Biomedical subjects

M Baudry

Publications and source records attributed to M Baudry.

At least 19 recordsLinked to original sources

PubMed1996

beta-Amyloid toxicity in organotypic hippocampal cultures: protection by EUK-8, a synthetic catalytic free radical scavenger.

Oxygen free radicals have been proposed to mediate amyloid peptide (beta-AP)-induced neurotoxicity. To test this hypothesis, we evaluated the effects of EUK-8, a synthetic catalytic superoxide and hydrogen peroxide scavenger, on neuronal injury produced by beta-AP in organotypic hippocampal slice cultures. Cultures of equivalent postnatal day 35 (defined as mature) and 14 (defined as immature) were exposed to various concentrations of beta-AP (1-42 or 1-40) in the absence or presence of 25 microM EUK-8 for up to 72 hours. Neuronal injury was assessed by lactate dehydrogenase release and semiquantitative analysis of propidium iodide uptake at various times after the initiation of beta-AP exposure. Free radical production was inferred from the relative increase in dichlorofluorescein fluorescence, and the degree of lipid peroxidation was determined by assaying thiobarbituric acid-reactive substances. Treatment of mature cultures with beta-AP (50-250 microg/ml) in serum-free conditions resulted in a reproducible pattern of damage, causing a time-dependent increase in neuronal injury accompanied with formation of reactive oxygen species. However, immature cultures were entirely resistant to beta-AP-induced neurotoxicity and also demonstrated no dichlorofluorescein fluorescence or increased lipid peroxidation after beta-AP treatment. Moreover, mature slices exposed to beta-AP in the presence of 25 microM EUK-8 were significantly protected from beta-AP-induced neurotoxicity. EUK-8 also completely blocked beta-AP-induced free radical accumulation and lipid peroxidation. These results not only support a role for oxygen free radicals in beta-AP toxicity but also highlight the therapeutic potential of synthetic radical scavengers in Alzheimer disease.

Amyloid beta-Protein Precursor↗

PubMed1996

Seizure activity results in a rapid induction of nuclear factor-kappa B in adult but not juvenile rat limbic structures.

Previous studies have indicated that increased formation of oxygen free radicals is likely to participate in the cascade of events leading to neuronal damage following kainic acid (KA)-induced seizure activity. As reactive oxygen species are involved in signal transduction pathways leading to nuclear factor-kappaB (NF-kappaB) activation, we examined the effects of KA treatment on the activation of NF-kappaB in adult and juvenile rat brain. For comparison, changes in two other transcription factors, activator protein-1 (AP-1) and Sp1, were also determined. In adult rat piriform cortex and hippocampus, significant induction of NF-kappaB was observed at 4 h after KA injection, and the maximal increase was reached at 8-16 h posttreatment. NF-kappaB binding activities returned to control levels by 5 days after injection. NF-kappaB binding activities were slightly decreased in adult rat cerebellum at 8 and 16 h after KA treatment. In the juvenile rat, no significant changes in NF-kappaB binding activity were observed in piriform cortex, hippocampus, and cerebellum after KA injection. Changes in AP-1 binding activity were qualitatively similar to those observed with NF-kappaB in adult but not juvenile rat brain, as AP-1 was significantly induced in juvenile piriform cortex and hippocampus following KA injection. On the other hand, little or no changes in Sp1 activity were detected in adult and juvenile rat brain. Our results provide further evidence that oxidative stress participates in neuronal damage resulting from KA-induced seizure activity.

Age Factors↗

PubMed1996

Evidence of true protein kinase CKII activity in mitochondria and its spermine-mediated translocation to inner membrane.

A true protein kinase CKII (CKII) activity was characterized in liver mitochondria by its phosphorylating activity on the specific peptide substrate of CKII, the binding and elution profile of the enzyme on a phosphocellulose column and immunostaining of a 36 kDa polypeptide with antibodies against the alpha-subunit of human CKII. This CKII activity was located predominantly in the intermembrane space of quiescent mitochondria. A translocation of the enzyme to inner membrane of energized mitochondria occurred in the presence of spermine. Translocated CKII activity was tightly bound to inner membrane, and high salt concentrations were necessary to release the activity. The inner face of the inner membrane could constitute the in vivo localization of mitochondrial CKII since the potential substrates of the enzyme are 4 matrix proteins.

Amino Acid Sequence↗

PubMed1995

Effect of kainate-induced seizure activity on the polyamine interconversion pathway in juvenile rat brain.

