Biomedical subjects

M Baudry

Publications and source records attributed to M Baudry.

At least 109 records · Page 6Linked to original sources

PubMed1994

Differential subcellular localization of two populations of glutamate/AMPA receptors in the rat telencephalon.

The distribution of glutamate AMPA receptors in the synaptosomal and microsomal fractions of neonatal and adult rat telencephalon was studied by determining the saturation kinetics at equilibrium of 3H-AMPA and 3H-CNQX binding. At both ages, synaptosomal preparations exhibited two populations of 3H-AMPA binding sites with a small number of high affinity sites and a large number of low affinity sites. 3H-AMPA binding to microsomal preparations from both neonatal and adult rat telencephalon exhibited a much higher proportion of high affinity relative to low affinity sites. 3H-CNQX binding to the same fractions did not parallel 3H-AMPA binding, but was correlated with the low affinity 3H-AMPA binding and with a marker of plasma membranes. The results suggest that nonsynaptic glutamate/AMPA receptors have a high affinity for agonist and become low affinity when inserted into postsynaptic membranes and that 3H-CNQX binds synaptic but not nonsynaptic glutamate/AMPA receptors with high affinity.

Animals↗

PubMed1994

Emergence neophobia correlates with hippocampal and cortical glutamate receptor binding in rats.

Previous work from our laboratory indicated that emergence neophobia is highly correlated with perforant path long-term potentiation (LTP) in rats. In the present study, we examined the relationship between hippocampal and cortical alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors and emergence behavior in rats. Emergence neophobia was assessed in an exploratory task that provided a choice between a novel alley and a familiar nest box. Quantitative autoradiography using radiolabeled ligands specific for the AMPA subclass of glutamate receptors was performed on frozen brain sections. Both [3H]AMPA and [3H]CNQX (6-cyano-7-nitro-[3H]quinoxaline- 2,3-dione, an AMPA receptor antagonist) binding in the dentate gyrus (stratum moleculare), hippocampal area CA1 (stratum radiatum), and the parietal cortex overlying the hippocampus were significantly correlated with emergence behavior. The correlations indicated that neophobic rats, which had longer latencies to enter the novel alley, made fewer entries into the alley, and spent less time in the novel alley during a 10-min test than their neophilic counterparts, had higher levels of AMPA receptor binding. These results suggest that individual differences in specific hippocampal AMPA receptors reflect variability in a specific class of hippocampal-dependent behaviors.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed1994

[3H]dizocilpine association kinetics distinguish stimulatory and inhibitory polyamine sites of N-methyl-D-aspartate receptors.

Spermine and other polyamines both stimulate and inhibit N-methyl-D-aspartate receptor function, probably by interacting with two separate sites. To characterize these two actions, the effect of spermine on the binding kinetics of the channel blocker [3H]dizocilpine was studied in the presence of glutamate and glycine. Low concentrations (10 microM) of spermine increased the association and dissociation rates without modifying equilibrium binding, indicating that spermine increases the accessibility of [3H]dizocilpine to the channel by interacting with a high-affinity, stimulatory site. At higher concentrations (1 mM), spermine markedly decreased equilibrium [3H]dizocilpine binding by decreasing both affinity and Bmax, indicating that spermine allosterically inhibits binding by interacting with a second, low-affinity site. The presumed polyamine antagonists arcaine, diethylenetriamine, and 1,10-diaminodecane completely inhibited equilibrium [3H]dizocilpine binding, probably by interacting with the inhibitory polyamine site or other sites, but not with the stimulatory polyamine site. Low concentrations (10 microM) of ifenprodil completely reversed the increase in association rate produced by spermine, whereas higher concentrations (IC50 = 123 microM) inhibited equilibrium binding, indicating that ifenprodil is both a potent antagonist of the stimulatory site and a low-affinity ligand of the inhibitory site. The polyamine agonists spermine, spermidine, and neomycin interacted with the inhibitory site, but produced only partial inhibition of equilibrium [3H]dizocilpine binding.

