Gliosis in human brain: relationship to size but not other properties of astrocytes

Ethanol alters the physiology of neuron-glia communication

In the central nervous system (CNS), both neurones and astrocytes play crucial roles. On a cellular level, brain activity involves continuous interactions within complex cellular circuits established between neural cells and glia. Although it was initially considered that neurones were the major cell type in cerebral function, nowadays astrocytes are considered to contribute to cerebral function too. Astrocytes support normal neuronal activity, including synaptic function, by regulating the extracellular environment with respect to ions and neurotransmitters. There is a plethora of noxious agents which can lead to the development of alterations in organs and functional systems, and that will end in a chronic prognosis. Among the potentially harmful external agents we can find ethanol consumption, whose consequences have been recognized as a major public health concern. Deregulation of cell cycle has devastating effects on the integrity of cells, and has been closely associated with the development of pathologies which can lead to dysfunction and cell death. An alteration of normal neuronal-glial physiology could represent the basis of neurodegenerative processes. In this review we will pay attention on to the recent findings in astrocyte function and their role toward neurons under ethanol consumption.

Neuroprotective and neurotoxic properties of glial cells in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) affects more than 18 million people worldwide and is characterized by progressive memory deficits, cognitive impairment and personality changes. The main cause of AD is generally attributed to the increased production and accumulation of amyloid-β (Aβ), in association with neurofibrillary tangle (NFT) formation. Increased levels of pro-inflammatory factors such as cytokines and chemokines, and the activation of the complement cascade occurs in the brains of AD patients and contributes to the local inflammatory response triggered by senile plaque. The existence of an inflammatory component in AD is now well known on the basis of epidemiological findings showing a reduced prevalence of the disease upon long-term medication with anti-inflammatory drugs, and evidence from studies of clinical materials that shows an accumulation of activated glial cells, particularly microglia and astrocytes, in the same areas as amyloid plaques. Glial cells maintain brain plasticity and protect the brain for functional recovery from injuries. Dysfunction of glial cells may promote neurodegeneration and, eventually, the retraction of neuronal synapses, which leads to cognitive deficits. The focus of this review is on glial cells and their diversity properties in AD.

Implantation of a new porous gelatin-siloxane hybrid into a brain lesion as a potential scaffold for tissue regeneration

For brain tissue regeneration, any scaffold for migrated or transplanted stem cells with supportive angiogenesis is important once necrotic brain tissue has formed a cavity after injury such as cerebral ischemia. In this study, a new porous gelatin-siloxane hybrid derived from the integration of gelatin and 3-(glycidoxypropyl) trimethoxysilane was implanted as a three-dimensional scaffold into a defect of the cerebral cortex. The porous hybrid implanted into the lesion remained at the same site for 60 days, kept integrity of the brain shape, and attached well to the surrounding brain tissues. Marginal cavities of the scaffolds were occupied by newly formed tissue in the brain, where newly produced vascular endothelial, astroglial, and microglial cells were found with bromodeoxyuridine double positivity, and the numbers of those cells were dose-dependently increased with the addition of basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF). Extension of dendrites was also found from the surrounding cerebral cortex to the newly formed tissue, especially with the addition of bFGF and EGF. The present study showed that a new porous gelatin-siloxane hybrid had biocompatibility after implantation into a lesion of the central nervous system, and thus provided a potential scaffold for cell migration, angiogenesis and dendrite elongation with dose-dependent effects of additive bFGF and EGF.

Astrocyte activation and apoptosis: their roles in the neuropathology of HIV infection

Astrogliosis is a common neuropathological finding in the brains of HIV infected individuals; both activation and apoptosis of astrocytes are seen. This review aims to discuss the Fas pathway in the context of proliferation and apoptosis of astrocytes during HIV infection, and as a result of astrogliosis, the dysregulation of astrocyte-neuron networks. The presence of molecules reflecting astrocyte activation, which are derived from the solubilization of receptor/ligand from the surface of proliferating astrocytes, in the cerebrospinal fluid may be used to evaluate the degree of brain cell activation during HAART therapy. A better understanding of the molecular pathway(s) leading to increase activation and apoptosis of astrocytes, in parallel with studies conducted to unravel the molecules involved in T-cell apoptosis during HIV infection, may lead to the development of new therapeutic strategies for controlling HIV replication and tissue damage.

Distribution of GFAP+ astrocytes in adult and neonatal rat brain

Astrocytes can proliferate as a result of trauma to the brain, such as occurs in a variety of diseases. Understanding the normal distribution of astrocytes is necessary before the extent of astrogliosis can be clearly determined. However, little is known about the normal distribution of GFAP+ astrocytes especially during development. This study examined distribution of GFAP+ astrocytes in regions of the cortex, cerebellum, and brainstem of adult and rat pup brains by immunocytochemistry using antibodies against GFAP. The findings showed a differential distribution of GFAP+ astrocytes in the rat brain. A paucity of GFAP expression was found in most regions of the normal adult rat brainstem, whereas GFAP+ astrocytes were abundantly distributed in all areas of the cortex and cerebellum. A similar regional heterogeneity in the distribution of GFAP+ astrocytes was seen in the neonatal rat brain. These findings suggest that the development of the differential pattern of GFAP+ astrocytes seen in the rat brain does not occur postnatally, but instead is present at birth and appears to be determined during fetal development.

