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C W Cotman

Publications and source records attributed to C W Cotman.

At least 127 records · Page 7Linked to original sources
PubMed1995

Roles of metabotropic glutamate receptors in brain plasticity and pathology.

In summary, the mGluRs are a large family of receptor subtypes with diverse properties in terms of transduction coupling, pharmacology, and anatomical distribution. Many divergent studies have demonstrated that activation of these receptors can result in either neuroprotection or neuropathology. We hypothesized that the mGluRs of astrocytes may have a role in determining the response following administration of mGluR agonists in vivo, and we have defined a suitable in vitro model for the study of these receptors. The experimental plasticity demonstrated in the astrocyte culture model may represent a more general principle that conditions in the microenvironment may differentially alter mGluR subtype expression as part of development, functional specialization, or pathology. This astrocyte model of receptor regulation provides a system suitable for studying the effects of specific growth factors, neurotrophins, cytokines, and other substances released by neurons and glia that may act in both autocrine and paracrine fashions. Alteration in the ratios of receptors by such variables could then modify future signaling properties and neuroglial interactions, a form of conditioning of the astrocytic response that would alter the physiological output following glutamate release. One measure of the value of this model will be its usefulness in stimulating the generation of hypotheses that can be tested in vivo. For example, the morphology of the astrocytes when cultured in the defined medium has similarities to the morphology of astrocytes undergoing reactive gliosis in pathological states. It is also interesting to note that treatments that have been reported to increase excitatory amino acid-stimulated PI hydrolysis in ex vivo brain slices (lesions, ischemia, and kindling) are accompanied by reactive gliosis. Those findings combined with the present in vitro results lead us to speculate that mGluR5 expression may also be altered in vivo during reactive gliosis. If so, it will be important to examine the functional consequences of such a change with regard to the astrocytic response to injury and maintaining the balance between excitatory transmission and excitotoxicity.

Animals↗
PubMed1995

Vulnerability of the hippocampus to kainate excitotoxicity in the aged, mature and young adult rat.

Sensitivity to excitotoxic damage was assessed in young adult, mature and aged male Sprague-Dawley rats. Kainic acid was injected into the hippocampus and the size of the hippocampal lesion rated. Intrahippocampal injection of kainic acid produced lesions in aged animals that were significantly smaller than lesions in the young rats (P < 0.05), while lesion size in mature rats was intermediate. Excitotoxic damage was localized primarily to the CA3 region of the hippocampus in the aged rats. Young adult rats had more damage to the hippocampus with involvement of CA1 pyramidal and dentate granule cells. These results suggest that increased age may reduce susceptibility to excitotoxic damage.

Aging↗
PubMed1995

Calretinin-immunoreactive neurons are resistant to beta-amyloid toxicity in vitro.

The molecular pathways by which beta-amyloid protein (A beta) induces neurotoxicity in vitro are unknown. We report that cultured hippocampal neurons exhibiting immunoreactivity for the calcium binding protein calretinin are relatively resistant to degeneration resulting from exposure to either beta 25-35 or beta 1-42. These findings suggest that intrinsic characteristics of calretinin cells, possibly including enhanced calcium buffering capacity, underlie the resistance of these cells to A beta toxicity in vitro and perhaps similar insults in Alzheimer's disease.

Amyloid beta-Peptides↗
PubMed1995

Differential regulation by beta-amyloid peptides of intracellular free Ca2+ concentration in cultured rat microglia.

We have previously shown that exposure to beta-amyloid peptides alters microglial activity and viability. It is thought that beta-amyloid peptides induce toxicity in neuronal cultures by destabilizing Ca2+ homeostasis. To investigate the effects of beta-amyloid peptides on intracellular free Ca2+ concentration ([Ca2+]i) in cultured microglia, we used Fura-2 imaging. Exposure to 25 microM beta-amyloid-(25-35) induced increases in 2+]i within 1 h. In contrast, exposure to 25 microM beta-amyloid-(1-42), the full-length homolog to the beta-amyloid protein deposited in plaques, does not, over the same time period. However, the average [Ca2+]i of microglia is increased by a 6 h exposure to beta-amyloid-(1-42). Thus, beta-amyloid-(25-35) can alter [Ca2+]i in microglia on a different time scale than beta-amyloid-(1-42), indicating a specificity in the response of these cells as compared to neurons.

