神经干细胞移植对AD鼠基底前脑NOS阳性神经元的影响

目的 探讨神经干细胞（neural stem cells,NSCs）移植对老年性痴呆鼠基底前脑一氧化氮合酶（NOS）阳性神经元的影响.方法 切断成年SD大鼠左侧穹窿海马伞（fimbria-fornix,FF）,于基底前脑行神经干细胞移植,4周后行组织化学染色结合图像分析技术观察各组大鼠基底前脑NOS阳性神经元数量和形态学参数的变化. 结果 损伤后大约1个月,损伤侧基底前脑内侧隔核（MS）和斜角带垂直支（VDB）内可观察到NOS阳性神经元明显减少,分别为正常组的35.5%和55.8%,（与正常组相比P＜0.01）;移植组NOS阳性神经元数恢复到正常组的74.7%和95.7%,（与损伤组相比P＜0.01）.细胞形态学参数提示移植组NOS阳性神经元中含部分中等大小的未成熟细胞.结论 神经干细胞移植治疗,对AD模型鼠基底前脑MS、VDB的NOS阳性神经元有明显的补充和保护作用。     

神经干细胞移植对192-IgG-saporin阿尔茨海默病模型鼠基底前脑神经元p75NGFR阳性神经元和行为学的影响

神经干细胞能够在体外持续扩增,具有较强的增殖能力和较强的可塑性,能够在成年宿主中枢神经系统中存活、迁移、分化以及与宿主组织整合较好。 目的：分析神经干细胞移植对侧脑室注射192-IgG-saporin 老年性阿尔茨海默病模型鼠基底前脑神经元p75NGFR阳性神经元和行为学的影响。 方法：24只SD大鼠随机数字表法均分为3组：对照组、模型组、移植组。10只新生SD鼠(<24 h)用于神经干细胞分离培养。模型组及移植组192-IgG-saporin侧脑室注射SD大鼠建立阿尔茨海默病模型。造模后,移植组行基底前脑神经干细胞移植。4周后行Y迷宫检测,结合图像分析技术观察大鼠基底前脑p75NGFR阳性神经元数目和形态学参数的变化。 结果与结论：注射192-IgG-saporin 1个月,模型组损伤侧基底前脑内侧隔核和斜角带垂直支p75NGFR阳性神经元数明显减少(P < 0.01),移植组分别恢复到对照组的74.85%和71.66%,与模型组损伤侧相比较,差异显著(P < 0.01)。Y迷宫测试结果显示,移植组大鼠的空间学习能力和记忆能力有改善(P < 0.05),基底前脑p75NGFR阳性神经元细胞数与大鼠的空间学习记忆能力呈正相关。提示,神经干细胞移植对注射192-IgG-saporin致阿尔茨海默病鼠基底前脑胆碱能神经元有明显的补充和保护作用,可改善大鼠的学习记忆能力。     

神经生长因子缓释微球植入后阿尔茨海默病模型鼠基底前脑神经生长因子受体阳性神经元的变化

背景：已有研究表明,神经营养因子对中枢和周围神经损伤后的存活修复有促进作用。然而,神经生长因子是大分子蛋白类物质,生物半衰期很短,很难透过血脑屏障,寻找有效的神经营养因子投递系统至关重要。 目的：观察了神经生长因子微球对阿尔茨海默病模型鼠基底前脑神经生长因子受体阳性神经元的保护作用。 设计、时间及地点：随机对照动物实验,于2005-11/2006-07在广州医学院神经生物学实验室完成。 材料：采用双乳化技术制备神经生长因子缓释微球。28只SD大鼠,随机分为3组：正常对照组8只,模型对照组8只,神经生长因子缓释微球植入组12只。 方法：模型对照组和神经生长因子缓释微球植入组左侧穹隆海马伞切断制备阿尔茨海默病模型,正常对照组不做任何处理。神经生长因子缓释微球植入组切断后即刻行基底前脑注射神经生长因子缓释微球。正常对照组和模型对照组注射等量生理盐水。 主要观察指标：注射4周后,利用免疫组化法观察各组大鼠基底前脑神经生长因子受体阳性神经元变化。 结果：28只大鼠均进入结果分析。模型对照组损伤侧的内侧隔核和斜角带核的神经生长因子受体阳性神经元大量减少,分别减少59.7%和54.4%;神经生长因子缓释微球植入组损伤侧的内侧隔核和斜角带核细胞数分别减少17.9%和19.8%,明显高于模型对照组损伤侧的神经生长因子受体阳性神经元存活数（P < 0.05）。 结论：神经生长因子缓释微球植入对阿尔茨海默病模型鼠基底前脑神经生长因子受体阳性神经元有明显的保护作用。     

