| Objective: To observe the changes of gross brain and morphologic changes of brain cell, the production of growth-associated protein-43 (GAP-43) and nerve growth inhibitor Nogo-A after hypoxic-ischemic brain damage (HIBD) and hyperbaric oxygen (HBO) at different time points, and to study the effect of HBO on the expression of GAP-43 and Nogo-A after HIBD in rats, so as to probe into the protection effect of HBO and its mechanisms on HIBD rats, and to provide some new ideas for the treatment of hypoxic ischemic encephalopathy (HIE).Methods: A total of 144 female or male Wistar rats aged 7d, with the birth weight of 12~18 gram were randomly divided into normal control (CON) group, HIBD group and HBO group, n=48 in each group. Then each group was randomly divided into six subgroups (n=8 in each subgroup) based on different time points at 1, 4, 7, 10, 14, 21d after HIBD. HIBD model rats were prepared by keeping rats into hypoxic environment of 8% O2 concentration for 1~2 hours after clamping right common carotid artery. And behaviors of all rats were observed. HBO treatment (2.0 ATA for pressure-stabilizing for 1h every time, pressure-elevating and depressurization for 30min) was carried out daily for HBO group rats at 1h after HIBD, 1d and 4d subgroups lasted one and four days respectively. And rats in other subgroups had been treated for seven days. After decapitation and collecting brain, gross brain was observed. The pathological changes of brain tissue were observed under light microscope, and the expressions of GAP-43 and Nogo-A in cerebral cortex were detected via immunohistochemical staining and image semiquantitative analysis at every time point.Results: Neonatal rats had various abnormal behaviors after HIBD. After HIBD, Abnormal changes of gross brain at different degrees were observed; above-mentioned changes weakened after HBO therapy. Under light microscope, we can find that both the structure and cell layers in every part of brain in control group cases were distinct, the cell morphouses were normal, and no nerve cell was absent. Cell swelling was significant on the first postoperative day, and the cells had started to become degenerated and necrotic; on the fourth postoperative day the pyknotic nucleus and nuclear debris were found, and cell degeneration and necrosis were significant, cell layers were indiscriminate. On the seventh postoperative day, lamellar necrosis and vacuolation could be found, some cells disappeared significantly. In HBO group, the pathological change at each time point was less than that of HIBD group, and cell still spreaded regularly. GAP-43expression: GAP-43 positive staining showed buffy fine grain deposition, GAP-43 positive cells were found in cerebral cortex and hippocampus, and positive staining was mainly in cytoplasm and axon process of nerve cell, the expression of GAP-43 increased with the increase of their days of age, and the peak value was at the 10d after HIBD. The expression of GAP-43 at each time point in HIBD group was increased compared with that of CON group, there was statistical significant difference between them (P<0.01). The expression of GAP-43 at each time point in HIBD group was increased compared with that of CON group, there was statistical significant difference between them (P<0.05). Expression of Nogo-A: Positive staining of Nogo-A was buffy fine grain deposition, and distributed at cerebral cortex extensively, positive staining was main in glial cell, and the expression of Nogo-A increased with their days of age increased. The expression of Nogo-A at each time point in HIBD group was increased compared with that of CON group, there was statistical significant difference between them (P<0.01). Whereas, expression of Nogo-A at each time point in HBO group reduced remarkably compared with that of HIBD group, there was statistical significant difference between them (P<0.01).Conclusion: 1. HBO therapy can reduce hypoxic ischemic brain damage is confirmed from gross brain and pathology. 2. The expression of GAP-43 in cortex of neonatal rat increased after HIBD compared with CON group, which suggestes the CNS after HIBD have self-remodeling and repairing ability, and HBO therapy can increase the expression of it after HIBD, and make it at higher level in a long time. 3.The expression of Nogo-A in cerebral cortex of neonatal rat with HIBD keeps higher level in a longer time(1~21d), which suggested that the Nogo-A is related with neural regeneration disorder after HIBD; HBO therapy can promote the regeneration of central nerve after HIBD by reducing Nogo-A in cerebral cortex.
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