Neuromagnetic dialogue between neuronal minicolumns and astroglial network: a new approach for memory and cerebral computation

Rapidly accumulating experimental data over the past two decades discloses extremely complex neuro-glial interactions and provides new insights regarding novel roles of glial cells, particularly astrocytes, in complex functions. Widespread astrocytic processes, interconnected by gap junctions, form an extremely large physiological syncytium. This structure in conjunction with neuronal activity, very likely contributes to cognitive functions. Based on electrophysiological and neuroanatomical data, the present hypothesis proposes a self-organised, iterative and reciprocal magnetic interaction between neurones and astrocytes to explain neurocomputation, including memory processing, in the human neocortex.     

β/A4-Amyloid increases nerve growth factor production in rat primary hippocampal astrocyte cultures

Nerve growth factor (NGF), a member of the neurotrophin family, is an essential mediator of neuronal activity and synaptic plasticity of basal forebrain cholinergic neurons (BFCN). In processes of chronic degeneration of BFCN like in Alzheimer's disease (AD), characterized among others by amyloid containing plaques, NGF has been shown to improve cognitive decline and rescue BFCN but also to reduce survival of hippocampal neurons via p75 neurotrophin receptor (p75). Little is known about the mechanisms of NGF regulation in glial cells under pathological conditions in AD. This study investigates the influence of amyloid administration on the NGF protein secretion in rat primary hippocampal astrocytes. Astrocytes were stimulated with "aged" beta/A4-Amyloid (1-40), and NGF was measured in different fractions, such as supernatant, vesicles, and cytosol fraction. Treatment with amyloid at a final concentration of 10 microM for 72 h led to increased NGF protein levels up to 30-fold increase compared to unstimulated controls. This observation may be an endogenous neuroprotective mechanism possibly contributing to a delay of amyloid-dependent loss of cholinergic neurons or contribute to accelerated neuronal death by activation of p75 within Alzheimer pathology.     

Src suppressed C kinase substrate regulates the lipopolysaccharide-induced TNF-α biosynthesis in rat astrocytes

The protein kinase C (PKC) is known to be a critical component in the signaling cascades that lead to astrocyte-activation. To further understand the mechanism of PKC signaling in astrocyte-activation, we investigated the effect of SSeCKS, a PKC substrate, on LPS-induced cytokine expression in astrocytes by RT-PCR and enzymelinked immunosorbent assay. Exposure of the cells to LPS induced rapid translocation of SSeCKS to the perinuclear sides, ERK activation and pronounced TNF-α production, which can be inhibited by the PKC inhibitor Gö6983. By using siRNA knockdown of SSeCKS expression, LPS-induced signaling events were partly inhibited, including ERK activation, inducible TNF-α biosynthesis and secretion. These results suggest that SSeCKS is involved in the LPS-induced TNF-α expression in astrocytes mediated by PKC.     

Phosphorylation and cleavage of tau in non-AD tauopathies

The tau protein, well known as the primary component of neurofibrillary tangles, also comprises the Pick bodies found in Pick’s disease (PiD) and the glial lesions associated with progressive supranuclear palsy (PSP) and cortico-basal ganglionic degeneration (CBD). Many of the tau alterations that are characteristic of Alzheimer’s disease have also been identified in PSP and CBD. In this report, we examine three non-AD tauopathies (PSP, CBD, and PiD) for the presence of two specific tau alterations, phosphorylation at Ser422 and truncation at Asp421. We find that truncation at Asp421 is an alteration that is unique to neuronal lesions, occurring in Pick bodies as well as in neurofibrillary tangles, but not in lesions associated with glia. Conversely, phosphorylation at Ser422 is not only present in all these lesions, but identifies additional glial and neuronal pathology in disease-susceptible cortical regions. These results suggest that the molecular alterations of tau that occur during the initial process of tangle formation in AD are similar in non-AD tauopathies, but the middle and later changes are not common to all diseases. This work is supported by grants AG021184 and AG09466 from the NIH.     

Factors involved in inflammation-induced developmental white matter damage

Developmental white matter damage is a brain pathology associated with several long-term neurological disorders. An inflammatory insult has been suggested as the major instigating event. This study investigated the relative influence of inflammation, blood–brain barrier permeability and glial ontogeny in white matter damage. Systemic inflammation was induced in Monodelphis domestica (opossum) by serial intraperitoneal injections of lipopolysaccharide at different stages of brain development. Volume of white matter was estimated for the external capsule. Blood–brain barrier permeability was assessed immunocytochemically. Quantitative RT-PCR was used to measure relative levels of mRNA for IL-1β, IL-6 and COX-2. Developmental changes in numbers and appearance of microglia and astrocytes were estimated. Results showed that in response to systemic inflammation, white matter was reduced in the external capsule during a circumscribed period only. At the same developmental stage blood–brain barrier permeability was altered, cerebral inflammatory response was present and numbers of microglia increased. However, the periods of altered blood–brain barrier permeability and the cerebral inflammatory response were longer than the period of the external capsule's susceptibility to white matter damage, which coincided with the developmental increase in the number of astrocytes in this tract. Thus, the mechanism of white matter damage following systemic inflammation is multifactorial, including cerebral inflammation and breakdown of brain barriers occurring simultaneously at specific stages of glial cell development.     