神经干细胞移植对老年痴呆模型鼠基底前脑小白蛋白阳性神经元和 学习记忆能力的影响*☆

目的：基底前脑是老年性痴呆患者脑皮质下神经元丢失最严重的区域，实验拟验证经神经干细胞移植治疗后老年痴呆鼠基底前脑小白蛋白阳性神经元的变化以及对其空间学习记忆能力方面的影响。 方法：实验于2005-12/2006-07在广州医学院解剖学教研室完成。①动物：清洁级SD雄性大鼠28只，随机数字表法分为3组：正常对照组8只、模型对照组8只、细胞移植组12只。另取10只新生SD鼠用于神经干细胞的分离培养。实验过程中对动物的处置符合动物伦理学标准。②实验方法：模型对照组、细胞移植组大鼠切断左侧穹隆海马伞，建立老年性痴呆动物模型。利用无血清培养技术获得鼠基底前脑神经干细胞，吸取2.5×1010 L－1细胞悬液4 μL，术后即刻细胞移植组损伤侧行细胞移植，坐标为前囟+0.6 mm，外侧+0.6 mm插入，腹侧-5.5 mm。③实验评估：移植后4周，采用Y型迷宫对各组动物进行学习记忆能力检测。麻醉后取脑制备组织切片，ABC法免疫组化染色结合图像分析观察各组大鼠基底前脑小白蛋白阳性神经元的变化。 结果：①对空间学习记忆能力的影响：细胞移植组空间学习能力、记忆能力均显著高于模型对照组（P < 0.05或P < 0.01），基本达到正常水平（P > 0.05）。②对小白蛋白阳性神经元的影响：与正常对照组比较，模型对照组损伤侧内侧隔核和斜角带核的小白蛋白阳性神经元数目分别减少62.5%和30.4%；细胞移植组降低幅度明显小于模型对照组（P < 0.01）。与正常对照组比较，模型对照组损伤侧内侧隔核、斜角带核小白蛋白阳性神经元的面积、周长、灰度均显著降低（P < 0.05或0.01）；细胞移植组上述指标较模型对照组均显著增加（P < 0.05或0.01）。③相关性分析：小白蛋白阳性神经元数目与大鼠在Y型迷宫中的学习次数呈显著负相关（r =-0.76~-0.79，P < 0.01），与记忆能力呈显著正相关（r = 0.78~0.84，P < 0.01）。 结论：神经干细胞移植对老年性痴呆模型鼠基底前脑退变的小白蛋白阳性神经元具有补充和保护作用，并能够明显改善其学习记忆能力，二者呈正性相关。     

雌激素对双侧穹隆-海马伞切断及去势大鼠脑源性神经营养因子表达的影响

目的　采用双侧穹隆-海马伞切断及双侧卵巢切除方法制作大鼠认知障碍模型,观察4个脑区脑源性神经营养因子(BDNF)表达的变化,以及补充外源性雌激素对BDNF的影响。方法选择健康雌性Wistar大鼠30只,先按2×2方差分析设计分别建立4个模型组:穹隆-海马伞切断组(FF组)、卵巢切除组(OVX组)、卵巢切除加穹隆-海马伞切断组(OF组)和对照组,然后再建立OF组同时给予雌二醇(E2 )治疗组(OF+E2 组)和双侧穹隆-海马伞切断加卵巢切除对照组,每组5只。E2 剂量为1mg/kg,每7天1次皮下注射,共4次28天。观察各组大鼠海马CA1区、皮质区、杏仁复合体区、基底前脑Meynert核区BDNF蛋白表达的变化。结果　(1)经F分析,双侧卵巢切除和双侧穹隆-海马伞切断与否存在主效应和显著交互效应(P<0 001)。FF组、OVX组和OF组的BDNF阳性细胞计数在海马CA1区、皮层、杏仁复合体、Meynert核均明显少于对照组(P<0 001),其中OF组在Meynert核区的BDNF阳性细胞计数少于FF组和OVX组(P<0 01); (2)OF组+E2 组在4个脑区的BDNF阳性细胞数均多于OF对照组(均P<0 01和<0 05)。结论　双侧穹隆-海马伞切断和(或)双侧卵巢切除均可导致大鼠脑内BDNF表达减少,补充外源性雌激素可显著增加BDNF的表达。     