Animals↗

PubMed1994

Specificity of rat liver plasma membrane serine/threonine protein kinases and phosphatases over endogenous proteins.

The specificity of rat liver plasma membrane protein kinases and phosphatases was examined over endogenous substrates, using specific effectors of these enzymes. cAMP-dependent protein kinase was shown to phosphorylate the 77, 60 and 51 kDa phosphoproteins and type II casein kinase, a specific 24 kDa one. On the contrary, types 1 and 2A protein phosphatases seemed to have a broad specificity in plasma membranes. An analysis of the phosphoprotein pattern based on the endogenous substrates of plasma membrane enzymes was deduced from these and other results from our laboratory. The specificity of some enzymes might arise from the anchorage in plasma membrane which might restrict their activity to their immediate environment.

Animals↗

PubMed1993

Co-expression of HSP72 and c-fos in rat brain following kainic acid treatment.

The relationship between heat shock protein 72 (HSP72) and c-fos gene expression following systemic administration of kainic acid was investigated by combining immunocytochemistry for HSP72 with in situ hybridization for c-fos. Increased HSP72 expression was detected in adult rat hippocampus 4 h after seizure-onset. Transient co-expression of c-fos and HSP72 occurred in neurons that are resistant to kainic acid, whereas prolonged co-expression was observed in vulnerable neurons. The spatial distribution and developmental time course of kainic acid-induced HSP72 expression were similar to those of kainic acid-induced neurodegeneration. The results demonstrate a relationship between c-fos and HSP72 gene expression and suggest that prolonged co-expression of these genes plays a role in kainic acid-induced neuronal death.

Animals↗

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

Glycine-induced changes in synaptic efficacy in hippocampal slices involve changes in AMPA receptors.

Brief applications of high glycine concentrations to hippocampal slices have been shown to produce long-lasting changes in synaptic efficacy. In the present study, we show that glycine application transiently and reversibly increases the amplitude and prolongs the duration of synaptic potentials mediated by N-methyl-D-aspartate (NMDA) receptors. The long-lasting changes in synaptic potentials mediated by AMPA receptors are correlated with changes in the binding of [3H]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid ([3H]AMPA) to membranes prepared from glycine-treated slices. The changes in binding properties of AMPA receptors in adult slices are due to an increase in affinity of the agonist for the receptor. Furthermore, glycine-induced increases in [3H]AMPA binding and in synaptic potentials in adult hippocampal slices are markedly reduced in the presence of low extracellular calcium or of the phospholipase inhibitor bromophenacylbromide. Finally, glycine-induced potentiation of synaptic potentials is associated with an increased potency of the glutamate receptor antagonist, 6,7-dinitroquinoxaline (DNQX), to inhibit synaptic potentials. The results indicate that glycine-induced changes in synaptic efficacy are likely triggered by the activation of NMDA receptors and expressed by changes in the properties of AMPA receptors. As similar events underly long-term potentiation (LTP), this phenomenon might provide important clues to elucidate the molecular mechanisms involved in LTP maintenance.

Animals↗

PubMed1993

Postsynaptic factors in the expression of long-term potentiation (LTP): increased glutamate receptor binding following LTP induction in vivo.

Several lines of evidence indicate that LTP in the hippocampus is associated with a change in the properties of postsynaptic glutamate receptors. In the present study, we used quantitative autoradiography to examine the binding properties of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (AMPA) and N-methyl-D-aspartate subclasses of glutamate receptors in frozen brain sections obtained from rats in which perforant-path LTP was induced in vivo. Induction of LTP resulted in a selective increase in [3H]AMPA binding in those hippocampal subfields receiving perforant-path axons. Increases in [3H]AMPA binding in dentate gyrus (stratum moleculare) were highly correlated with the magnitude of LTP recorded in this structure. Scatchard analyses of [3H]AMPA and 6-cyano-7-nitro-[3H]quinoxaline-2,3-dione (an AMPA receptor antagonist) binding in the dentate gyrus indicated that LTP induction resulted in an increase in the number of AMPA receptor binding sites. No changes in the binding of 3H-labeled N-[1-(thienyl)cyclohexyl]piperidine (an N-methyl-D-aspartate receptor antagonist) were observed in any hippocampal subfield. These results suggest that a modification in postsynaptic AMPA receptors plays a role in the expression of synaptic enhancement following LTP induction in the hippocampus.

