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M Baudry

Publications and source records attributed to M Baudry.

At least 181 records · Page 10Linked to original sources
PubMed1988

Phorbol ester-induced synaptic facilitation is different than long-term potentiation.

The studies described here tested the hypothesis that the changes in synaptic efficacy produced by phorbol esters in hippocampal slices are equivalent to the long-term potentiation (LTP) induced by high-frequency stimulation. In contrast to the extremely stable synaptic potentiation induced by electrical stimulation, the facilitatory effects of phorbol 12,13-diacetate and phorbol 12,13-dibutyrate were transient: washout of the drugs restored normal responses in approximately 1-2 and 2-4 hr for phorbol diacetate and phorbol dibutyrate, respectively. It is noteworthy that the more liposoluble of the phorbol esters required longer washout periods. Robust LTP still occurred in response to high-frequency stimulation after washout of phorbol esters and to a lesser degree during their application. Treatment of slices with H-7, an inhibitor of protein kinase C, did not prevent LTP induction although it significantly affected neuronal excitability and produced effects opposite to those of phorbol esters. Finally, phorbol esters altered responses to repetitive stimulation in a way that could account for the reduced LTP elicited in their presence. These results indicate that the increases in synaptic responses caused by phorbol esters and high-frequency electrical stimulation are quite different and thus do not support the hypothesis that activation of protein kinase C, the presumed target of the phorbol esters, triggers LTP.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1988

Effects of thiol-reagents on [3H]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid binding to rat telencephalic membranes.

The binding of [3H]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid ([3H]AMPA), a ligand for the quisqualate subtype of excitatory amino acid receptors, was measured after chemical modifications of rat brain synaptic membranes. Treatment with oxidizing or thiol-alkylating agents did not modify [3H]AMPA binding, whereas treatment with several sulfhydryl reagents produced marked increases in binding. The involvement of free sulfhydryl groups in the regulation of the properties of [3H]AMPA binding sites was suggested by the specificity of p-chloromercuribenzoic acid (PCMB), its sulfonate analog p-chloromercuriphenyl-sulfonic acid (PCMBS), and HgCl2, plus the reversal of their effects after reduction with dithiothreitol. Pretreatment of synaptic membranes with the oxidizing agent 5,5'-dithiobis(2-nitrobenzoic acid) or the alkylating agent N-ethylmaleimide did not significantly affect [3H]AMPA binding but markedly reduced the enhancing effect of PCMBS. On the other hand, the increase in [3H]AMPA binding produced by PCMBS was not prevented by treatment with agonists such as quisqualate or L-glutamate and was produced equally well in resealed postsynaptic membranes with both lipophilic or nonlipophilic SH-reagents. Using filtration assays, two types of binding sites could be detected with high and low affinity for [3H]AMPA. Treatment with SH-reagents produced an increase in the Bmax for the high affinity component and a decrease in the Bmax for the low affinity component, accompanied by an increase in its affinity for the ligand. Using centrifugation assays, the same two types of sites could be detected under control conditions but treatment with SH-reagents produced an increase in affinity of the large component that prevented the analytical differentiation of the two sites. Treatment with SH-reagents also increased the binding of [3H] glutamate to the N-methyl-D-aspartate receptors but did not modify the binding of [3H]kainate to the kainate receptors or the strychnine-insensitive [3H]glycine binding. These results suggest that free sulfhydryl groups allosterically modulate the affinity of the quisqualate subtype of excitatory amino acid receptors and also indicate that different types of glutamate receptors might be differentially affected by chemical modification.

Allosteric Regulation↗
PubMed1987

Functional reconstitution of N-methyl-D-aspartate receptors in artificial lipid bilayers.

Functional reconstitution of the N-methyl-D-aspartate (NMDA) receptors was achieved by adding synaptic membranes from rat brain to large planar bimolecular lipid membranes (BLMs). The reconstituted receptors exhibited several properties of the NDMA receptors described using a variety of biochemical and electrophysiological techniques. Addition of NMDA at concentrations between 5 and 50 microM produced large, voltage-dependent increases in membrane conductivity. The selective antagonist of NMDA receptors, amino-2-phosphonopentanoate (AP-7), totally blocked the response of the bilayers to NMDA as did micromolar concentrations of magnesium; this latter effect was also voltage-dependent. These results indicate that BLMs can be used to study the ion channels and regulatory processes associated with NMDA receptors from adult brain in ways that could not be accomplished with conventional neurophysiological techniques.

Aspartic Acid↗
PubMed1987

Use of cystine to distinguish glutamate binding from glutamate sequestration.