脑源性神经营养因子修饰的神经干细胞移植对阿尔茨海默病大鼠的学习及p75表达的影响

目的研究脑源性神经营养因子(BDNF)修饰的神经干细胞(NSC)移植对阿尔茨海默病大鼠的学习及p75表达的影响。方法 36只SD成年大鼠被选为受试对象。采用Aβ1-40立体定向注射法制作阿尔茨海默病模型(AD),并将AD模型大鼠随机分为3组:BDNF修饰的神经干细胞(BDNF-NSC)移植组、神经干细胞移(NSC)植组和溶剂(Vehicle)对照组(n=6),然后分别向这3组大鼠的海马区注入500μl的BDNF-NSC悬液(5×105)、NSC悬液(5×105)和相同剂量的不含细胞的培养基。注射4w后,采用Y迷宫方法检测AD大鼠的空间学习和记忆能力,随之用过量麻醉的方法处死受试大鼠,立即取脑并分别采用免疫组织化学方法检测BDNF-NSC在海马区的表达和Western blot法检测p75蛋白在海马区的表达。结果 BDNF-NSC组大鼠的行为学能力较NSC组和Vehi-cle组明显提高(P<0.05),同时免疫组化检测显示在海马区的BDNF-NSC阳性细胞数明显增多而Western blot检测显示p75蛋白在该区的表达显著降低(P<0.05)。结论 BDNF修饰的神经干细胞能够通过抑制海马区p75表达来防止由Aβ1-40造成的神经损害。     

神经营养因子NGF、BDNF对AD模型鼠海马移植的影响

目的:研究神经营养因子NGF、BDNF对AD模型鼠海马移植后行为和形态学变化。方法:24.只AD模型鼠随机分成4组:单纯胚基底前脑细胞悬液移植组(ST组)、含NGF或BDNF胚基底前脑细胞悬液移植组(NGF组)、(BD-NF组)和模型对照组(M组),移植后3月进行行为测试并比较移植区AchE细胞数和纤维密度,运用方差分析和SNK检验进行组间比较。结果:行为测试移植3组明显优于模型M组,含因子组又较ST组效果好(P<0.01),两因子组间差异无显著性(P>0.05);因子组存活细胞数均高于ST组,NGF组细胞数多于BDNF组(P<0.05),纤维密度两组相似(P>0.05)。结论:海马内存活胆碱能神经元能代偿受损胆碱能神经元的功能,改善动物的学习记忆功能;NGF、BDNF均能促进胆碱能神经元存活,增加AchE细胞数目和突起,但BDNF促进神经元突起延伸作用较好,而NGF则对神经元保护作用较强。     

Meynert核注射β-淀粉样蛋白后大鼠脑NGF、BDNF神经元的表达变化及其机制

目的:探讨Meynert核注射β-淀粉样蛋白(Aβ)后大鼠脑神经生长因子(nerve growth factor，NGF)和脑源性神经营养因子(brain derived neurotropic factor，BDNF)免疫反应性神经元的表达变化及其可能机制。方法将1μL Aβ1-40(10μg／μL)在立体定向仪下注入大鼠右侧Meynert核，分别于1、4周时测定其学习记忆能力和脑组织中NGF、BDNF免疫反应阳性神经元的表达。结果：Aβ1-40注射1周后，实验组出现学习记忆障碍，呈渐进性加重，4周时更为显著。在Meynert核及其周边、海马区和额、顶部皮层区，对照组有少量NGF、BDNF免疫反应阳性神经元分布，染色较浅；而实验组在1周时，较对照组无明显变化，4周时实验组NGF、BDNF免疫反应阳性神经元表达数量显著增加，以海马区最为显著，皮层区次之。结论：皮层和海马至基底前脑神经元的NGF、BDNF运输障碍，使基底前脑的神经元缺乏神经营养，致神经元变性及死亡，可能是阿尔茨海默病(Alzlaeimer disease，AD)学习记忆障碍和痴呆形成的重要因素之一。     

