Inhibition of endogenous VEGF impedes revascularization and astroglial proliferation: roles for VEGF in brain repair

Vascular endothelial growth factor (VEGF) is upregulated following injury to the CNS. Our previous work has shown that exogenous application of VEGF promotes angiogenesis, blood-brain barrier permeability, and astroglial mitogenicity in the traumatized brain. To develop a model that could link endogenously secreted VEGF to brain tissue repair, a specific neutralizing antibody to VEGF was infused by osmotic minipump directly into the neocortex and striatum for up to 1 week. Tissues adjacent to the infusion/wound site were analyzed for specific vascular and astroglial protein markers and proliferation, necrosis/apoptosis (via TUNEL staining), VEGF, the VEGF receptors flt-1 and flk-1, and bFGF expression using immunohistochemistry and semi-quantitative RT-PCR. Neutralization of native VEGF caused significant decreases in angiogenic activity, astroglial proliferation, and nestin immunoexpression, while vascular and astroglial degeneration was substantially increased, resulting in much larger wound cavities when compared to controls. The hindrance of brain tissue repair occurred despite an increase in bFGF expression at the wound sites. VEGF appears to be an integral factor in CNS wound healing that is essential for vascular endothelial proliferation and survival and may also be necessary for astroglial proliferation and maintenance during the repair of brain injury.     

Vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) and its receptor flt-1 in microcystic meningiomas

We investigated the immunohistochemical expression of vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) and of its endothelial cell receptor flt-1 in relationship to microcyst formation in meningiomas. Expression of VPF/VEGF was studied in 60 meningiomas (6 microcystic, 38 partially microcystic and 16 with no microcystic areas) and 30 meningiomas from these three subgroups were evaluated for flt-1 expression. VPF/VEGF immunoreactivity was mainly observed in vessel endothelium. Positive vessels were present in 75% (33/44) of meningiomas with any amount of microcystic pattern and in 38% (6/16) of the solid meningiomas (P < 0.02). Densities and percentages of both VPF/VEGF-positive and flt-1-positive vessels were higher in meningiomas with microcystic areas than in solid meningiomas (P≤ 0.002). The 6 microcystic meningiomas showed the highest densities and percentages of both VPF/VEGF-positive (P≤ 0.0002) and flt-1-positive vessels (P≤ 0.01). Vessel expression of VPF/VEGF and flt-1 were positively correlated (r≥ 0.75, P < 0.0001). A strong positive correlation between VPF/VEGF-positive vessel density and proportion of microcystic pattern in all 60 specimens was found (r = 0.75, P < 0.0001). We conclude that accumulation of flt-1-bound VPF/VEGF on endothelial cells of meningiomas is associated with microcyst formation that leads to the histologic appearance of microcystic meningiomas. Received: 18 January 1999 / Revised, accepted: 31 March 1999     

Cellular distribution of vascular endothelial growth factor A (VEGFA) and B (VEGFB) and VEGF receptors 1 and 2 in focal cortical dysplasia type IIB

Members of the vascular endothelial growth factor (VEGF) family are key signaling proteins in the induction and regulation of angiogenesis, both during development and in pathological conditions. However, signaling mediated through VEGF family proteins and their receptors has recently been shown to have direct effects on neurons and glial cells. In the present study, we immunocytochemically investigated the expression and cellular distribution of VEGFA, VEGFB, and their associated receptors (VEGFR-1 and VEGFR-2) in focal cortical dysplasia (FCD) type IIB from patients with medically intractable epilepsy. Histologically normal temporal cortex and perilesional regions displayed neuronal immunoreactivity (IR) for VEGFA, VEGFB, and VEGF receptors (VEGFR-1 and VEGFR-2), mainly in pyramidal neurons. Weak IR was observed in blood vessels and there was no notable glial IR within the grey and white matter. In all FCD specimens, VEGFA, VEGFB, and both VEGF receptors were highly expressed in dysplastic neurons. IR in astroglial and balloon cells was observed for VEGFA and its receptors. VEGFR-1 displayed strong endothelial staining in FCD. Double-labeling also showed expression of VEGFA, VEGFB and VEGFR-1 in cells of the microglia/macrophage lineage. The neuronal expression of both VEGFA and VEGFB, together with their specific receptors in FCD, suggests autocrine/paracrine effects on dysplastic neurons. These autocrine/paracrine effects could play a role in the development of FCD, preventing the death of abnormal neuronal cells. In addition, the expression of VEGFA and its receptors in glial cells within the dysplastic cortex indicates that VEGF-mediated signaling could contribute to astroglial activation and associated inflammatory reactions.     

