| ObjectiveIn this study,we established the young rat model of chronic intermittent hypoxia and chronic persistent hypoxia to explore the effects of different hypoxia on the expression of HIF-1α and BDNF,the hippocampal morphology and cognitive function of young Wistar rats and its possible mechanism.MethodsExperiments were performed on 24(20±2)days of male Wistar rats,they were randomly divided into 3 groups:normal control group(NC)group,chronic intermittent hypoxia(CIH)group and chronic sustained hypoxia(CSH)group.Rats in NC group were raised normally,those in CIH group suffered 8H intermittent hypoxia and others in CSH group suffered 8H sustained hypoxia,the duration of experiment was 30 days.The body weight was recorded and the growth and development were observed of rats in each groups at the end of experiment.The spatial learning and memory abilities of rats were assessed with Morris water maze.The levels of serum HIF-1α and BDNF were detected by ELISA.The morphological changes were observed by HE staining and Nissl staining,and the ultrastructure of hippocampal CA1 neurons was observed by electron microscope.Results1.Growth and development of ratsRats in NC group have good mental condition,hair bright,action freely,quick response.CSH group and CIH group were wasted,apathetic,lethargy,dull or sparse hair,slow action and response.The weight of NC group[(218.63 ±15.287)g]was significantly higher than that of CIH group[(195.75±6.497)g]and CSH group[(180.88±12.017)g],P<0.05.2.Morris water maze experiment2.1 Positioning navigation experiment After 4 days of training,the escape latency of rats in different days in the three groups were significant difference(F=64.18,P<0.05),and that in CIH group and CSH group were significant difference(P<0.05).The escape latency time was shortened gradually in NC group,CIH group and CSH group with the increase of training time and frequency(F=54.355,P<0.05;F=109.809,P<0.05;F=272.514,P<0.05).There were significant deviation of escape latency time in the three groups on dayl-2(F =19.248,P<0.05;F=5.021,P<0.05).There were no significant deviation of escape latency time in the three groups on day3-4(F =0.706,P>0.05;F =0.219,P>0.05).2.2 Space exploration experiment There were significant differences in the frequency of crossing the platform between the three groups(F =8.913,P<0.05),but there was no significant difference between CIH group and CSH group(P>0.05).3.The expression of Serum HIF-1α,BDNF levelsThe levels of serum HIF-1 a and BDNF were significantly different between the three groups(F=19.524,P<0.05)and(F=8.552,P<0.05).The expression of HIF-1 a and BDNF in CIH group and CSH group was significantly higher than that in NC group(P<0.05),while the expression of HIF-1α and BDNF in CIH group was higher than that in CSH group,the difference was statistically significant(P<0.05).There was no significant correlation between HIF-1αand BDNF in the three groups(P>0.05).4.Morphological changes of hippocampal neurons4.1 HE staining The cells of the hippocampal CA1 region in NC group were intact and neat,well arranged,morphological rules,and clear nuclei.The cells in the CSH group and CIH group were scatter,disorder,a small amount of nuclear pyknosis and appeared early necrosis of cytoplasmic.The cells of CIH group were partial loss and the number of living cells were decreased.4.2 Nissl stainingCA1 region The hippocampal cells in the NC group arranged closely,the nucleus is clear,rich in nissl bodies of fine particles or plaque.The pyramidal cells in CIH group arranged scattered and the number of cells were decreased,and there are necrotic cells in the Ⅰ and Ⅳ layers.The pyramidal cells in CSH group arranged disorder,swell,change in vacuoles,a small amount of necrotic cells.Part of the nissl body in CIH group and CSH group were partially dissolved,decreased or disappeared.The number of positive cells in CIH group and CSH group was less than that in NC group(F=321.25,P<0.05).There was no significant difference between CIH group and CSH group(P<0.05).CA3 region The pyramidal of cells hippocampal in NC group arranged closely with clear structure and rich nissl body.The band of pyramidal cell in CIH group and CSH group were interrupted,and cells arranged disorder,changed in vacuoles of Ⅱ layer and a small amount of necrotic cells.The nissl body in CIH group and CSH group were both dissociated and reduced in different degrees.DG region The granulocytes of hippocampal in NC group arranged closely with clear structure and rich Nissl body.The number of living cells were decreased and the necrotic cells concentrated in the Ⅱ and Ⅲ layer in CIH group.The number of living cells were decreased in the dentate gyrus with a large number of cytoplasm deep staining,nuclear disappearance of necrotic cells of Ⅱ layer in CSH group.4.3 Ransmission electron microscopy The nuclei of the neurons in hippocampal CA1 region in NC group were round or oval,and there was clear and complete nuclear membrane.Still the chromatin was distributed evenly and the organelles were abundant and the structure was clear.The hippocampal neurons in CIH group have round nuclear,edge set of chromatin,unclear endoplasmic reticulum,swelling of the mitochondrial,cristae fracture and decreasing organelles.The hippocampal neuronal cell in CSH group were deformed,mitochondria and endoplasmic reticulum were partial destructed,and organelles were decreased significantly.ConclusionChronic hypoxia inhibits the growth and development of rats,leading to decreased cognitive function in young rats.HIF-1α is involved in the nervous system hypoxia response,The compensatory increase level of BDNF may be involved in neuronal cell injury regulation,the two may be independent Involved in maintaining neurocognitive function;The unique hypoxia of CIH was more severe in the hippocampal neuronal injury and more severe cognitive dysfunction occurred.The high levels of HIF-1α and BDNF of CIH showed that the body was in hypoxia stress state.Hippocampal(CA1,CA3,DG)region had different sensitivity to hypoxia injury and different degree of neuronal cell injury.CA1 region of hippocampal with CIH was more sensitive to hypoxia injury and has significantly cognitive impairment. |
PDF Full Text Request