In the presence of danger：the extracellular matrix defensive response to central nervous system injury

Glial cells in the central nervous system （CNS） contribute to formation of the extracellular matrix, which provides adhesive sites, signaling molecules, and a diffusion barrier to enhance efficient on and axon potential propagation. In the normal adult CNS, the extracellular matrix （ECM） is relatively stable except in selected regions characterized by dynamic remodeling. However, after trauma such as a spinal cord injury or cortical contusion, the lesion epicenter becomes a focus of acute neuroinflammation. The activation of the surrounding glial cells leads to a dramatic change in the composition of the ECM at the edges of the lesion, creating a perilesion environment dominated by growth inhibitory molecules and restoration of the peripheral/ central nervous system border. An advantage of this response is to limit the invasion of damaging cells and diffusion of toxic molecules into the spared tissue regions, but this occurs at the cost of inhibiting migration of endogenous repair cells and preventing axonal regrowth. The following review was prepared by reading and discussing over 200 research articles in the field published in PubMed and selecting those with significant impact and/or controversial points. This article highlights structural and functional features of the normal adult CNS ECM and then focuses on the reactions of glial cells and changes in the perilesion border that occur following spinal cord or contusive brain injury. Current research strategies directed at modifying the inhibitory perilesion microenvironment without eliminating the protective functions of glial cell activation are discussed.     

Young neurons from the adult subependymal zone proliferate and migrate along an astrocyte,extracellular matrix-rich pathway

The subependymal zone (SEZ) of the lateral ventricle of adult rodents has long been known to be mitotically active. There has been increased interest in the SEZ, since it has been demonstrated that neuroepithelial stem cells residing there generate neurons in addition to glia in vitro. In the present study, we have examined parasagittal sections of the adult mouse brain using immunocytochemistry for extracellular matrix (ECM) molecules (tenascin and chondroitin sulfate-containing proteoglycans), glial fibrillary acidic protein (GFAP, a cytoskeletal protein prominently expressed by immature and reactive astrocytes), RC-2 (a radial glial and immature astrocyte cytoskeletal marker), TuJ1 (a class III β-tubulin isoform expressed solely by postmitotic and adult neurons), nestin (a cytoskeletal protein associated with stem cells), neuron-specific enolase, and bromodeoxyuridine (BrdU, which is taken up by dividing cells). Our results demonstrate that a population of young neurons reside within an ECM-rich, GFAP-positive astrocyte pathway from the rostral SEZ all the way into the olfactory bulb. Furthermore, BrdU labeling studies indicate that there is a high level of cell division along the entire length of this path, and double-labeling studies indicate that neurons committed to a neuronal lineage (i.e., TuJ1+) take up BrdU (suggesting they are in the DNA synthesis phase of the cell cycle), again along the entire length of the SEZ “migratory pathway.” Thus, the SEZ appears to retain the ability to produce neurons and glia throughout the life of the animal, functioning as a type of “brain marrow.” The implications of these findings are discussed in relation to the role that such a glial/ECM-rich boundary (as seen in the embryonic cortical subplate and other developing areas) may play in: confining the migratory populations and maintaining them in a persistent state of immaturity; facilitating their migration to the olfactory bulb, where they are incorporated into established adult circuitries; and potentially altering SEZ cell cycle dynamics that eventually lead to cell death. © 1996 Wiley-Liss, Inc.     

Expression of polypeptide variants of receptor-type protein tyrosine phosphatase β: The secreted form,phosphacan, increases dramatically during embryonic development and modulates glial cell behavior in vitro

Glial cells express three splicing variants of a receptor-type protein tyrosine phosphatase called RPTPβ. Two are receptor forms that differ in a large extracellular domain. The third is a secreted proteoglycan called phosphacan that lacks the cytoplasmic phosphatase domains. We have now identified, by immunoblotting, proteins corresponding to these three forms of RPTPβ in rat C6 glioma cells and brain. The short receptor form is much more prevalent than the full-length receptor in C6 glioma cells. Phosphacan is much more abundant than either of the receptor forms in rat brain, and its expression increases progressively during embryonic development, while the receptor forms show only moderate changes. In contrast to the long form and phosphacan that were detected as proteoglycans, the short receptor form, lacking the large alternatively spliced domain, was not detected as a chondroitin sulfate proteoglycan. We recently showed that phosphacan binds to the neuron-glia cell adhesion molecule, Ng-CAM, and we now report that glia expressing RPTPβ adhere and extend processes on substrates coated with Ng-CAM. After one day in culture, however, the glia retract their processes and often lift off the substrate. Conditioned medium from glial cells, which contains large amounts of phosphacan, inhibits glial adhesion to Ng-CAM, and depletion of phosphacan from the conditioned medium by immunoadsorption reduces the inhibitory activity. The results show that phosphacan increases dramatically during development, and indicate that secreted forms of RPTPβ can modulate glial cell adhesion and behavior. © 1996 Wiley-Liss, Inc.     