Amyloid beta-Peptides↗
PubMed1995

Acquisition and long-term retention of a fine motor skill in Alzheimer's disease.

This study investigated the acquisition and long-term retention of the rotary pursuit task under varying amounts of practice in 12 moderate-to-severely demented AD patients and 12 healthy older adults. Equal numbers of AD and control subjects were randomly assigned to either 40, 80, or 120 trials of training (40 trials/day) on the rotary pursuit task, followed by 15-trial retention tests 20 min, 2 days, 7 days, and 37 days following the end of practice. Performance improved significantly in both groups during the first 40 trials, while additional practice provided no ensuing positive or negative effects. Further, subjects in both groups showed minimal forgetting across the four retention tests. Therefore, the results demonstrated that AD patients can effectively learn and retain a motor skill for at least 1 month.

Aged↗
PubMed1995

Possible coordinated gene expressions for FGF receptor, FGF-5, and FGF-2 following seizures.

We have examined the influence of afferent activity that may trigger a coordinated response between ligands and their signal transduction receptors, as part of the regulation of the fibroblast growth factor (FGF) system. Epileptiform activity was induced by kainic acid injection, and in situ hybridization was used to assess the progress of changes in distribution and intensities of FGF receptor 1 (FGFR-1), FGF-5, and FGF-2 mRNAs. Our results showed that at early stages (3 h) afferent activity triggered a transient increase in both of the ligand mRNAs, whereas the receptor mRNA response was increased only in the dentate gyrus. At later stages, the FGFR-1 mRNA response was more complex, in which the various regions examined exhibited a broader range of values within the same time-points. This contrasted with the uniform pattern of FGF-5 and FGF-2 mRNAs responses, which in most of the brain regions examined showed a peak by 12 h following seizure induction and returned to normal values by 24 h. Immunohistochemistry showed an induction of FGFR-1 and FGF-2, 6 h postseizure induction which remained elevated up to 24 h later. The distinctive pattern of the FGFR-1 mRNA response appears to indicate that FGFR-1 is a factor in the modulation of the cellular response for FGF-5 and FGF-2. These results demonstrate that brain activity exerts influences at the gene expression levels of FGFR-1 and its ligands FGF-5 and FGF-2.

Animals↗
PubMed1995

Cultured rat microglia express C1q and receptor for C1q: implications for amyloid effects on microglia.

Senile plaques, the pathological hallmark of Alzheimer's disease (AD), are associated with complement components, including C1q. Reactive microglia appear to be involved in the later stages of plaque development. Since tissue macrophages are known to synthesize C1q, cultured rat microglia were examined for C1q immunoreactivity. Anti-C1q staining was detected, particularly in process-bearing microglia, indicating constitutive expression of C1q. Thus, microglia could provide a source of C1q for plaques even before becoming reactive. Since it has been previously shown that C1q binds beta 1-42, the major constituent of senile plaques, and since beta 1-42 is toxic to microglia in vitro, we asked if preincubation of beta 1-42 with C1q alters either metabolic indices of amyloid-induced degeneration in microglial cultures or the formation of amyloid deposits on these cells. While electron microscopic analysis of negatively stained amyloid fibrils confirmed that pre-incubation with C1q induced the association of C1q with the fibrils, no effect of the binding of C1q to beta 1-42 on beta 1-42 toxicity in microglia was observed. Interestingly, immunoreactivity for the C1q receptor that is known to modulate phagocytosis was found and was up-regulated in non-process-bearing microglia by interferon-gamma. While these data exclude a role for the C1q receptor in beta 1-42 toxicity in microglia, the observed expression and up-regulation of C1q receptor on microglia by interferon-gamma would be consistent with a role for C1q in complement-mediated inflammatory responses in AD and as a potential activator of microglial function in plaques.

Alzheimer Disease↗
PubMed1995

A potential role for apoptosis in neurodegeneration and Alzheimer's disease.

Previous studies have shown that beta-amyloid (A beta) peptides are neurotoxic. Recent data suggest that neurons undergoing A beta-induced cell death exhibit characteristics that correspond to the classical features of apoptosis, suggesting that these cells may initiate a program of cell death. This chapter explores the criteria and precautions that must be applied to evaluate mechanisms of cell death in vitro and in vivo, discusses the evidence supporting an apoptotic mechanism of cell death in response to A beta in cultured neurons, and describes potential correlations for these findings in the Alzheimer's disease brain. In addition, cellular signaling pathways that may be associated with apoptosis in response to A beta are examined, and support for apoptosis as a mechanism of cell death for other neurodegeneration-inducing stimuli (e.g., oxidative injury) is described. The connection of multiple stimuli that induce neuronal cell death to an apoptotic mechanism suggests that apoptosis could play a central role in neurodegeneration in the brain.

