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M Baudry

Publications and source records attributed to M Baudry.

At least 19 recordsLinked to original sources
PubMed2001

Cyclic changes in estradiol regulate synaptic plasticity through the MAP kinase pathway.

Hippocampal synaptic structure and function exhibit marked variations during the estrus cycle of female rats. Estradiol activates the mitogen-activated protein (MAP) kinase pathway in numerous cell types, and MAP kinase has been shown to play a critical role in the mechanisms underlying synaptic plasticity. Here, we report that endogenous estrogen produces a tonic phosphorylation/activation of extracellular signal-regulated kinase 2 (ERK2)/MAP kinase throughout the female rat brain and an increase in tyrosine phosphorylation of NR2 subunits of N-methyl-D-aspartate (NMDA) receptors. Moreover, cyclic changes in estrogen levels during the estrus cycle of female rats are associated with corresponding changes in the levels of activation of ERK2, the state of tyrosine phosphorylation of NR2 subunits of NMDA receptors, and the magnitude of long-term potentiation in hippocampus. Thus, cyclic changes in female sexual hormones result in marked variations in the state of activation of a major cellular signaling pathway critical for learning and memory and in a cellular model of learning and memory.

Animals↗
PubMed2001

Kainate excitotoxicity in organotypic hippocampal slice cultures: evidence for multiple apoptotic pathways.

The mechanisms underlying kainate (KA) neurotoxicity are still not well understood. We previously reported that KA-mediated neuronal damage in organotypic cultures of hippocampal slices was associated with p53 induction. Recently, both bax and caspase-3 have been demonstrated to be key components of the p53-dependent neuronal death pathway. Caspase activation has also been causally related to the release of mitochondrial cytochrome c (Cyto C) in the cytoplasm as a result of the collapse of the mitochondrial membrane potential (Deltapsi(M)) and the opening of mitochondrial permeability transition pores (mPTP). In the present study, we observed a rapid induction of bax in hippocampal slice cultures after KA treatment. In addition, the levels of Cyto C and caspase-3 were increased in the cytosol while the level of the caspase-9 precursor was decreased. There was also a complete reduction of Rhodamine 123 fluorescence after KA treatment, an indication of Deltapsi(M) dissipation. Furthermore, inhibition of mPTP opening by cyclosporin A partially prevented Cyto C release, caspase activation and neuronal death. These data suggest the involvement of bax, several caspases, as well as Cyto C release in KA-elicited neuronal death. Finally, inhibition of caspase-3 activity by z-VAD-fmk only partially protected neurons from KA toxicity, implying that multiple mechanisms may be involved in KA excitotoxicity.

Amino Acid Chloromethyl Ketones↗
PubMed2001

Toxic effects of MPP(+) and MPTP in PC12 cells independent of reactive oxygen species formation.

MPTP is a toxin presumed to damage dopamine-secreting neurons by an oxygen free radical-mediated mechanism. Two steps in MPTP metabolism are the primary candidates for oxygen free radical generation: (a) MPTP oxidation to MPP(+) by a monoamine oxidase and (b) NADH dehydrogenase inhibition by MPP(+). In order to test the idea that MPTP toxicity is mediated by oxygen free radicals, we assessed lipid peroxidation and the effects of antioxidants in dopaminergic PC12 cells treated with MPTP or MPP(+). For comparison purposes, we also examined the effects of the pro-oxidant tert-butyl-hydroperoxide (TBHP) and of the dopaminergic toxin 6-hydroxydopamine (6-OHDA) in PC12 cells. MPTP and MPP(+), unlike TBHP, failed to induce lipid peroxidation in PC12 cells after a 4-h exposure. All toxins tested (MPTP, MPP(+), TBHP and 6-OHDA) caused a dose-dependent decrease in [(3)H]dopamine ((3)H-DA) uptake in PC12 cultures. The hydroperoxide scavengers glutathione and N-acetyl-cysteine and the superoxide and peroxide scavenger EUK-134 protected PC12 cells from TBHP- and 6-OHDA-induced decrease in (3)H-DA uptake. However, no protection by these antioxidants at various concentrations and time regimens was observed against MPTP- or MPP(+)-induced decreases in (3)H-DA uptake in PC12 cells. In addition, incubation of PC12 cells with the energy-rich substrate, NADH, attenuated MPP(+)-induced decrease in (3)H-DA uptake. These results suggest that MPTP-induced toxicity in dopaminergic PC12 cell cultures, does not involve oxygen free radical production, but rather may be caused by impairment in energy metabolism.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed2001