骨形态发生蛋白4在Aβ诱导的神经毒性病变中的表达变化

目的探讨骨形态发生蛋白4(bone morphogenetic protein 4,BMP4)在β淀粉蛋白(amyloidβ,Aβ)诱导的神经毒性病变中的变化。方法 SD大鼠海马神经元原代培养,经过不同浓度(10、15、20μmol/L)Aβ25-35毒性片段处理后,通过定量PCR技术检测BMP4mRNA表达水平。SD大鼠双侧基底前脑注射Aβ1-40建立大鼠痴呆模型,通过免疫组化及免疫印迹检测基底前脑及海马区BMP4蛋白表达水平。结果 Aβ25-35处理组海马神经元内BMP4mRNA表达较空白对照组明显减少(P0.05)。免疫组化和免疫印迹实验结果显示,与对照组比较,Aβ1-40注射组大鼠基底前脑区BMP4蛋白表达减少,海马区其表达升高(P0.05)。结论 Aβ直接下调神经元内BMP4转录及表达,不同脑区内BMP4蛋白可能存在负反馈调节作用。     

血管内皮生长因子基因修饰C17.2神经干细胞移植治疗脑梗死的实验研究

目的 探讨血管内皮生长因子（VEGF）基因修饰神经干细胞（NSC）移植治疗脑梗死大鼠模型的治疗效果，以及基因的表达情况和神经保护作用。方法 通过移植腺病毒载体介导的VEGF165基因转染的C17-2NSC到大鼠大脑中动脉阻断（MCAO）的局灶性脑缺血模型脑梗死半暗带区，观察移植后大鼠神经功能变化，神经特异性烯醇化酶（NSE）、CD31免疫组化检查观察细胞存活分化和血管新生情况。结果 VEGF病毒组、NSC移植组和VEGF基因修饰NSC组神经功能严重度评分均较对照组显著减少（P〈0．05），以VEGF基因修饰NSC组最为显著（P〈0．05）；NSC移植后NSE阳性细胞数较对照组显著增多（P〈0．05），VEGF基因修饰NSC组更为碌著（P〈0．05）；VEGF病毒组和VEGF基因修饰NSC移植组脑梗死灶周围血管数较对照组显著增多（P〈0．05），以VEGF基因修饰NSC组更为显著（P〈0．05）。结论 转染VEGF基因的C17．2NSC脑内移植治疗MCAO脑梗死模型可促进NSC向神经元分化，可促进新生血管形成，改善神经功能。VEGF基因修饰NSC移植治疗效果优于单纯的C17．2NSC移植或VEGF基因治疗。     

p75(NGFR) and cholinergic neurons in the developing forebrain: a re-examination

The low-affinity nerve growth factor receptor (p75(NGFR)) apparently can mediate apoptosis in a variety of cells in vitro and in vivo. Previously, our laboratory suggested that p75(NGFR) induced apoptosis in a subpopulation of cholinergic forebrain neurons during postnatal development, i.e., the number of choline acetyltransferase (ChAT)-positive neurons in a control strain of mice decreased whereas it remained higher in p75(NGFR)-deficient (-/-) mice. Discrepancies with subsequent data sets in our laboratory caused us to thoroughly re-analyze the fate of these cholinergic medial septum and neostriatal neurons in new sets of p75(NGFR) -/- and two DNA control strains of mice during development. Between postnatal day (P)6 and P15 the number of ChAT-positive neurons detected in the medial septum of 129/Sv mice and Balb/c mice increased by approximately 64% and approximately 62%, respectively. This increase is contrary to previous reports from our laboratory and indicative of normal postnatal development (including an increase in ChAT-enzyme) of the cholinergic forebrain neurons. In p75(NGFR) -/- mice the number of ChAT-positive neurons in the medial septum remained constant between P6 and P15 and was approximately 31% and approximately 56% higher at P6 than 129/Sv and Balb/c mice, respectively. At P15 and adulthood, p75(NGFR) -/- mice had similar numbers of cholinergic neurons as control mice. In the developing neostriatum, the number of ChAT-positive neurons increased by approximately 56% between P6 and P15 and did not differ between p75(NGFR) -/- and control mice at any time. Analyses for apoptotic DNA fragmentation (TUNEL labeling) at P8 revealed no differences between p75(NGFR) -/- and control mice in 12 forebrain regions, including the septum and neostriatum. At all times, all mice had similar levels of acetylcholinesterase-positive cholinergic innervation of the molecular layer in the dorsal dentate gyrus. These findings suggest that the p75(NGFR) does not necessarily mediate apoptosis in medial septum or neostriatal cholinergic neurons during the postnatal time period. The discrepant results of the previous study are most likely due to a less rigorous application of criteria for data acquisition, including anatomical boundaries that define the nucleus.     