Alzheimer Disease↗
PubMed1995

Early association of reactive astrocytes with senile plaques in Alzheimer's disease.

The fibrillar beta-amyloid protein (A beta) plaques of Alzheimer's disease (AD) are associated with reactive astrocytes and dystrophic neurites and have been suggested to contribute to neurodegenerative events in the disease. We recently reported parallel in vitro and in situ findings, suggesting that the adoption of a reactive phenotype and the colocalization of astrocytes with plaques in AD may be mediated in large part by aggregated A beta. Thus, A beta-mediated effects on astrocytes may directly affect disease progression by modifying the degenerative plaque environment. Alternatively, plaque-associated reactive astrocytosis may primarily represent a glial response to the neural injury associated with plaques and not significantly contribute to AD pathology. To investigate the validity of these two positions, we examined the differential colocalization of reactive astrocytes and dystrophic neurites with plaques. Hippocampal sections from AD brains--ranging in neuropathology from mild to severe--were triple-labeled with antibodies recognizing A beta protein, reactive astrocytes, and dystrophic neurites. We observed not only plaques containing both or neither cell type, but also plaques containing (1) reactive astrocytes but not dystrophic neurites and (2) dystrophic neurites but not reactive astrocytes. The relative proportion of plaques colocalized with reactive astrocytes in the absence of dystrophic neurites is relatively high in mild AD but significantly decreases over the course of the disease, suggesting that plaque-associated astrocytosis may be an early and perhaps contributory event in AD pathology rather than merely a response to neuronal injury. These data underscore the potentially significant contributions of reactive astrocytosis in modifying the plaque environment in particular and disease progression in general.

Adult↗
PubMed1995

A detailed analysis of hydrogen peroxide-induced cell death in primary neuronal culture.

A variety of neurodegenerative disease states have been associated with oxidative damage or stress. Such stress is thought to be mediated by excessive exposure of cells to reactive oxygen species such as free radicals, which can be generated following cell lysis, oxidative burst (as part of the immune response) or by the presence of an excess of free transition metals. Since the neuronal death observed in neurodegenerative diseases may be related to free radical damage, we were interested in developing a model system to investigate the mechanisms by which reactive oxygen species may damage or kill neurons. To this end, we have recently reported that brief exposure of cultured cortical neurons to H2O2 can induce neuronal death that proceeds via an apoptotic cell suicide pathway. The studies reported here investigate H2O2-induced cell death in more detail. Our data suggest that exposure of cultured cortical neurons to H2O2 can induce apoptotic cell death within 3 h, as assessed by cell viability, morphological and ultrastructural measures. In addition, experiments presented show that exposure to high concentrations of H2O2 (100 microM) causes increases in intracellular free calcium within 3 h, suggesting that increased intracellular calcium may be associated with some aspects of H2O2-induced cell death. However, at intermediate concentrations of H2O2 (30 microM), intracellular calcium remained stable during a 3 h exposure, during which time membrane blebbing was observed in ultrastructural studies. This suggests that some aspects of apoptotic cell death induced by H2O2 may not be associated with increased intracellular free calcium. Thus, this model appears valuable for studies of the mechanism(s) by which oxidative injury may induce apoptotic cell death and damage to neurons in the CNS.

Animals↗
PubMed1995

Spatial learning and memory as a function of age in the dog.

Spatial learning and memory were studied in dogs of varying ages and sources. Compared to young dogs, a significantly higher proportion of aged dogs could not acquire a spatial delayed nonmatching-to-sample task. A regression analysis revealed a significant age effect during acquisition. Spatial memory was studied by comparing performance at delay interval of 20, 70, and 110 s. At short delays aged and young dogs were similar; at longer delays, errors increased to a greater extent in old than in young dogs; however this was not statistically significant. It was possible to identify 2 groups of aged animals, age-impaired and age-unimpaired. Several of the dogs were also tested on an object recognition memory task, which was more difficult to learn than the spatial task. The possibility that these findings are confounded by breed differences is considered. Overall, the present results provide further evidence of the value of a canine model of aging.

