| Heat stroke(HS)is a serious condition brought on by exposure to high temperatures,high humidity,or vigorous exercise.It causes a core temperature rise of ≥40.5°C and central nervous system dysfunction.According to the heat source,there are two types of HS: classic heat stroke(CHS)and exertional heat stroke(EHS).Extreme heat events are happening more frequently due to global climate change,endangering about one-third of humanity.EHS is more dangerous than CHS in terms of long-term neurological issues.Surprisingly,EHS is now the third-leading cause of death in sports.The incidence of heat stroke is gradually increasing in the army officers and soldiers.An epidemiological survey showed that the total incidence of HS in 3000 soldiers of an army brigade was 2.19%,and EHS was the main type,which greatly restricted the combat ability of the army.Therefore,to develop more effective clinical treatments for the condition,it is crucial to comprehend how heat stroke causes damage to the central nervous system.The Paraventricular Nucleus(PVN)is a vital and vulnerable region of the Central Nervous System.Small cell neurons in PVN are vulnerable to damage after heat stress exposure,leading to decreased heat tolerance and impaired thermoregulation.The prognosis of an individual may be significantly impacted by these consequences.According to studies,heat stress can cause the apoptotic of hypothalamic neuronal cells,resembling the pathology of ischemic-hypoxic brain disease.Yet,it has been discovered that promoting autophagy improves the survival of neurons in areas of the brain damaged by ischemic-hypoxic injury.Rapamycin has been demonstrated in studies to be able to reduce neuronal damage by increasing and regulating the mTOR pathway.Its potential significance in ischemic-hypoxic brain disorders and Parkinson’s disease has been researched.However,there has been limited research on the impact of Rapa on hypothalamic neuronal damage caused by EHS.Therefore,looking into how Rapa affects EHS and hypothalamic autophagy is essential.By doing so,we will better comprehend the mechanisms underlying the central nervous system damage in EHS and gain new ideas on preventing and treating the condition.To achieve this,we will establish an EHS rat model.We will assess the effects of Rapa on survival rate,pathology of the hypothalamus,serum indicators of brain tissue damage,and neuronal dysfunction by carefully measuring levels of neuron-specific enolase(NSE)and brain-derived peptide 100(S100β),inflammatory cytokines IL-6 and TNF-α,hypothalamic neuronal apoptosis,and mitochondrial autophagy.The main objective of this investigation is to investigate potential mechanisms underlying Rapa’s protective effects on hypothalamic neurons in EHS rats.We randomly divided 80 male Wistar rats into four groups and conducted a study.There were four groups,each consisting of 20 rats:the standard control group(CON),the regular control group supplemented with rapamycin(CON+Rapa),the exertional heat stroke group(EHS),and the exertional heat stroke group treated with rapamycin(EHS+Rapa).Before establishing the exertional heat stroke model(which simulates a high-temperature and high-humidity environment),all rats underwent a 7-day treadmill acclimation training.For four days before modeling,rapa(1 mg/kg,once daily)was continuously injected intraperitoneally into the CON+Rapa and EHS+Rapa groups of rats.The 0.9% saline solution dosage was the same for the CON and EHS groups.To simulate extreme heat and humidity,we established a rat model for EHS.Draw a survival curve for the 80 rats(11 from each group,chosen randomly)and note their general health,including their mental state,hair luster,respiratory condition,and activity level.Blood from the abdominal aorta,and tissues including the hypothalamus,were removed after anesthetic collection.We used the ELISA technique to determine the arterial serum expression levels of NSE,S100 β protein,TNF-α,and IL-6.The study examines macroscopic morphological changes in the tissue of various rat groups’ hypothalamus,such as size,shape,color,luster,congestion,and swelling.Apoptotic changes will be identified using the one-step TUNEL method,and we will also assess histopathological changes in hypothalamic tissue using HE and Nissl staining.The mammalian target of rapamycin(mTOR)and its phosphorylated form(pmTOR),as well as the expression of Beclin-1,p62,and the microtubule-associated protein one light chain 3(LC3),were all examined using the Western blot technique as indicators of autophagy in the rat hypothalamic tissue.Additionally,we determined the LC3-II/LC3-I and pmTOR/mTOR ratios.The survival rate of the rats in the EHS+Rapa group was significantly higher than that of the EHS group(P<0.05).On the other hand,rats in the EHS group displayed a worse overall state,with clearly enlarged,spherical,and dark-colored hypothalamic tissue that expanded noticeably on both sides.However,the hypothalamic tissue swelling was significantly reduced in the EHS+Rapa group,and the surface color and appearance of this group resembled that of the CON group,appearing light pink.The pathological staining showed that the EHS group of rats had more severe hypothalamic neuronal pathology than the CON group.Numerous neuronal cell bodies saw deep staining,shrinkage,and glial cell proliferation.The resulting score was [(3.83±0.41 vs 1.17±0.41,P<0.05)].However,in the EHS+Rapa group,there was a significant decline in hypothalamic neurons,accompanied by a slight uptick in glial cell proliferation and a decrease in the signs of deep staining and shrinkage of the neuron cell body.The resulting score was[(2.5 ± 0.55,P<0.05)].Nissl bodies vanished from the hypothalamic neurons of the EHS group rats when we used the Nissl staining method to compare them to the CON group.The neuronal cell bodies also exhibited nuclear shrinkage and intense staining.On the other hand,the hypothalamic neurons’ Nissl bodies were visible in the EHS+Rapa group of rats,alleviating the signs of nuclear shrinkage and deep staining in the neuronal cell bodies.In the EHS group of rats compared to the CON group,the immunofluorescence results showed a noticeably higher number of apoptotic cells and an apoptotic index(P<0.05).As opposed to what was seen in the EHS group,the EHS+Rapa group’s hypothalamus had fewer apoptotic cells and a lower apoptotic index(P<0.05).According to the ELISA results,the serum from the EHS group had significant levels of NSE,S100β protein,and TNF-αexpression(P<0.05).However,there was no significant difference in the expression level of IL-6 in serum of EHS group(P>0.05).The expression levels of NSE,S100β protein,IL-6,and TNF-α in the serum of the EHS+Rapa group were significantly lower than those of the EHS group(P<0.05).The ratio of pmTOR/mTOR in the hypothalamus of rats in the EHS group was significantly higher than that in the CON group,according to the results of a Western blot analysis(1.03±0.01 vs0.09±0.03,P<0.05).The pmTOR/mTOR ratio was significantly lower(0.53±0.02,P<0.05)in the EHS+Rapa group.In the hypothalamic tissue of rats in the EHS group compared to the CON group,the LC3-II/LC3-I ratio was significantly higher(3.74±0.44 vs 1.65±0.01,P<0.05).Additionally,the EHS group rats’ expression levels of p62 were significantly lower(0.49 vs 0.76,P<0.05)than those of Beclin-1(0.75 vs 0.43,P<0.05),which was also considerably higher.While the expression level of p62 significantly decreased(0.29±0.01,P<0.05),the LC3-II/LC3-I ratio(14.94±0.92,P<0.05)and Beclin-1 expression level(1.12±0.02,P<0.05)increased in the EHS+Rapa group of rats.In conclusion,exertional heat stroke can cause hypothalamic enlargement and congestion,neuronal shrinkage,and dark staining in the tissue.Rapamycin can improve brain function,lower levels of inflammatory factors,and lower tissue cell apoptosis.It can also lessen the damage exertional heat stroke causes to hypothalamic neurons.The increase in autophagy levels within hypothalamic neurons can be attributed to the inhibition of the mTOR signaling pathway. |
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