Edema and neuronal apoptosis in the hippocampus and cortex of elderly rats following transient cerebral ischemia/reperfusion injury

摘要

BACKGROUND: Previous studies of cerebral ischemia have used young animals, with an ischemictime greater than 5 minutes (safe time limit). Despite an increased understanding of neuronalapoptosis, it remains uncertain whether brief cerebral ischemic events of 5 minutes or less damagebrain tissue in elderly rodents.OBJECTIVE: To investigate the effects of transient cerebral ischemia (5 minutes)/reperfusion injuryon brain cortical and hippocampal edema, aquaporin-4 (AQP-4) expression, and neuronal apoptosisin aged rats, and to compare ischemic sensitivity between cortex and hippocampus.DESIGN, TIME AND SETTING: A randomized, controlled, animal experiment was performed at theInstitute of Cerebrovascular Disease, Qingdao University Medical School from April 2008 to March2009.MATERIALS: Rabbit anti-AQP-4 polyclonal antibody, TUNEL kit, and SABC immunohistochemistrykit were purchased from Wuhan Boster Bioengineering, China.METHODS: A total of 160 healthy, male, aged 19-21 months, Wistar rats were randomly assignedto 4 groups: sham-surgery, and ischemia 1-, 3-, and 5-minute groups, with 40 rats in each group.The global cerebral ischemia model was established using the Pusinelli four-vessel occlusion, andthe three cerebral ischemia groups were subdivided into reperfusion 12-hour, 1-, 2-, 3-, and 7-daysubgroups, with 8 rats in each subgroup. The sham-surgery group was subjected to exposure of thefirst cervical bilateral alar foramina and bilateral common carotid arteries.MAIN OUTCOME MEASURES: The dry-wet weight assay was used to measure brain water contentand histopathology of the cortex and hippocampus was observed following hematoxylin-eosinstaining. In addition, cortical and hippocampal AQP-4 expression was detected by streptavidin-biotincomplex immunohistochemistry, and neuronal apoptosis was detected by the TUNEL method.RESULTS: There was no significant difference in brain water content or AQP-4 expression in thecortex and hippocampus between ischemia 1- and 3-minute groups and the sham-surgery group orbrain water content or AQP-4 expression in the cortex between ischemia 5-minute group andsham-surgery group (P> 0.05). However, brain water content and AQP-4 expression in thehippocampus after 5 minutes of cerebral ischemia were significantly increased compared with thesham-surgery group (P < 0.05 or P < 0.01 ). Several TUNEL-positive cells were observed in thecortex and hippocampus of the sham-surgery group and ischemia 1-minute group, as well as in thecortex of the ischemia 3-minute group. In addition, the number of apoptotic neurons in thehippocampus of ischemia 3-minute group and in the cortex and hippocampus of ischemia 5-minutegroup was significantly increased (P < 0.05 or P < 0.01). Neuronal apoptosis was increased after 12hours of ischemia/reperfusion, and it reached a peak by 2 days (P < 0.01).CONCLUSION: Transient cerebral ischemia (5 minutes) resulted in increased hippocampal edema,AQP-4 expression, and neuronal apoptosis. Moreover, cerebral ischemia had a greater effect onneuronal apoptosis than brain edema or AQP-4 expression, and the hippocampus was moresensitive than the cortex.