SEK1/MKK4, c-Jun and NFKappaB are differentially activated in forebrain neurons during postnatal development and injury in both control and p75NGFR-deficient mice

The common neurotrophin receptor (p75NGFR) can signal in vitro through activation of the c-Jun N-terminal kinase (JNK) pathway and nuclear translocation of NFKappaB. Activation of JNK and its substrate c-Jun can lead to apoptosis. We investigated these activities in vivo by comparing immunoreactivity for phosphorylated(p) SEK-1 (or MKK4, which activates JNK), c-Jun (ser63, ser73) and nuclear translocation of NFKappaB-p50 in tissue sections through the forebrain of control and p75NGFR-deficient mice. During postnatal development, SEK1p-immunoreactivity was detectable in p75NGFR-positive cholinergic neurons and p75NGFR-negative neurons throughout the forebrain in control mice. During development, few cells contained c-Junp, although many neurons contained c-Jun. No obvious c-Jun immunostaining was present in the adult forebrain. At any age, NFKappaB-p50 immunoreactivity was seen in nuclei of most cells throughout the forebrain. Following fimbria fornix transection in adult mice, few basal forebrain neurons contained SEK1p while many axotomized choline acetyltransferase (ChAT)-positive neurons contained c-Junp and nuclear NFKappaB-p50. The immunostaining patterns of SEK1p, c-Junp and NFKB during development and following injury were largely similar in p75NGFR-deficient mice. During development, cells throughout the forebrain had TdT-mediated dUTP-biotin nick end labelling (TUNEL)-labelling (a potential marker for apoptosis), however, their presence was not predicted by number of neurons stained for SEK1p or c-Junp. These results suggest that the expected activation of the JNK pathway by p75NGFR, as well as the expected relationship between SEK1 and downstream activation of c-Jun do not occur in the mammalian forebrain. Also, these results suggest that this activation does not necessarily lead to cell death.     

Effects of estrogen and fimbria/fornix transection on p75NGFR and ChAT expression in the medial septum and diagonal band of Broca.

NGF receptor-expressing cells located in the basal forebrain have recently been shown to contain estrogen (E) receptors (Toran-Allerand and MacLusky. 1989. Soc. Neurosci. Abstr. 15: 954). In the present study, we have examined the effects of E-treatment on p75NGFR and choline acetyltransferase (ChAT) expression by neurons in the medial septum (MS) and the vertical (VDB) and horizontal (HDB) limbs of the diagonal band of Broca using immunocytochemical and in situ hybridization techniques. First, since E-treatment has been shown to affect neuronal survival and to stimulate synaptic reorganization and growth within various regions of the brain, we hypothesized that E-treatment might attenuate the loss of p75NGFR immunoreactivity (IR) which occurs in the MS and VDB following transection of the fimbria/fornix. Contrary to our hypothesis, E-treatment did not attenuate the effects of fimbria/fornix transection. In fact, E-treatment alone produced a significant decrease in the number of p75NGFR-IR cells detected in the MS. Subsequent experiments confirmed that chronic E-treatment produces a down-regulation of both p75NGFR-IR and p75NGFR mRNA in the MS and VDB. In the MS, estrogen appeared to affect a subpopulation of p75NGFR-expressing neurons which were also affected by fimbria/fornix transection since the effects of these two treatments were not additive. In addition, effects of E-treatment on p75NGFR-IR were sex-specific (observed in females but not in males) and were reversible in the MS after 2 weeks, but not after 4 weeks (allowing 2 weeks recovery), of E-treatment. A time-course analysis revealed that effects of E-treatment on p75NGFR-IR were not observed until after 16 days (MS) or 30 days (VDB) of E-treatment and were preceded by a significant and transient increase in ChAT expression in both the MS and VDB. The data are consistent with the possibility that continuous, long-term exposure to gonadal steroids may contribute to a loss of p75NGFR-expressing neurons with age. In addition, the data suggest that p75NGFR expression may play a role in regulating the functioning of specific basal forebrain cholinergic neurons. Different mechanisms by which E-treatment might influence ChAT and p75NGFR expression in brain are discussed.     