The activity of the polyamine interconversion pathway was investigated in the hippocampus and piriform cortex after systemic KA administration in juvenile rats. Pretreatment of 7-day-old rats with the polyamine oxidase inhibitor, MDL 72527, induced a similar accumulation of N-acetylspermidine and N-acetylspermine in control and kainate-treated animals. The results indicate that KA-induced seizure activity has no effect on the polyamine interconversion pathway in developing rat brain.

Acetylation↗

PubMed1995

Synaptotagmin IV is an immediate early gene induced by depolarization in PC12 cells and in brain.

Subtractive library construction and differential screening were used to identify a cDNA for a cell type-specific immediate early gene induced in rat PC12 pheochromocytoma cells. Sequencing identified the protein product of this gene as rat synaptotagmin IV (SytIV). Synaptotagmins are synaptic vesicle proteins thought to play a role in depolarization-induced, calcium-mediated exocytosis and neurotransmitter release. SytIV mRNA accumulation is transiently induced in PC12 cells by potassium depolarization, calcium ionophore, ATP, and forskolin. In contrast, growth factors and phorbol 12-myristate 13-acetate induce little or no SytIV mRNA accumulation. Kainic acid-induced seizures in rats are followed by accumulation of SytIV message in the hippocampus and piriform cortex. The SytIV gene may provide a direct link between depolarization-induced neuronal gene expression and subsequent modulation of synaptic structure and function.

Adrenal Gland Neoplasms↗

PubMed1995

Melittin increases AMPA receptor affinity in rat brain synaptoneurosomes.

Recent experimental evidence suggests that phospholipase-induced changes in binding properties of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) subtype of glutamate receptors account for the increase in synaptic response observed in long-term potentiation (LTP). In the present study, we report that treatment of rat telencephalic synaptoneurosomes with the bee venom peptide melittin, a potent activator of endogenous phospholipases, increased [3H]AMPA binding to the AMPA receptor. The action of melittin was concentration-dependent (EC50 value = 10 micrograms/ml) and did not require the presence of extracellular calcium. Saturation kinetic experiments revealed that the increase in [3H]AMPA binding produced by melittin was due to an enhancement in the affinity of the AMPA receptor, an effect markedly reduced by the phospholipase A2 (PLA2) inhibitor bromophenacyl bromide (BPB). In contrast to BPB, inhibitors of cyclooxygenase and lipoxygenase pathways of arachidonic acid metabolism did not interfere with the melittin-induced increase in [3H]AMPA binding. In neonatal synaptoneurosomes, the effect of melittin on [3H]AMPA binding was significantly reduced when compared to adult synaptoneurosomes, an effect which is consistent with the observation that LTP is not present in very young animals. The results indicate that activation of endogenous phospholipases may be an important mechanism in the regulation of AMPA receptor properties in LTP.

Aging↗

PubMed1995

Properties and mechanisms of long-term synaptic plasticity in the mammalian brain: relationships to learning and memory.

Long-term potentiation (LTP) in the hippocampus and long-term depression (LTD) in the cerebellum are two forms of long-lasting synaptic plasticity that currently serve as our primary experimental models of learning and memory formation in mammals. In recent years, there have been considerable advances in our understanding of the cellular and molecular mechanisms of these and other forms of synaptic plasticity. This article presents an overview of these developments, considers the relationship of long-term synaptic plasticity mechanisms to learning and memory in view of these developments, and suggests future directions for research in this rapidly growing area of neuroscience.

Animals↗

PubMed1995

Development of kainic acid and N-methyl-D-aspartic acid toxicity in organotypic hippocampal cultures.

