The Effects And Mechanism Of Dexamethasione On Myelin Basic Protein Development In Premature Rats And Hypoxic-ischemic Brain Damage In Neonatal Rats

Objective: Hypoxic-ischemic encephalopathy(HIE) is the serious complication of neonatal asphyxia, which is a major cause of high mortality and chronic neurological in survivors, such as mental retardation, epilepsy, cerebral palsy, spasm and incoordination. Scholars have studied HIE for many years, they believe its pathogenesis is still unclear and referring to some paths, such as a lot of release of excitatory amino acid(EAA) or the failure of energy, acidosis, apoptosis and reperfusion injury. While HIE is short of effective therapical method yet. Recently, Barks found pretreatment with Dexamethasone(DEX) could relieve hypoxic-ischemic brain injury of neonatal animals, and the neuroprotective effects are dose and time dependent. But the mechanism is not clear. There are two patterns of cell death in HIBD, apoptosis and necrosis, in which apoptosis is more important, its peaking time occurrenc at 24h-72h after cerebral hypoxia-ischemia. Recent research found that pretreatment with DEX could reduce cytokine expression and nerve cell apoptosis in HIBD model which offered a new approach about prevention and treatment of DEX on brain damage. This research use rat model to study injured brain tissue histological feature, apoptosis cell counting, the expressions of Interleukin-1βand Myelin basic protein, rats behavior and observe their changes after therapy with DEX. The objective of this research is to demonstrate the effects of DEX on neonatal rats'brain damage and by which mechanisms it works. This study also provides the evidences to the treatment of DEX on HIBD.Methods: (1) Immature rat model: 18 SD rats which weigh 240～260g were randomly divided into: H-Dex P group, L-Dex P group and P NS group. L-Dex P group were injected Dex (0.1mg/kg.d) into pregnant rats'celiac from 16 to 18 of pregnancy; H-Dex P group were injected Dex (0.5mg/kg.d) into pregnant rats'celiac from 16 to 18 of pregnancy; P NS group were injected 0.9%Nacl (0.5mg/kg.d) into pregnant rats from 16 to 18 of pregnancy. All of the fetal rats were received after we administrated caesarean operation on the day 19 of pregnancy. In every group we selected 8 newborns randomly for research. (2) HIBD model: 100 4-day-old SD rats were randomly divided into: L-Dex1 group, H-Dex1 group, L-Dex2 group, H-Dex2 group, NS group. L-Dex1 group and H-Dex1 group were respectively injected Dex 0.1mg/kg.d and 0.5mg/kg.d for 3days. Then the rats were be made into HIBD models. Dex2 group were be made into HIBD at first, then 7-day-old rats were respectively injected Dex 0.1mg/kg.d and 0.5mg/kg.d for 3days. NS group were injected 0.5mg/kg.d 0.9%Nacl for 3days following HIBD. We respectively execute newborns 3days and 7days after HIBD. (3) Normal group: 20 7-day-old SD rats were respectively executed on 10-day-old and 14-day-old. (4) Sample collect, target detect and data processing: the surroundings is germfree. Rats were killed at the directed time and brain tissue, serum were prepared. Using hematoxylin-eosin (HE) and light-microscopy observed the histological feature of the left brain. Level of apoptosis was measured by flow cytometry (FCM). The expression of MBP and IL-βin blood serum and brain tissue homogenate were examined by ELISA. The water content of brains also observed and so on. The datum were analyzed by statistics software SPSS12.0 include Q-test, one-way-ANOVA .Result:1 (1) The brain water content of NS group is significantly higher than Normal group(P<0.01); The brain water content of Dex1 group and Dex2 group are lower than NS group(P<0.05). L-Dex1 group is higher than H-Dex1 group(P<0.05). L-Dex2 group is higher than H-Dex2 group(P<0.05). No significant difference shows between the same dose of Dex1 groups and Dex2 groups(P>0.05). (2) Compared with P NS group, the brain water content of L-Dex P group and H-Dex P group are lower(P<0.05). No significant difference shows between the same dose of L-Dex P group and H-Dex P group (P>0.05).2 Observing brain minute structure by the light microscope: compared with NS group, pathology change of brain in Dex1 groups and Dex2 groups had obviously relieved. 3 Level of apoptosis in NS group is significantly higher than Normal group(P < 0.01). Level of apoptosis in Dex treated groups are significantly less than those in the same time NS group(P<0.01). L-Dex1 group is higher than H-Dex1 group(P<0.05). L-Dex2 group is higher than H-Dex2 group (P<0.05). Difference shows between the same dose of Dex1 group and Dex2 group (P<0.05). Compared with P NS group, levels of apoptosis in L-Dex P group and H-Dex P group are higher(P<0.05). Difference shows between the same dose of L-Dex P group and H-Dex P group (P>0.05).4 The expression of MBP and IL-1βin serum and brain tissue: The expression of MBP and IL-1βin NS group are significantly higher than Normal group(P<0.01, P<0.05). The expression of MBP and IL-1βin Dex treated groups are significantly less than those in the same time NS group(P<0.01). L-Dex1 group is higher than H-Dex1 group(P<0.05). L-Dex2 group is higher than H-Dex2 group(P < 0.05). No significant difference shows between the same dose of Dex1 groups and Dex2 groups(P>0.05).5 Compared with P NS group, the expression of MBP in brain tissue of H-Dex P group and L-Dex P group are higher(P<0.05); the expression of IL-1βin brain tissue of H-Dex P group and L-Dex P group are lower(P<0.05). No significant difference shows between the same dose of H-Dex P group and L-Dex P group (P>0.05).Conclusion 1 The effect of DEX on premature newborns: promoting glial cell mature, increasing MBP contents and apoptosis cells, decreasing IL-1βcontents. It is dose-dependent. This indicates that DEX can possibly promote the development of alba and myelinogenesis; At the same time, DEX possibly negatively effect on brain normal development. We should pay attention to it, and should supply low dose.2 The effect of DEX on HIBD newborns: decreasing MBP,IL-1βcontents and apoptosis cell, obviously ease brain edema. It is dose-dependent. This indicates that DEX has protection on HIBD.3 The protection between remedial utilize DEX and prophylactic utilize DEX are similar except restraining apoptosis cell.4 Dex plays major role in maturation of fetal brain: restraining excessive expression of IL-1βand inflammation mediator, lightening inflammation cascade reaction, repressing alba demyelinate and apoptosis. It is dose-dependent.5 In clinical we can detection the contents of MBP in serum, to guide the therapy of HIBD.