Effects of fimbria-fornix and angular bundle transection on expression of the p75NGFR mRNA by cells in the medial septum and diagonal band of Broca: correlations with cell survival, synaptic reorganization and sprouting.

Quantitative in situ hybridization techniques were used to examine the effects of lesions which sever hippocampal cholinergic and cortical afferents on p75NGFR mRNA-expressing cells located in the medial septum (MS) and the vertical (VDB) and horizontal (HDB) limbs of the diagonal band of Broca. Animals received either bilateral transection of the fimbria/fornix, unilateral transection of the angular bundle, or sham surgery. Four days later, animals were sacrificed and sections through the MS, VDB and HDB were processed for detection of the p75NGFR mRNA using in situ hybridization techniques previously described (Mol. Brain Res., 6 (1989) 275-287). Transection of the fimbria/fornix and angular bundle differentially affected p75NGFR-expressing cells in the MS, VDB and HDB within 4 days after injury, in ways which were consistent and correlate with subsequent effects on cell survival, synaptic reorganization and growth. In particular, in the MS and VDB, transection of the fimbria/fornix resulted in a significant decrease in the size of p75NGFR-expressing cells (reductions of 25.9% and 15.1% respectively) which was accompanied by a significant reduction (37.9% and 12.7% fewer grains/cell) in relative levels of p75NGFR mRNA. In contrast, in the HDB, transection of the fimbria/fornix had no significant effect on the average size of p75NGFR-expressing cells; however, a significant increase (49%) in the mean relative level of p75NGFR mRNA was observed which may, in turn, reflect a large increase (as much as 2-3 fold) in the levels of p75NGFR mRNA expressed by a subpopulation of hippocampally projecting cholinergic neurons located in the HDB. Finally, transection of the angular bundle resulted in small, but significant increases (9.4% and 10.9%) in relative levels of p75NGFR mRNA in the MS and VDB, as well as an increase (19.6%) in the number of p75NGFR mRNA-expressing cells in the HDB, on the injured side. No increases in p75NGFR expression in the MS, VDB or HDB contralateral to the lesion were observed; however, a decrease in the size (6.9%) and message content (19.4%) of p75NGFR-expressing cells was detected in the MS contralateral to the lesion. Most importantly, all of these effects are consistent with the subsequent effects of these lesions on the survival of basal forebrain cholinergic cells, and the reorganization and growth of cholinergic afferents to the hippocampal formation.(ABSTRACT TRUNCATED AT 400 WORDS)     

Expresgions of nerve growth factor and p75 low affinity receptor after transient forebrain ischemia in gerbil hippocampal CA1 neurons

Expressions of nerve growth factor (NGF) and low affinity p75 NGF receptor (p75 NGFR) in gerbil hippocampal neurons after 3.5-min transient forebrain ischemia were studied. Most hippocampal CAI neurons were lost (neuronal density = 44 ± 12/mm) at 7 days after recirculation, while no cell death was found in the sham-control neurons (220 ± 27/min). NGF immunoreactivity was normally present in the sham-control hippocampal neurons. However, it decreased in hippocampal CAI neurons, and slightly decreased in the neurons of CA3 and dentate gyrus areas from 3 hr after recirculation. By 7 days, NGF immunoreactivity returned almost completely to the sham-control level in the CA3 and dentate gyrus neurons but decreased markedly in the CAI neurons. In contrast, p75 NGFR immunoreactivity was scarcely present in the sham-control hippocampal neurons but was induced from 1 hr after recirculation in the CAI and CA3 neurons and from 3 hr in the dentate gyrus. At 7 days, p75 NGFR immunoreactivity was expressed greatly in the surviving CAI neurons and the reactive astrocytes but was not seen in the other hippocampal neurons. The markedly decreased NGF and greatly induced p75 NGFR immunoreactivity found in the CAI neurons after transient forebrain ischemia suggests that NGF and p75 NGFR may be involved in the mechanism of delayed neuronal death. © 1995 Wiley-Liss, Inc.     