The excitotoxic effects of N-methyl-D-aspartic acid (NMDA) and kainic acid (KA) were studied in organotypic hippocampal slices maintained in vitro for various periods of time. Cultures aged to equivalent Postnatal Day (EPD) 10-12, 15-17, and 23-26 were exposed to 50 microM KA or 50 microM NMDA and were analyzed at 0, 3, 6, 9, 12, 24, 48 h, or 5 days after the initiation of the excitotoxin exposure. Neuronal injury was determined by: (1) propidium iodide (PI) uptake; (2) lactate dehydrogenase (LDH) release; (3) morphological damage in hematoxylin and eosin (H/E) stained sections; (4) loss of Nissl stain. Changes in PI uptake and LDH release after KA or NMDA treatment indicated that there was a developmental shift towards increasing sensitivity to KA toxicity during in vitro development, whereas cultures of all ages were equally sensitive to NMDA toxicity. The profile of damage in H/E-stained sections after treatment with KA or NMDA indicated a transient phase of damaged morphology at 12 and 24 h that was not evident after 5 days. To determine whether the disappearance of morphological manifestations of neuronal damage 5 days after treatment was due to recovery of morphology or to neuronal death, neuronal loss in Nissl-stained sections was also quantified. KA treatment did not cause significant neuronal loss in any hippocampal region in EPD 10-12 cultures, indicating that the neurons were able to successfully recover from the damage demonstrated in H/E sections at 12 and 24 h in these cultures. KA treatment in mature cultures (EPD 23-26) and NMDA treatment in all cultures produced a marked loss of identifiable Nissl-stained neurons at 5 days, indicating neuronal death and disintegration. The results provide further support for the similarities between the organotypic hippocampal culture model and in vivo excitotoxic models and also confirm that excitotoxic neuronal injury can be reversible under some conditions.

Animals↗

PubMed1995

Selective neuronal vulnerability in the hippocampus--a role for gene expression?

Proposed mechanisms of neurodegeneration focus generally on the triggering of toxic biochemical pathways by an increased intracellular concentration of Ca2+. Recent evidence also suggests that Ca2+ causes transcriptional activation of so-called 'cell-death genes'. Efforts to elucidate the basis of selective vulnerability have relied on animal models of delayed neuronal death in the hippocampus. Biochemical and morphological data indicate that delayed neuronal death is a form of programmed cell death, or apoptosis. Observations that specific genes are activated transcriptionally for prolonged times in neuronal populations that are undergoing delayed death suggest that active gene expression is part of the neuronal-death cascade. Although a direct causal role remains to be proven, evidence implicates certain genes in neuronal-death pathways.

Animals↗

PubMed1995

Developmental changes in alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor properties and expression in the rat hippocampal formation.

The developmental changes in alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor properties in rat hippocampus were evaluated with quantitative autoradiography of ligand binding and in situ hybridization performed in adjacent sections with antisense oligonucleotides for AMPA receptor subunits (GluR1-3, flip and flop splice variants). Specific 3H-AMPA binding in different hippocampal subfields increased between postnatal day 7 and 15 and was higher in CA3 during the postnatal period when compared to adult levels. This effect was mostly due to high levels of high affinity binding sites in cell body layers during the developmental period. By contrast, autoradiograms of 3H-AMPA binding predominantly to the low affinity binding sites indicated an absence of these sites in cell body layers and the overall levels of binding exhibited little overshoot compared to adult levels during the developmental period. The changes in binding of the antagonist of the AMPA receptor, 6-nitro-7-cyanoquinoxaline-2,3-dione were markedly different from those for the high affinity AMPA binding sites but quite similar to those for the low affinity sites. The binding was extremely low at postnatal day 7 and increased rapidly between postnatal day 7 and 15 and slowly between postnatal day 15 and adult. Low levels of binding were observed in the cell body layer at every postnatal age. The changes in expression of messenger RNAs for the different subunits of the AMPA receptors were well correlated with the modifications in high affinity AMPA binding sites measured in the cell body layers also exhibiting an increased expression of the receptors at the transcriptional level during the developmental period as compared to adult levels. The relative expression of the GluR2 subunits decreased during the postnatal period and the time course for this reduction paralleled that for the increased vulnerability of hippocampal pyramidal neurons to a variety of insults. The results indicate that both the messenger RNAs for the subunits and the AMPA receptors exhibit increased levels of expression during the postnatal period compared to adult levels. They also suggest that nascent receptors might bind AMPA with high affinity before their insertion in membranes into functional receptors that have low affinity for agonists and high affinity for antagonists. The changes in subunit composition of the receptors during the postnatal period may have important implications for mechanisms of plasticity as well as of neuropathology.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed1995

Oxygen free radicals in rat limbic structures after kainate-induced seizures.