Neural precursor cells division and migration in neonatal rat brain after ischemic/hypoxic injury

Ischemia/hypoxia (I/H) causes severe perinatal brain disorders such as cerebral palsy. The neonatal brain possesses much plasticity, and to enhance new cell production would be an innovative means of therapy for such disorders. In order to elucidate the dynamic changes of neural progenitor cells in the neonatal brain after ischemia, we investigated new cells production in the subventricular zone and subsequent migration of these cells to the injured area. Newly produced cells were confirmed by incorporation of bromodeoxyuridine (BrdU), and attempt for differentiation was investigated by immunohistochemistry for molecular markers of each cellular lineage. In the sham-control brain, there were many BrdU-labeled cells which gradually decreased as the animal becomes older. Many of these cells were oligodendroglial progenitor or microglial cells. Although there were only few neuronal cells labeled for BrdU in the sham-control, they dramatically increased after I/H. They were located at just beneath the subventricular zone where the progenitor cells reside and to the injured area, indicating that newly produced cells migrated to the infarct region and differentiated into neuronal precursor cells in order to compensate the lost neural cells. We found that BrdU-labeled astroglial, oligodendroglial progenitor, and microglial cells were also increased after I/H, suggesting that they also play active roles in recovery. Progenitor cells may have potential for treating perinatal brain disorders.

Astrocyte apoptosis: implications for neuroprotection

Astrocytes, the most abundant glial cell types in the brain, provide metabolic and trophic support to neurons and modulate synaptic activity. Accordingly, impairment in these astrocyte functions can critically influence neuronal survival. Recent studies show that astrocyte apoptosis may contribute to pathogenesis of many acute and chronic neurodegenerative disorders, such as cerebral ischemia, Alzheimer's disease and Parkinson's disease. We found that incubation of cultured rat astrocytes in a Ca(2+)-containing medium after exposure to a Ca(2+)-free medium causes an increase in intracellular Ca(2+) concentration followed by apoptosis, and that NF-kappa B, reactive oxygen species, and enzymes such as calpain, xanthine oxidase, calcineurin and caspase-3 are involved in reperfusion-induced apoptosis. Furthermore, we demonstrated that heat shock protein, mitogen-activated protein/extracellular signal-regulated kinase, phosphatidylinositol-3 kinase and cyclic GMP phosphodiesterase are target molecules for anti-apoptotic drugs. This review summarizes (1) astrocytic functions in neuroprotection, (2) current evidence of astrocyte apoptosis in both in vitro and in vivo studies including its molecular pathways such as Ca(2+) overload, oxidative stress, NF-kappa B activation, mitochondrial dysfunction, endoplasmic reticulum stress, and protease activation, and (3) several drugs preventing astrocyte apoptosis. As a whole, this article provides new insights into the potential role of astrocytes as targets for neuroprotection. In addition, the advance in the knowledge of molecular mechanisms of astrocyte apoptosis may lead to the development of novel therapeutic strategies for neurodegenerative disorders.

Expression of connexin genes in hippocampus of kainate-treated and kindled rats under conditions of experimental epilepsy

We have analyzed whether the expression of connexin genes is altered in the hippocampus of kindled and kainate-treated rats, i.e., animal models of human temporal lobe epilepsy. We have tested this hypothesis by analyzing mRNA, protein abundance and cellular location of connexins (Cx) 43, 36, 32 and 30. The expression of glial fibrillary acid protein and mRNA was also monitored both in kainate-treated and kindled rats, in order to take into account reactive gliosis under these conditions. We found significantly increased expression of GFAP mRNA (100%) and protein (178%) in kainate-treated rats 4 weeks after kainate application, whereas in kindled rats only moderate increases of GFAP mRNA and protein were detected 2-3 weeks (group 2) or 4-6 weeks (group 1) after the last stage 5 induced seizure. Under gliotic conditions, connexins 43 and 30 mRNA or protein expression in astrocytes of kainate-treated rats were nearly unaffected. Cx36 mRNA expression (presumably in neurons) was significantly reduced (44%), whereas abundance of Cx36 protein was only slightly reduced. In both groups of kindled rats, Cx30 and Cx43 mRNA or protein expression were either slightly decreased or unchanged. Again, Cx36 mRNA and protein expression were reduced by about half in group 2. Immunofluorescence analysis of Cx43, Cx36 and Cx30 expression revealed that 4 weeks after the last kainate administration or kindling, cellular localization of these connexins was indistinguishable from control animals.

Expression of vascular endothelial growth factor by reactive astrocytes and associated neoangiogenesis

Injury to the central nervous system (CNS) invokes a reparative response known as astrogliosis, characterized largely by hypertrophy, proliferation and increased expression of glial fibrillary acidic protein (GFAP), resulting in reactive astrocytosis. Based on our prior observation that peritumoral reactive astrocytes express Vascular Endothelial Growth Factor (VEGF), a highly potent and specific angiogenic growth factor, we have hypothesized that reactive astrocytosis also contributes to the neovascularization associated with astrogliosis. To evaluate this hypothesis we evaluated human surgical/autopsy specimens from a variety of CNS disorders that induce astrogliosis and an experimental CNS needle injury model in wild type and GFAP:Green Fluorescent Protein (GFP) transgenic mice. Using computer image semi-quantitative analysis we evaluated the number of GFAP-positive reactive astrocytes, degree of VEGF expression by these astrocytes, associated Factor VIII-positive microvascular density (MVD) and Ki-67 proliferating endothelial cells. The degree of reactive astrocytosis correlated to levels of VEGF immunoreactivity and MVD in the neuropathological specimens. The mouse-needle-stick brain injury model demonstrated this correlation was temporally and spatially related and maximal after 1 week. These results, involving both human pathology specimens augmented by experimental animal data, supports our hypothesis that the neoangiogenesis associated with reactive astrogliosis is correlated to increased reactive astrocytosis and associated VEGF expression.

