Microglial reactivity to β-amyloid is modulated by astrocytes and proinflammatory factors

The brains of Alzheimer's disease (AD) patients present activated glial cells, amyloid plaques and dystrophic neurites. The core of amyloid plaques is composed of aggregated amyloid peptide (Abeta), a peptide known to activate glial cells and to have neurotoxic effects. We evaluated the capability of glial cells to mediate Abeta(1-42) cytotoxicity in hippocampal cultures. Conditioned media obtained from microglial cultures exposed to Abeta induced apoptosis of hippocampal cells. This pro-apoptotic effect was not observed in hippocampal cultures exposed to conditioned media obtained from mixed glial (astrocytes and microglia) cultures that had been exposed to Abeta. Microglia exposed to Abeta responded with reactive morphological changes, induction of iNOS, elevated nitric oxide production and decreased reductive metabolism. All these responses were attenuated by the presence of astrocytes. This astrocyte modulation was however, not observed when glial cells were exposed to proinflammatory factors (LPS+Interferon-gamma) alone or in combination with Abeta. Our results suggest that astrocytes and proinflammatory molecules are determining factors in the response of microglia to Abeta.

A synthetic peptide blocking the apolipoprotein E/beta-amyloid binding mitigates beta-amyloid toxicity and fibril formation in vitro and reduces beta-amyloid plaques in transgenic mice

Alzheimer's disease (AD) is associated with accumulation of beta-amyloid (Abeta). A major genetic risk factor for sporadic AD is inheritance of the apolipoprotein (apo) E4 allele. ApoE can act as a pathological chaperone of Abeta, promoting its conformational transformation from soluble Abeta into toxic aggregates. We determined if blocking the apoE/Abeta interaction reduces Abeta load in transgenic (Tg) AD mice. The binding site of apoE on Abeta corresponds to residues 12 to 28. To block binding, we synthesized a peptide containing these residues, but substituted valine at position 18 to proline (Abeta12-28P). This changed the peptide's properties, making it non-fibrillogenic and non-toxic. Abeta12-28P competitively blocks binding of full-length Abeta to apoE (IC50 = 36.7 nmol). Furthermore, Abeta12-28P reduces Abeta fibrillogenesis in the presence of apoE, and Abeta/apoE toxicity in cell culture. Abeta12-28P is blood-brain barrier-permeable and in AD Tg mice inhibits Abeta deposition. Tg mice treated with Abeta12-28P for 1 month had a 63.3% reduction in Abeta load in the cortex (P = 0.0043) and a 59.5% (P = 0.0087) reduction in the hippocampus comparing to age-matched control Tg mice. Antibodies against Abeta were not detected in sera of treated mice; therefore the observed therapeutic effect of Abeta12-28P cannot be attributed to an antibody clearance response. Our experiments demonstrate that compounds blocking the interaction between Abeta and its pathological chaperones may be beneficial for treatment of beta-amyloid deposition in AD.

Microdissection genotyping of mixed glial and primitive neuroectodermal central nervous system neoplasm

A 22-year-old man with previous radiation treatment for childhood astrocytoma underwent resection of a right parietooccipital lesion. Histopathology revealed a malignant neoplasm with areas of astrocytic and primitive neuroectodermal components. To resolve the relationship and cellular origin, representative tissue was microdissected from several targets, obtaining a balanced mixture of each element. Nonneoplastic brain parenchyma was separately microdissected to determine polymorphic marker informativeness and to serve as an internal negative control. Despite the relatively small quantity of tissue removed for each microdissection target, sufficient material was available for reliable, balanced, polymerase chain reaction-format genotyping encompassing a panel of tumor suppressor genes and genetic loci associated with these forms of neoplasia. The findings revealed distinct discordant genotypic profiles for each of the neoplastic components. The efficacy of the approach used for molecular analysis of this complex neoplasm and the implication of the genotypic findings are discussed.

Glutamate uptake by oligodendrocytes: Implications for excitotoxicity in multiple sclerosis

BACKGROUND

Excitotoxic damage is a common pathologic event in a number of neurologic diseases occurring after accumulation of excess extracellular glutamate in the CNS and subsequent overstimulation of glutamate receptors. In gray matter, astrocytes take up synaptically released glutamate and are thus key cells in maintaining glutamate homeostasis. In white matter, oligodendrocytes have been shown to express glutamate transporters, but their role in extracellular glutamate removal is unclear.

OBJECTIVE

To investigate whether cultured human fetal oligodendrocytes functionally express the main glutamate transporters EAAT-1 and EAAT-2.