Aging↗
PubMed1995

Structure-activity analyses of beta-amyloid peptides: contributions of the beta 25-35 region to aggregation and neurotoxicity.

The neurodegeneration of Alzheimer's disease has been theorized to be mediated, at least in part, by insoluble aggregates of beta-amyloid protein that are widely distributed in the form of plaques throughout brain regions affected by the disease. Previous studies by our laboratory and others have demonstrated that the neurotoxicity of beta-amyloid in vitro is dependent upon its spontaneous adoption of an aggregated structure. In this study, we report extensive structure-activity analyses of a series of peptides derived from both the proposed active fragment of beta-amyloid, beta 25-35, and the full-length protein, beta 1-42. We examine the effects of amino acid residue deletions and substitutions on the ability of beta-amyloid peptides to both form sedimentable aggregates and induce toxicity in cultured hippocampal neurons. We observe that significant levels of peptide aggregation are always associated with significant beta-amyloid-induced neurotoxicity. Further, both N- and C-terminal regions of beta 25-35 appear to contribute to these processes. In particular, significant disruption of peptide aggregation and toxicity result from alterations in the beta 33-35 region. In beta 1-42 peptides, aggregation disruption is evidenced by changes in both electrophoresis profiles and fibril morphology visualized at the light and electron microscope levels. Using circular dichroism analysis in a subset of peptides, we observed classic features of beta-sheet secondary structure in aggregating, toxic beta-amyloid peptides but not in nonaggregating, nontoxic beta-amyloid peptides. Together, these data further define the primary and secondary structures of beta-amyloid that are involved in its in vitro assembly into neurotoxic peptide aggregates and may underlie both its pathological deposition and subsequent degenerative effects in Alzheimer's disease.

Alzheimer Disease↗
PubMed1995

Amyloid beta-protein induces its own production in cultured degenerating cerebrovascular smooth muscle cells.

The progression of Alzheimer's disease and related disorders involves amyloid beta-protein (A beta) deposition and pathologic changes in the parenchyma as well as cerebral blood vessels. The cerebrovascular A beta deposits in these disorders are associated with degenerating smooth muscle cells in the vessel wall, which have been shown to express the A beta precursor (A beta PP) and A beta. Here, we show that A beta 1-42, an abundant cerebrovascular form of A beta, causes cellular degeneration in cultured human cerebrovascular smooth muscle cells. This stress response is accompanied by a striking increase in the levels of cellular A beta PP and soluble A beta peptide produced in these degenerating cells. These data provide the first experimental evidence that A beta can potentially contribute to the onset and progression of the cerebrovascular pathology. The present findings suggest that this mechanism may involve a molecular cascade with a novel product-precursor relationship that results in the adverse production and subsequent accumulation of A beta.

Amyloid beta-Peptides↗
PubMed1995

Differential induction of immediate early gene proteins in cultured neurons by beta-amyloid (A beta): association of c-Jun with A beta-induced apoptosis.

beta-Amyloid (A beta) is a 39-42 amino acid that is the primary component of plaques in Alzheimer's disease (AD). Previous studies from our laboratory and others have shown that A beta induces neurodegeneration via apoptosis in vitro, suggesting that A beta may also initiate an apoptotic pathway of cell death in AD. Apoptosis has been suggested to proceed by a gene-directed program in several systems. Accordingly, we have investigated whether A beta-mediated apoptosis is associated with the induction of genes that may regulate or play a role in cell death in vitro. Immediate early genes (IEGs) respond to cellular stimuli and participate in cellular signaling pathways. The protein products of some IEGs, e.g., c-jun, are capable of forming dimers and acting as transcriptional regulatory proteins, and have been implicated in apoptosis in both nonneuronal and neuronal cells. In this study, we report a selective and abnormally sustained induction of c-Jun in cultured hippocampal neurons treated with A beta. In addition, we describe the lack of induction of c-Jun in neurons that are relatively resistant to A beta-mediated toxicity, and a correspondence between immunoreactivity for c-Jun and changes in nuclear morphology that are indicative of apoptosis. These data demonstrate that c-Jun is induced in cultured neurons that undergo A beta-mediated apoptosis and suggest that c-Jun may participate in a cell death program in these neurons.

Amyloid beta-Peptides↗
PubMed1995

Thrombin receptor activation protects neurons and astrocytes from cell death produced by environmental insults.