Effect of transforming growth factor-beta1 on microglial MHC-class II expression

In the present report, the effects of IFN-gamma and transforming growth factor beta1 (TGF-beta1) on major histocompatibility complex class II (MHC-II) gene expression in isolated mouse brain microglial cells, in the MH-S macrophage cell line and in the primary mouse macrophage cultures were examined. IFN-gamma is a potent inducer of MHC-II gene and this induction was further elevated in microglia by TGF-beta1, while TGF-beta1 inhibited IFN-gamma, induction in macrophages. The enhancing effect of TGF-beta1 was also detected in microglia at the protein level. Transient transfection of microglia with 5' deletional mutants of the MHC-II IAalpha promoter linked to the chloramphenicol acetyltransferase reporter gene demonstrated that TGF-beta1 acts at the transcriptional level to enhance the MHC-II expression induced by IFN-gamma.

Overexpression of the neuritotrophic cytokine S100beta precedes the appearance of neuritic beta-amyloid plaques in APPV717F mice

Homozygous APPV717F transgenic mice overexpress a human beta-amyloid precursor protein (betaAPP) minigene encoding a familial Alzheimer's disease mutation. These mice develop Alzheimer-type neuritic beta-amyloid plaques surrounded by astrocytes. S100beta is an astrocyte-derived cytokine that promotes neurite growth and promotes excessive expression of betaAPP. S100beta overexpression in Alzheimer's disease correlates with the proliferation of betaAPP-immunoreactive neurites in beta-amyloid plaques. We found age-related increases in tissue levels of both betaAPP and S100beta mRNA in transgenic mice. Neuronal betaAPP overexpression was found in cell somas in young mice, whereas older mice showed betaAPP overexpression in dystrophic neurites in plaques. These age-related changes were accompanied by progressive increases in S100beta expression, as determined by S100beta load (percent immunoreactive area). These increases were evident as early as 1 and 2 months of age, months before the appearance of beta-amyloid deposits in these mice. Such precocious astrocyte activation and S100beta overexpression are similar to our earlier findings in Down's syndrome. Accelerated age-related overexpression of S100beta may interact with age-associated overexpression of mutant betaAPP in transgenic mice to promote development of Alzheimer-like neuropathological changes.

Overexpression of s100beta in Down's syndrome: correlation with patient age and with beta-amyloid deposition

S100beta is an astrocyte-derived uritotrophic' cytokine which has been implicated in the pathogenesis of Alzheimer's disease. S100beta overexpression by plaque-associated astrocytes correlates with growth of abnormal (strophic') neurites in beta-amyloid plaques, one of the major neuropathological hallmarks of Alzheimer's disease. As the characteristic neuropathological changes of Alzheimer's disease are virtually universal in middle-aged Down's syndrome patients, studies of Down's syndrome patients provide a unique opportunity to investigate the pathophysiological processes underlying the development of Alzheimer-type neuropathological changes. Computerized morphometric analysis was used to quantify astrocyte activation and astrocytic expression of S100beta, and to correlate these with beta-amyloid deposition, in a clinically well-characterized cohort of Down's syndrome subjects, aged 13-65 years. There were significant positive correlations between S100beta expression and patient age, and between S100beta expression and cerebral cortical beta-amyloid deposition. Moreover, the numbers of activated (enlarged) astrocytes overexpressing S100beta showed a significant correlation with the numeric density of beta-amyloid plaques, from the youngest to the oldest ages and within age ranges where pathology is most florid, while no such relationship was found between the numbers of small, non-activated S100beta-immunoreactive cells and numerical density of beta-amyloid plaques. These correlations, together with established functions of S100beta, are consistent with the idea that S100beta overexpression promotes beta-amyloid plaque formation and progression in Down's syndrome.

Glial cell changes in the white matter in temporal lobe epilepsy

Temporal lobe gliosis and neuronal loss are pathological hallmarks of complex partial seizures. However, the specificity of glial cell changes is not clear. To assess this we studied surgically resected temporal lobes containing either medial temporal sclerosis (MTS) or temporal lobe epilepsy with tumour (TLET) and compared them with idiopathic epilepsy cases and normal controls. We quantitatively assessed glial cell density and mean nuclear volume in the white matter of various temporal gyri and the deep white matter. There was an increase in mean glial cell nuclear volume in MTS and TLET cases in the white matter of superior temporal gyrus, parahippocampal gyrus and deep white matter but not in the white matter of the middle temporal gyrus. In contrast, the densities of glial cells immunopositive for glial fibrillary acidic protein in the MTS and TLET groups were reduced in all white matter regions when compared with the controls. These changes may indicate that glial cells in the white matter have an active role to play in epilepsy pathogenesis.