Estrogen treatment suppresses forebrain p75 neurotrophin receptor expression in aged,noncycling female rats

There is increasing evidence that estrogen has beneficial effects on cognition, both in humans and in rodents, and may delay Alzheimer's disease onset in postmenopausal women. Several rodent studies have utilised the ovariectomy model to show estrogen regulation of the p75 neurotrophin receptor, TrkA, and markers of acetylcholine synthesis in the cholinergic basal forebrain. We studied estrogenic effects in aged (16-17-month-old), noncycling rats. Estrogen treatment for 10 days drastically reduced p75(NTR) immunoreactivity in the rostral parts of the basal forebrain. The number of p75(NTR)-immunoreactive neurons was decreased, and those neurons remaining positive for p75(NTR) showed reduced p75(NTR) staining intensity. In vehicle-treated rats, almost all choline acetyltransferase-immunoreactive neurons were p75(NTR) positive (and vice versa), but, in estrogen treated rats, large numbers of choline acetyltransferase-immunoreactive cells were negative for p75(NTR). Similar levels of p75(NTR) down-regulation in the rostral basal forebrain were found when estrogen treatment was extended to 6 weeks. There was no reduction in the number of p75(NTR)-immunoreactive neurons in the caudal basal forebrain after 10 days of treatment. After 6 weeks of treatment, however, there was evidence of p75(NTR) down-regulation in the caudal basal forebrain. There was no evidence of hypertrophy or atrophy of cholinergic neurons even after 6 weeks of estrogen treatment. Considering the evidence for the role of p75(NTR) in regulating survival, growth and nerve growth factor responsiveness of cholinergic basal forebrain neurons, the results indicate an important aspect of estrogen's effects on the nervous system.     

Enlarged cholinergic forebrain neurons and improved spatial learning in p75 knockout mice

The p75 low affinity neurotrophin receptor (p75) can induce apoptosis in various neuronal and glial cell types. Because p75 is expressed in the cholinergic neurons of the basal forebrain, p75 knockout mice may be expected to show an increased number of neurons in this region. Previous studies, however, have produced conflicting results, suggesting that genetic background and choice of control mice are critical. To try to clarify the conflicting results from previous reports, we undertook a further study of the basal forebrain in p75 knockout mice, paying particular attention to the use of genetically valid controls. The genetic backgrounds of p75 knockout and control mice used in this study were identical at 95% of loci. There was a small decrease in the number of cholinergic basal forebrain neurons in p75 knockout mice at four months of age compared with controls. This difference was no longer apparent at 15 months due to a reduction in numbers in control mice between the ages of 4 and 15 months. Cholinergic cell size in the basal forebrain was markedly increased in p75 knockout mice compared with controls. Spatial learning performance was consistently better in p75 knockout mice than in controls, and did not show any deterioration with age. The results indicate that p75 exerts a negative influence on the size of cholinergic forebrain neurons, but little effect on neuronal numbers. The markedly better spatial learning suggests that the function, as well as the size, of cholinergic neurons is negatively modulated by p75.     

Differential regulation of p75 and trkB mRNA expression after depolarizing stimuli or BDNF treatment in basal forebrain neuron cultures

Extensive evidence suggests that BDNF regulates neural function and architecture after depolarization. Expression of BDNF is increased after depolarization, and the ability of BDNF to modulate synaptic function is well documented. To further investigate BDNF signaling after activity, we analyzed the effects of depolarization or BDNF treatment on receptor mRNA expression in cultured basal forebrain neurons. Levels of mRNA coding for the cognate BDNF receptor, trkB, as well as the common neurotrophin receptor, p75, were quantitated simultaneously using a sensitive solution hybridization technique. Depolarization or BDNF treatment increased p75 mRNA expression 94% and 195%, respectively. In contrast, trkB message decreased 23% after depolarization but was unchanged by BDNF treatment. Together, these changes resulted in significant increases in the p75/trkB ratio after depolarization or BDNF treatment that could alter BDNF binding or signal transduction.