胶质细胞源性神经营养因子对大鼠局灶脑缺血损伤的保护作用

目的 从胶质细胞源性神经营养因子(GDNF)对大鼠局灶脑缺血梗死灶、半胱氨酸蛋白酶(Caspase-3)表达、细胞凋亡等方面的影响,研究其对大鼠局灶脑缺血的作用及其机制。方法 健康雄性Wistar大鼠120只,随机分为GDNF组和生理盐水组,每组又分为假手术组、缺血oh、3h、6h、24h组,采用大脑中动脉线栓模型,于栓塞同时大鼠脑室内分别给予GDNF和生理盐水5μL。检测脑梗死体积百分比、Caspase-3的表达、细胞凋亡等改变。结果 GDNF组脑梗死体积比明显小于生理盐水组;神经元损伤明显轻于生理盐水组,特别是海马区神经元在GDNF组无明显损伤;GDNF组(Caspase-3表达和TUNEL染色阳性细胞数明显少于生理盐水组。结论 GDNF对大鼠局灶脑缺血有保护作用,抑制Caspase-3的表达和细胞凋亡是其保护机制之一。     

RNAi靶向沉默预处理星形胶质细胞胶质细胞源性神经营养因子对神经元凋亡的影响

研究表明外源性的胶质细胞源性神经营养因子可对脑缺血损伤时的神经元有保护作用,但关于内源性的胶质细胞源性神经营养因子的神经元保护作用目前机制不清。鉴于此,实验以正常培养的星形胶质细胞培养基,胶质细胞源性神经营养因子高表达星形胶质细胞培养基和采用RNAi技术沉默胶质细胞源性神经营养因子表达的星形胶质细胞培养基,作用于缺血神经元,观察不同条件培养基对神经元凋亡的影响。结果验证RNAi靶向沉默预处理星形胶质细胞胶质细胞源性神经营养因子的表达可促进神经元凋亡,氧糖剥夺预处理可上调星形胶质细胞的胶质细胞源性神经营养因子的表达,能明显降低神经元的凋亡。     

氟西汀对大鼠星形胶质细胞分泌的胶质源性神经营养因子的影响

目的 探讨氟西汀对大鼠星形胶质细胞分泌的胶质源性神经营养因子(GDNF)的影响.方法 以氟西汀干预体外培养的大鼠海马星形胶质细胞,通过四甲基偶氮唑盐法(MTT)检测不同浓度氟西汀对细胞活力的影响;采用酶联免疫吸附测定法(ELISA)检测细胞培养液GDNF浓度及Real-time PCR法检测GDNFmRNA的表达.结果 (1)氟西汀浓度超过35 μmol/L浓度时,可降低细胞活性,差异有统计学意义(P<0.01或P<0.05);(2)10 μmol/L氟西汀干预星形胶质细胞不同时间后,48 h组细胞培养液GDNF浓度[(68±13)fg/L]高于0 h组[(32±11)fg/L]、6 h组[(34±12)fg/L]、12 h组[(41±17)fg/L]、24 h组[(45±13)fg/L],差异均有统计学意义(P均<0.01);(3)不同浓度氟西汀作用星形胶质细胞48 h后,10 μmol/L浓度组的细胞培养液GDNF浓度[(64±17)fg/L]高于0 μmol/L[(39±15)fg/L]和1 μmoVL浓度组[(39±18)fg/L],差异均有统计学意义(P均<0.05);(4)氟西汀作用星形胶质细胞48 h后,撤离氟西汀24 h后星形胶质细胞仍明显分泌GDNF,差异有统计学意义(P<0.01或P<0.05);(5)不同浓度氟西汀作用星形胶质细胞24 h后,10 μmol/L和20 μmol/L浓度组细胞GDNFmRNA表达量[分别为(0.008 1±0.001 1)和(0.006 3±0.000 3)]高于0 μmol/L、1 μmol/L及5 μmol/L浓度组[分别为(0.003 1±0.000 7)、(0.003 9±0.000 3)和(0.004 1±0.000 2)],差异均有统计学意义(P均<0.01).结论 氟西汀可能通过促进星形胶质细胞GDNF的分泌来发挥其神经保护作用.     