Antibody neutralization of vascular endothelial growth factor (VEGF) fails to attenuate vascular permeability and brain edema in experimental pneumococcal meningitis

To determine the contribution of vascular endothelial growth factor (VEGF) to cerebral edema formation in bacterial meningitis, we used a VEGF neutralizing antibody to block VEGF in rabbits, following induction of meningitis by intracisternal inoculation with 10⁹ heat-killed pneumococci. At 8 h, cerebrospinal fluid (CSF) VEGF was significantly elevated in infected untreated animals, and correlated with CSF white blood cell (WBC) count (r=0.56, P=0.004), and brain water content (r=0.42, P=0.04). Blocking of VEGF did not attenuate brain edema, blood–brain barrier disruption, or CSF pleocytosis. The functional role of VEGF in the pathophysiology of BM remains elusive.     

Immunohistochemical detection of vascular endothelial growth factor (VEGF) in the vasculature of oligodendrogliomas

C. Christov, H. Adle-Biassette, C. Le Guerinel, S. Natchev and R. K. Gherardi (1998) Neuropathology and Applied Neurobiology 24, 29–35 Immunohistochemical detection of vascular endothelial growth factor (VEGF) in the vasculature of oligodendrogliomas Vascular endothelial growth factor (VEGF) appears to be implicated in tumour angiogenesis. In the present study immunohistochemical expression of VEGF was evaluated in 34 oligodendrogliomas (13 grade II, 21 grade III [WHO]). VEGF immunoreactivity was found in 31 of 34 cases. Expression of VEGF was observed in endothelial cells and some vascular smooth muscle cells, but not in neoplastic oligodendrocytes. Vessel counts, percentages of VEGF-positive vessels and vessels with vascular endothelial proliferation were assessed. The degree of VEGF labelling and vascular-endothelial proliferation in each vessel were evaluated using a 3 degree intensity score. Expression of VEGF was higher in grade III than in grade II oligodendrogliomas as assessed by percentage of VEGF positive vessels (55.8 ± 29.2% vs 17.0 ± 19.0% [P < 0.001]) and by VEGF immunostaining intensity (1.90 ± 0.60 vs 0.90 ± 0.40 [P < 0.001]). VEGF expression did not correlate with vessel density. Intensity of VEGF expression correlated positively with that of vascular-endothelial proliferation in grade III tumours (r=+0.47 [P < 0.05]). The percentage of VEGF positive vessels showed some degree of positive correlation with the percentage of vessels showing vascular-endothelial proliferation (r=+408 [P < 0.10]). Within individual grade III tumours 67.5 ± 29.6% of all vessels with vascular-endothelial proliferation were VEGF-positive and 31.0 ± 20.5% of all VEGF-positive vessels showed no evidence of vascular-endothelial proliferation. We conclude that (i) expression of VEGF is observed in the vasculature of oligodendrogliomas; (ii) marked expression of VEGF is observed in grade III oligodendrogliomas; (iii) VEGF may be one of the interrelated causative stimuli acting in concert to induce vascular-endothelial proliferation.     

颈动脉粥样硬化性狭窄患者血管内皮生长因子检测及意义

目的探讨颈动脉粥样硬化性狭窄(CAS)患者血管内皮生长因子(VEGF)水平变化。方法用酶联免疫法测定73例颈动脉粥样硬化性狭窄(CAS)患者和40例正常对照组血清中VEGF的水平。结果CAS组VEGF水平均高于正常对照组(P<0.05)。结论颈动脉粥样硬化性狭窄患者的血清VEGF水平明显升高。血清VEGF高水平可能成为CAS出现及以后发展为缺血性脑卒中的预测因素和危险因素之一。     