Receptor-mediated calcium signalling in glial cells from mouse corpus callosum slices

We addressed the question of whether glial cells in intact white matter tracts express neurotransmitter receptors and we used Ca⁺⁺ signalling as a probe to detect the receptor activation. Corpus callosum slices from postnatal mice were bulk-loaded with the Ca⁺⁺- sensitive fluorescent dye fluo-3, and confocal microscopy was used to measure Ca⁺⁺ transients in response to neuroligands. Glial cell bodies were intensely dye-loaded and could be discriminated from the diffuse fluorescence of axons. Subpopulations of glial cells from slices obtained at postnatal days 3 to 7 responded with Ca⁺⁺ signals to ATP, glutamate, histamine, GABA, norepinephrine, serotonin, angiotensin II, bradykinin, and substance P. These subpopulations showed a distinct overlap; cells which were responsive to substance P always showed Ca⁺⁺ signalling in response to histamine, ATP, GABA, and high K⁺ (membrane depolarization). GABA-responsive cells almost always showed a [Ca⁺⁺], increase after membrane depolarization. In brain slices from postnatal day 11 to 18 animals, the Ca⁺⁺ responses were evident for glutamate, ATP, and norepinephrine, while GABA, substance P, serotonin, histamine, or angiotensin II rarely elicited a response. This study demonstrates that white matter glial cells in slices exhibit a large repertoire of neurotransmitter responses linked to Ca⁺⁺ signalling and that these receptor systems are differentially distributed on sub-populations of glial cells. © 1996 Wiley-Liss, Inc.     

Olfactory Schwann cells are derived from precursor cells in the olfactory epithelium

In this morphological and immunohistochemical study we show that olfactory schwann cells (OSC) are derived from precursor cells residing in the olfactory epithelium. During development, they migrate out of the epithelium and extend processes to ensheath the olfactory axons. Olfactory mucosa from E14 rat embryos and juvenile rats were treated with trypsin-pancreatin to remove the underlying connective tissue. The epithelial explant was then maintained for two days in culture, during which cells migrated out from the explant. Among them were spindly bipolar cells which were identified as OSC by their positive immunoreaction for glial fibrillary acidic protein, ultrastructure, and association with growing axons. Axonal growth was significantly more profuse in the embryonic explants, in which the polarity of the OSC was oriented parallel with the axons. Ultrastructural observations showed that ensheathment of the bundles of axons resembled those in vivo.     

Long-term proliferation and dopaminergic differentiation of human mesencephalic neural precursor cells

We report on generation of dopamine neurons from long-term cultures of human fetal mesencephalic precursor cells. These CNS precursor cells were successfully expanded in vitro using the mitogens epidermal growth factor (EGF) and fibroblast growth factor-2 (FGF-2). Incubation of these cultures in 3% atmospheric oxygen resulted in higher cellular yields than room air. Following incubation in differentiation media containing interleukin (IL)-1b (IL-1b), IL-11, leukemia inhibitory factor (LIF), and glial cell line-derived neurotrophic factor (GDNF), up to 1% of the precursor cells converted into cells immunoreactive for tyrosine hydroxylase (TH), a marker for dopamine neurons. The TH immunoreactive cells exhibited morphological and functional properties characteristic of dopamine neurons in culture. These precursor cells might serve as a useful source of human dopamine neurons for studying the development and degeneration of human dopamine neurons and may further serve as a continuous, on-demand source of cells for therapeutic transplantation in patients with Parkinson's disease.     