胶质细胞源性神经营养因子治疗缺血性脑血管疾病的新进展

胶质细胞源性神经营养因子(GDNF)作为转化生长因子(TGF)-β超家族成员,是1993年从B19神经胶质瘤细胞的条件培养液中纯化的具有神经营养作用的蛋白质,损伤后的中枢神经元具有可塑性,在神经营养因子作用下其再生速度及质量均显著增强.GDNF作为对抗缺血性损伤的有效保护因子,其效应的发挥依赖于与受体的结合,GDNF受体系统由两部分构成:一部分为膜外糖磷脂酰肌醇(GPI),耦联的是GDNF     

大鼠局灶性脑缺血时活化小胶质细胞和巨噬细胞上调TGF—β1、NGF、和GDNF的表达及意义

目的 研究早期活化小胶质细胞和巨噬细胞在局灶性脑缺血性损伤中的作用。方法 阻塞大鼠大脑中动脉2h再灌流0.5-48h制成局灶性脑缺血模型。免疫组化法观察转化生长因子（TGF-β1）、神经生长因子（NGF）和胶质源性神经营养因子（GDNF）在胶质细胞的表达特点,结果 正常组和假手术组小胶质细胞TGF-β1阴性,再灌注3h组髓质小胶质细胞呈弱阳性,再灌流6-48h缺血区皮质,尾壳核和视前区活化小胶质细胞呈强阳性。正常组和假手术组内囊,胼胝体等处的髓质小胶质细胞GDNF、NGF呈弱阳性,再灌流48h位于视前区的梗死周边区活化小胶质细胞和巨噬细胞GDNF呈中等阳性,再灌流0.5h组视前区的脑膜巨噬细胞NGF呈强阳性,再灌流12h组视前区,尾壳核有少量的活化小胶质细胞呈弱阳性,再灌注24-48h组位于视前区的梗死周边区内层有一圈强阳性的巨噬细胞。结论 活化小胶质细胞,巨噬细胞强力上调TGF-β1、NGF、GDNF表达且呈明显的次序性,提示缺血再灌流早期小胶质细胞活化对神经元具有一定的神经保护作用。     

缺血再灌流时胶质源性神经营养因子在大鼠脑组织的分布特点

目的 观察大鼠脑缺血再灌流时胶质源性神经营养因子（GDNF）在脑组织的分布特点，及其在缺血性脑损伤中的作用。方法 阻断大鼠大脑中动脉（MCA）血流2小时，再灌流0．5－48小时制成局灶性脑缺血模型，HE染色评价缺血性脑损伤的组织学特点，免疫组化法观察GDNF在脑组织的分布特点。结果 再灌流0．5小时组有灶性缺血区，24小时组面积最大，包括视前区、纹状体和皮质。再灌注6小时组开始出现神经元不可逆变性，24小时组梗死形成。再灌注0．5小时组，缺血区皮质神经元GDNF弱阳性，缺血周边区中等阳性；再灌流3－48小时组，缺血区神经元GDNF阴性。再灌流48小时组视前区的梗死周边区巨噬细胞GDNF呈强阳性。GDNF阳性细胞计数显示缺血区各实验组与正常组相比均减少（均P＜0．01）；24小时和48小时组分别与0．5小时组和3小时组相比，GDNF阳性细胞数减少（分别P＜0．01）。结论 缺血性脑损伤时，变性死亡的神经元GDNF不表达，存活的神经元和活化的小胶质细胞或巨噬细胞的GDNF表达增加。     