METHODS

Cultures of fetal human oligodendrocytes were examined by immunocytochemistry and [3H]glutamate uptake, and the findings were correlated with glutamate transporter expression in normal and multiple sclerosis (MS) CNS tissue.

RESULTS

Both EAAT-1 and EAAT-2 were expressed by human oligodendrocytes in vitro. Incubation of oligodendrocytes with the proinflammatory cytokine tumor necrosis factor-alpha (TNFalpha) reduced EAAT-1 expression and inhibited glutamate uptake by >75%. Furthermore, in normal human white matter, oligodendrocytes were found to be the predominant cells to express EAAT-1 and EAAT-2, both at the mRNA and at the protein level. A small number of astrocytes in white matter expressed these receptors, more so EAAT-1 than EAAT-2. In MS white matter, oligodendrocytes lost expression of EAAT-1 and EAAT-2 receptors in the lesion vicinity.

CONCLUSIONS

Oligodendrocytes appear to be predominant cells for glutamate clearance in human white matter. Glutamate receptor expression and glutamate removal were defective in MS white matter, possibly mediated by TNFalpha, changes that might underlie high extracellular glutamate and an increased risk for glutamate excitotoxicity.

Morphologic change and astrocyte response to unilateral spinal cord compression in rabbits

In myelopathy, unilateral compression of the spinal cord in cases of disc herniation would be expected to produce Brown-Séquard syndrome. However, a transverse lesion syndrome occurs in most clinical cases. In order to reveal the mechanism by which unilateral compression induces transverse damage to the spinal cord, damage of the gray and white matter in each half of the spinal cord were evaluated quantitatively to determine the density of GFAP-positive astrocytes. The cervical spinal cord in rabbits was unilaterally compressed with a small screw. The area of each half of the damaged cord and the density of GFAP-positive astrocytes of the compressed and contralateral halves were investigated one week after the surgery. No apparent paralysis was observed during the period of observation. As the compression increased, the area of the compressed half of the spinal cord decreased significantly compared to the contralateral half. The densities of GFAP-positive astrocytes in the gray matter and the anterior funiculus increased significantly in the compressed half. There were no significant differences in the densities at the lateral and dorsal funiculi between the compressed and contralateral halves. The tissue damage in the gray matter of the compressed half was markedly higher. No significant difference between the two halves in damage was seen in the lateral funiculus, where in the lateral pyramidal and the dorsal spinocerebellar tracts are found. These findings provide evidence of the mechanistic basis for the spinal cord damage that leads to transverse lesion syndrome in unilateral compression myelopathy.

Glial scar and axonal regeneration in the CNS: lessons from GFAP and vimentin transgenic mice

Astrocytes play an active role in the brain and spinal cord. For example, they have a function in formation and maintenance of the blood-brain barrier, ion homeostasis, neurotransmitter transport, production of extracellular matrix, and neuromodulation. Moreover, they play a role in preserving or even restoring the structural and physiological integrity after tissue injury. Currently, the function of astrocytes was studied with regard to the controversially discussed aspects of permissivity on the one-hand-side and inhibition of the other side exerted by reactive astrocytes for axonal regrowth in the adult CNS. Accordingly, knock-out mice deficient in vimentin (VIM) and/or glial fibrillary acidic protein (GFAP), the two major IF-proteins of astrocytes, were investigated. In addition, in vitro studies were carried out, on whether the absence of one or both proteins (VIM, GFAP) influences axonal regeneration. In experimental animals, a hemisection of the spinal cord was performed utilizing the above mentioned double-mutant mice. The knock-out mice were generated by gene targeting. Double-mutants were obtained by crossing single null mice. The in vitro results indicate that both VIM and GFAP were absent in astrocytic cultures obtained from double-mutant mice. On the other side, the proteins were detected in more than 85%, of cultured cells from wild types. Co-culture of mutant mice astrocytes with neurons revealed that the neuronal density was different from that obtained in culture with wild type astrocytes. On the other side, there was a marked increase in neuronal density in co-cultures utilizing both GFAP knock-out- or double-mutant mice astrocytes again as compared to co-cultures with wild type astrocytes. Moreover, the neurite length of neurons was significantly increased in experiments with neurons growing on astrocytes from GFAP-knock-out or double-mutant mice. The in vivo experiments demonstrate an increase of nestin (NES) immunoreactivity at three days in the sectioned side of the spinal cord, in the perikaryon and astroglial processes. In double-mutant mice only a slight increase in NES-immunoreactivity was found in the lesion side, albeit confined to the perikaryon of astrocytes. Below the lesion, serotonin immunostaining was dramatically reduced three days after the insult in both sides, particularly in the lesion side. The decrease was more pronounced in double-mutant than in wild type mice. On the other side, double-mutant mice had a much higher density of serotonergic fibers in the ventral horn in the lesioned side. In conclusion, the findings demonstrate that in the absence of important astrocytic proteins as VIM and GFAP, the astroglial response to injury is significantly modified underlying reduced scar formation. Attenuation of scar formation may enhance axonal sprouting of serotonergic axons below the lesion, which specifically reinnervate motoneuron pools.