Animals↗

PubMed1993

Transcriptional activation of ornithine decarboxylase in adult and neonatal hippocampal slices.

Ornithine decarboxylase (ODC) is the rate-limiting enzyme in polyamine synthesis and is regulated by both transcription-dependent and transcription-independent mechanisms. We compared the effects of asparagine, an amino acid previously shown to increase ODC activity in adult hippocampal slices, on ODC mRNA and activity in adult and neonatal hippocampal slices. In addition, we evaluated the effects of asparagine on ODC activity following seizure activity elicited by systemic administration of kainic acid (KA) in both adult and neonatal rats. Asparagine produced an increase in ODC gene expression and activity in both adult and neonatal hippocampal slices. The increase in ODC activity elicited by asparagine in hippocampal slices was the same in control animals as in animals sacrificed 16 h after KA-induced seizure activity. The asparagine-elicited increase in ODC activity in neonatal and adult hippocampal slices was blocked by the RNA synthesis inhibitor, actinomycin D. Finally, polyamines produced an inhibition of ODC activity in neonatal hippocampal slices. The results indicate that the regulation of the expression and activity of ODC is similar in neonatal and adult hippocampus.

Aging↗

PubMed1993

Receptor activation by two agonists: analysis by nonlinear regression and application to N-methyl-D-aspartate receptors.

The activation of a receptor by two agonists is described by a mathematical model based on the assumption that the response of the receptor is a linear function of its occupancy. The model has six parameters: the basal response, three efficacies corresponding to two binary and one ternary complexes, the affinities of the two agonists, and a parameter describing mutual changes in the affinity of the agonists. A method is described to determine the parameters of the model by two successive fittings to the logistic sigmoidal function using nonlinear regression. This method was applied to study the activation of N-methyl-D-aspartate receptors by glutamate and glycine, measured with [3H]-dizocilpine binding under nonequilibrium conditions. Experimental data fitted the model well, and consistent parameter values were obtained in three independent experiments. The efficacies with one agonist (glutamate or glycine) were very low compared with the efficacy with the two agonists combined, indicating that both glutamate and glycine are required for the activation of N-methyl-D-aspartate receptors. Glutamate and glycine also mutually increased their affinities for the receptor. This method may be useful for characterizing partial agonists, antagonists, and inverse agonists of receptors with multiple modulatory sites.

Animals↗

PubMed1993

Salen-manganese complexes are superoxide dismutase-mimics.

Complexes of manganese have previously been shown to exhibit SOD activity. In this study, we tested the ability of several (salen)-manganese complexes to scavenge O2.. Both neutral and cationic complexes were determined to be SOD-mimics. The activity of the complexes was not affected by the presence of bovine serum albumin in the assay. For most compounds, the activity was inhibited by the addition of EDTA. The stability and high catalytic activity of some of these molecules suggest that they might have potential use in a variety of conditions which involve overproduction of oxygen free radicals.

Edetic Acid↗

PubMed1993

Seizure activity causes a rapid increase in sulfated glycoprotein-2 messenger RNA in the adult but not the neonatal rat brain.

The present study investigated the changes in sulfated glycoprotein-2 (SGP-2) messenger RNA at various times following kainic acid-induced seizure onset in adult and neonatal rat brain. Double labelling using immunostaining of the astrocyte-specific glial fibrillary acidic protein indicated that SGP-2 expression was rapidly and transiently increased in granule cells of the dentate gyrus up to 8 hours after seizure onset. Thereafter, and up to 7 days following seizure onset, the majority of cells exhibiting increased SGP-2 expression were astrocytes located in the molecular layer of the dentate gyrus and in the alveus, as well as in regions adjacent to CA3 and CA1 pyramidal cells. No increase in SGP-2 mRNA was detected in pyramidal neurons selectively damaged by KA. In addition, increased expression of SGP-2 following KA administration was not observed in neonatal rat hippocampus prior to postnatal day 21. The results argue against a role for SGP-2 in KA-induced neuronal death and demonstrate a surprisingly rapid increase in astroglial gene expression following seizure activity, thus supporting a role for SGP-2 in synaptic plasticity.