GDNF基因转染的细胞侧脑室内移植对缺血性脑损伤大鼠的神经保护作用

目的 研究胶质源性神经营养因子GDNF基因转导的细胞侧脑室内移植治疗局灶性缺血性脑损伤大鼠的可行性,并探讨GDNF的神经保护作用机制.方法 体外培养SH-SY5Y细胞株,并用分子克隆技术转导入GFP-GDNF基因,使其可持续分泌绿色荧光蛋白GFP和GDNF.取75只体重150～180 g的健康雄性大鼠,分为移植缺血组、注射缺血组、缺血对照组和正常组等.在立体定向仪介导下向移植缺血组大鼠侧脑室注入转导GDNF基因的SY5Y细胞,向注射缺血组大鼠侧脑室内注射入5U/10μL的GDNF,24 h后采用线栓法对移植缺血组、注射缺血组和缺血对照组动物进行手术,建立局灶性脑缺血损伤模型（即大脑中动脉阻断,MCAO）,在缺血后2 d时用Longa五分法评测行为学改变,TTC染色判断梗塞体积大小,用Western-blot法检测凋亡相关蛋白Bcl-2/Bax的表达水平.结果 在缺血损伤两天后,移植缺血组动物的肢体功能恢复效果优于缺血对照组,TTC染色亦提示移植缺血组脑梗死体积小于缺血对照组和注射缺血组（P＜0.01）.缺血灶周围脑组织凋亡相关蛋白Bcl-2和Bax含量均明显增高,移植缺血组Bcl-2/Bax的比值高于缺血对照组和注射缺血组.结论 GD-NF对缺血性脑损伤大鼠有神经保护作用,用GDNF基因转导的细胞移植治疗是一种可行的途径,效果优于经侧脑室直接给药.GDNF可调节凋亡相关蛋白Bcl-2/Bax的表达,这可能为其神经保护作用的机制之一.     

鱼藤酮对中脑星形胶质细胞的损伤及阿糖胞苷的干预作用

目的 观察鱼藤酮毒性作用及阿糖胞苷(ara-c)干预对体外培养中脑腹侧星形胶质细胞增殖、还原型谷胱甘肽(GSH)含量及胶质细胞源性神经营养因子(GDNF)表达的影响. 方法 体外培养大鼠中脑腹侧星形胶质细胞随机分成9组,分别为对照组,10、20、40及60nmol/L鱼藤酮短时程损伤组(用相应浓度鱼藤酮处理24 h),10及20 nmol/L鱼藤酮长时程损伤组(相应浓度鱼藤酮处理30 d),10及20 nmol/L鱼藤酮长时程损伤+ara-c处理组(相应浓度鱼藤酮处理30 d,500nmol/L ara-c处理6 d).增殖细胞核抗原(PCNA)免疫细胞化学染色观察细胞增殖情况,GSH检测试剂盒检测细胞GSH含量.免疫细胞化学方法 和Western blot检测GDNF的表达情况. 结果短时程损伤各组10和20 nmol/L鱼藤酮作用 24 h未能使细胞GSH含量及GDNF表达最降低,但40和60 nmol/L鱼藤酮作用24 h可使细胞GSH含量降低、GDNF表达减少.长时程损伤组10和20nmol/L鱼藤酮作用30 d后处于增殖状态的星形胶质细胞比例增高,GSH含量未见降低.但GDNF表达量减少:500nmol/L ara-c抑制细胞增殖后,可使GDNF的表达回升至接近对照组水平且GSH含量明显提高. 结论 鱼藤酮可影响中腩腹侧旱形胶质细胞的增殖和功能,恶化多巴胺能神经元的生存微环境;低浓度ara-c可通过抑制旱形胶质细胞的过度增殖,恢复GDNF表达量并明显提高GSH含量,提示ara-c对帕金森病具有潜在的治疗价值.     

成年大鼠神经元和星形胶质细胞细胞周期蛋白依赖性激酶抑制因子表达的差异研究

目的比较研究成年大鼠细胞周期蛋白依赖性激酶抑制因子在神经元和星形胶质细胞的表达差异。方法应用免疫荧光和激光扫描共聚焦显微镜观察成年大鼠生理状态下大脑皮层或海马CA1、CA3、DG区神经元和星形胶质细胞细胞周期蛋白依赖性激酶抑制因子(CDKI)p15Ink4b、p21cipl的表达。结果成年大鼠海马区和大脑皮层的神经元有p15Ink4b和p21cipl的表达,细胞核和细胞浆均有表达,且以胞核为主;星形胶质细胞也有上述细胞周期调控蛋白的表达,便细胞数目较少,并且表达这些指标的星形胶质细胞多聚集在海马区。结论成年大鼠大脑皮层和海马区的神经元和星形胶质细胞均表达p15Ink4b和p21cipl,而其在神经元的表达较星形胶质细胞更为普遍。     