Independent mechanisms of potassium clearance by astrocytes in gliotic tissue

The "glial impairment hypothesis" states that astrocytes which change from normal into the reactive type lose their ability to clear extracellular K+, which in turn leads to hyperexcitability in the gliotic tissue. As this hypothesis was never proven or disproven, the question of glial efficiency in K+ clearance in gliotic tissue is still controversial, mainly due to the lack of direct measurements of the intracellular K+ concentration of reactive astrocytes. In order to investigate K+ accumulation by glial cells of gliotic tissue, we used hippocampal slices. Adult rats, previously treated with kainic acid, exhibited loss of neurons and gliosis in the CA1 layer of the hippocampus within 3 days. After this time period, double-barrelled microelectrodes were used to inject Lucifer yellow into cells of the stratum radiatum of the CA1 subfield in 400-microm-thick hippocampal slices. These cells had electrophysiological and morphological characteristics of astrocytes. Most injected cells (70%) were dye-coupled to other cells and were glial fibrillary acidic protein (GFAP)-positive (80%). We found, however, that GFAP-positive cells were dye-coupled not only to each other, but also to GFAP-negative cells. In another set of experiments, we investigated the glial membrane potential during reduction of the extracellular Cl-concentration and the use of the Cl- channel blocker 4,4'-diisothiocyanostilbene-2,2' disulphonic acid (DIDS). The results suggest that reactive astrocytes have a significant resting Cl- conductance. K+-selective microelectrodes were used to analyze the intracellular glial K+ concentration. When the extracellular K+ concentration was increased from 3.5 mM to 10 mM, the intracellular K+ concentration increased by 23 mM. Experiments in which different ion transport systems were blocked with ouabain and DIDS suggest that this increase is dependent on two mechanisms, which can substitute each other: the Na+, K+-ATPase and passive K+ and anion fluxes. Inhibition of either of the two mechanisms did not block the K+ uptake. If, however, the Na+, K+-ATPase and Cl- channels were inhibited at the same time, the net accumulation of K+ was blocked. It appears, therefore, that astrocytes in the gliotic stratum radiatum of the hippocampal slice have the capacity to limit increases in extracellular K+ that are produced by hyperactive surviving hippocampal neurons by passive mechanisms and hence independently of blood and oxygen supply.

The neuropathology of schizophrenia. A critical review of the data and their interpretation

Despite a hundred years' research, the neuropathology of schizophrenia remains obscure. However, neither can the null hypothesis be sustained--that it is a 'functional' psychosis, a disorder with no structural basis. A number of abnormalities have been identified and confirmed by meta-analysis, including ventricular enlargement and decreased cerebral (cortical and hippocampal) volume. These are characteristic of schizophrenia as a whole, rather than being restricted to a subtype, and are present in first-episode, unmedicated patients. There is considerable evidence for preferential involvement of the temporal lobe and moderate evidence for an alteration in normal cerebral asymmetries. There are several candidates for the histological and molecular correlates of the macroscopic features. The probable proximal explanation for decreased cortical volume is reduced neuropil and neuronal size, rather than a loss of neurons. These morphometric changes are in turn suggestive of alterations in synaptic, dendritic and axonal organization, a view supported by immunocytochemical and ultrastructural findings. Pathology in subcortical structures is not well established, apart from dorsal thalamic nuclei, which are smaller and contain fewer neurons. Other cytoarchitectural features of schizophrenia which are often discussed, notably entorhinal cortex heterotopias and hippocampal neuronal disarray, remain to be confirmed. The phenotype of the affected neuronal and synaptic populations is uncertain. A case can be made for impairment of hippocampal and corticocortical excitatory pathways, but in general the relationship between neurochemical findings (which centre upon dopamine, 5-hydroxytryptamine, glutamate and GABA systems) and the neuropathology of schizophrenia is unclear. Gliosis is not an intrinsic feature; its absence supports, but does not prove, the prevailing hypothesis that schizophrenia is a disorder of prenatal neurodevelopment. The cognitive impairment which frequently accompanies schizophrenia is not due to Alzheimer's disease or any other recognized neurodegenerative disorder. Its basis is unknown. Functional imaging data indicate that the pathophysiology of schizophrenia reflects aberrant activity in, and integration of, the components of distributed circuits involving the prefrontal cortex, hippocampus and certain subcortical structures. It is hypothesized that the neuropathological features represent the anatomical substrate of these functional abnormalities in neural connectivity. Investigation of this proposal is a goal of current neuropathological studies, which must also seek (i) to establish which of the recent histological findings are robust and cardinal, and (ii) to define the relationship of the pathological phenotype with the clinical syndrome, its neurochemistry and its pathogenesis.

Increased density of metallothionein I/II-immunopositive cortical glial cells in the early stages of Alzheimer's disease

We have examined the possible role of metallothionein I/II (MT I/II) in Alzheimer's disease (AD), with a focus on the cellular localization of MT I/II relative to the astrocyte marker, glial fibrillary acidic protein (GFAP). In AD and preclinical AD cases, MT I/II immunolabeling was present in glial cells and did not show a spatial relationship with beta-amyloid plaques or neurofibrillary pathology. There was a six- to sevenfold increase in both MT I/II- and GFAP-labeled cells in the gray matter of AD cases, relative to non-AD cases. However, there was a threefold increase in MT I/II-immunoreactive cells, but not GFAP-labeled cells, in the gray matter of preclinical AD cases compared to non-AD cases. Therefore, the specific increase in MT I/II is associated with the initial stages of the disease process, perhaps due to oxidative stress or the mismetabolism of heavy metals.

Temporal changes in gene expression following cryogenic rat brain injury

Expression of 18 genes was examined at 8 different time points between 1 h and 28 days following cryogenic rat brain injury. The genes include thymidine kinase (TK), p53 tumor suppressor, c-fos, renin, myelin basic protein (MBP), proteolipid protein (PLP), transferrin, transferrin receptor, platelet-derived growth factor A (PDGF A), platelet-derived growth factor B (PDGF B), platelet-derived growth factor receptor alpha (PDGF alpha receptor), platelet-derived growth factor receptor beta (PDGF beta receptor), glial fibrillary acidic protein (GFAP), transforming growth factor-beta 1 (TGF-beta 1), basic fibroblast growth factor (bFGF), fibroblast growth factor receptor-1 (FGF-R1), insulin-like growth factor-1 (IGF-1), and somatostatin. Time courses of gene expression were determined for RNAs derived from hippocampus and cortex. Genes were divided into categories based upon those in which statistically significant changes in expression were first observed at or before 24 h (early genes) and those in which changes were first observed at or after 72 h (late genes). In the present model, many genes demonstrate elevated RNA levels in the cortex prior to hippocampus, following injury. RNAs transcribed from late genes tend to be elevated concurrently in cortex and hippocampus.