Synthetic superoxide dismutase/catalase mimetics reduce oxidative stress and prolong survival in a mouse amyotrophic lateral sclerosis model.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder that causes motoneuron degeneration, paralysis and death. Mutations in Cu, Zn superoxide dismutase (SOD1) are one cause of this disease. It is widely suspected that increased reactive oxidative species (ROS) is involved in motoneuron degeneration but whether such an involvement plays a role in ALS progression in vivo is uncertain. We treated mice expressing human mutant SOD1 G93A with EUK-8 and EUK-134, two synthetic SOD/catalase mimetics that have shown efficacy in several animal models of human diseases. These treatments reduced levels of oxidative stress and prolonged survival. The results suggest that oxidative stress plays an active role in ALS and illustrate the potential for treatment strategies aimed specifically against ROS.

Amyotrophic Lateral Sclerosis↗
PubMed2001

Involvement of the secretory pathway for AMPA receptors in NMDA-induced potentiation in hippocampus.

A chemical form of synaptic potentiation was produced with a brief bath application of NMDA to rat hippocampal slices. Two methods were used to assess changes in membrane-bound AMPA receptors. Traditional subcellular fractionation was used to isolate synaptic membranes; alternatively, membrane receptors were cross-linked with the membrane-impermeable reagent bis(sulfosuccinimidyl) suberate, and levels of nonmembrane receptors were determined. In both cases, Western blots were used to determine the content of receptor subunits in various subcellular fractions. NMDA-induced potentiation was associated with increased levels of glutamate receptor 1 (GluR1) and GluR2/3 subunits of AMPA receptors in synaptic membrane preparations, whereas no change was observed in whole homogenates. Both KN-62, an inhibitor of calcium/calmodulin kinase, and calpain inhibitor III, a calpain inhibitor, inhibited NMDA-induced potentiation and changes in GluR1 and GluR2/3 subunits of AMPA receptors. Brefeldin A (BFA) inhibits protein trafficking between the Golgi apparatus and cell membranes. Pretreatment of hippocampal slices with BFA significantly decreased NMDA-induced potentiation and completely prevented an NMDA-induced increase in GluR1 levels in membrane fractions. Thus, the levels of GluR1 and GluR2/3 subunits of AMPA receptors are rapidly upregulated in synaptic membranes under conditions associated with potentiation of synaptic responses, and this upregulation requires a functional secretory pathway.

Animals↗
PubMed2001

Inositol hexakisphosphate-mediated regulation of glutamate receptors in rat brain sections.

D-myo-inositol 1,2,3,4,5,6-hexakisphosphate (InsP6), one of the most abundant inositol phosphates within cells, has been proposed to play a key role in vesicle trafficking and receptor compartmentalization. In the present study, we used in vitro receptor autoradiography, subcellular fractionation, and immunoblotting to investigate its effects on alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) and N-methyl-D-aspartate (NMDA) receptors. Qualitative and quantitative analysis of 3H-AMPA binding indicated that incubation of frozen-thawed brain sections with InsP6 at 35 degrees C enhanced AMPA receptor binding in several brain regions, with maximal increases in the hippocampus and cerebellum. Moreover, saturation kinetics demonstrated that InsP6-induced augmentation of AMPA binding was due to an increment in the maximal number of AMPA binding sites. At the immunological level, Western blots performed on crude mitochondrial/synaptic (P2) fractions revealed that InsP6 (but not InsP5 and InsP3) treatment increased glutamate receptor (GluR)1 and GluR2 subunits of AMPA receptors, an effect that was associated with concomitant reductions in microsomal (P3) fractions. Interestingly, the InsP6-induced modulation of AMPA receptor binding was blocked at room temperature, and pretreatment with heparin also dampered its action on both AMPA receptor binding and GluR subunits. These effects of InsP6 appear to be specific to AMPA receptors, as neither 3H-glutamate binding to NMDA receptors nor levels of NR1 and NR2A subunits in P2 and P3 fractions were affected. Taken together, our data strongly suggest that InsP6 specifically regulates AMPA receptor distribution, possibly through a clathrin-dependent process.

Animals↗
PubMed2001

Attenuation of staurosporine-induced apoptosis, oxidative stress, and mitochondrial dysfunction by synthetic superoxide dismutase and catalase mimetics, in cultured cortical neurons.