PD模型中GDNF与星形胶质细胞对黑质DA能神经元的影响

目的探讨星形胶质细胞和胶质细胞源性神经营养因子(glial cell line-derived neurotrophic factor,GDNF)在帕金森病(Parkinson's disease,PD)中对多巴胺(dopamine neurons,DA)能神经元损伤的影响。方法成年大鼠右侧前脑侧束注射6羟多巴胺(6-OHDA)制备PD模型。PD模型右侧黑质内注射GDNF,于注射后第6周采用免疫组织化学方法观察星形胶质细胞神经纤维酸性蛋白(glial fibrillary acidic protein,GFAP)以及多巴胺能神经元酪氨酸羟化酶(tyrosine hydroxylasa,TH)的变化。结果模型组、PBS和GDNF组注射侧与非注射侧星形胶质细胞相比,均发现GFAP阳性细胞明显增多,DA能神经元数量明显减少(P<0.05)。GDNF组与模型组相比,发现GFAP阳性细胞明显增多,同时残存的DA能神经元数量有所增加(P<0.05)。结论黑质内注射GDNF可能通过激活的星形胶质细胞保护PD大鼠模型黑质DA能神经元。     

PGDFR-β/GDNF信号通路介导星形胶质细胞调控脑缺血后血脑屏障的功能恢复

目的 探讨血小板源性生长因子受体β(Platelet-derived growth factor receptor-β,PDGFR-β)/血小板源性生长因子(Platelet-derived growth factor, PDGF)信号通路在介导星形胶质细胞调控脑缺血后血脑屏障(Blood-brain barrier, BBB)功能恢复的分子机制。方法 利用siRNA尾静脉注射干扰星形胶质细胞胶质纤维酸性蛋白(Glial fibrillary acidic protein, GFAP)的基因表达;利用插线法制作脑缺血再灌注模型;免疫组织荧光染色分析GFAP基因干扰后星形胶质细胞的数量变化;利用绿色荧光示踪剂渗透实验分析GFAP基因干扰后BBB渗透性改变;利用苏木精-伊红染色法(Hematoxylin-eosin staining, HE)分析GFAP基因干扰后脑微出血改变。在PDGFR-β生后全身性基因敲除鼠(Estrogen-knockout, Esr-KO)诱导脑缺血模型,利用免疫印迹试验分析GDNF的表达水平;脑室泵入外源性GDNF之后分析脑缺血后脑水肿形成、神经功能恢复及内皮细...     

Astrocytic endogenous glial cell derived neurotrophic factor production is enhanced by bone marrow stromal cell transplantation in the ischemic boundary zone after stroke in adult rats

Bone marrow stromal cells (BMSCs) facilitate functional recovery in rats after focal ischemic attack. Growing evidence suggests that the secretion of various bioactive factors underlies BMSCs' beneficial effects. This study investigates the expression of glial cell derived neurotrophic factor (GDNF) in the ischemic hemisphere with or without BMSC administration. Adult male Wistar rats were subjected to 2 h of middle cerebral artery occlusion followed by an injection of 3 × 10⁶ BMSCs (n = 11) or phosphate‐buffered saline (n = 10) into the tail vein 24 h later. Animals were sacrificed seven days later. Single and double immunohistochemical staining was performed to measure GDNF, Ki67, doublecortin, and glial fibrillary acidic protein expression as well as the number of apoptotic cells along the ischemic boundary zone (IBZ) and/or in the subventricular zone (SVZ). BMSC treatment significantly increased GDNF expression and decreased the number of apoptotic cells in the IBZ (P < 0.05). GDNF expression was colocalized with GFAP. Meanwhile, BMSCs increased the number of Ki‐67 positive cells and the density of DCX positive migrating neuroblasts (P < 0.05). GDNF expression was significantly increased in single astrocytes collected from animals treated with BMSCs, and in astrocytes cocultured with BMSCs after OGD (P < 0.05). Our data suggest that BMSCs increase GDNF levels in the ischemic hemisphere; the major source of GDNF protein is reactive astrocytes. We propose that the increase of GDNF in response to BMSC administration creates a hospitable environment for local cellular repair as well as for migrating neuroblasts from the SVZ, and thus contributes to the functional improvement. © 2010 Wiley‐Liss, Inc.     