大鼠星形胶质细胞与运动神经元VSC4.1共培养体系中活性氧产生水平的变化

目的： 探讨野生型星形胶质细胞（ASC）和运动神经元VSC4.1（VSC）共培养时两者产生活性氧（ROS）的相互影响。方法: MTT法测定比较ASC和VSC在单独培养和共培养时受到兴奋性刺激后生长抑制率;ASC与Hoechst 33342标记的VSC共培养或分别单独培养时,激光共聚焦显微镜实时观察2种情况下两者产生ROS的能力。结果: 较高浓度谷氨酸刺激可使共培养的混合细胞抑制率（IRVSC+ASC）明显高于星形胶质细胞抑制率（IRASC）,而较低浓度时IRVSC+ASC高于IRVSC。激光共聚焦显微镜实时观察发现共培养时VSC产生ROS水平明显低于单独培养的VSC,且前者在15 min时出现明显升高,而单独培养的VSC产生的ROS在5 min内达到峰值后即逐渐降低;共培养时ASC产生的ROS在10 min时出现明显升高。结论: ASC和VSC共培养时ASC可降低VSC静息时的ROS水平,在受到兴奋性刺激后ASC延长VSC产生高水平ROS的时程。     

星形胶质细胞体外缺血缺氧损伤后炎症模型的建立及应用

目的 建立SD大鼠星形胶质细胞缺血缺氧损伤后炎症模型,探讨亚低温对星形胶质细胞缺血缺氧及损伤后炎症反应的影响.方法 体外原代培养新生SD大鼠星形胶质细胞,免疫荧光染色检测胶质纤维酸性蛋白(GFAP)进行鉴定.实验分正常对照组(C组)、单纯缺氧组(H组)和缺氧+白细胞组(H+W组),以无糖DMEM培养基、5%CO2+95%N2混合气体培养4 h诱导细胞缺氧模型.H+W组加入1 mLSD大鼠外周血白细胞(1×106/mL),C组加入等量培养液.将3组细胞分别置入37℃、34℃、32℃、30 ℃ CO2孵箱中作用24 h,应用速率法和LIVE/DEAD染色分别检测3组细胞在不同温度下乳酸脱氢酶(LDH)释放率的变化和形态学变化.结果 缺氧4 h即可造成星形胶质细胞的损伤.37℃时C组、H组、H+W组细胞LDH释放率依次升高,差异有统计学意义(P<0.05);与37℃相比,亚低温状态(34℃、32℃)下H组、H+W组细胞LDH释放率均降低;但在30℃时,则有明显升高,与32℃相比差异具统计学意义(P<0.05).结论 亚低温状态可明显降低星形胶质细胞的缺血缺氧性损伤及炎症性损伤,其机制可能并非通过单纯的抑制代谢来实现的.     

血管紧张素Ⅱ对新生大鼠脑星形胶质细胞组织因子表达的影响

目的观察血管紧张素Ⅱ（AngⅡ）对新生大鼠脑星形胶质细胞组织因子（TF）表达的影响及机制。方法培养Wistar新生大鼠脑星形胶质细胞。细胞促凝活性（PCA）的检测采用一期凝固法;细胞TF抗原测定采用ELISA法。结果AngⅡ（10^-9～10^-7M）可剂量依赖性诱导新生大鼠脑星形胶质细胞PCA、TF抗原的增加,并有明显的时效关系。洛沙坦（losartan）浓度在10^-6～10^-5M可不同程度地阻断AngⅡ的作用。结论AngⅡ可诱导新生大鼠脑星形胶质细胞组织因子的表达,该作用是通过血管紧张素Ⅱ1型受体实现的。     

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.     

Japanese Encephalitis Virus infection induces IL-18 and IL-1beta in microglia and astrocytes: correlation with in vitro cytokine responsiveness of glial cells and subsequent neuronal death

IL-1β and IL-18 are members of the IL-1 family of ligands, and their receptors are members of the IL-1 receptor family. Although several biological properties overlap for these cytokines, differences exist. In order to assess functional importance of these two cytokines in viral encephalitis, we have exploited an experimental model of Japanese Encephalitis (JE) and subsequent in vitro cell culture system. We report for the first time that in Japanese Encephalitis, microglia and astrocytes both produce IL-18 and IL-1β. In vitro, these two cytokines differentially activate microglia and astrocyte, and also alter the by stander neuronal survival following treatment with these two cytokines.