Life-long overexpression of S100beta in Down's syndrome: implications for Alzheimer pathogenesis

Chronic overexpression of the neurite growth-promoting factor S100beta has been implicated in the pathogenesis of neuritic plaques in Alzheimer's disease. Such plaques are virtually universal in middle-aged Down's syndrome, making Down's a natural model of Alzheimer's disease. We determined numbers of astrocytes overexpressing S100beta, and of neurons overexpressing beta-amyloid precursor protein (beta-APP), and assayed for neurofibrillary tangles in neocortex of 20 Down's syndrome patients (17 weeks gestation to 68 years). Compared to controls, there were twice as many S100beta-immunoreactive (S100beta+) astrocytes in Down's patients at all ages: fetal, young, and adult (p = 0.01, or better, in each age group). These were activated (i.e., enlarged), and intensely immunoreactive, even in the fetal group. There were no neurofibrillary changes in fetal or young Down's patients. The numbers of S100beta+ astrocytes in young and adult Down's patients correlated with the numbers of neurons overexpressing beta-APP (p < 0.05). Our findings are consistent with the idea that conditions--including Down's syndrome--that promote chronic overexpression of S100beta may confer increased risk for later development of Alzheimer's disease.

Lesioning of the inferior olive using a ventral surgical approach. Characterization of temporal and spatial astrocytic responses at the lesion site and in cerebellum

Activated astrocytes, intrinsic components of both local and remote (axonal target regions) central nervous system injury responses, are now recognized as active metabolic and regulatory mediators in many neurological disorders. To further define these responses, we devised a new ventral surgical approach to unilaterally lesion the inferior olivary nuclear complex, which has a single predominant remote target, the cerebellum. Activated astrocyte number, volume, and density, as well as the total volume of brainstem involved in the astrocytic response, all peaked at postlesion day (pld) 4, returning toward, but not to, unoperated control values at pld 24 (p < 0.05). In contrast, the peak astrocyte response in the cerebellum was delayed, being greatest at pld 6 (p < 0.05 compared to control or pld 2). These responses were associated with increases in overexpression of S100 beta, an astrocyte-derived neurite growth factor, and with an increase in cerebellar steady-state levels of a neuronal injury response protein, the beta-amyloid precursor protein (beta-APP). This is similar to correlated increases in these two proteins that are found in epilepsy and Alzheimer disease. Our studies defining remote astrocytic and neuronal responses may be important for understanding glial-neuronal mechanisms underlying the spread of neuropathological changes in conditions such as Alzheimer disease.

Hippocampal connexin 43 expression in human complex partial seizure disorder

An increase in the cellular production of gap junction proteins and increased numbers of gap junctions in the neuronoglial syncytium of an epileptic focus have been proposed as a possible mechanism underlying synchronization of discharge. To study this issue, both Northern and Western blot analyses of the gap junction protein connexin 43 mRNA and protein abundance were performed on hippocampal tissue resected from patients presenting with a complex partial seizure disorder arising from the medial temporal area and the hippocampus in particular. Samples from 15 patients with medically intractable seizures were compared to those from 5 nonepileptic patients requiring temporal lobectomy in life-threatening situations. Six of the 15 epileptic patients underwent noninvasive electrographic recording, whereas the remaining 9 patients required intracerebral electrodes for extraoperative recording and therefore showed a more discrete focality than the noninvasive recordings. A decline in the mean levels of connexin 43 mRNA expressed predominantly in astrocytes was noted in the epileptic patient groups, particularly for those cases requiring intracranial electrode placement where ictal onset was more clearly established to be intrahippocampal. Quantitation of connexin 43 protein in both epileptogenic and nonepileptogenic hippocampal tissues showed no significant differences in expression. Although mean values for mRNA showed a decline, clinical outcomes postoperatively showed no correlation with either mRNA or protein expression individually in our epileptic population. The findings indicate that there is effectively no upregulation of mRNA and no increased production of connexin 43 protein in response to the development of epileptogenicity. Rather it appears the influence of gap junctions as a substrate of epileptogenicity in any mechanism(s) underlying synchrony or electrical propagation may be a function of the dynamic state (open versus closed) of the membrane-bound gap junction.

IL-6 and TNFalpha expression in brains of twitcher, quaking and normal mice

Cytokines have been postulated to play a pathogenic role in twitcher mice, which are an animal model of globoid cell leukodystrophy. In particular, TNFalpha promotes oligodendrocyte and myelin pathology, and IL-6 expression is induced in astrocyte and microglial cultures that have been incubated with TNFalpha or myelin debris, respectively. It is unknown whether these cytokines are expressed in twitcher mice. The objectives of the present study were to develop an immunohistochemical method to detect TNFalpha and IL-6 in the mouse CNS, and then utilize this method to identify the cell types expressing these cytokines, and their spatial distribution, in the brains of normal, twitcher and quaking mice. In normal mice, IL-6 was found in ependymal cells, Bergmann glia, in processes that were adjacent or attached to the ventricles or pial surface, and in lightly stained processes in white matter. These processes were identified to belong to astrocytes and microglia. IL-6 staining was dramatically increased in twitcher mice. Astrocytes, with reactive features, and microglia were labeled in the cerebral cortex, basal ganglia, subcortical white matter, pons, medulla and cerebellar white matter. IL-6-positive reactive astrocytes were less abundant in quaking mice than twitcher mice. Cells expressing TNFalpha were rare or absent in normal and quaking mice. In twitcher mice, TNFalpha-positive macrophages were present at a lower concentration in cerebral white matter than in the pons and medulla, which have more advanced demyelination. These data demonstrate that pathological events induce the expressions of TNFalpha and IL-6 in the CNS of twitcher mice.