Ischemia-related changes of glial-derived neurotrophic factor and phosphatidylinositol 3-kinase in the hippocampus: their possible correlation in astrocytes

In the present study, we observed the changes of endogenous expression of glial-cell-line-derived neurotrophic factor (GDNF) and phosphatidylinositol 3-kinase (PI-3 kinase) in the gerbil hippocampus after transient forebrain ischemia and investigated the correlation between GDNF and PI-3 kinase in the ischemic hippocampus. In the sham-operated group, GDNF and PI-3 kinase immunoreactivity was not found in any cells in the hippocampal CA1 region. GDNF, not PI-3 kinase, immunoreactivity was expressed in non-pyramidal cells in the CA1 region at 6 h after ischemic insult. At 12-24 h after ischemia, GDNF and PI-3 kinase immunoreactivity in the CA1 region was similar to that of the sham-operated group. From 2 days after ischemic insult, GDNF- and PI-3-kinase-immunoreactive astrocytes were detected in the CA1 region, and GDNF and PI-3 kinase immunoreactivity in astrocytes was highest in the CA1 region 4 days after ischemic insult. Moreover, at this time point, GDNF and PI-3 kinase were co-localized in some astrocytes. Western blotting showed that ischemia-related changes of GDNF and PI-3 kinase protein levels were similar to the immunohistochemical changes after ischemia. These results suggest that GDNF and PI-3 kinase may be related to delayed neuronal death and that GDNF and PI-3 kinase may be involved in activation of astrocytes.     

Protection of ischemic brain cells is dependent on astrocyte-derived growth factors and their receptors

An in vitro ischemia model (oxygen, glucose, and serum deprivation) is used to investigate the possible cellular and molecular mechanisms responsible for cerebral ischemia. We have previously demonstrated that supernatants derived from ischemic microglia can protect ischemic brain cells by releasing GDNF and TGF-beta1. In the present study, we investigate whether products of ischemic astrocytes can also protect ischemic microglia, astrocytes, and neurons in a similar manner. Supernatants from ischemic astrocytes were collected after various periods of ischemia and incubated with microglia, astrocytes, or neurons individually, under in vitro ischemic conditions. The components responsible for the protective effects of astrocyte-derived supernatants were then identified by Western blot, ELISA, trypan blue dye exclusion, and immunoblocking assays. Results showed that under conditions of in vitro ischemia the number of surviving microglia, astrocytes, and neurons was significantly increased by the incorporation of the astrocyte-derived supernatants. Astrocyte supernatant-mediated protection of ischemic microglia was dependent on TGF-beta1 and NT-3, ischemic astrocytes were protected by GDNF, and ischemic neurons were protected by NT-3. In addition, protein expression of TGF-beta1 and NT-3 receptors in microglia, GDNF receptors in astrocytes, and NT-3 receptors in neurons was increased by in vitro ischemia. These results suggest that astrocyte-derived protection of ischemic brain cells is dependent not only on factors released from the ischemic astrocytes, but also on the type of receptor present on the responding cells. Therapeutic potential of TGF-beta1, GDNF, and NT-3 in the control of cerebral ischemia is further suggested.     

Expression of glial cell line-derived neurotrophic factor induced by transient forebrain ischemia in rats.