Mechanism of acute ischemic injury of oligodendroglia in early myelinating white matter: the importance of astrocyte injury and glutamate release

In developing CNS white matter (WM), the period of early myelination is characterized by a heightened sensitivity to ischemic injury. Using an in situ (isolated) preparation, we show that the mechanism of acute ischemic injury of immature WM oligodendroglial involves Ca2+ influx though non-NMDA type glutamate receptors (GluRs). The Ca2+-influx and acute cell death that was evoked by ischemic conditions (oxygen and glucose withdrawal) in identified P10 rat optic nerve oligodendroglia were blocked by removing extracellular Ca2+ or by CNQX, a selective non-NMDA GluR antagonist. The selective Na-K-Cl cotransport (NKCC) inhibitor bumetanide was also highly protective, even though NKCC expression is restricted to astrocytes in this tissue. Bumetanide largely prevented the non-NMDA GluR-mediated [Ca2+]i rise evoked by ischemia in oligodendroglia, suggesting that it interfered with ischemic glutamate release. In control WM, glutamate-like reactivity was located mainly in astrocytes and oligodendroglia identified using ultrastructural criteria. In ischemic WM, astrocyte glutamate-like reactivity was reduced, an effect countered by bumetanide. We suggest a model in which NKCC-dependent injury and release of glutamate from astrocytes activates glutamate receptors on oligodendroglia, resulting in Ca2+-influx and acute cell death.

Acute ischemic injury of astrocytes is mediated by Na-K-Cl cotransport and not Ca2+ influx at a key point in white matter development

Cerebral palsy is a common birth disorder that frequently involves ischemic-type injury to developing white matter (WM). Dead glial cells are a common feature of this injury and here we describe a novel form of acute ischemic cell death in developing WM astrocytes. Ischemia, modeled by the withdrawal of oxygen and glucose, evoked [Ca2+]i increases and cell death in astrocytes in post-natal day 10 (P10) rat optic nerve (RON). Removing extracellular Ca2+ prevented increases in [Ca2+]i but increased the amount of cell death. Astrocytes showed rapid [Na+]i increases during ischemia and cell death was reduced to control levels by substitution of extracellular Na+ or Cl- or by perfusion with bumetanide, a selective Na-K-Cl cotransport (NKCC) blocker. Astrocytes showed marked swelling during ischemia in the absence of extracellular Ca2+, which was blocked by bumetanide. Raising the extracellular osmolarity to limit water uptake reduced ischemic astrocyte death to control levels. Ultrastructural examination showed that post-ischemic astrocytes had lost their processes and frequently were necrotic, effects partially prevented by bumetanide. At this point in development, therefore, NKCC activation in astrocytes during ischemia produces an osmo-regulatory challenge. Astrocytes can subsequently regulate their cell volume in a Ca2+-dependent fashion but this will require ATP hydrolysis and does not protect the cells against acute cell death.

Astrocytic degeneration relates to the severity of disease in frontotemporal dementia

The main unifying feature of cases with frontotemporal dementia (FTD) is the pattern of brain atrophy. Surprisingly, there are a variety of underlying histopathologies in cases with the clinical features and typical pattern of atrophy characterizing FTD. This suggests that the degenerative mechanism(s) associated with pyramidal cell loss and gliosis in FTD is likely to be similar in the different histopathological forms of the disease. In this study we tested this hypothesis by analysing a common cell death mechanism, apoptosis, in cases of FTD with either Pick's disease (PiD) (n = 9) or frontotemporal lobar degeneration (FTLD) (n = 7) compared with normal controls (n = 10). Tissue sections from previously analysed cases were stained using anti-activated caspase-3 immunohistochemistry, TUNEL, propidium iodide, and cell- and pathology-specific labels. These markers of apoptosis identified both astrocytes and neurons in regions vulnerable to degeneration in all cases of FTD. However, neuronal apoptosis was rare (<2% of neurons), even at early disease stages where there is considerably less frontotemporal atrophy or pyramidal cell loss. This suggests that other cell death mechanisms account for the progressive neuronal loss in FTD. In contrast, astrocytes with beaded processes and other apoptotic features were very frequent in both PiD and FTLD, with the severity of astrocytosis and astrocytic apoptosis correlating with both the degree of neuronal loss and the stage of disease. These findings provide evidence that astrocytic apoptosis occurs as an early event in different histopathological forms of FTD. Furthermore, this astrocytic apoptosis directly relates to the degree of degeneration in FTD, and becomes the overwhelming pathological feature as the disease progresses.