Several indices of free radical generation were determined in limbic structures after kainate (KA)-induced seizure activity in adult and postnatal day (PND) 12 and 17 rats. Superoxide dismutase, catalase, and glutathione peroxidase activities were measured in piriform cortex and hippocampal subfields at 8, 16, 48 h, and 5 days after KA injection in adults and pups, and also at 3 weeks postinjection in adults. KA-induced seizure activity had no significant effect on enzyme activities in PND 12 and 17 rats. In adults, superoxide dismutase and catalase activities were significantly increased at 5 days after KA administration, and returned to preinjection levels by 3 weeks. Glutathione peroxidase activity was also increased significantly at 5 days postinjection, but remained elevated at 3 weeks. Lipid peroxidation, as indicated by malondialdehyde (MDA) concentration, exhibited an early significant increase at 8 and 16 h, followed at 48 h and 5 days by a significant decrease. At 3 weeks postinjection, MDA levels were still significantly decreased in CA3 and dentate gyrus. KA administration in PND 12 and 17 rats had no significant effect on MDA content. KA-induced seizure activity in adults also resulted in a large and sustained increase in protein oxidation in piriform cortex and hippocampus. The early increase in MDA and protein oxidation in adult rats strongly suggests the involvement of oxygen free radicals in the initial phases of KA-induced pathology, whereas the changes in scavenging enzyme activities and MDA content at 5 days and 3 weeks post KA injection possibly reflect glial proliferation subsequent to neuronal death.

Animals↗

PubMed1994

Calpain-mediated regulation of AMPA receptors in adult rat brain.

Changes in AMPA receptors have been proposed to underlie changes in synaptic efficacy in hippocampus and other brain structures. Activation of calpain has also been discussed as a potential mechanism to produce lasting modifications of synaptic structure and function. We report here that preincubation of thin (10 microns) frozen rat brain sections with calcium at physiological temperature changes the immunological properties of AMPA receptors, an effect totally blocked by calpain inhibitors. Immunocytochemistry indicates that in situ calpain activation produces a decreased immunoreactivity for GluR1, and to a lesser extent for GluR2/3, in the neuropil throughout the brain and an increased immunoreactivity in cell bodies, particularly in hippocampus. Western blots of calcium-treated sections suggest that the decreased immunoreactivity for GluR subunits is due to partial proteolysis. These results strongly suggest the involvement of calpain in the regulation of glutamatergic synapses.

Animals↗

PubMed1994

Allosteric interactions and modulator requirement for NMDA receptor function.

Activation of NMDA receptors by glutamate, glycine and spermine was assessed using non-equilibrium [3H]dizocilpine binding. Glutamate and glycine mutually increased their efficacies and affinities to stimulate [3H]dizocilpine binding, which were further increased by spermine. Enhancement curves by glycine in the presence of increasing concentrations of the glycine antagonist 7-chlorokynurenate revealed that spermine markedly increased the affinity of glycine but not that of 7-chlorokynurenate, and that glycine was also required for [3H]dizocilpine binding in the presence of spermine. Spermine had a biphasic effect on [3H]dizocilpine binding, with a stimulatory phase followed by an inhibitory phase. The potency of spermine for both phases was increased by glutamate, but not by glycine. These observations indicate that there are positive cooperative interactions between the glutamate, the glycine and the stimulatory and inhibitory polyamine sites of the NMDA receptor. Moreover, glutamate and glycine, but not spermine, are required to activate the receptor.

Allosteric Regulation↗

PubMed1994

p53 induction is associated with neuronal damage in the central nervous system.

The p53 tumor-suppressor gene encodes a growth-regulatory protein that has been implicated in programmed cell death. To investigate the possible role of p53 in neuronal death, we studied p53 expression associated with excitotoxicity in the adult rat brain. Within hours of systemic administration of the glutamate analogue kainic acid, p53 mRNA levels were increased in neurons exhibiting morphological features of damage within kainate-vulnerable brain regions. A similar distribution was found for neurons exhibiting DNA damage as evidenced by in situ end-labeling of fragmented DNA. Pretreatment with the protein synthesis inhibitor cycloheximide prevented both kainate-mediated p53 induction and neuronal damage. The distinctive pattern of excitotoxin-mediated p53 expression suggests that p53 induction is a marker of irreversible injury in postmitotic cells of the central nervous system and could have functional significance in determining selective neuronal vulnerability.

Animals↗

PubMed1994

Neural tropomodulin: developmental expression and effect of seizure activity.