Neuronal apoptosis induced by staurosporine (STS) involves multiple cellular and molecular events, such as the production of reactive oxygen species (ROS). In this study, we tested the efficacy of two synthetic superoxide dismutase/catalase mimetics (EUK-134 and EUK-189) on neuronal apoptosis, oxidative stress, and mitochondrial dysfunction produced by STS in primary cortical neuronal cultures. Exposure of cultures to STS for 24 h increased lactate dehydrogenase (LDH) release, the number of apoptotic cells, and decreased trypan blue exclusion. Pretreatment with 20 microM EUK-134 or 0.5 microM EUK-189 significantly attenuated STS-induced neurotoxicity, as did pretreatment with the caspase-1 inhibitor, Ac-YVAD-CHO, but not the caspase-3 inhibitor, Ac-DEVD-CHO. Posttreatment (1-3 h following STS exposure) with 20 microM EUK-134 or 0.5 microM EUK-189 significantly reduced STS-induced LDH release, in a time-dependent manner. Exposure of cultures to STS for 1 h produced an elevation of ROS, as determined by increased levels of 2,7-dichlorofluorescein (DCF). This rapid elevation of ROS was followed by an increase in lipid peroxidation, and both the increase in DCF fluorescence and in lipid peroxidation were significantly blocked by pretreatment with EUK-134. STS treatment for 3-6 h increased cytochrome c release from mitochondria into the cytosol, an effect also blocked by pretreatment with EUK-134. These results indicate that intracellular oxidative stress and mitochondrial dysfunction are critically involved in STS-induced neurotoxicity. However, there are additional cellular responses to STS, which are insensitive to treatment with radical scavengers that also contribute to its neurotoxicity.

Animals↗
PubMed2001

A biosensor for detecting changes in cognitive processing based on nonlinear systems analysis.

A new type of biosensor, based on hippocampal slices cultured on multielectrode arrays, and using nonlinear systems analysis for the detection and classification of agents interfering with cognitive function is described. A new method for calculating first and second order kernel was applied for impulse input-spike output datasets and results are presented to show the reliability of the estimations of this parameter. We further decomposed second order kernels as a sum of nine exponentially decaying Laguerre base functions. The data indicate that the method also reliably estimates these nine parameters. Thus, the state of the system can now be described with a set of ten parameters (first order kernel plus nine coefficients of Laguerre base functions) that can be used for detection and classification purposes.

Animals↗
PubMed2001

Proteolysis of glutamate receptor-interacting protein by calpain in rat brain: implications for synaptic plasticity.

Activation of the calcium-dependent protease calpain has been proposed to be a key step in synaptic plasticity in the hippocampus. However, the exact pathway through which calpain mediates or modulates changes in synaptic function remains to be clarified. Here we report that glutamate receptor-interacting protein (GRIP) is a substrate of calpain, as calpain-mediated GRIP degradation was demonstrated using three different approaches: (i) purified calpain I digestion of synaptic membranes, (ii) calcium treatment of frozen-thawed brain sections, and (iii) NMDA-stimulated organotypic hippocampal slice cultures. More importantly, calpain activation resulted in the disruption of GRIP binding to the GluR2 subunit of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptors. Because GRIP has been proposed to function as an AMPA receptor-targeting and synaptic-stabilizing protein, as well as a synaptic-organizing molecule, calpain-mediated degradation of GRIP and disruption of AMPA receptor anchoring are likely to play important roles in the structural and functional reorganization accompanying synaptic modifications in long-term potentiation and long-term depression.

Animals↗
PubMed2001

Tyrosine phosphorylation of ionotropic glutamate receptors by Fyn or Src differentially modulates their susceptibility to calpain and enhances their binding to spectrin and PSD-95.

Both tyrosine phosphorylation and calpain-mediated truncation of ionotropic glutamate receptors are important mechanisms for synaptic plasticity. Previous work from our laboratory has shown that calpain activation results in truncation of the C-terminal domains of several glutamate receptor subunits. To test whether and how tyrosine phosphorylation of glutamate ionotropic receptor subunits modulates calpain susceptibility, synaptic membranes were phosphorylated by Fyn or Src, two members of the Src family tyrosine kinases. Tyrosine phosphorylation of synaptic membranes by Src significantly reduced calpain-mediated truncation of both NR2A and NR2B subunits of NMDA receptors, but not of GluR1 subunits of AMPA receptors. In contrast, phosphorylation with Fyn significantly protected calpain-mediated truncation of GluR1 subunits of AMPA receptors, but enhanced calpain-mediated truncation of NR2A subunits of NMDA receptors. Similar results were observed with NR2A and NR2B C-terminal domain fusion proteins phosphorylated by Fyn or Src before incubation with calpain and calcium. In addition, phosphorylation of NR2A and NR2B C-terminal fusion proteins by Fyn or Src enhanced their binding to spectrin and PSD-95. Thus, tyrosine phosphorylation impairs or facilitates calpain-mediated truncation of glutamate receptor subunits, depending on which tyrosine kinase is activated. Such mechanisms could serve to regulate receptor integrity and location, in addition to modulating channel properties.

