Biomedical subjects

M Baudry

Publications and source records attributed to M Baudry.

At least 127 records · Page 7Linked to original sources

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↗

PubMed1993

Stabilization of phospho-intermediates of rat liver plasma membrane alkaline phosphatase by uncompetitive inhibition. Relation with phosphate uptake into hepatocytes.

Rat liver plasma membrane alkaline phosphatase (ALP) phospho-intermediates, which have molecular masses of 151 and 135 kDa bands, were labelled at physiological pH with either (gamma-32P) ATP or 32Pi. This labeling was stabilized by a potent enzyme inhibitor, bromolevamisole (BL), and not by bromodexamisole (BD). BL augmented the rate and extent of autophosphorylation and slowed down the rate of autodephosphorylation of ALP. The phospho-intermediates labeling presented nearly the same kinetic behaviour with either (gamma-32P) ATP or 32Pi. In the presence of BL a marked decrease of the phosphorylation state of many proteins was observed in hepatocytes. BL also produced a decrease of the 32Pi uptake into hepatocytes and a decrease of the specific radioactivity of cellular ATP. BD had nearly the same effect as BL on protein phosphorylation and 32Pi uptake. These results argued against a direct involvement of ALP in Pi transport across hepatocyte plasma membrane.

Adenosine Triphosphate↗

PubMed1993

Alkaline phosphatase activity at physiological pH: kinetic properties and biological significance.

The activity of rat liver alkaline phosphatase (ALP) was studied at physiological pH, using para-nitrophenyl phosphate (pNPP) as substrate. At this pH, the purified enzyme had optimal catalytic efficiency and its activity was maximal for the very low substrate concentrations. During thermal inactivation of rat liver plasma membranes activities, the ratio of the measured residual activities (pH 10.5/pH 7.5) varied, showing that ALP was not the only plasma membranes pNPP hydrolase. Indeed, the proportion of pNPP hydrolase activities attributable to ALP in plasma membranes at pH 7.5 was relatively low. Effectively, it was shown using bromolevamisole, a potent and specific inhibitor of ALP, that contrary to what it was previously reported, ALP was not the major pNPP hydrolase of liver plasma membrane.

Alkaline Phosphatase↗

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↗

PubMed1992

Effects of the novel NMDA receptor antagonist, CGP 39551, on field potentials and the induction and expression of LTP in the dentate gyrus in vivo.

The effects of the novel competitive N-methyl-D-aspartate (NMDA) receptor antagonist, CGP 39551 [the carboxyethylester of CGP 37849; DL-(E)-2-amino-4-methyl-5-phosphono-3-pentenoic acid], on extracellular field potentials and long-term potentiation (LTP) induced in the dentate gyrus by stimulation of the perforant path were studied in anesthetized rats. CGP 39551 attenuated the population spike (PS) and excitatory postsynaptic potential (EPSP) amplitude of dentate field potentials, reduced the NMDA receptor-mediated component of train-evoked burst potentials, and prevented the induction of LTP. The decrease in PS and EPSP amplitude produced by CGP 39551 was observed mainly in non-potentiated synaptic populations; potentiated field potentials were only minimally affected by drug treatment. These results are consistent with receptors may contribute in a tonic manner to the state of dentate granule cell excitability. Finally, the differential modulation of potentiated and non-potentiated synapses by CGP 39551 suggests that a change in some properties of postsynaptic AMPA receptors is involved in the expression of LTP.

2-Amino-5-phosphonovalerate↗

PubMed1992

Changes in polyamine levels and spectrin degradation following kainate-induced seizure activity: effect of difluoromethylornithine.

The induction of ornithine decarboxylase (ODC) in adult CNS and the resulting changes in polyamine levels are often observed under conditions associated with activation of NMDA receptors, calpain stimulation and spectrin degradation. The present study was directed at evaluating the links between these two sets of events. We measured the effects of an acute treatment of adult rats with difluoromethylornithine (DFMO), an irreversible inhibitor of ODC, on biochemical alterations following kainate-induced seizure activity. Beside ODC activity and polyamine levels, we assayed the in situ spectrin degradation and the in vitro binding of 3H-Ro5-4864, a ligand for the peripheral benzodiazepine binding sites which is a good marker of glial proliferation, at various time intervals following systemic kainic acid (KA) injection. Kainate-induced seizure activity was followed by a transient increase in ODC activity, a long-lasting increase in putrescine levels and spectrin degradation, and a delayed increase in 3H-Ro5-4864 binding, mainly in hippocampus and piriform cortex. Treatment of the animals with DFMO markedly reduced the increase in putrescine levels up to 7 days after KA injection. It also reduced the increase in spectrin breakdown observed at 16 h but not at 4 and 7 days after KA injection. Finally, it did not modify the increase in 3H-Ro5-4864 binding measured 4 and 7 days after KA injection. The levels of putrescine were positively correlated with the extent of spectrin proteolysis in KA-treated animals whether or not they were treated with DFMO, at 16 h but not at 7 days after KA injection. The results indicate that the extent of spectrin breakdown observed shortly after KA-induced seizure activity is causally related to the changes in ODC activity and putrescine levels. Although the data are consistent with the idea that putrescine could be a marker for acute pathology, they do not support a role for polyamines in delayed neurotoxicity.