Induction of secretory phospholipase A2 in reactive astrocytes in response to transient focal cerebral ischemia in the rat brain

Although mRNA expression of group IIA secretory phospholipase A2 (sPLA2-IIA) has been implicated in responses to injury in the CNS, information on protein expression remains unclear. In this study, we investigated temporal and spatial expression of sPLA2-IIA mRNA and immunoreactivity in transient focal cerebral ischemia induced in rats by occlusion of the middle cerebral artery. Northern blot analysis showed a biphasic increase in sPLA2-IIA mRNA expression following 60-min of ischemia-reperfusion: an early phase at 30 min and a second increase at a late phase ranging from 12 h to 14 days. In situ hybridization localized the early-phase increase in sPLA2-IIA mRNA to the affected ischemic cortex and the late-phase increase to the penumbral area. Besides sPLA2-IIA mRNA, glial fibrillary acidic protein (GFAP) and cyclo-oxygenase-2 mRNAs, but not cytosolic PLA2, also showed an increase in the penumbral area at 3 days after ischemia-reperfusion. Immunohistochemistry of sPLA2-IIA indicated positive cells in the penumbral area similar to the GFAP-positive astrocytes but different from the isolectin B4-positive microglial cells. Confocal microscopy further confirmed immunoreactivity of sPLA2-IIA in reactive astrocytes but not in microglial cells. Taken together, these results demonstrate for the first time an up-regulation of the inflammatory sPLA2-IIA in reactive astrocytes in response to cerebral ischemia-reperfusion.

Heterogeneity between hippocampal and septal astroglia as a contributing factor to differential in vivo AMPA excitotoxicity

Astroglial participation in the regional differences of vulnerability to alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-induced neurodegeneration was investigated in the rat hippocampus and medial septum using L-alpha-aminoadipate (alpha-AA) as a specific astroglial toxin. alpha-AA was microinjected in the hippocampus and the medial septum and a time-course study was carried out between 2 hr and 3 days. When compared to controls, microinjection of alpha-AA in the hippocampus induced within 3 days a reversible loss of glial fibrillary acidic protein (GFAP) immunostaining and a microglial reaction without any neuronal loss, whereas in the medial septum it caused no effects on astroglial, microglial, or neuronal populations. Differences in hippocampus and medial septum vulnerability were also evidenced when alpha-AA was co-injected with AMPA and neurodegeneration was assessed in terms of neuronal loss, glial reactions, calcification, and atrophy of the area. In the hippocampus, alpha-AA increased AMPA excitotoxicity with marked disorganization of all hippocampal subfields, increased neuronal loss, a more important astroglial reaction, a larger area of microgliosis, and a greater abundance of calcium deposits. By contrast, in the medial septum alpha-AA did not modify any parameter of the AMPA-induced lesion. In conclusion, the presence of different astroglial populations in hippocampus and medial septum results in a different participation to AMPA excitotoxicity that may determine, at least in part, the specific regional vulnerability to neurodegeneration.

The cerebral cortex of spontaneously hypertensive rats: a quantitative microanatomical study

The morphology of cerebral cortex was investigated in male spontaneously hypertensive rats (SHR) aged 2, 4 and 6 months (pre-hypertensive, developing hypertension and established hypertension respectively) and in age-matched normotensive Wistar-Kyoto (WKY) rats using quantitative microanatomical techniques. Analysis included frontal and occipital cortex as a paradigm of motor and sensory cerebrocortical areas respectively. Values of systolic pressure were slightly higher in 2-month-old SHR compared to age-matched WKY rats and augmented progressively with increasing age in SHR. In frontal cortex of SHR a decrease of nerve cell number and of cortical volume was observed in layers V and VI of 4- and 6- month-old SHR, and in layers I-IV of 6- month-old SHR. In occipital cortex a decrease of the number of nerve cells and of cortical volume was observed in layers V and VI of 2-, 4-, 6- month-old SHR, and in layers I-IV of 6-month-old SHR. Numerical decrease of neurons in SHR affected to a greater extent occipital cortex than frontal cortex. An increase in the number of glial fibrillary acidic protein (GFAP)-immunoreactive astrocytes (hyperplasia) as well as in the mean immune reaction area (hypertrophy) was found in the two cerebrocortical areas investigated of 6-month-old SHR. The occurrence of apoptosis and/or necrosis identified using the terminal deoxyribo-nucleotidyl transferase (TdT)-mediated biotin-16-dUTP nick-end labeling (TUNEL) technique was also observed in frontal and occipital cortex of 6-month-old SHR, but not of younger cohorts. These findings indicate the development of microanatomical changes in the cerebral cortex of SHR, the extent of which increases parallel with the progression of hypertension. The occurrence of cerebrocortical apoptosis and/or necrosis as well as the obvious astrogliosis occurring in established hypertension may account for the increased risk of vascular dementia that represents a specific trait of complicated hypertension.