血管内皮细胞生长因子在人脑血管母细胞瘤中的表达及临床意义

目的研究血管内皮细胞生长因子(VEGF)在正常人脑组织和人脑血管母细胞瘤中的表达,以了解其在血管母细胞瘤发病机制中所起的作用。方法应用链霉菌抗生物素蛋白-过氧化物酶法(S-P法)对32例人脑血管母细胞瘤、10例正常脑组织中VEGF的表达进行检测和统计学分析。结果脑血管母细胞瘤组织中VEGF高于正常脑组织中VEGF表达,差异有统计学意义(P<0.01)。结论检测VEGF可以为人脑血管母细胞瘤的发病机制研究及临床治疗提供新的思路。抗VEGF治疗可能成为治疗人脑血管母细胞瘤的新方法。     

步长脑心通对血管性痴呆大鼠学习记忆及血管内皮细胞生长因子作用的影响

目的观察步长脑心通对VD模型学习记忆能力、海马区血管内皮细胞生长因子(VEGF)的影响。方法将50只大鼠随机分为正常组、假手术组、模型组、西药(喜德镇)组及步长脑心通组,建立实验动物模型。分别于制模后、30d后进行跳台实验进行大鼠行为学检测;应用免疫组化法分析大鼠海马部位VEGF分布情况。结果步长脑心通组学习记忆成绩优于模型组,其大鼠海马组织内VEGF明显增加。结论步长脑心通能改善模型大鼠的学习记忆能力,能明显增强VD模型大鼠海马组织VEGF表达,从而减轻VD模型大鼠的缺血性损伤。     

血管内皮生长因子在类风湿关节炎周围神经病变患者中的应用价值

目的探讨血管内皮生长因子在类风湿性关节炎(类风湿关节炎)合并周围神经病变患者诊断与治疗中的应用价值。方法选取2013—2015年类风湿关节炎合并周围神经病变患者40例及仅类风湿关节炎患者40例,同时选择40例健康体检者,对受检者血清VEGF水平进行检验。结果类风湿关节炎组患者血清VEGF明显高于健康人群(P0.05),类风湿关节炎合并周围神经病变患者VEGF水平明显高于类风湿关节炎患者(P0.05),类风湿关节炎患者中重度与轻中度神经损伤患者血清VEGF水平无显著差异(P0.05),类风湿关节炎患者神经损伤范围与血清VEGF无明显关系(P0.05)。结论类风湿关节炎合并周围神经病变患者血清相比健康人群与单纯类风湿关节炎患者明显升高,VEGF水平能够提示类风湿关节炎患者是否存在周围神经病变,但无法有效标识神经受损区域及程度。     

一氧化氮、血管内皮生长因子与胶质瘤血管形成的关系

目的 探讨一氧化氮（NO）和血管内皮生长因子（VEGF）在脑胶质瘤血管形成中的作用。方法 采用免疫组化法检测40例不同级别胶质瘤标本中的诱导型NO合酶（iNOS）、VEGF和Ⅷ因子相关抗原（FⅧRAg）的表达,分析其相互关系。结果①对照组无iNOS表达,胶质瘤组iNOS阳性表达率为62.5％,二者有显著性差异（P<0.001）;②iNOS阴性组微血管密度为（22.40±12.62）个·视野-1,iNOS阳性组为（36.90±22.21）个·视野-1,两者间有显著性差异（P<0.05）;③胶质瘤VEGF阳性表达率为65.0％,明显高于对照组（P<0.01）;④VEGF阳性组微血管密度为（38.09±21.69）个·视野-1,阴性组为（19.19±9.05）个·视野-1,两者间差异显著（P<0.01）;⑤iNOS阳性组中VEGF阳性细胞数明显高于iNOS阴性组（P<0.01）。结论 NO和VEGF参与了胶质瘤的血管形成及肿瘤生长,其具有重要的临床和病理学价值。     

步长脑心通对血管性痴呆大鼠血管内皮细胞生长因子作用的影响

目的:观察步长脑心通对VD模型海马区血管内皮细胞生长因子(VEGF)的影响。方法:将50只大鼠随机分为正常组、假手术组、模型组、西药(喜德镇)组及步长脑心通组,建立实验动物模型。分别于制模后、30天后应用免疫组化法分析大鼠海马部位VEGF分布情况。结果:步长脑心通组大鼠海马组织内VEGF明显增加。结论:步长脑心通能明显增强VD模型大鼠海马组织VEGF表达,从而减轻VD模型大鼠的缺血性损伤。     

Vascular endothelial growth factor (VEGF) is elevated in brain tumor cysts and correlates with tumor progression

