Biomedical subjects

M Baudry

Publications and source records attributed to M Baudry.

At least 19 recordsLinked to original sources

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

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

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↗

PubMed1993

The phospholipase A2 inhibitor bromophenacyl bromide prevents the depolarization-induced increase in [3H]AMPA binding in rat brain synaptoneurosomes.

We previously demonstrated that potassium (KCl)-induced depolarization of synaptoneurosomes prepared from rat telencephalon increased [3H]amino-3-hydroxy-5-methylisoxazole-4-propionate ([3H]AMPA) binding to the AMPA receptor. In the present study, we determined the effects of inhibitors of various calcium-dependent enzymes on this response to depolarization. Treatment of intact synaptoneurosomes with the phospholipase A2 (PLA2) inhibitor, bromophenacyl bromide (BPB), produced a marked and dose-dependent reduction in KCl-induced enhancement in [3H]AMPA binding. BPB had no significant effect on [3H]TPP accumulation in intact synaptoneurosomes, an index of membrane depolarization. In contrast to BPB, inhibitors of calcium-dependent kinases and proteases did not reduced the KCl-induced increase in [3H]AMPA binding. The results strengthen the hypothesis that phospholipase-induced modifications of AMPA receptor properties may be an important component of synaptic plasticity.

Acetophenones↗

PubMed1993

Single channel recordings of reconstituted AMPA receptors reveal low and high conductance states.

Glutamate receptors belonging to the AMPA (alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid) subclass were partially purified 30- to 60-fold from forebrain of adult rats and incorporated into planar bimolecular lipid membranes. The channel conductance associated with the reconstituted receptors was activated by kainate and AMPA in a manner that suggests cooperative binding of two to three agonist molecules is required to induce channel opening. This conductance was blocked by the specific antagonist DNQX (6,7-dinitroquinoxaline-2,3-dione). When the partially purified AMPA receptors were reconstituted by the tip-dipping method in asymmetric saline conditions ('outside-out configuration'), the addition of 300 nM AMPA to the pseudo-extracellular solution elicited single channel current fluctuations that were also inhibited by DNQX. Analyses of the currents revealed that the ion channels of reconstituted AMPA receptors have two distinct conductance levels of 12 and 60 pS with the great majority of receptors belonging to the former variety. These results suggest that reconstitution may be useful in identifying factors that regulate the binding and conductance properties of AMPA receptors.

Animals↗

PubMed1993

Further studies concerning the role of nitric oxide in LTP induction and maintenance.

Nitric oxide (NO) has recently been proposed to act as a retrograde messenger to produce long-term potentiation (LTP) in hippocampal area CA1. This notion is based largely on the absence of LTP when hippocampal slices are incubated in the presence of inhibitors of NO synthase (NOS) or of NO scavengers. In the present study, we tested the effects of such compounds on both the induction and maintenance of LTP in field CA1 of hippocampal slices. Incubation of slices in the presence of N-methyl-L-arginine (MLA) or L-nitro-arginine (LNA), two inhibitors of NOS, or in the presence of hemoglobin (Hb), a NO scavenger, produced a large reduction in the magnitude of LTP induced by a theta burst stimulation (TBS) paradigm. These compounds had no effect on the degree of paired-pulse facilitation but produced a significant reduction of the facilitation of postsynaptic responses occurring during TBS. On the other hand, MLA did not prevent the potentiation induced by application of tetraethylammonium (TEA). These results suggest that the inhibition of LTP produced by these agents could be due to an effect on a physiological mechanism that triggers LTP and not necessarily on an event that follows the triggering step.

2-Amino-5-phosphonovalerate↗

PubMed1993

Thiocyanate equally increases affinity for two DL-alpha-amino-3-hydroxy-5-methylisoxazolepropionic acid (AMPA) receptor states.

The effects of potassium thiocyanate on the binding of DL-alpha-amino-3-hydroxy-5-methylisoxazolepropionic acid (AMPA), 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), and L-glutamate to the AMPA receptor complex were studied in rat brain membranes. Thiocyanate increased the affinity of AMPA receptors for both AMPA and L-glutamate and decreased the affinity for CNQX. Displacement of [3H]CNQX binding by AMPA revealed that the affinity for AMPA of both the high and the low affinity states of the receptor increased in the presence of thiocyanate, whereas the proportion of the two states was unchanged. In soluble fractions, which exhibit an apparently homogeneous population of the high affinity state of the receptor, the affinity for AMPA was increased by a magnitude similar to that seen for the high affinity state in the membranes. These results indicate that thiocyanate enhances AMPA binding not by converting low affinity receptors into the high affinity state but by equally increasing the affinities of the high and the low affinity states of AMPA receptors.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed1992

Seizure activity-induced changes in polyamine metabolism and neuronal pathology during the postnatal period in rat brain.