Brain-IL-1 beta triggers astrogliosis through induction of IL-6: inhibition by propranolol and IL-10

BACKGROUND

Gliosis is a characteristic pathology in many central nervous system (CNS) diseases. Cytokines are considered to be effectors of gliosis. It has been shown that pro-inflammatory cytokines such as interleukin (IL)-1 and IL-6 boost glia scar formation. On the other hand, anti-inflammatory cytokines, such as IL-10 and IL-1 receptor antagonist (ra), can act neuroprotectively. Furthermore, various immune mediators and neurotransmitters can modulate the onset of gliosis.

MATERIAL/METHODS

We used 100 male Sprague-Dawley rats to investigate the mechanisms of brain-cytokine-induced astrogliosis using an in vivo model of convection-enhanced delivery of cytokines (IL-beta, IL-6, tumor necrosis factor (TNF)-alpha) into the cerebro-ventricular system. The protective effects of the anti-inflammatory cytokine IL-10 and the neurotransmitter propranolol were also investigated.

RESULTS

With this paradigm, we could clearly demonstrate that IL-6 is a key cytokine mediating astrogliosis, noticeable in the increased expression of glial fibrillary acidic protein (GFAP). Thus intra-cerebroventricular infusion of IL-6 increased GFAP expression in a dose-dependent manner. Furthermore, GFAP expression was also increased by IL-beta, which correspondingly triggered an IL-6 release into the CSF. Accordingly, TNF-alpha, which did not induce IL-6 release, also did not induce gliosis. On the other hand, substances which decrease IL-beta-induced IL-6 production, such as propranolol and IL-10, also dramatically decreased IL-beta triggered gliosis.

CONCLUSIONS

IL-6 infusion, as well as IL-beta-induced IL-6 release into the CSF, increase GFAP expression in the cerebral cortex and hippocampus. Accordingly, blockade of the IL-beta-induced IL-6 release by IL-10 and propranolol decreases GFAP expression.

Periventricular and Subcortical Leukoencephalopathy in two Dachshund Puppies

Two wirehaired dachshund puppies were presented with generalized tremor and gait abnormalities characterized by mild ataxia, tetraparesis and slightly abnormal proprioception. Neurological examination led to the suspicion of a diffuse generalized white matter lesion. Computerized tomography and pathological examination revealed a remarkable unilateral dilatation of the lateral ventricles in each dog. Histopathological examination showed a severe reduction of stainable myelin, widespread mild perineuronal oedema with vacuolations and multifocal reactive astrocytosis affecting the subcortical and deep periventricular white, and to a lesser degree, grey matter of the cerebral hemispheres, most prominently at the level of the optic chiasm. Axons showed a moderately reduced packing density; some axons were irregularly shaped and slightly thickened. There was no evidence of myelin breakdown products and neurones appeared to be well preserved. Brain stem, cerebellum and spinal cord were normal, as was the peripheral nervous system. This leukoencephalopathy in two dachshund puppies most closely resembles human periventricular leukomalacia caused by pre- or perinatal hypoxia-ischaemia.