Tropomodulin is a 40.6 kDa tropomyosin-binding protein associated with actin filaments in muscle and the membrane cytoskeleton in erythrocytes. We have detected tropomodulin mRNA and protein in brains of rats by northern and western blot analyses. In situ hybridization of rat brain and spinal cord sections shows tropomodulin expression in the cerebellum, neocortex, hippocampus, and anterior horn of the spinal cord. Tropomodulin expression is first observed around day 15 after birth and increases through day 24. The temporal and spatial changes in tropomodulin expression during cerebellar development parallel those for brain tropomyosin. Tropomodulin mRNA increases in the dentate gyrus of the hippocampus following prolonged seizure activity induced by kainic acid administration; the increase is clearly evident 8 h after initiation of seizures and is still present 1 week later. However, Western blot analysis of tropomodulin protein level in the dentate gyrus before and after seizure induction show only slight increases in tropomodulin protein concentration, suggesting tight regulation of tropomodulin expression at the translational level. The developmental expression of tropomodulin, together with the induction of tropomodulin mRNA production in the dentate gyrus after kainic acid treatment, suggests a role for tropomodulin in neuronal organization and plasticity.

Animals↗

PubMed1994

Kainate-induced seizure activity stimulates the polyamine interconversion pathway in rat brain.

Systemic injection of kainic acid in adult rat is accompanied by a large increase in the accumulation of acetylated derivatives of spermidine and spermine in the hippocampus and piriform cortex of animals pretreated with the polyamine oxidase inhibitor, MDL 72527. Furthermore, the activity of the enzyme spermine/spermidine acetyltransferase is increased at 8 and 16 h after kainate injection in piriform cortex and hippocampus. These results indicate that the polyamine interconversion pathway is rapidly activated in limbic areas following kainate-induced seizure activity, and suggest that this pathway might participate in the resulting neuronal damage.

Acetylation↗

PubMed1994

Blockade of long-term depression in neonatal hippocampal slices by a phospholipase A2 inhibitor.

Low-frequency stimulation of the Schaffer-commissural pathways in slices prepared from juvenile rats (postnatal day 10-15) results in a long-term depression (LTD) of synaptic transmission. 30 min after 5 min of stimulation at 5 Hz, the response to the stimulated pathway was decreased by 36%, whereas the response to an unstimulated pathway projecting to the same neuronal population was decreased by 20%. Stimulation in the presence of the NMDA receptor antagonist AP5 completely prevented homosynaptic LTD. The phospholipase A2 inhibitor, bromophenacylbromide, also significantly reduced the extent of LTD in both the stimulated and control pathways. LTD was accompanied by a decrease in paired-pulse facilitation, suggesting a change in transmitter release. It also resulted in an increased effect of iontophoretically applied perchlorate, an ion which increases both the affinity of glutamate for the synaptic alpha-amino-3-hydroxy-5-methyl-4- isoxazole propionate (AMPA) receptors and synaptic responses, suggesting a change in postsynaptic receptors. These findings indicate that certain stimulation paradigms produce a combination of pre- and postsynaptic modifications that could underlie changes in synaptic efficacy.

2-Amino-5-phosphonovalerate↗

PubMed1994

Effects of EUK-8, a synthetic catalytic superoxide scavenger, on hypoxia- and acidosis-induced damage in hippocampal slices.

Anoxia produces deleterious effects on synaptic transmission in the hippocampal slice preparation. A proposed source of damage is the superoxide radical (.O2-) produced during the earlier period of reoxygenation. The present study tested the effects of a synthetic, catalytic superoxide radical scavenger (EUK-8) on CA1 pyramidal cell responses elicited by electrical stimulation of the Schaffer-commissural pathway after severe anoxic episodes. Following reoxygenation, slices incubated with EUK-8 (50 microM) exhibited significantly better recovery of excitatory postsynaptic potentials (EPSPs) than control slices. In addition, repeated episodes of anoxia produced irreversible loss of synaptic transmission in the majority of control slices (93 +/- 7%, n = 15), compared to a small fraction in EUK-8-incubated slices (27 +/- 12%, n = 15). A thiobarbituric acid (TBA) test was used to assess the effect of EUK-8 on lipid peroxidation elicited in hippocampal slices by acidosis and lactic acid (pH 5.0 and 30 mM lactic acid). Incubation in the presence of EUK-8 totally prevented the increase in lipid peroxidation produced by acidosis and lactic acid in both the incubation medium and the slice homogenates. These results indicate that a superoxide scavenger like EUK-8 prevents damage produced by acidosis and anoxia in hippocampal slices and suggest the possibility of using this type of molecule under various pathological conditions.

Acidosis↗