This study examined the expression of glial cell line-derived neurotrophic factor (GDNF) mRNA and the cellular localization of GDNF production in rats subjected to transient forebrain ischemia induced by four-vessel occlusion. Transient forebrain ischemia induced GDNF mRNA expression in the hippocampus from 3 h to 3 days after the ischemic episode, with peak expression at 6 h. The GDNF mRNA increase in the cerebral cortex was similar to that in the hippocampus, whereas no increase in GDNF mRNA was observed in the striatum and brainstem. Western blot analysis showed that GDNF in the hippocampal CA1 region was increased slightly from 3 to 24 h after the ischemia, and then subsequently declined to below the baseline level. In the hippocampus, GDNF was evenly produced in pyramidal neurons of both sham-operated rats and normal rats, as determined by immunohistochemistry. Interestingly, we found that ischemia-induced reactive astrocytes, as well as surviving neurons, produced GDNF in 3-7 days after the ischemia. On the other hand, in other regions, such as the cerebral cortex, striatum, and brainstem, there was no change in GDNF-positive cells secondary to ischemia. These findings suggest that expression of GDNF mRNA is regulated in part via ischemia-induced neuronal degeneration. They also suggest that ischemia-induced reactive astrocytes may produce GDNF to protect against neuronal death. Therefore, GDNF may play an important role in ischemia-induced neuronal death in the brain.     

Bimodal upregulation of glial cell line-derived neurotrophic factor (GDNF) in the neonatal rat brain following ischemic/hypoxic injury

In order to delineate the spatial and temporal patterns of glial cell line-derived neurotrophic factor (GDNF) expression following ischemic/hypoxic injury in immature and neonatal brain, GDNF protein levels and immunocytochemistry were studied in rats subjected to a modified Levine procedure. Significant upregulation of GDNF protein occurred in a bimodal fashion in the damaged left cerebral cortex and hippocampus, while the levels in the right cerebral hemisphere of both control and ischemic groups remained relatively unchanged. Immunocytochemical studies indicated that the early rise in GDNF levels was most likely to be related to enhanced neuronal release of GDNF. The second rise was probably related to progressive astrogliosis that occurred in response to injury. In contrast to the lack of GDNF expression among astrocytes in normal mature brains, reactive astrocytes in the neonate appear to possess a ready capacity to express GDNF. Spatial and temporal changes in the pattern of GDNF expression following injury, as determined in this study may provide insight into the functions of GDNF in vivo and into possible therapeutic approaches toward prevention of damage or rescue of neurons following brain injury.     

Early expressions of hypoxia-inducible factor 1alpha and vascular endothelial growth factor increase the neuronal plasticity of activated endogenous neural stem cells after focal cerebral ischemia

Endogenous neural stem cells become "activated" after neuronal injury, but the activation sequence and fate of endogenous neural stem cells in focal cerebral ischemia model are little known. We evaluated the relationships between neural stem cells and hypoxia-inducible factor-1α and vascular endothelial growth factor expression in a photothromobotic rat stroke model using immunohistochemistry and western blot analysis. We also evaluated the chronological changes of neural stem cells by 5-bromo-2′-deoxyuridine(BrdU) incorporation. Hypoxia-inducible factor-1α expression was initially increased from 1 hour after ischemic injury, followed by vascular endothelial growth factor expression. Hypoxia-inducible factor-1α immunoreactivity was detected in the ipsilateral cortical neurons of the infarct core and peri-infarct area. Vascular endothelial growth factor immunoreactivity was detected in bilateral cortex, but ipsilateral cortex staining intensity and numbers were greater than the contralateral cortex. Vascular endothelial growth factor immunoreactive cells were easily found along the peri-infarct area 12 hours after focal cerebral ischemia. The expression of nestin increased throughout the microvasculature in the ischemic core and the peri-infarct area in all experimental rats after 24 hours of ischemic injury. Nestin immunoreactivity increased in the subventricular zone during 12 hours to 3 days, and prominently increased in the ipsilateral cortex between 3–7 days. Nestin-labeled cells showed dual differentiation with microvessels near the infarct core and reactive astrocytes in the peri-infarct area. BrdU-labeled cells were increased gradually from day 1 in the ipsilateral subventricular zone and cortex, and numerous BrdU-labeled cells were observed in the peri-infarct area and non-lesioned cortex at 3 days. BrdU-labeled cells rather than neurons, were mainly co-labeled with nestin and GFAP. Early expressions of hypoxia-inducible factor-1α and vascular endothelial growth factor after ischemia made up the microenvironment to increase the neuronal plasticity of activated endogenous neural stem cells. Moreover, neural precursor cells after large-scale cortical injury could be recruited from the cortex nearby infarct core and subventricular zone.     