Vascular endothelial growth factor (VEGF), a key regulatory protein in neoangiogenesis, is strongly expressed in a variety of primary brain tumors, particularly malignant gliomas. In previous studies, high levels of VEGF were also reported in tumor cysts of glioblastomas. Using an ELISA method we measured the concentration of VEGF in matched samples of aspiration fluid from tumor cysts and serum. Samples were collected from 14 patients with primary brain tumors of various histology (six glioblastomas, one protoplasmatic astrocytoma, two pilocytic astrocytomas, one ependymoma, one meningioma, and three craniopharyngiomas) and two patients with solitary cystic brain metastases from adenocarcinomas of the lung. Aspiration fluids of tumor cysts from all patients revealed high VEGF levels ranging between 882 and 1,263,000 pg/ml, which were 2 to more than 2,000 times higher than the corresponding serum levels. Maximum VEGF levels were detectable in cyst fluids from recurrent glioblastoma. Serum VEGF levels ranged between 125 and 716 pg/ml and did not differ from serum levels in 145 healthy volunteers. In a single patient with metastatic lung cancer the concentration of VEGF in serum and cyst fluid was determined during disease progression. During 60 days of follow-up VEGF concentrations in the cyst fluid collected by puncture of an Ommaya reservoir increased 650-fold, while serum levels remained rather constant. These findings indicate that immunoreactive VEGF is produced at the tumor site and abundantly released into the cyst fluid of primary and metastatic brain tumors. Interestingly, this abundant local release is not reflected in serum VEGF levels, even in the case of very high VEGF concentrations in tumor cysts. Thus, VEGF may be biologically relevant for the formation of tumor cysts in brain tumors and correlates with local disease progression. Received: 29 March 1999 / Revised / Accepted: 13 October 1999     

急性脑梗死患者血清中血管内皮生长因子的检测及临床意义

目的：探讨急性脑梗死患者血清血管内皮生长因子（ＶＥＧＦ）的改变及临床价值。方法：采用双抗体ＥＬＩＳＡ法检测３０例急性脑梗死患者及２０例健康对照组血清ＶＥＧＦ水平，进行动态观察，并分析其与临床特征的关系。结果：初发各性脑梗死患者血清ＶＥＧＦ水平显著升高，第７天达高峰，第１４天仍维持在高水平。血清ＶＥＧＦ水平在大面积脑梗死患者最高，小面积脑梗死者最低，中等面积脑梗死者居中；大血管受累者，显著高于累及小血管者；并发缺血性心脏病者，显著高子未并发者。血清ＶＥＧＦ水平与外周血ＷＢＣ呈正相关，与血糖、血脂、血压值无关。结论：血清ＶＥＧＦ与急性脑梗死严重程度有关，并与外周血ＷＢＣ呈正相关，提示ＶＥＧＦ可能在急性脑梗死的病理生理过程中起重要作用。     

Enhancement of sciatic nerve regeneration after vascular endothelial growth factor (VEGF) gene therapy

F. R. Pereira Lopes, B. C. G. Lisboa, F. Frattini, F. M. Almeida, M. A. Tomaz, P. K. Matsumoto, F. Langone, S. Lora, P. A. Melo, R. Borojevic, S. W. Han and A. M. B. Martinez (2011) Neuropathology and Applied Neurobiology 37, 600–612 Enhancement of sciatic nerve regeneration after vascular endothelial growth factor (VEGF) gene therapy Aims: Recent studies have emphasized the beneficial effects of the vascular endothelial growth factor (VEGF) on neurone survival and Schwann cell proliferation. VEGF is a potent angiogenic factor, and angiogenesis has long been recognized as an important and necessary step during tissue repair. Here, we investigated the effects of VEGF on sciatic nerve regeneration. Methods: Using light and electron microscopy, we evaluated sciatic nerve regeneration after transection and VEGF gene therapy. We examined the survival of the neurones in the dorsal root ganglia and in lumbar 4 segment of spinal cord. We also evaluated the functional recovery using the sciatic functional index and gastrocnemius muscle weight. In addition, we evaluated the VEGF expression by immunohistochemistry. Results: Fluorescein isothiocyanate‐dextran (FITC‐dextran) fluorescence of nerves and muscles revealed intense staining in the VEGF‐treated group. Quantitative analysis showed that the numbers of myelinated fibres and blood vessels were significantly higher in VEGF‐treated animals. VEGF also increased the survival of neurone cell bodies in dorsal root ganglia and in spinal cord. The sciatic functional index and gastrocnemius muscle weight reached significantly higher values in VEGF‐treated animals. Conclusion: We demonstrate a positive relationship between increased vascularization and enhanced nerve regeneration, indicating that VEGF administration can support and enhance the growth of regenerating nerve fibres, probably through a combination of angiogenic, neurotrophic and neuroprotective effects.     