Aging↗

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

High concentrations of glycine induce long-lasting changes in synaptic efficacy in rat hippocampal slices.

Brief perfusion of adult rat hippocampal slices with high concentrations of glycine results in a slowly developing, long-lasting increase in synaptic responses in field CA1. Two observations indicated that the effect requires the activation of NMDA receptors by glycine. First, the glycine-induced potentiation is reduced by ketamine, an NMDA receptor channel blocker. Second, glycine potentiates the NMDA receptor-mediated epileptiform activity recorded in the presence of low magnesium concentration and picrotoxin. In slices prepared from rat pups (5-8 postnatal day), perfusion with glycine results in a slowly developing, long-lasting depression of EPSP amplitude. These results provide a new way of producing potentiation of synaptic efficacy and suggest new properties of NMDA receptors.

Animals↗

PubMed1993

NMDA receptor activation by spermine requires glutamate but not glycine.

Stimulation by spermine of [3H]MK-801 binding to N-methyl-D-aspartate (NMDA) receptors was additive with the effect of glutamate and glycine, but was completely abolished by the glutamate antagonist 3-(carboxypiperazin-4-yl)propyl-1-phosphonate (CPP, 10 microM) or the glycine antagonist 7-chlorokynurenate (10 microM). Blockade by 7-chlorokynurenate could be overcome in the presence of glutamate, whereas blockade by CPP was unaffected by glycine. Therefore, NMDA receptors can be activated by glutamate and spermine but not by glycine and spermine.

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

Cycloheximide prevents kainate-induced neuronal death and c-fos expression in adult rat brain.

The present study was directed at evaluating the possible involvement of protein synthesis in excitotoxin-induced neuronal damage and prolonged expression of the proto-oncogene, c-fos. Kainic acid-induced seizure activity elicited varying degrees of neuronal damage and cell loss in selectively vulnerable regions of the adult rat limbic system. Pretreatment with cycloheximide, a protein synthesis inhibitor, did not alter behavioral seizure characteristics, but markedly attenuated damage to susceptible neuronal populations. A prolonged increase in c-fos mRNA was observed by in situ hybridization up to 16 h after the onset of seizures in regions exhibiting neuronal death. Pretreatment with cycloheximide did not affect the transient induction of c-fos observed in numerous structures, but significantly reduced the prolonged expression of c-fos mRNA in kainate-vulnerable regions. Despite producing massive seizure activity, systemic kainic acid administration during the early postnatal period did not induce any neuronal death, and did not result in prolonged c-fos expression in any brain structures. The developmental onset of selective neuronal vulnerability coincided with that of prolonged c-fos expression in susceptible neuronal populations. In adult rats, seizure activity induced by pentylenetetrazole did not produce neuronal damage nor did it produce prolonged c-fos expression. These results not only demonstrate that kainate-induced neurotoxicity and the prolonged expression of c-fos are both prevented by cycloheximide, but also strengthen idea that prolonged c-fos expression is a marker of neuronal death.

Aging↗

PubMed1993

Localization of the cellular expression pattern of cdc25NEF and ras in the juvenile rat brain.

In this report, we demonstrate that the brain-specific ras nucleotide-exchange factor, cdc25NEF-B, is expressed in specific neuronal populations in the juvenile rat brain. Because cdc25NEF-B likely regulates one or more of the vertebrate ras proteins, H-, K- and N-ras, we also examined their levels of expression and pattern of expression in the juvenile rat brain. We find cdc25NEF-B to be highly expressed in the hippocampus, some deep nuclei, neocortex, and the granule cell layer of the anterior lobules of the cerebellum. Our observations suggest a functional link between cdc25NEF-B and H-ras in a neuronal signal transduction pathway.

Animals↗