Glial cells in transected optic nerves of immature rats. I. An analysis of individual cells by intracellular dye-injection

The glial response to Wallerian degeneration was studied in optic nerves following unilateral enucleation in immature rats, aged 21 days old (P21). The three-dimensional morphology of dye-filled glia was determined in intact nerves, at post-enucleation day 21 in normal nerves from untreated P21 rats, by correlating laser scanning confocal microscopy and camera lucida drawings of single cells. In normal and transected nerves, the majority of dye-filled cells comprized astrocytes (54% and 65%, respectively). In normal P21 nerves, the predominant astrocyte form had a complex stellate morphology and had a centrally-located cell body from which branching processes extended randomly. Two other distinct forms were transverse and longitudinal astrocytes, which had a polarized process extension in a plane perpendicular or parallel to the long axis of the nerve, respectively. These forms were recognized in transected nerves also, but astrocytes in transected nerves had a simple morphology on the whole, and extended few, dense processes which branched infrequently. Quantitative analysis of astrocyte morphology confirmed that individual astrocytes underwent considerable remodelling in response to Wallerian degeneration. A prominent reaction was that astrocytes had withdrawn radial processes and extended a greater proportion of processes longitudinally, parallel to the long axis of the nerve and along the course of degenerated axons. A further, notable feature of transected nerves was the development of novel longitudinal forms and of hypertrophic astroglia. These results indicated that all astrocytes became reactive following enucleation and that glial scar formation was not the function of a single astrocyte subtype. Oligodendrocytes in transected nerves had lost their myelin sheaths and appeared as small cells with numerous bifurcating processes which extended radially, but a small number of oligodendrocytes were recognized which apparently supported myelin sheaths (9%, compared to 40% in normal nerves). In addition, there was a significant population of indeterminate cells in transected nerves (26%, compared to 6% in normal nerves) and, although some of these were identified as microglia/macrophages, it was concluded that many were likely to be dedifferentiated oligodendrocytes.

Correlation of astrocytic S100 beta expression with dystrophic neurites in amyloid plaques of Alzheimer's disease

The neurite extension factor S100 beta is overexpressed by activated astrocytes associated with amyloid-containing plaques in Alzheimer's disease, and has been implicated in dystrophic neurite formation in these plaques. This predicts (a) that the appearance of S100beta- immunoreactive (S100beta+) astrocytes precedes that of dystrophic neurites in diffuse amyloid deposits and (b) that the number of these astrocytes correlates with the degree of dystrophic neurite proliferation in neuritic plaques. As a test of the first prediction, we determined the number of S100beta+ astrocytes associated with different plaque types: diffuse non-neuritic, diffuse neuritic, dense-core neuritic, and dense-core non-neuritic. Diffuse non-neuritic plaques had small numbers of associated S100beta+ astrocytes (1.3 +/- 0.1 S100beta astrocytes per plaque [mean +/- SEM]; 80% of plaques had one or more). These astrocytes were most abundant in diffuse neuritic plaques (4.2 +/- 0.2; 100%), were somewhat less numerous in dense-core neuritic plaques (1.6 +/- 0.2; 90%), and were only rarely associated with dense-core non-neuritic plaques (0.15 +/- 0.05; 12%). As a test of the second prediction, we correlated the number of S100beta+ astrocytes per plaque with the area of beta-amyloid precursor protein (beta-APP) immunoreactivity per plaque (an index of the size of the plaques' dystrophic neurite shells) and found a significant positive correlation (r = 0.74, p < 0.001). This correlation was also evident at the tissue level: the numbers of S100beta+ astrocytes per plaque-rich field correlated with the total area beta-APP immunoreactivity in these fields (r = 0.66, p < 0.05). These correlations support the idea that astrocytic activation and S100 beta overexpression are involved in the induction and maintenance of dystrophic neurites in amyloid deposits, and support the concept of a glial cytokine-mediated cascade underlying the progression of neuropathological changes in Alzheimer's disease.

In vivo and in vitro evidence supporting a role for the inflammatory cytokine interleukin-1 as a driving force in Alzheimer pathogenesis

Interleukin-1 (IL-1), an inflammatory cytokine overexpressed in the neuritic plaques of Alzheimer's disease, activates astrocytes and enhances production and processing of beta-amyloid precursor protein (beta-APP). Activated astrocytes, overexpressing S100 beta, are a prominent feature of these neuritic plaques, and the neurite growth-promoting properties of S100 beta have been implicated in the formation of dystrophic neurites overexpressing beta-APP in neuritic plaques. These facts collectively suggest that elevated levels of the inflammatory cytokine IL-1 drive S100 beta and beta-APP overexpression and dystrophic neurite formation in Alzheimer's disease. To more directly assess this driver potential for IL-1, we analyzed IL-1 induction of S100 beta expression in vivo and in vitro, and of beta-APP expression in vivo. Synthetic IL-1 beta was injected into the right cerebral hemispheres of 13 rats. Nine additional rats were injected with phosphate-buffered saline, and seven rats served as uninjected controls. The number of astrocytes expressing detectable levels of S100 beta in tissue sections from IL-1-injected brains was 1.5 fold that of either control group (p < 0.01), while tissue S100 beta levels were approximately threefold that of controls (p < 0.05). The tissue levels of two beta-APP isoforms (approximately 130 and 135 kDa) were also significantly elevated in IL-1-injected brains (p < 0.05). C6 glioma cells, treated in vitro for 24 h with either IL-1 beta or IL-1 alpha, showed significant increases in both S100 beta and S100 beta mRNA levels. These results provide evidence that IL-1 upregulates both S100 beta and beta-APP expression, in vivo and vitro, and support the idea that overexpression of IL-1 in Alzheimer's disease drives astrocytic overexpression of S100 beta, favoring the growth of dystrophic neurites necessary for evolution of diffuse amyloid deposits into neuritic beta-amyloid plaques.