Systemic injection of kainic acid (KA) does not cause neuronal pathology in limbic structures in rat brain prior to postnatal day (PND) 21. The present study tested if the development of the pathogenic response is associated with the maturation of a link between seizure activity and polyamine metabolism. Pathology was assessed with histological techniques and with the binding of [3H]Ro5-4864, a ligand for the peripheral type benzodiazepine binding sites (PTBBS), a marker of glial cell proliferation. In agreement with previous results, peripherally administered kainate at doses sufficient to induce intense behavioral seizures produced a loss of Nissl staining in hippocampus after PND 21 but not at earlier ages. The pattern of neuronal damage observed after PND 21 resembled that found in adult animals: extensive losses of Nissl staining in area CA3 of hippocampus and in piriform cortex, more modest effects in CA1 and sparing of the granule cells of the dentate gyrus. Similarly, no increase in [3H]Ro5-4864 binding as a result of KA administration was observed in hippocampus and piriform cortex until PND 21. Ornithine decarboxylase (ODC) activity and putrescine levels were high in the neonatal brain and decreased to reach adult values by PND 21. KA-induced seizure activity did not significantly alter both variables until PND 21. After PND 21, ODC activity and putrescine levels markedly increased 16 h after KA-induced seizure activity in hippocampus and piriform cortex. The magnitude of the effects increased between PND 21 and PND 30, at which point the changes in both parameters were comparable to those found in adults. Polyamines stimulate the activity of the calcium-dependent proteases calpain in brain fractions and may increase calpain-mediated proteolysis in situ. In accord with this, kainate-induced breakdown of spectrin, a preferred substrate of calpain, measured 16 h after KA injection followed a developmental curve parallel to that for kainate-induced increases in putrescine levels. These results indicate that the onset of vulnerability to seizure activity triggered by kainic acid is correlated with the development of an ODC/polyamine response to the seizures and further support a critical role for the ODC/polyamine pathway in neuronal pathology following a variety of insults.

Animals↗

PubMed1992

Increasing binding affinity of agonists to glutamate receptors increases synaptic responses at glutamatergic synapses.

This study examined the relationship between the affinity of glutamate agonists for the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors and the characteristics of the physiological responses elicited by endogenous activation of the AMPA receptors. We tested the effects of chaotropic ions on [3H]AMPA binding in synaptic membranes as well as on synaptic responses elicited in CA1 by electrical stimulation of the Schaffer/commissural pathway in the in vitro hippocampal slice preparation. Of the chaotropic ions tested, only perchlorate and thiocyanate produced large increases in [3H]AMPA binding to synaptic membranes. The effect was due to an increase in affinity for agonists, as shown by a shift of the displacement curves of 6-cyano-7-nitro[3H]-quinoxaline-2,3-dione binding by AMPA or glutamate. The effect of thiocyanate on [3H]AMPA binding was extremely sensitive to temperature, as the binding was increased almost 10-fold at 0 degree C but only 2- to 3-fold at 35 degrees C. The effect of perchlorate was only weakly temperature dependent. Similarly, thiocyanate and perchlorate were the only chaotropic ions tested that increased the initial slope and amplitude of the extracellularly recorded potentials evoked in CA1 dendritic field. Both ions did not change paired-pulse facilitation, an index of transmitter release, or fiber volley amplitude, an index of afferent recruitment. The chaotropic ions had no significant effects on either [3H]glutamate binding to the N-methyl-D-aspartate receptor or N-methyl-D-aspartate receptor-mediated synaptic responses. Finally, the effect of perchlorate on synaptic responses was significantly reduced after induction of long-term potentiation. These results indicate that an increase in affinity of the AMPA receptors for their agonists results in increased synaptic responses and strongly suggest that characteristics of the AMPA receptor are modified following long-term potentiation.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed1992

Postnatal changes in AMPA receptor regulation by phospholipase A2 treatment of synaptic membranes: temporally differential effects on agonist and antagonist binding.