Relationship between S100β and GFAP expression in astrocytes during infarction and glial scar formation after mild transient ischemia

The expression of astrocyte marker proteins (S100beta and GFAP) during infarction and glial scar formation after transient middle cerebral artery (MCA) occlusion was examined using double immunostaining. S100beta immunoreactivity markedly decreased in the core of the injured area when observed immediately after reperfusion and did not increase again. In the periphery, however, S100beta expression increased, showing that S100beta synthesis was up-regulated. S100beta+/iNOS+ astrocytes in the periphery were observed from day 1, when small infarct areas were detectable, up to day 5, when infarct expansion had almost ended. TUNEL+ cells in the periphery were present from days 1 to 5. S100beta+/TUNEL+ cells were observed centrally and around the periphery of the injured area, predicting that cell death contributes to the increase of S100beta concentration in the injured area. Our results suggest that (1) higher concentration of S100beta in the extracellular space due to S100beta leakage from damaged astrocytes leads to up-regulation of S100beta synthesis and induction of inducible nitric oxide synthase (iNOS) synthesis in astrocytes, contributing to infarct expansion that results in DNA damage or cell death via NO and ROS production, and (2) GFAP, but not S100beta, is a main contributor to glial scar formation. On day 1 postreperfusion, the microdiascopic images of the injured areas from the unstained thick sections or the areas detected by S100beta immunoreactivity were larger than those of the infarct areas detected by hematoxylin--eosin (HE)-staining. The difference between these sizes might be useful to predict infarct expansion.

Multinucleated astrocytes in old demyelinated plaques in a patient with multiple sclerosis

A 51-year-old woman with MS of 26 years duration is reported. The patient's MS history began at the age of 25 years with an initial relapsing-remitting course, followed by slow progression without distinct relapses. She became bed-ridden at the age of 40 years. A post-mortem examination revealed numerous demyelinated plaques that exhibited fibrillary gliosis with Rosenthal fibers, but without lymphocytic cuffing or foamy macrophages. Activated microglia were found mainly in the marginal portion of the plaques. These plaques were consistent with so-called 'slowly expanding plaques'. Interestingly, multinucleated astrocytes were observed within the plaques, being more numerous in the area where microglial infiltration had occurred. These findings suggest that mild persistent inflammatory processes are present even in old plaques and that certain inflammatory stimuli cause multinucleation of astrocytes. This might explain the gradual deterioration without definite relapses observed in the late stage of MS.

Immunohistochemical investigation of cerebellum in dogs infected with canine distemper virus

The cerebella of 21 dogs with canine distemper virus (CDV) infection and four normal dogs were examined histopathologically and immunohistochemically. Cerebella of CDV-infected dogs showed nonsuppurative demyelinating encephalomyelitis, classified as acute, subacute or chronic. Immunolocalisation of CDV antigen also confirmed the infection. Tissues were examined for co-localisation of the CDV antigen with either an astrocyte-specific marker, glial fibrillary acidic protein (GFAP), or an oligodendrocyte-specific marker, galactocerebroside (GalC). Immunoreactive cells were counted in demyelinating areas of the white matter. The number of astrocytes (GFAP positive) was significantly (p < 0.05) higher in CDV-infected dogs compared to controls. In contrast, the number of oligodendrocytes (GalC positive) was significantly (p < 0.001) lower in CDV-infected dogs and was much lower in chronic cases (p < 0.05). Approximately 41% of astrocytes and 17% of oligodendrocytes were immunoreactive for CDV. The ratio of CDV-infected oligodendrocytes and astrocytes remained almost constant during the progression of the disease (P > 0.05). In conclusion, CDV infects both astrocytes and oligodendrocytes. The gradual loss of oligodendrocytes is most likely responsible for the progressive demyelination in CDV infection. Astrocytosis in CDV infection should be further investigated if it occurs to stimulate oligodendrocytes for myelin production to compensate for the loss or to induce oligodendrocyte degeneration.

Hypoosmotic swelling increases protein tyrosine nitration in cultured rat astrocytes

Astrocyte swelling is observed in different types of brain injury. We studied a potential contribution of swelling to protein tyrosine nitration (PTN) by using cultured rat astrocytes exposed to hypoosmotic (205 mosmol/L) medium. Hypoosmolarity (2 h) increases total PTN by about 2-fold in 2 h. The hypoosmotic PTN is significantly inhibited by the NMDA receptor antagonist MK-801, the nitric oxide synthase (NOS) inhibitor L-NMMA, the extracellular Ca2+ chelator EGTA and the calmodulin antagonist W13, suggesting the involvement of NMDA receptor activation, influx of extracellular Ca2+ and Ca2+/calmodulin-dependent NO synthesis. Further, superoxide dismutase plus catalase and uric acid strongly inhibit hypoosmotic PTN, suggesting the involvement of the toxic metabolite peroxynitrite (ONOO-) as a nitrating agent. Hypoosmotic astrocyte swelling rapidly stimulates generation of reactive oxygen intermediates; this process is prevented by MK-801 and EGTA. In addition, MK-801 inhibits the hypoosmotic elevation of [Ca2+]i. The findings support the view that astrocyte swelling as induced, for example, by toxins relevant for hepatic encephalopathy is sufficient to produce oxidative stress and PTN and thus contributes to altered astroglial and neuronal function.

