| Objective:Hypoxic-ischemic brain damage(HIBD) in neonates is a major cause of a variety of serious human neurological disorders such as cerebral palsy,epilepsy,motor and learning disabilities,and even death during the perinatal period.It may lead to neurological sequelae in survivors and long-term effects on their family and society.Cell death takes place in two major phases in Neuropathology of HIBD:necrotic cell death and apoptosis.Despite the majority of the initial cell death is necrosis in 24 hours after the injury,apoptosis is indicated having activated early after neonatal HIBD by which cell death structure has been examined.Apoptosis induces delayed cell death by the continued effect in the vulnerable regions,such as Cerebral Cortex.And apoptosis has been reported to be responsible for a significant proportion of the final cell loss in HIBD.Abundant researches point out that timing is everything in apoptosis following HIBD,so the effect of the treatment must be correlated to its therapeutic window.Several experimental studies have shown that HBO is highly efficient in inhibition of apoptosis within the first period after HIBD.Lots of researches support that the best therapeutic window for HBO treatment exists during 2 to 24 hours following HIBD from different points of view.These findings also point out the treatment effect is poor when the administration is delayed.HBO at later time points(≥12 hours ) is harmful by increasing infarct volume in transient MCAO(middle cerebral artery occlusion) rats by a foreign research.Because of many limitations in the clinic,it is very difficult to start the HBO treatment in the early hours following the injury.Therefore, the study on the effect of delayed therapeutic window for HBO on nerve cell apoptosis is absolutely necessary and significant.This study evaluates the best therapeutic window of HBO and the effect on apoptosis of nerve cells in cerebral cortex by delayed therapeutic window after HIBD.Methods:Seven-day-old Sprague-Dawley rat pups were used and kept under controlled conditions.Animals were randomly assigned to the following groups(7 groups,n=8 in each group):group CON with no treatment;group HIBD;group 2H-HBO was treated by HBO(90 min at 2 absolute atmosphere for 7 days) which initiated 2 hours after HIBD; group 24H-HBO,group 48H-HBO,group 72H-HBO and group 96H-HBO were treated by HBO which initiated 24 hours,48 hours,72 hours and 96 hours after HIBD.The animals were killed 18 days after onset of HIBD when the HBO treatment of group 96H-HBO came to the end,and sections of the brains(4μm) were cut.The slides were costained with TUNEL for the evaluation of apoptosis.Quantitative(number of TUNEL-positive cells) analyses were performed at the cortex.Results:The results of our study showed that HBO could make a great effect on inhibition of apoptosis when it initiated at 2 to 24 hours after HIBD.The number of nerve cell apoptosis in cerebral cortex was gradually increasing with HBO initiated from 48 to 96 hours after HIBD and the objective analysis showed significantly difference between group 48H-HBO,group 72H-HBO and group 96H-HBO(P＜0.01).This demonstrated the effect of HBO on nerve cell apoptosis decreased by the delayed therapeutic window.And the later the treatment started,the poorer the protection was.The three groups of delayed therapeutic window still had a significantly decrease of apoptosis against group HIBD(P＜0.01).Even if HBO missed its best therapeutic window,early administration still appeared to be superior to late.Conclusions:In conclusion,we demonstrated that the best therapeutic window for HBO treatment was within 24 hours after HIBD. Following HIBD,HBO therapy initiated after 24 hours could only make a partial effect on inhibition of apoptosis in neonatal rats,but still not enhanced the apoptosis. |
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