Animals↗

PubMed1992

Amyloid precursor protein mRNA encoding the Kunitz protease inhibitor domain is increased by kainic acid-induced seizures in rat hippocampus.

A 168-nucleotide exon, found in alternatively spliced amyloid precursor protein (APP) mRNAs, encodes a Kunitz protease inhibitor (KPI) domain. Kainic acid (ip) caused a selective increase of KPI mRNA in rat hippocampus. By in situ hybridization, KPI mRNA was induced in the neuronal layers of the hippocampus 11-12 h after the onset of kainate-induced seizures. The kainate-induced elevation of the KPI-containing APP-770 mRNA was blocked by pretreatment with the anticonvulsant pentobarbital. These data suggest that kainate-induced seizures cause alterations in APP RNA stability and/or processing in rat hippocampal neurons.

Amino Acid Sequence↗

PubMed1992

Learning of a hippocampal-dependent conditioning task changes the binding properties of AMPA receptors in rabbit hippocampus.

The N-methyl-D-asparate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) subtypes of glutamate receptors have been shown to play critical roles in various forms of synaptic plasticity (i.e., learning and memory, long-term potentiation). We previously demonstrated that the binding of [3H]AMPA to the AMPA subtype of glutamate receptors was selectively increased in hippocampus following classical conditioning of the rabbit nictitating membrane response in a delay paradigm. We report here that the same effect was observed in a variant of this learning paradigm that requires the participation of the hippocampus, i.e., trace conditioning of the rabbit nictitating membrane. The binding of [3H]TCP (N-[1-(2-thienyl)cyclo-hexyl]-3,4-piperidine) to the NMDA receptor remained unchanged in all the experimental groups tested. Paired presentations of conditioned and unconditioned stimuli resulted in an increased binding of [3H]AMPA, an agonist of the AMPA receptors, in several hippocampal subfields while the binding of an antagonist, [3H]CNQX (6-nitro-7-cyanoquinoxaline-2,3-dione), was decreased. The results suggest that the learning-induced changes in binding of the ligands to the AMPA receptor reflect changes in affinity of the receptor rather than in the number of sites. These results support the hypothesis that changes in hippocampal glutamate receptors are a corollary of synaptic plasticity in certain forms of learning.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed1992

Regionally specific and rapid increases in brain-derived neurotrophic factor messenger RNA in the adult rat brain following seizures induced by systemic administration of kainic acid.

In situ hybridization techniques were used to analyse the spatiotemporal pattern of brain-derived neurotrophic factor messenger RNA elevation associated with kainic acid-induced seizure activity in the rat. Pronounced increases in hippocampal brain-derived neurotrophic factor messenger RNA levels were observed as early as 30 min following the onset of behavioral seizures. The greatest increase (10-fold) occurred in the dentate granule cell layer, while pyramidal layers CA1, CA3, and CA4 exhibited increases of two- to six-fold. Peak elevation of brain-derived neurotrophic factor messenger RNA in CA1 hippocampal region was evident at 4 h in CA3, and in the dentate granule layer at 30 min postseizure. Elevations persisted in the dentate and hilar regions to four days, while the increases in CA1 and CA3 returned to control levels by 16 h following seizure. Significant increases in brain-derived neurotrophic factor messenger RNA were also observed in the superficial layers of cortex (II and III) and in the piriform cortex which reached peak elevations by 8 h. No detectable changes were observed in the dorsomedial thalamus. Although histologically defined pyramidal and granule cell layers displayed relatively uniform increases in brain-derived neurotrophic factor messenger RNA in response to kainate, a closer examination of the labeling patterns using emulsion autoradiography revealed discrete areas of high grain densities overlapping uniform, moderate hybridization densities in the dentate granule cell layer and CA3, suggesting that the capacity to upregulate brain-derived neurotrophic factor messenger RNA in these regions may differ among individual neurons. In conclusion, our studies revealed that brain-derived neurotrophic factor messenger RNA induction in response to systemic kainate administration differs in hippocampal and cortical areas, in magnitude, time of onset and duration. The observed temperospatial pattern does not correspond in a simple way to increases in metabolic or electrical activity associated with seizures or neuronal vulnerability coincident with the seizures.