Oligodendrocytes within astrocytes ("emperipolesis") in the white matter in Creutzfeldt-Jakob disease

The occurrence of oligodendrocytes within astrocytes ("emperipolesis") has been described in demyelinating lesions in cases of multiple sclerosis and also in other non-demyelinating disorders. We found that this finding was common in the cerebral white matter of patients with Creutzfeldt-Jakob disease (CJD). Eight consecutive autopsy cases of sporadic CJD were reviewed, and in every case the gray matter exhibited classical histopathological features of CJD. In five cases with a long clinical course, the cerebral white matter was severely involved, and both axons and myelin sheaths were lost markedly. Within this devastated white matter, many hypertrophic astrocytes were found to engulf one to several oligodendrocytes within their cytoplasm (emperipolesis). The oligodendroglial nature of the engulfed cells was corroborated by nuclear immunoreactivity for anti-human Olig 2 antibody. In the remaining three cases, whose clinical course was short, the cerebral white matter was relatively well preserved, and emperipolesis was not or only very rarely found. The prevalence of emperipolesis of this type in the white matter in CJD was well correlated with the severity of the white matter lesions.

Desmoplastic infantile ganglioglioma -- a case report

Desmoplastic infantile ganglioglioma is a very rare supratentorial tumor occurring in the first two years of life. A five-month-old female infant presented with recurrent seizures, large head and loss of acquired milestones. Computerized Tomographic Scan of brain showed a large subarachnoid cyst with a solid intensely contrast enhancing tumor in the right temporoparietal region with severe degree of mass effect. Craniotomy and total excision of the tumor followed subsequently by subduro-peritoneal shunt for the extracerebral fluid collection was done. The child made good recovery. Histopathology revealed features of desmoplastic infantile ganglioglioma, viz., marked desmoplastic component with glial and neuronal elements. Immunohistochemistry showed positive staining for glial fibrillary acidic protein (GFAP) with areas of synaptophysin and chromogranin positivity. Desmoplastic infantile ganglioglioma is a rare tumor of infancy, which has excellent prognosis after total excision. No adjuvant therapy is required. This is the first Indian report of desmoplastic infantile ganglioglioma out of less than fifty cases reported worldwide.

BDNF-induced White Matter Neuroprotection and Stage-dependent Neuronal Survival Following a Neonatal Excitotoxic Challenge

Excitotoxicity may be critical in the formation of brain lesions associated with cerebral palsy. When injected into the murine neopallium at postnatal day (P) 5, ibotenate (activating NMDA and metabotropic glutamate receptors) produces neuronal death and white matter cysts. Such white matter cysts resemble those seen in periventricular leukomalacia, a lesion evident in numerous human premature newborns. The goal of this study was to assess BDNF neuroprotection against neonatal excitotoxic lesions. Cortical and white matter lesions induced by ibotenate at P5 were reduced by BDNF by up to 36 and 60%, respectively. BDNF neuroprotection involved TrkB receptors, MAPK pathway and reduced apoptosis. Although BDNF did not prevent the initial appearance of white matter lesions, it promoted secondary decrease of the lesion size. BDNF neuroprotection at P5 was maximal against lesions induced by NMDA or ibotenate but was moderate against lesions produced by an AMPA-kainate agonist. Finally, BDNF exacerbated neuronal death produced by ibotenate at P0 through increased apoptosis and p75(NTR) receptors, while BDNF had no detectable effect on lesions induced at P10. Altogether, these data showed that BDNF neuroprotection against neonatal excitotoxicity is dependent upon the type of activated glutamate receptors, the lesion localization and the developmental stage.

Chronic mild stress exacerbates the effects of permanent bilateral common carotid artery occlusion on CA1 neurons