痛刺激后大鼠三叉神经尾侧亚核星形细胞和神经元相互关系的电镜观察

目的：观察大鼠上唇皮下注射福尔马林后，三叉神经尾侧亚核（Sp5C)内反应性星形细胞和神经元之间相互关系的超微结构。方法：用DAB染色的抗胶质原纤维酸性蛋白（GFAP）、抗connexin43(Cx43）和金颗粒标记抗Cx32双标记免疫电镜方法。结果：电镜下观察到Sp5C内反应性星形细胞和神经元之间存在4种联系结构：第一种是突触样结构；第二种是三种成分的突触复合体，第三种是缝隙连接；第四种是由Cx32和Cx43构成的异源性缝隙连接（HGJ）。HGJ表现为两侧膜增厚，Cx43阳性物质和Cx32阳性金颗粒分别位于星形细胞和神经元一侧，痛刺激后HGJ数明明显增加。结论：神经元和星形细胞之间有多种信息通道，HGJ可能是一种快速，适应性信息通道。Sp5C星形细胞可能通过HGJ调节神经元的活动，共同参与中枢神经系统对刺激反应的调节。     

雌激素、褪黑素对Aβ诱导的大鼠海马的神经损害的影响

目的:探讨雌激素(Estrogen,E)、褪黑素(Melatonin,MT)对β淀粉样蛋白(Beta-amyloid,Aβ)注入海马齿状回(Dentate gyrus,DG)诱导的神经损害的影响。方法:将老年动物随机分为假手术、生理盐水(NS)对照、正常+Aβ、雌二醇(E_2)+Aβ、MT+Aβ、E_2+MT+Aβ组,将体外孵育的Aβ_(1-40)注入海马DG分子层后,E_2、MT注射组立即分别皮下、腹腔注射E_2 10μg、MT 0.5 mg·100 mg~(-1)体重,持续7 d,观察海马DG神经病理损害情况。结果:假手术组无海马DG损害,NS组仅针道处海马CA1锥体细胞带略有紊乱、中断、胶质细胞少量,两组偶有细胞凋亡。Aβ诱导的海马DG细胞带的受损长度、胶质细胞增生数及细胞凋亡,在正常+Aβ、E_2+Aβ、MT+Aβ、E_2+MT+Aβ各组依次显著减少(P<0.01),前两变量之间线性相关系数(r_1)=0.914(P<0.01),后两变量之间r_2=0.956(P<0.01)。结论:Aβ注入海马DG可导致神经毒性,细胞凋亡参与了神经毒性过程,其神经毒性与胶质细胞增生成正相关;E_2、MT可显著减轻Aβ神经毒性,而且E_2+MT>MT>E_2,其影响与E_2、MT可减轻胶质细胞增生有关。     

Definite familial multiple system atrophy with unknown genetics

Multiple system atrophy (MSA) is an oligodendrogliopathy of presumably sporadic origin, characterized by prominent α‐synuclein inclusions with neuronal multisystem degeneration, although a few Mendelian pedigrees have been reported. Here we report two familial cases of MSA of unknown genetic background. One patient was diagnosed as a possible MSA‐C (cerebellar dysfuntion) case, and the other as clinically possible MSA‐P (parkinsonism), which turned out to be definite MSA, based on a detailed autopsy. The neuropathology showed extensive deposition of α‐synuclein in the glia as well as in the neurons located in the cerebral cortices and hippocampal systems, although neither multiplication of the SNCA gene or mutations in COQ2 gene were identified in the family concerned.     

Lithium normalizes elevated intracellular sodium

BACKGROUND: Both mania and bipolar depression are characterized by elevations of intracellular sodium concentrations. This observation has been purported to be central to the pathophysiology of abnormal moods in bipolar illness. Reduction of sodium influx is a proposed shared mechanism of action of effective mood stabilizers, but direct documentation of this effect for lithium has never been demonstrated. METHODS: Flame spectroscopic determinations of intracellular sodium concentration were performed in the human glioma cell line, LN292, after treatment with the sodium pump inhibitor, ouabain, and co-treatment with ouabain and lithium. RESULTS: Ouabain 0.1 microM doubles the intracellular sodium concentration after 3 days. Pretreatment with lithium 1 mM for 1 week normalizes intracellular sodium. CONCLUSION: This is the first demonstration that lithium can normalize abnormally elevated intracellular sodium levels. This may be an important mechanism of lithium action.