VEGF在慢性硬膜下血肿液及其外膜中的表达

目的探讨血肿液及其外膜血管内皮生长因子（VEGF）的表达与慢性硬膜下血肿（CSDH）发生发展的关系。方法利用酶联免疫吸附分析法（ELISA）对CSDH患者血肿液和血清中VEGF的含量进行测定，利用免疫组织化学方法观察CSDH血肿外膜的VEGF蛋白表达，并根据F．Ⅷ因子在血管内皮中的表达情况进行微血管密度（MVD）的计数，利用电镜观察血肿外膜的超微结构，分析在CSDH中VEGF对血肿外膜毛细血管的生成作用及血肿外膜中毛细血管的形态学改变。结果血肿液中VEGF的含量明显高于血清中的含量（P〈0．01），血肿外膜中可见明显增生的毛细血管和大量的炎症细胞，VEGF与F-Ⅷ因子均呈强阳性染色。电镜结果显示血肿外膜中存在大量新生毛细血管，血管通透性增高。结论VEGF与CSDH血肿外膜的毛细血管生成及血管通透性增高密切相关。     

Ischemia induced neural stem cell proliferation and differentiation in neonatal rat involved vascular endothelial growth factor and transforming growth factor-beta pathways

Brain ischemia is a leading cause of mortality and morbidity in premature infants. Knowing the fate of neural stem cells in the subventricular zone (SVZ) after ischemia and the mechanisms that determine this fate would be useful in manipulating neural stem cell proliferation and differentiation and possibly in reversing ischemic damage. We sought to identify the genes involved in the proliferation and differentiation of neural stem cells after exposure to ischemia in a 3-day-old rat model that approximates ischemia in premature infants. Proliferating cells were labeled by bromodeoxyuridine (BrdU) through intraperitoneal injection. Using immunfluorescence assays, we observed the proliferation and differentiation of neural stem cells. Genes were identified with GeneChip and real-time quantitative polymerase chain reaction analysis. Ischemic rats had more BrdU-positive cells in the SVZ at all four time points and more neural stem cells differentiation into neurons, astrocytes, and oligodendrocytes. GeneChip analysis showed a 3- to 10-fold increase in the mRNA expression of vascular endothelial growth factor, transforming growth factor-beta, and their receptors in the SVZ. PCR assays and Western blot analyses confirmed these results, indicating that vascular endothelial growth factor and transforming growth factor-beta might be two of the factors that involve post-ischemic neural stem cell proliferation and differentiation.     

急性脑梗死患者血清血管内皮生长因子的测定

目的　探讨急性脑梗死与血管内皮生长因子 (VEGF)的关系。方法　对 3 0例急性脑梗死患者和 40例健康人血清血管内皮生长因子含量进行测定。患者采血时间为病后第 2天或第 3、4天 ,取均数与对照组比较。结果　 3 0例急性脑梗死患者血清 VEGF含量为 (2 95 .0 4± 3 5 .73 ) pg/ ml,对照组为 (13 7.71± 11.5 3 ) pg/ m l,两组比较差异显著。结论　急性脑梗死患者血清 VEGF升高 ,提示 VEGF是脑梗死急性期的自我保护机制之一。     

