment,and rapamycin group were intracerebroventricular administration of mTOR inhibitor rapamycin,DMSO group were intracerebroventricular administration of same amount of solvent.Two group were exposed in 5000 m hypobaric chamber and re-fed,animals were measures of food intake in 24 h.Repeat the assigned group,but the animals without the food,two group were sacrificed in 5000 m hypobaric chamber for 6h,hypothalamus were collected on the terminated time of experiment.Western blot were used to analysis the protein expression of mTOR and downstream target of mTOR action.Result1.after 1 day acute hypoxia,rats in hypoxia groups had a lower food intake(4.9±0.7g)than control group(15.5±2.7g).Food intake was increased with the hypoxia tolerant time,until 3~7days,it recover to a normal level as control group.After acute hypoxia,rats in hypoxia groups had a significant weight loss,on the second day it had the lowest weight.Then weight increased with time,but still lower than control group.2.After 1 day acute hypoxia,western blot analysis shows that the expression of CB1 receptor and c-Fos was lower than control group,but on the 7th day of hypoxia,there was no significant difference between hypoxia 7-day group and control group.Immune-histochemical analysis shows that CB1 receptor and c-Fos expressed in ARC,later hypothalamic area(LH)and ventromedial hypothalamic nucleus(VMH)in hypoxia 1-day group were lower than control group,the level of these proteins were increased with the hypoxia tolerant time,and regain the control group level on the 7th day.3.After 30 h hypoxia,western blot analysis shows that the expression of mTOR was increased than control group,and had a lower food intake.After central administration of mTOR inhibitor rapamycin,Western blot analysis shows that the expression of mTOR of rapamycin group was decreased than hypoxia group,and had more food intake(rapamycin group:24.0±1.6g vs DMSO group:6.9±1.7g).Conclusion1.Weight loss significant in the hypoxia group was related to the less food intake when suffered from acute hypoxia.2.Acute hypoxia would induce the expression decrease of CB1 receptor and c-Fos in ARC,LH and VMH,but the expression level regained after a long term hypoxia tolerance.The variation tendency of CB1 and c-Fos expression level was synchronized with the food intake level,it indicated that lower food intake in rats was induced by a lower level of CB1 receptor and c-Fos protein when suffered acute hypoxia.3.Acute hypoxia would induce the expression increase of mTOR in the hypothalamus.Intracerebroventricular administration of mTOR inhibitor rapamycin inhibited hypothalamic mTOR and the downstream target and increased the food intake,it indicated that mTOR pathway activity has linked to the lower food intake in rats when suffered acute hypoxia.