| Background: Cerebral ischemia tolerance (CIT) means that transient ischemia preconditioning can increase the tolerance obviously to severe ischemia injury later. The phenomenon of CIT in recent years has already got the proof. Mechanism of CIT, though it is not really understood, involves the expression of genes related to apoptosis, in which NF-ΚB and caspase-3 being widely concerned. Objective: To investigate effects of ischemia preconditioning on neurological function, brain water content, expression of NF-ΚB and caspase-3 in the hippocampal tissue in rats after brain ischemia again ,and to investigate the brain protecting mechanism produced by ischemia preconditioning. Methods: 48 healthy male Sprague-Dawley (SD) rats (weight 200~250g) were randomly divided into 3 groups: false operation group (n=16), ischemia preconditioning group (n=16), and ischemia group (n=16). False operation group: sewing up the skin after exposing the common carotid artery (CCA) in the right side. Ischemia preconditioning group: a focal-focal cerebral ischemic model, adopting the thread embolism method according to Koizumi. Exposing right common carotid artery (CCA), external carotid artery (ECA), and internal carotid artery (ICA) of anaesthetized rats, ligating ECA near head and cutting ECA away. Shearing a small mouth on the ECA near heart, and through it inserting a thread (a diameter 0.205mm carbon fishing line of high elasticity dripping candle for a round head at the end of the thread and dipping heparin before using) from ICA to anterior cerebral artery (ACA) to block MCA blood flow by 30 minutes, then pulling out the thread, ligating ECA nub, and sewing up the skin. After 24 hours, a thread was inserted to ACA in the right side again through CCA by 24 hours. Ischemia group: A thread was inserted to ACA in the right side directly through CCA by 24 hours. The following indexes in 3 groups were observed respectively: neurological function (according to Bederson method, 8 of each group); the water content of brain (wet weight and dry weight method, 8 of each group), and the expression of NF-ΚB and caspase-3 in hippocampal tissue of rats (immunohistochemistry method, 8 of each group). Results: The mean score of neurological function was 0,1.13±0.99 and 2.25±0.89 in false operation group, ischemia preconditioning group and ischemia group respectively, and the difference was significant (p<0.05).The water content of brain was 69.9±0.38,75.5±0.54 and 81.9±0.55 in 3 groups respectively, also, the difference was significant(p<0.05). And the expression of NF-ΚB was 11.2±2.59,25.4±3.78 and 38.6±7.67 in 3 groups respectively; the expression of caspase-3 was 0.8±0.84,27.2±3.42 and 37.8±4.49 in 3 groups respectively. The expressions of NF-ΚB and caspase-3 in ischemia preconditioning group were lower than those in ischemia group, but higher than those in false operation group, the difference was significant(p<0.05). Conclusion: Score of neurological function and water content of brain in preconditioning group were better than those in ischemia group, and the expression of NF-ΚB and caspase-3 in preconditioning group was lower than that in ischemia group. The results suggested that ischemia preconditioning could increase the tolerance obviously to severe ischemiainjury later. The decreasing expression of genes related to apoptosis such as NF-ΚB and caspase-3 might play an important role in this protecting mechanism of brain.
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