Glial cytokines in Alzheimer's disease: review and pathogenic implications

The roles of activated glia and of glial cytokines in the pathogenesis of Alzheimer's disease are reviewed. Interleukin-1 (IL-1), a microglia-derived acute phase cytokine, activates astrocytes and induces expression of the astrocyte-derived cytokine, S100 beta, which stimulates neurite growth (and thus has been implicated in neuritic plaque formation) and increases intracellular free calcium levels. Interleukin-1 also upregulates expression and processing of beta-amyloid precursor proteins (beta-APPs) (thus favoring beta-amyloid deposition) and induces expression of alpha 1-antichymotrypsin, thromboplastin, the complement protein C3, and apolipoprotein E, all of which are present in neuritic plaques. These cytokines, and the molecular and cellular events that they engender, form a complex of interactions that may be capable of self-propagation, leading to chronic overexpression of glial cytokines with neurodegenerative consequences. Self-propagation may be facilitated by means of several reinforcing feedback loops. beta-Amyloid, for instance, directly activates microglia, thus inducing further IL-1 production, and activates the complement system, which also leads to microglial activation with IL-1 expression. Self-propagation also could result when S100 beta-induced increases in intraneuronal free calcium levels lead to neuronal injury and death with consequent microglial activation. Such chronic, self-propagating, cytokine-mediated molecular and cellular reactions would explain the progressive neurodegeneration and dementia of Alzheimer's disease.

Microglial interleukin-1 alpha expression in brain regions in Alzheimer's disease: correlation with neuritic plaque distribution

Interleukin-1 alpha-immunoreactive (IL-1 alpha+) microglia are prominent components of neuritic plaques in Alzheimer's disease, and may be important in the evolution of neuritic plaques from diffuse amyloid deposits. Neuritic plaques show a characteristic distribution across cerebral regions and are absent in the cerebellum of patients with Alzheimer's disease. We used single- and dual-immunohistochemical labelling to investigate the possibility that the expression of IL-1 alpha is correlated with this regional distribution of neuritic (tau 2-immunoreactive, tau 2+) plaques. In Alzheimer's disease, tau 2+ neuritic plaques occurred with increasing frequency in grey matter of frontal and occipital lobes, temporal lobe, and hippocampus. There were positive correlations between the regional patterns of distribution of activated IL-1 alpha+ microglia and tau 2+ neuritic plaques as well as between activated IL-1 alpha+ microglia and activated astrocytes. No activated IL-1 alpha+ microglia, tau 2+ neuritic plaques, or activated astrocytes were observed in cerebellum of these Alzheimer patients. These regional relationships between activated IL-1 alpha+ microglia, tau 2+ neuritic plaques, and activated astrocytes, together with the established functions of IL-1, support a causal association between the overexpression of IL-1 and the evolution of beta-amyloid deposits into neuritic plaques in Alzheimer's disease.

A direct comparison of GFAP immunocytochemistry and GFAP concentration in various regions of ethanol-fixed rat and mouse brain

Glial fibrillary acidic protein (GFAP) immunostaining is the most commonly used method to examine the distribution of astrocytes and the hypertrophy of astrocytes in response to neural degeneration or injury. More recently, a variety of biochemical assays for GFAP have been developed. Both qualitative immunocytochemical evaluations of GFAP and quantitative biochemical measurements of GFAP have been used to examine the regional distribution of GFAP within the central nervous system (CNS). The former method has largely been based on aldehyde-fixed tissue, while the latter approach has been based on the use of fresh tissue extracts or homogenates. In the present study, we used ethanol as a fixative to permit both immunocytochemical and biochemical procedure to be carried out on brain tissue from a single animal. Normal adult rats and mice were perfused with a 70% ethanol/saline solution, and each brain was hemisectioned. The concentration of GFAP was measured in regions of 1 hemisection, using an enzyme-linked immunosorbent assay (ELISA), while the other hemisection was used for GFAP immunostaining. Regional differences occurred in the brains of both species, with the highest concentration of GFAP found in the brainstem, and the lowest concentrations found in the striatum and cortex. The specific patterns of GFAP immunoreactivity corresponded to regional concentrations in most brain area of both species. These data show that it is possible to assay GFAP concentrations in tissue prepared for immunocytochemical analysis, providing both qualitative and quantitative information from one set of tissue.

An early increase in somatostatin mRNA expression in the frontal cortex of rhesus monkeys infected with simian immunodeficiency virus

Motor and cognitive impairment is common in human immunodeficiency virus disease in humans and simian immunodeficiency virus (SIV) disease in rhesus monkeys. We have examined peptide neurotransmitter expression in the frontal cortex of SIV-infected rhesus monkeys to identify alterations in cortical neurons that might explain this impairment. A 2-fold higher number of preprosomatostatin (SRIF) mRNA-positive interneurons was observed in layer IV of frontal cortex in two separate cohorts of SIV-infected animals compared to uninfected controls. Increased SRIF mRNA expression in layer IV was independent of clinical signs of immunodeficiency disease and was associated with both motor and cognitive impairment. Altered SRIF mRNA expression in deeper cortical layers was associated specifically with motor impairment. Increased SRIF mRNA expression occurred without detectable changes in cortical cell density. These data suggest two mechanisms for cortical dysfunction associated with lentivirus infection. Increased SRIF mRNA expression in layer IV may be due to altered patterns of activity in cortical afferents that project to layer IV, while increased SRIF mRNA expression in deeper cortical layers could reflect susceptibility to locally generated mediators in response to primate lentivirus infection of the brain. Altered function of somatostatinergic interneurons may contribute to primate lentivirus-induced encephalopathy.