Animals↗

PubMed1992

Effect of seizure activity and calpain inhibitor I on LTP in juvenile hippocampal slices.

Kainic acid-induced seizure activity in adult rats produces an impairment of long-term potentiation induction in hippocampal slices. As the consequences of seizure activity are different in adult and juvenile rats, we tested the ability of hippocampal slices prepared from kainate-treated juvenile rats to exhibit long-term potentiation. Long-term potentiation was induced by theta-burst stimulation and was not significantly different in slices prepared from control or kainate-injected juvenile rats (16-18 postnatal days). Short-term potentiation, however, was reduced in the kainate-treated juveniles. Calpain inhibitor I has been shown to prevent long-term potentiation formation in adult hippocampal slices, and we evaluated its effect on long-term potentiation in hippocampal slices from juvenile rats. Calpain inhibitor I produced a significant reduction in the degree of long-term potentiation induced by theta-burst stimulation in hippocampal slices prepared from 14-20 postnatal day-old animals. The results are consistent with the notion that, although similar mechanisms participate in the formation of long-term potentiation in juvenile and adult animals, juvenile animals are much more resistant than adult animals to the consequences of seizure activity.

Animals↗

PubMed1992

BDNF mRNA expression in the developing rat brain following kainic acid-induced seizure activity.

Brain-derived neurotrophic factor (BDNF) mRNA expression was studied in the hippocampus at various developmental stages in normal rats and following kainic acid (KA)-induced seizure activity. Systemic administration of KA strongly elevated BDNF mRNA levels in all hippocampal subregions after postnatal day 21. In contrast, even though KA induced intense behavioral seizure activity at postnatal day 8, the seizures were not associated with elevations of BDNF mRNA levels, indicating a clear dissociation between behavioral seizures and increases in BDNF mRNA levels and contradicting the view that BDNF mRNA expression is principally regulated by neuronal activity. In the dentate gyrus at postnatal day 13, intense BDNF mRNA expression was limited to a defined area at the border between granule cell and molecular layers, suggesting the possibility that segregation of BDNF mRNA into defined subcellular compartments may play a role in establishing the well-delineated patterns of innervation in the hippocampus.

Animals↗

PubMed1992

Potassium-induced depolarization of rat telencephalic synaptoneurosomes increases [3H]amino-3-hydroxy-5-methylisoxazole-4-propionate receptor binding.

Potassium-induced depolarization of synaptoneurosomes prepared from rat telencephalon was found to increase [3H]amino-3-hydroxy-5-methylisoxazole-4-propionate ([3H]AMPA) binding to the AMPA receptor. The effect required the presence of calcium because it was blocked by the calcium chelator EGTA but was not blocked by an antagonist of the N-methyl-D-aspartate receptor, aminophosphonopentanoate. The depolarization-induced increase in [3H]AMPA binding was markedly reduced by a blocker of voltage-dependent calcium channels, verapamil. Saturation kinetic experiments revealed that the increase in [3H]AMPA binding produced by potassium depolarization was due to an increase in the affinity of the AMPA receptor. These results provide additional support for a critical role of calcium in the regulation of the AMPA receptors. The synaptoneurosome preparation might represent an interesting tool to determine the role of different calcium-dependent enzymes involved in the regulation of the AMPA receptor.

Animals↗

PubMed1992

Phospholipase A2-induced changes in AMPA receptor: an autoradiographic study.

The expression of long-term potentiation and learning of a classical conditioning task increase [3H]-AMPA binding in hippocampus. Phospholipase A2 (PLA2) has been proposed to underly these changes, as PLA2 treatment of membrane preparations increases the affinity of AMPA receptors for agonists. We demonstrate here that preincubation of thin (10 microns) frozen rat brain sections with exogenous PLA2 and calcium at physiological temperature changes the binding properties of AMPA receptors. Quantitative autoradiography reveals that PLA2-treatment produces a differential increase in [3H]-AMPA binding across brain regions. The same treatment also decreases the binding of an antagonist ([3H]-CNQX) throughout the brain. We propose that PLA2 treatment results in a modification of the AMPA receptors which is regionally specific, probably due to different AMPA receptor subunit compositions.

6-Cyano-7-nitroquinoxaline-2,3-dione↗