Animals↗
PubMed2001

Role of polyamine metabolism in kainic acid excitotoxicity in organotypic hippocampal slice cultures.

Polyamines are ubiquitous cations that are essential for cell growth, regeneration and differentiation. Increases in polyamine metabolism have been implicated in several neuropathological conditions, including excitotoxicity. However, the precise role of polyamines in neuronal degeneration is still unclear. To investigate mechanisms by which polyamines could contribute to excitotoxic neuronal death, the present study examined the role of the polyamine interconversion pathway in kainic acid (KA) neurotoxicity using organotypic hippocampal slice cultures. Treatment of cultures with N1,N(2)-bis(2,3-butadienyl)-1,4-butanediamine (MDL 72527), an irreversible inhibitor of polyamine oxidase, resulted in a partial but significant neuronal protection, especially in CA1 region. In addition, this pre-treatment also attenuated KA-induced increase in levels of lipid peroxidation, cytosolic cytochrome C release and glial cell activation. Furthermore, pre-treatment with a combination of cyclosporin A (an inhibitor of the mitochondrial permeability transition pore) and MDL 72527 resulted in an additive and almost total neuronal protection against KA toxicity, while the combination of MDL 72527 and EUK-134 (a synthetic catalase/superoxide dismutase mimetic) did not provide additive protection. These data strongly suggest that the polyamine interconversion pathway partially contributes to KA-induced neurodegeneration via the production of reactive oxygen species.

Animals↗
PubMed2000

Prevention of 1-methyl-4-phenylpyridinium- and 6-hydroxydopamine-induced nitration of tyrosine hydroxylase and neurotoxicity by EUK-134, a superoxide dismutase and catalase mimetic, in cultured dopaminergic neurons.

Oxidative stress has been implicated in the selective degeneration of dopaminergic (DAergic) neurons in Parkinson's disease (PD). In this study, we tested the efficacy of EUK-134, a superoxide dismutase (SOD) and catalase mimetic, on the nitration of tyrosine hydroxylase (TH), a marker of oxidative stress, and neurotoxicity produced by 1-methyl-4-phenylpyridinium (MPP(+)) and 6-hydroxydopamine (6-OHDA) in primary DAergic neuron cultures. Exposure of cultures to 10 microM MPP(+) reduced dopamine (DA) uptake and the number of tyrosine hydroxylase immunoreactive (THir) neurons to 56 and 52% of control, while exposure to 30 microM 6-OHDA reduced DA uptake and the number of THir neurons to 58 and 59% of control, respectively. Pretreatment of cultures with 0.5 microM EUK-134 completely protected DAergic neurons against MPP(+)- and 6-OHDA-induced neurotoxicity. Exposure of primary neuron cultures to either MPP(+) or 6-OHDA produced nitration of tyrosine residues in TH. Pretreatment of cultures with 0.5 microM EUK-134 completely prevented MPP(+)- or 6-OHDA-induced nitration of tyrosine residues in TH. Taken together, these results support the idea that reactive oxygen species (ROS) are critically involved in MPP(+)- and 6-OHDA-induced neurotoxicity and suggest a potential therapeutic role for synthetic catalytic scavengers of ROS, such as EUK-134, in the treatment of PD.

1-Methyl-4-phenylpyridinium↗
PubMed2000

Src-mediated tyrosine phosphorylation of NR2 subunits of N-methyl-D-aspartate receptors protects from calpain-mediated truncation of their C-terminal domains.

Src-mediated tyrosine phosphorylation of N-methyl-d-aspartate receptor subunits has been shown to modify the functional properties of N-methyl-d-aspartate receptors. Moreover, calpain-mediated truncation of N-methyl-d-aspartate receptor subunits has been found to alter the structure of the receptors. In the present study, we first used immunoprecipitation with a variety of antibodies against N-methyl-d-aspartate receptor subunits and anti-phosphotyrosine antibodies to show that tyrosine-phosphorylated subunits of N-methyl-d-aspartate receptor are protected against calpain-mediated truncation of their C-terminal domains. A GST fusion protein containing the C-terminal domain of NR2A was used to identify the calpain cutting sites in the C-terminal domain. One site was identified at residues 1278-1279, corresponding to one of the preferred calpain truncation sites. This site is adjacent to a consensus sequence for Src-mediated tyrosine phosphorylation, and Src-mediated tyrosine phosphorylation of the GST-NR2A C-terminal fusion protein also inhibited calpain-mediated truncation of the fusion protein. We propose that phosphorylation of NR2 subunits and the resulting inhibition of calpain-mediated truncation of their C-terminal domains provide for the stabilization of the N-methyl-d-aspartate receptors in postsynaptic structures.