大鼠持续脑缺血后星形胶质细胞的时空分布及其变化

目的 本实验研究星形胶质细胞在持续脑缺血后的时空分布及其变化。方法 选用SD雄性大鼠54只，随机分为分成假手术组和手术组。手术组又按缺血时间（3、6、12、24及48 h）分为5个亚组。假手术组和每亚组各9只大鼠。采用颈内动脉线栓加环扎法复制大鼠持续脑缺血模型，相应时间点灌注取脑，常规固定包埋切片，HE和TdT介导的dUTP缺口末端标记（TUNEL）、胶质纤维酸性蛋白（GFAP）染色。结果 随着持续脑缺血时间的延长，中心区神经细胞及星形胶质细胞的数量逐渐减少，缺血边缘区凋亡的神经细胞数量逐渐增多，而星形胶质细胞在12 h达到最低点之后，数量逐渐增多，并呈空泡状改变。结论 在持续缺血12 h之后，缺血中心区与半暗带区星形胶质细胞数量变化不一致，在半暗带其数量逐渐增多，提示星形胶质细胞在缺血后的不同阶段，其作用可能不同。     

Relationship between activated astrocytes and hypoxic cerebral tissue in a rat model of cerebral ischemia/reperfusion

Following cerebral infarction, hypoxic tissues remains in the ischemic cortex for long periods of time. Glial fibrillary acidic protein (GFAP) is a specific marker of astrocytes, which is thought to be essential for neuronal survival. We aimed to clarify the relationship between hypoxic tissue and astrocytes following cerebral infarction. Rats with middle cerebral artery occlusion were randomly divided into a 1.5-hour ischemia-reperfusion(1.5-hour IR) group and a permanent ischemia (PI) group. Hypoxic tissue and GFAP fluorescence intensity in the ischemic cortex were observed postoperatively on days 1, 3, 7, and 14. Results showed that hypoxic tissue was present from day 1 to 14 in the 1.5-hour IR group and on days 1 and 3 in the PI group. The GFAP fluorescence intensity in the 1.5-hour IR group was stronger than that in the PI group at the same time point of observation. Over time, GFAP expression increased and peaked at 7 days in each group, followed by a decrease in signal. In hypoxic tissue, the GFAP fluorescence intensity was stronger than that in the surrounding tissue at all observation time points. These data indicate that astrocytes were strongly activated in hypoxic tissue induced by temporary ischemia followed by reperfusion. The activation of astrocytes may partially contribute to the survival and repair of hypoxic tissue following brain ischemia.     

Dexamethasone enhances upregulation of nerve growth factor mRNA expression in ischemic rat brain.

Nerve growth factor (NGF) is well-established as a trophic factor that plays a crucial role in neuroregeneration and plasticity after brain insults. Dexamethasone (DEX), a powerful glucocorticoid steroid, has long been used in the clinical management of neurological disorders. We examined the relationship between NGF and DEX after an ischemic insult to the brain. In situ hybridization was used to measure NGF mRNA expression in the rat hippocampus after 20 min of transient forebrain ischemia. Immunostaining for NGF protein was performed using the avidin-biotin peroxidase method. Immunohistochemistry for glial fibrillary acidic protein (GFAP) was also used to study the astrocyte reaction in the hippocampal CA1 area. Ischemic brain from rats not treated with DEX had a 2 and 3 fold increase in NGF mRNA compared to sham-operated rats at 4 and 6 h after ischemia, respectively. The NGF mRNA expression returned to basal levels 12 h to 7 days post-ischemia. Treatment with DEX potentiated the ischemia-induced increase of NGF mRNA to 4 times that of sham-operated rats at 6 h following reperfusion and NGF protein expression was similarly elevated. Additionally, the number of GFAP positive astrocytes in the CA1 region in the ischemic rats was markedly increased. These data suggest that DEX may play a role in modulating NGF mRNA expression in the hippocampal neuronal response to brain ischemia.