Thrombin is a multifunctional serine protease that is rapidly produced from prothrombin at sites of tissue injury and catalyzes the final steps in blood coagulation. Thrombin also regulates gene expression and process outgrowth in neurons and astrocytes and stimulates proliferation of astrocytes. Since thrombin is produced immediately upon breakdown of the blood-brain barrier we examined its effects on astrocytes and neurons cultured under conditions which resemble those found in vivo following cerebrovascular injury. These studies showed that thrombin markedly protected rat primary astrocytes from cell death induced by hypoglycemia or oxidative stress. Thrombin also protected rat primary hippocampal neurons from cell death produced by hypoglycemia or growth supplement deprivation. Synthetic peptides which directly activate the thrombin receptor also protected astrocytes and neurons from these environmental insults, demonstrating that the thrombin effects were mediated through the thrombin receptor. In contrast to these results with stressed cells, high concentrations of thrombin killed both astrocytes and neurons cultured under normal conditions. All of the effects of thrombin on astrocytes and neurons were blocked by the brain thrombin inhibitor, protease nexin-1 (PN-1). This shows that the effects required the proteolytic activity of thrombin and is consistent with the known proteolytic mechanism by which thrombin activates its receptor. These results indicate that thrombin and PN-1 may regulate the viability of both astrocytes and neurons in early moments following trauma to the CNS or other conditions that alter the blood-brain barrier.

Animals↗
PubMed1995

Growth factor upregulation of a phosphoinositide-coupled metabotropic glutamate receptor in cortical astrocytes.

CNS function depends on a capacity for plasticity during development, following injury, and in response to changing environmental conditions. Functional alterations in signal transduction pathways and in neurotransmitter receptor expression are possible mechanisms for the expression of such plasticity. In the present report, we demonstrate that exposure of astrocytes to specific growth factors alters both the functional activity and the protein levels of a specific glutamate receptor. Exposure of astrocytes to basic fibroblast growth factor, epidermal growth factor, or transforming growth factor-alpha produced marked increases in the ability of metabotropic glutamate receptor (mGluR) agonists to stimulate phosphoinositide hydrolysis. Using Western immunoblotting, we demonstrate that an increase in the levels of one of the phosphoinositide-coupled mGluR subtypes, mGluR5, accompanies the increased ability of mGluR agonists to stimulate phosphoinositide hydrolysis. In contrast, another phosphoinositide-coupled subtype of this receptor family, mGluR1 alpha, was not present at detectable levels in these cultures. The enhanced stimulation of phosphoinositide hydrolysis showed little sensitivity to pertussis toxin, and appeared to be selective to mGluR agonists, as there was not a similar increase in the ability of norepinephrine or carbachol to stimulate phosphoinositide hydrolysis. These findings demonstrate that expression of mGluRs in astrocytes is plastic, and indicate a novel pathway through which specific growth factors may selectively modulate neurotransmitter action.

Animals↗
PubMed1995

Regulation of astrocyte proliferation by FGF-2 and heparan sulfate in vivo.

The goal of this study was to examine the ability of basic fibroblast growth factor (FGF-2) to promote reactivity and/or proliferation of astrocytes in vivo following brain injury, and the possible mechanisms involved. A small bilateral lesion in the motor-sensory cortex was performed, and either FGF-2, FGF-2 plus heparan sulfate, heparan sulfate, or saline was applied unilaterally in a piece of Gelfoam within the wound cavity. Following lesions, there was an increase in FGF-2 and FGF receptor (FGFR) immunoreactivities in the area surrounding the lesion in all the treatment groups. Rats that received treatment with recombinant FGF-2 alone showed an increase in the density of astrocytes as compared to the control group. The same group of rats exhibited an increase in the density of cells displaying FGF-2 immunoreactivity and cells displaying FGFR-1 immunoreactivity and cells displaying FGFR-1 immunoreactivity, and also an induction of FGF-2 mRNA in the tissue surrounding the lesion. The group of rats that received FGF-2 combined with heparan sulfate showed a larger increase in the same cellular parameters. Our results suggest that the FGF-2/FGFR system is involved in the regulation of astrocytic reactivity and/or proliferation in the brain and its action is potentiated by heparan sulfate. The action of FGF-2 on CNS injury appears to be part of an autocrine cascade that involves induction of FGF-2 and its receptor, thereby enhancing the ability of astrocytes to respond to FGF-2.

Animals↗