Focal brain injury and upregulation of a developmentally regulated extracellular matrix protein

Tenascin is an extracellular matrix glycoprotein expressed during both normal development and neoplastic growth in both neural and nonneural tissues. During development of the central nervous system (CNS), tenascin is synthesized by glial cells, in particular by immature astrocytes, and is concentrated in transient boundaries around emerging groups of functionally distinct neurons. In the mature CNS, only low levels of the glycoprotein can be detected. The present study demonstrates that following trauma to the adult human cerebral cortex, discrete populations of reactive astrocytes upregulate their expression of tenascin and dramatically increase their transcription of the tenascin gene. The enhanced expression of tenascin may be involved in CNS wound healing, and may also affect neurite growth within and around a brain lesion.

S100 beta protein expression in Alzheimer disease: potential role in the pathogenesis of neuritic plaques

Increased synthesis and release of S100 beta protein from activated astrocytes has been implicated in the overgrowth of dystrophic neurites in neuritic plaques in Alzheimer disease (AD). To evaluate the quantitative relationships between tissues levels of S100 beta and the numbers of neuritic plaques in AD patients, we counted neuritic plaques, by Tau-2 immunoreactive (Tau-2+) labeling, in tissue sections of hippocampus and adjacent temporal cortex and measured the levels of S100 beta protein, by Western immunoblot labeling, in samples of analogous regions from contralateral hemisphere of the same patients. In AD, tissue levels of S100 beta (two- to fivefold that of controls) were significantly correlated with the number of Tau-2+ plaques (R = 0.82, P < .01). Dual-label immunohistochemical analysis showed that most S100 beta+ cells were activated GFAP+ astrocytes. These results were substantiated by a significant correlation between S100 beta and GFAP tissue levels (R = 0.81, P < .05). Many of the S100 beta+ astrocytes were clustered around and within Tau-2+ plaques. Indeed, no Tau-2+ plaques were found without associated activated S100 beta+ astrocytes. Our findings provide further evidence of a role for S100 beta protein in dysregulation of neurons that leads to apparently nonsensical growth of imperfect neurites in AD, a potential key element in early stages of neuritic plaque pathogenesis.

S100 beta expression in Alzheimer's disease: relation to neuropathology in brain regions

S100 beta levels in tissue homogenates and distribution of S100 beta-containing activated astrocytes were examined by S100 beta-specific ELISA and immunohistochemistry, respectively, in brain regions exhibiting many, some, few, or no neuritic plaques in Alzheimer's disease (AD). Compared to samples collected at similar postmortem intervals from control patients of similar ages, S100 beta levels were elevated in specific brain regions from AD patients, and the overexpression of S100 beta correlated relatively well with the pattern of regional involvement by neuritic plaques. The largest increases in S100 beta levels were in hippocampus and temporal lobe, followed by frontal lobe and pons, with no elevation in occipital lobe or cerebellum. Immunohistochemical analysis showed S100 beta localization primarily in activated astrocytes surrounding neuritic plaques. These results demonstrate that S100 beta overexpression is brain region-specific and related to astrocyte activation and suggest that elevation of S100 beta above some threshold is related to the degree of neuropathological involvement of different brain regions in AD.

Microglial interleukin-1 alpha expression in human head injury: correlations with neuronal and neuritic beta-amyloid precursor protein expression

Activated microglia containing IL-1 alpha-immunoreactive (IL-1 alpha +) product were increased 3-fold in number in the acute phase following head injury, a risk factor for later development of Alzheimer's disease, and this increase was correlated with a 7-fold increase in the number of neurons with elevated beta-amyloid precursor protein (beta-APP) levels (R = 0.78; P < 0.05). Furthermore, clusters of beta-APP+ dystrophic neurites present in these patients were invariably associated with activated IL-1 alpha + microglia. These findings suggest that early overexpression of IL-1 alpha and beta-APP is a priming event for later neuropathological changes evident at end stages of Alzheimer's disease.

Control of astrocytosis by interleukin-1 and transforming growth factor-beta 1 in human brain

Astrocytosis is a common neurocellular manifestation of brain pathology in individuals with a variety of diseases. It is comprised of astrocytic hyperplasia (an increase in number of astrocytes) and astrocytic hypertrophy (an increase in size of astrocytes). The precise cause(s) of astrocytosis remains unknown. We morphometrically measured the relative extent of astrocytosis in brains of 22 individuals who died with seven different diseases. The relative amounts of interleukin-1 (IL-1) and transforming growth factor-beta 1 (TGF-beta 1) immunoreactive products (IRPs) were next assessed in sections serial to those in which astrocytosis was measured because these cytokines were shown in animal and in vitro experiments to be associated with astrocytosis. The data demonstrate that astrocytosis and these cytokines were co-localized in all examined human tissues. Relative increase in density of astrocytes was correlated with the increase in total IL-1 but not TGF-beta 1. In contrast, the increase in size of astrocytes was correlated with TGF-beta 1 associated only with astrocytes but not with total IL-1. Both IL-1 and TGF-beta 1 IRPs were present in GFAP IRP-containing and other cells, as assessed by double label immunocytochemistry. These observations suggest that IL-1 acts on astrocytes by both, paracrine and autocrine mechanisms whereas, TGF-beta 1 only acts by an autocrine mechanism. Because these correlations were statistically significant and also because a change in number and size of astrocytes constitutes the most frequent response of astrocytes to several diseases or injury, we conclude that these cytokines may mediate the most common pathological change in human brain.