The effect of chronic mild stress (CMStress) was examined in an animal model of chronic cerebral hypoperfusion. Eight-month-old male Sprague-Dawley rats underwent permanent bilateral occlusion of the carotid arteries (2VO) or sham surgery. At 7 days postsurgery, animals from these groups were randomly assigned to undergo CMStress consisting of relatively mild stressor exposure 6 days a week for 6 weeks or a no-stress regimen. They were perfused 24 h thereafter and stereology was used to estimate the total number of hippocampal CA1 and CA3 pyramidal cells. Glial fibrillary acid protein (GFAP) immunoreactivity in the hippocampus was also measured. Degenerating neurons were quantified with the Fluoro-Jade B staining technique. CMStress significantly potentiated CA1 cell loss in 2VO rats (17% loss), compared to a 7% loss of CA1 cells in nonstressed 2VO rats. CMStress had no effect on CA3 cell number. CMStress also caused a significant reduction in GFAP-immunoreactive astrocyte density in CA1, CA3, and the hilus of both sham and 2VO rats. Fluoro-Jade staining was absent, indicating that cell loss probably occurred in the early stage of combined 2VO and CMStress. It was concluded that CMStress exacerbates the consequences of chronic cerebral hypoperfusion on CA1 probably by reducing astrocytes, thereby increasing extracellular glutamate and/or diminishing free radical defense systems. These findings have particular relevance to understanding the contribution of chronic stress to Alzheimer's disease, which, in its premorbid stage, is characterized by cerebral hypoperfusion, and, in its clinical stage, is characterized by CA1 cell loss.

Immunohistochemical detection of EGFRvIII in high malignancy grade astrocytomas and evaluation of prognostic significance

The purpose of this study was to establish an accurate and accessible immunohistochemical (IHC) method for detecting vIII Egf receptor and to assess the prognostic significance of the method as applied to the detection of vIII in malignant astrocytomas. The accuracy of the method was determined by comparing vIII immunoreactivity in formalin-fixed and paraffin-embedded tumor sections versus RT-PCR results from the analysis of RNA extracted from corresponding frozen specimens. RT-PCR revealed vIII transcript in 18 of 44 cases in this series, and IHC analysis of matched formalin-fixed and paraffin-embedded sections showed EGFRvIII reactivity in each of these 18 tumors, as well as 1 additional tumor that was negative for vIII transcript. EGFR amplification was evident in all tumors expressing vIII; none of the 15 tumors lacking amplified EGFR were positive for vIII transcript or vIII protein. IHC analysis for vill expression was next applied to a large series of anaplastic astrocytomas (AAs) and glioblastoma multiforme (GBMs) from clinical trial patients with complete follow-up and that had been previously examined by FISH for amplified EGFR. Among the GBMs, vIII detection by IHC was determined in 19 of 46 cases (41.3%) with EGFR amplification, and in only 3 of 59 tumors lacking amplified EGFR (5.1%). Among the AAs, vIII expression was observed in 3 of 14 cases with amplified EGFR (21.4%) and in 6 of 49 cases without EGFR amplification (12.2%). GBM and AA patient survival analysis as a function of vIII expression showed contrasting results, with vIII positivity having no association with survival among GBM patients (p = 0.84), but being highly associated with reduced survival among AA patients (p = 0.0016). This latter finding, though quite possibly a result of vIII's association with increasing AA patient age, suggests that vIII IHC will be useful for identifying and/or confirming the identity of malignant astrocytomas whose clinical behavior is consistent with that of GBM.

Apolipoprotein E: diversity of cellular origins, structural and biophysical properties, and effects in Alzheimer's disease

Apolipoprotein E4 (apoE4) is a major risk factor for Alzheimer's disease (AD). Several hypotheses have been proposed to explain the association of the APOE epsilon4 allele with AD; however, the mechanisms underlying this association are largely unknown. Initially, apoE was thought to be synthesized primarily by astrocytes but not by neurons in the brain. However, subsequent studies have demonstrated that central nervous system neurons also express apoE under diverse physiological and pathological conditions. Detailed studies of the structure and biophysical properties of apoE isoforms have demonstrated unique properties distinguishing apoE4 from apoE3. Because the structural and biophysical properties of a protein determine how it functions under normal and abnormal conditions, apoE4, with its multiple cellular origins and multiple structural and biophysical properties, might contribute to the pathology of AD through several different mechanisms. Some of these mechanisms might be suitable targets for the development of new treatments for AD.

Cellular pathology of Parkinson?s disease: astrocytes, microglia and inflammation

Parkinson's disease (PD) is a frequent neurological disorder of the basal ganglia, which is characterized by the progressive loss of dopaminergic neurons mainly in the substantia nigra pars compacta (SNpc). Inflammatory processes have been shown to be associated with the pathogenesis of PD. Activated microglia, as well as to a lesser extent reactive astrocytes, are found in the area associated with cell loss, possibly contributing to the inflammatory process by the release of pro-inflammatory prostaglandins or cytokines. Further deleterious factors released by activated microglia or astrocytes are reactive oxygen species. On the other hand, they may mediate neuroprotective properties by the release of trophic factors or the uptake of glutamate. In this review, we will discuss the different aspects of activated glial cells and potential mechanisms that mediate or protect against cell loss in PD.