基质金属蛋白酶-9和血管内皮生长因子在颅内动脉瘤中的表达

目的通过观察基质金属蛋白酶-9(MMP-9)和血管内皮生长因子(VEGF)在颅内动脉瘤中的表达情况,并且与正常脑动脉血管组织中两者的表达相比较,为研究动脉瘤的发病原因及机制提供线索。方法用免疫组织化学方法对16例经手术和病理证实的脑动脉瘤标本中的MMP-9、VEGF的表达进行检测,同时将7例颞叶癫痫间患者手术切除颞极的颞叶皮层动脉血管组织标本作为相对正常脑动脉血管组织的对照,进行MMP-9、VEGF的表达检测,将所得染色标本在光镜下观察,并用医学图像分析系统进行定量分析。结果7例正常脑动脉血管组织中无MMP-9、VEGF阳性表达,而动脉瘤的MMP-9、VEGF阳性表达率分别为81.2%(13/16)和87.5%(14/16),2组标本相对照具有显著差异(P<0.05);MMP9-在动脉瘤壁内、中、外膜中均有表达,其中外、中膜阳性表达较高;VEGF主要在动脉瘤壁中、外膜表达,而内膜表达较少。结论动脉瘤的发生、生长和破裂是个很复杂的过程,MMP-9及VEGF可能是主要的影响因素之一,两者可能与动脉瘤的发生,增长以及结构维持有关。     

丰富环境对脑梗死大鼠缺血侧海马区血管内皮生长因子受体的影响

目的 研究丰富环境对大鼠局灶性脑梗死后缺血侧海马区血管内皮生长因子(VEGF)受体的影响.方法 采用开颅电凝法制作SD大鼠右侧大脑中动脉缺血(MCAO)模型.术后24h随机分为丰富环境(EE)组和标准环境(SE)组.以免疫组织化学法检测缺血侧海马区VEGF受体Flt-1及Flk-1的表达.结果 大鼠大脑中动脉闭塞后,Flt-1和Flk-1在缺血侧海马区表达明显增加,经丰富环境干预后,Flt-1和Flk-1表达大量增加,与SE组相比有显著性意义.结论 丰富环境可促使海马区VEGF受体表达上调.进而促进该区微血管新生,有利于脑损伤修复.

Abstract：

Objective To evaluate the effect of enriched environment on vascular endothelial growth factor receptor (VEGFR)expression in hippocampus of rats after unilateral local cerebral infarction.Methods The,4sat middle cerebral artery occlusion (MCAO)wag performed with electric coagulation in SD rata,then the animals were randomly divided into a enriched environment stimulation group(EE group)and a control group(standard environment stimulation group,SE group).The expression of VEGFR-1(Flt-1)and VEGFR-2(Flk-1)in hippocampus gone of brain infarction were measured at 1,3,7,14,28d after operation.Results After MCAO operation,the expression of Flt-1 and Flk-1 in hippocampus of rats in EE group was significantly hisher than that in SE group at all time points.Conclusions Enriched environment stimulation can increase the expression of VEGFR in hippocampus of rats.It can promote the blood vessel proliferation and reeovery in hippocampus of rats after unilateral local cerebral infarction.     

Expression and distribution of vascular endothelial growth factor protein in human brain tumors

Marked neovascularization is a hallmark of many neoplasms in the nervous system. Recent reports indicate that the endothelial mitogen vascular endothelial growth factor (VEGF) may play a critical role in the regulation of vascular endothelial proliferation in malignant gliomas. Using novel monoclonal antibodies to the VEGF polypeptide we have determined the expression and cellular distribution of VEGF protein in a representative series of 171 human central nervous system (CNS) tumors by immunohistochemistry and immunoblotting. In agreement with previous in situ hybridization data, 19 out of 20 glioblastomas (95%) showed immunoreactivity for VEGF, whereas both the percentage of immunoreactive tumors and the extent of immunoreactivity for VEGF were significantly lower in astrocytomas. Of the pilocytic astrocytomas (WHO grade I) 44% were immunoreactive for VEGF, but we observed several cases with pronounced vascular proliferates in the absence of VEGF. In ependymomas, meningiomas, hemangioblastomas, and primitive neuroectodermal tumors, there was no correlation between VEGF expression, vascular endothelial proliferation and the grade of malignancy. Oligodendrogliomas and the oligodendroglial component of mixed gliomas lacked immunoreactive VEGF, indicating that endothelial growth factors other than VEGF may regulate tumor angiogenesis in these neoplasms. Western blot analysis showed a predominant VEGF protein species of 23 kDa and confirmed the immunohistochemical data in all cases. Our findings demonstrate that VEGF is expressed in a wide spectrum of brain tumors in which it may induce neovascularization. However, other angiogenic factors also appear to contribute to the vascularization of CNS neoplasms. Received: 18 April 1996 / Revised, accepted: 20 August 1996