脑源性神经营养因子预处理对沙土鼠脑缺血-再灌注损伤的影响

目的 探讨脑源性神经营养因子(brain-derived neurotrophic factor,BDNF)预处理对沙土鼠脑缺血-再灌注(ischemia-reperfusion,I/R)后神经细胞凋亡及Bcl-2、Bax蛋白表达的影响.方法 蒙古种沙土鼠48只,随机分为6组,每组各8只:正常对照组(C);缺血-再灌注组(I/R),全脑缺血20 min后再灌注24 h;BDNF预处理6,12,24,48 h组(PR6,PR12,PR24,PR48),PR6,PR12,PR24,PR48各组分别于脑缺血前6,12,24,48 h经侧脑室注射BDNF(0.5 μg/只)进行预处理,缺血20 min后分别再灌注24 h.实验地点在贵阳医学院动物实验中心.采用夹闭沙土鼠双侧颈总动脉20 min后去除动脉夹使血流再通的方法制作全脑I/R损伤模型,夹闭过程中出现瞳孔散大、对光反射消失及翻正反射消失等则说明产生全脑缺血.除C组外的所有动物分别于脑缺血20 min再灌注24 h结束时断头取脑,取视交叉后1～4 mm处的额叶皮层组织制备石蜡切片,TUNEL法检测脑皮层凋亡神经细胞,免疫组化法检测Bcl-2,Bax蛋白的表达.统计分析采用方差分析法.结果 C组未检测到凋亡细胞及Bcl-2,Bax蛋白阳性表达细胞;I/R组及BDNF预处理各组沙土鼠脑皮层均可检测到凋亡细胞,且BDNF预处理各组细胞凋亡指数均明显低于I/R组,P值均为0.000;与I/R组比较,BDNF预处理各组脑皮层Bcl-2蛋白阳性细胞指数均显著增高,而Bax蛋白的阳性细胞指数均显著降低,P值均为0.000;BDNF预处理各组中以6,12 h预处理组的细胞凋亡指数及Bax蛋白阳性细胞指数较低,P值分别为0.056和0.001,而Bcl-2蛋白阳性细胞指数较高,P值为0.005.结论 不同时间窗的BDNF预处理均能不同程度的减轻脑I/R后神经细胞凋亡,有明显脑保护作用,以脑I/R损伤前6,12 h时间窗内给予BDNF预处理的脑保护效果较明显;其机制可能是通过上调Bcl-2蛋白的表达及抑制Bax蛋白的表达而实现.

Effects of BDNF pretreatment against cerebral ischemia-reperfusion injury in gerbils

Objective To investigate the effects of brain-derived neurotrophic factor (BDNF) pretreatment on neuron apoptosis and the expression of Bcl-2 and Bax protein following global cerebral ischemia-reperfusion (I/R) injury in gerbils. Method Forty-eight mongolian gerbils were randomly divided into six groups in equal number (n = 8): normal control group (group C), ischemia-reperfusion group (group I/R) and four BDNF pretreatment groups according to various lengths of time from BDNF pretreatment to ischemia-reperfusion. The BDNF pretreat-ment was carried out in gerbils with lateral ventricular injection of BDNF 0.5μg 6 h, 12 h,24 h and 48 hours be-fore cerebral ischemia, and those gerbils assigned into PR6, PR12, PR24 and PR48 groups. The global cerebral is-chemia-reperfusion was induced by occlusion of bilateral common carotid arteries for 20 minutes and then the arter-ies were released for 24 hours reperfusion. The confirmation of global cerebra ischemia was evidenced by the ap-pearance of mydriasis and disappearance of light reflex and righting reflex. Twenty-four hours later, all gerbils including those of control group were sacrificed and a piece of tissue was taken from frontal cortex just behind the optic chiasma 1～4 millimeter for making paraffin sections. Neuron apoptosis was identified by using TUNEL and immunohischemistry was used to detect the expression of Bcl-2 and Bax protein in cerebral cortex. The data were analyzed by using analysis of variance. Results There were no apoptotic cells, and expression of Bcl-2 and Bax protein positive cells found in group C. Neuron apoptosis in brain cortex was detected in I/R group and BDNF pre-treatment groups. The indexes of neuron apoptosis in BDNF pretreatment groups were markedly lower than those in group I/R (P < 0.01). Compared with group I/R, the index of expression of Bcl-2 protein positive cells was in-creased significantly in BDNF pretreatment groups (P = 0.005), while the index of expression of Bax protein posi-tive cells were decreased significantly (P < 0.01 in all groups). Among 4 BDNF pretreatment group, the lowest apoptosis index and lowest of expression of Bax protein positive cells were found in PR6 and PR12 BDNF pretreat-ment groups (P = 0.0056 and 0.001, respectively). Conclusions Different time windows of BDNF pretreatment can decrease the neuron apoptosis in different degree, and protect brain against cerebral ischemia-reperfusion injury significantly. Among BDNF pretreatment time windows, pretreatment of 6 hours and 12 hours are the better ones.The mechanism of protection of BDNF pretreatment may be attributed to inducing Bcl-2 protein expressions and in-hibiting Bax protein expressions, and thereby inhibiting neuron apoptosis.