Amino Acid Sequence↗
PubMed2000

Calpain-mediated degradation of PSD-95 in developing and adult rat brain.

PSD-95 is a major postsynaptic density protein that is degraded as a result of synaptic activity. We used four different methods to test the hypothesis that calpain is involved in PSD-95 turnover. Treatment of synaptic membranes with purified calpain resulted in a decrease in immunoreactivity of the native 95 kDa protein and the appearance of two smaller molecular weight species, migrating at 50 and 36 kDa, respectively. Calcium treatment of frozen-thawed brain sections produced an identical digestion pattern, an effect blocked by calpain inhibitors. N-methyl-D-aspartate treatment of organotypic hippocampal cultures produced truncation of PSD-95 and accumulation of the 36 kDa species. Finally, calpain-generated degradation products of PSD95 were prominent in neonatal hippocampus, and disappeared with postnatal development. Our data suggest that PSD-95 is a substrate for calpain, and that calpain-mediated truncation contributes to PSD-95 turnover.

Age Factors↗
PubMed2000

Calpain-mediated truncation of rat brain AMPA receptors increases their Triton X-100 solubility.

Previous studies have indicated that calpain activation results in the truncation of the C-terminal domains of AMPA and NMDA receptor subunits. The present study determined the distribution of the truncated species of the subunits between Triton-soluble and -insoluble fractions. Western blots were performed with various antibodies to quantify the amounts of the various species of GluR1, GluR2, GluR3 and NR2B subunits. The results indicate that calpain activation decreased the amount of all the intact subunits in Triton-insoluble fractions. Calpain-generated truncated forms of GluR1 and GluR2, but not NR2B, were absent in these fractions, and were recovered in Triton-soluble fractions. These findings suggest that calpain-mediated truncation of AMPA but not NMDA receptor C-terminal domains results in modifications of the interactions between the receptors and postsynaptic densities, and that this mechanism could be involved in activity-dependent changes in the subcellular distribution of AMPA receptors.

Animals↗
PubMed2000

The tyrosine kinase and mitogen-activated protein kinase pathways mediate multiple effects of estrogen in hippocampus.

Estrogen replacement therapy in women is associated with improvement of cognitive deficits and reduced incidence of Alzheimer's disease. The present study indicates that estrogen is neuroprotective against N-methyl-d-aspartate (NMDA)- and kainate-mediated neurotoxicity, an effect mediated by tyrosine kinase/mitogen-activated protein kinase (MAPK) pathways. Estrogen also stimulates tyrosine phosphorylation of NMDA receptors via an src tyrosine kinase/MAPK pathway. Finally, estrogen-mediated enhancement of long-term potentiation in hippocampal slices is mediated by activation of an src tyrosine kinase pathway. Thus, estrogen, by activating an src tyrosine kinase and the extracellular signal-related protein kinase/MAPK signaling pathway, both enhances NMDA receptor function and long-term potentiation and retains neuroprotective properties against excitotoxicity. These findings warrant further evaluation of the usefulness of estrogenic compounds for the treatment of Alzheimer's disease and other neurodegenerative diseases.

Action Potentials↗
PubMed2000

The role of glycosylation in ionotropic glutamate receptor ligand binding, function, and trafficking.

Members of the ionotropic glutamate receptor (iGluR) family have between 4 and 12 consensus asparagine (N)-linked glycosylation sites. They are localized on the extracellular N-termini, and the loop between the penultimate and last transmembrane domains. These regions also contain the essential elements for formation of the ligand binding site. N-linked glycosylation does not appear to be essential for formation of the ligand binding site per se, but there are demonstrated interactions between glycosylation state and ligand binding affinity, receptor physiology, susceptibility to allosteric modulation and, in some cases, trafficking. There is no indication of a general role for N-linked glycosylation in iGluRs; instead the effects of glycosylation vary among glutamate receptor subtypes and splice variants, with specific effects on structure or function with different subunits.

Animals↗