Previous results have indicated that phospholipase A2 (PLA2) treatment of telencephalic membranes produced opposite effects on [3H]amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) binding in neonatal and adult rats. In the present study, we compared the effects of PLA2 treatment of telencephalic membranes on the binding characteristics of agonists and antagonists of the AMPA receptors in the developing rat brain. Whereas PLA2 treatment of telencephalic membranes from postnatal day (PND) 5 and 10 animals produced an important decrease in [3H]AMPA binding, the same treatment performed on PND 20, 25 and adult membranes resulted in a marked increase in [3H]AMPA binding; the shift from decreased to increased [3H]AMPA binding occurred at about PND 15. In contrast to [3H]AMPA binding, [3H]6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) binding was substantially reduced following PLA2 treatment at PND 5, 10 and 20, and effect due to a decrease in the maximal number of [3H]CNQX binding sites. In adult membranes, the effect of PLA2 treatment on [3H]CNQX binding was markedly reduced when compared to neonatal membranes. Pretreatment of synaptic membranes with PCMBS (a sulfhydryl reagent) increased [3H]AMPA binding in both young (PND 10) and adult telencephalic membranes, without significantly changing [3H]CNQX binding. The various effects of PLA2 treatment on agonist and antagonist binding did not appear to be due to major differences in the pharmacological properties of the AMPA receptors at different ages. The present results indicate that the characteristics of the binding sites for agonists and antagonists of the AMPA receptors are differentially modulated by the lipid environment during the postnatal period.(ABSTRACT TRUNCATED AT 250 WORDS)

4-Chloromercuribenzenesulfonate↗

PubMed1992

Long-term potentiation is associated with increased [3H]AMPA binding in rat hippocampus.

The location and nature of the changes underlying long-term potentiation (LTP) remain controversial issues. In this study, we tested the possibility that changes in binding properties of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (AMPA/quisqualate and N-methyl-D-aspartate (NMDA) subtype of glutamate receptors are associated with LTP. LTP was elicited in vivo by stimulation of the perforant pathway in anesthetized rats. One hour following stimulation the animals were sacrificed. We performed quantitative ligand binding autoradiography on frozen brain sections using [3H]AMPA and [3H]N-(1-(2-thienyl)cyclohexyl)-3,4-piperidine ([3H]TCP) to label the AMPA/quisqualate and the NMDA receptors, respectively. No changes in [3H]TCP binding were detected in any of the treatment groups. However, increases in [3H]AMPA binding were observed only in animals that exhibited LTP. These increases were bilateral and present in several subfields of the hippocampus and cortical areas. Administration of the NMDA receptor antagonist, ketamine, prior to tetanic stimulation prevented both the increase in binding and the induction of LTP. These results suggest that changes in the characteristics of AMPA/quisqualate receptors are a biochemical correlate of LTP.

Analysis of Variance↗

PubMed1992

Absence of c-fos induction in neonatal rat brain after seizures.

Induction of the proto-oncogene c-fos is often considered to be a marker of increased neuronal activity. We have used in situ hybridization to study the pattern of c-fos expression in limbic structures following kainic acid-induced seizures during the postnatal period in the rat. Prior to postnatal day 13 (P13), seizure activity did not result in c-fos induction in any limbic structure. Between P13 and P25, a gradual increase in c-fos expression was observed in hippocampus and cortical structures. These results were corroborated by nuclear run-off transcription assay. Thus, alterations in c-fos transcription that may facilitate stimulus-transcription coupling occur during postnatal development. The possible relationship between the postnatal maturation of c-fos expression and the increase in susceptibility of specific neuronal populations to seizure-induced cell damage is discussed.

Age Factors↗

PubMed1992

Endogenous phosphorylation and dephosphorylation of rat liver plasma membrane proteins, suggesting a 18 kDa phosphoprotein as a potential substrate for alkaline phosphatase.

Purified rat liver plasma membranes were incubated for 0-60 min with [gamma-32P]ATP and analysis of 32P-labeled proteins by means of sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography revealed the presence of two shifted kinetic phenomena. The use of 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7), a potent inhibitor of protein kinases, allowed the identification of one as the endogenous protein phosphorylation. The other was shown to be the labeling of two phospho-intermediate forms of alkaline phosphatase (orthophosphoric monoester phosphohydrolase (alkaline optimum, EC 3.1.3.1.], which have apparent molecular masses of 151 and 135 kDa. Bromolevamisole, a potent inhibitor of the enzyme, stabilized these phospho-intermediates, and consequent on this inhibition the labelling of a 18 kDa phosphoprotein was augmented. So, when alkaline phosphatase was studied in its native plasma membrane environment, a specificity of this enzyme over the endogenous phosphoproteins was established.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