Cystine is shown to be a high-affinity substrate for the chloride-dependent glutamate exchange system in brain membranes, which mediates what has previously been considered chloride-dependent glutamate 'binding'. Similarities in the pharmacological profile and in kinetic properties suggest that this transport system may be a high-affinity adaptation of the transport system xc- present in somatic cells. Since cystine selectively inhibits glutamate sequestration and does not interact with the major glutamate binding sites, it can be used to assess the contribution of sequestration to overall 'binding' of glutamate or glutamate-analogs or to suppress sequestration in receptor binding assays. As an example, it is shown that more than 90% of 'bound' [3H]aminophosphonobutyrate [( 3H]APB) is displaced by cystine and should be interpreted as APB sequestration.

Animals↗
PubMed1987

Calmodulin stimulates the degradation of brain spectrin by calpain.

Brain spectrin has been shown to be a preferential substrate of calcium-dependent proteases (Baudry, Bundman, Smith, and Lynch: Science 212:937-938, 1981) and a major calmodulin-binding protein (Kakiuchi, Sobue, and Fujita: FEBS Lett. 132:144-148, 1981). Since calmodulin, spectrin, and a proteolytically derived spectrin fragment are all components of isolated postsynaptic density preparations (Grab, Berzins, Cohen, and Siekevitz: J. Biol. Chem. 254:8690-8696, 1979; Carlin, Bartelt, and Siekevitz: J. Cell Biol. 96:443-448, 1983), we investigated the functional role of calmodulin binding to brain spectrin with respect to its susceptibility to digestion by proteases. We report that calmodulin's interaction with brain spectrin results in a marked acceleration of the rate of spectrin degradation by calcium-dependent proteases (calpains I and II), but not by chymotrypsin. The cleavage of erythrocyte spectrin (which lacks a high-affinity calmodulin binding site) by calpain I is unaffected by the presence of calmodulin. The stimulatory effect of calmodulin is blocked by trifluoperazine, a calmodulin antagonist, which by itself does not modify brain spectrin proteolysis by calcium-dependent proteases. These results suggest a novel role for calmodulin in neuronal function--namely, a synergistic interaction with calcium-dependent proteases in the regulation of cytoskeletal integrity.

Animals↗
PubMed1987

Subcellular compartmentalization of calcium-dependent and calcium-independent neutral proteases in brain.

In the present experiments, we studied the subcellular distribution of three types of extralysosomal, neutral proteolytic activities in rat telencephalon: (1) nonthiol proteases (NTP), (2) thiol proteases (TP), and (3) calcium-activated thiol proteases (calpains I and II). Subcellular fractionation was performed by using conventional differential and sucrose-gradient centrifugation techniques. The only significant proteolytic activity detected in crude homogenates could be assigned to calpain II, the high-threshold calcium-activated protease. Within the primary fractions prepared from the homogenates, the highest levels of calpain II were found in S3, or the soluble cytoplasmic fraction. Significant activity of the enzyme was also present in P2, the crude mitochondrial/synaptosomal fraction. In contrast, the specific activity of calpain I was greatest in P2 with somewhat lesser enzymatic activity in P1 and S3. Most of the calpain I in P2 was recovered after differential centrifugation through sucrose gradients and lysis of the resultant subfractions. In marked contrast, only a small percentage of the calpain II activity was recovered in the gradient bands. In all, calpain II appears to be predominantly localized in the soluble cytoplasmic compartment while the greatest concentrations of calpain I are found in the soluble components of small glial and neuronal processes (pinched off during homogenization) that constitute the P2 fraction. The highest specific activity of the calcium-independent proteases was obtained in P3, a fraction essentially devoid of calpain, with a secondary peak in P2. Subfractionation of P2 revealed that calcium-independent TP in P2 was associated with mitochondria while the calcium-independent NTP was more uniformly distributed across myelin, synaptosomes, and mitochondria.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Brain spectrin, calpain and long-term changes in synaptic efficacy.

This chapter discusses the possibility that proteolytic digestion of cytoskeletal proteins, in particular spectrin, is part of the mechanisms through which physiological activity elicits structural and chemical changes in brain synapses. Recent work from several laboratories has produced a description of the initial events that trigger the long-term potentiation (LTP) of synaptic responses that appears in hippocampus after brief episodes of high frequency electrical stimulation. A likely sequence is as follows: suppression of IPSPs, prolongation of EPSPs, activation of N-methyl-D-aspartate (NMDA) receptors, influx of calcium into target cells. After briefly describing the evidence for this triggering sequence, the review takes up the question of what types of calcium sensitive chemistries are available to synaptic region that could produce functional changes lasting for weeks (i.e., for LTP). It is argued that the partial degradation of spectrin by a calcium-activated protease (calpain) provides a mechanism of this type. Spectrin is a substrate for calpain and both it and a breakdown product comparable to that produced by calpain are found in postsynaptic densities. Moreover, there is substantial evidence that spectrin regulates the surface chemistry and morphology of cells and thus its partial degradation would be expected to produce pronounced and persistent modifications in synapses. To reinforce this point, the review discusses recent findings suggesting that calpain mediated proteolysis of spectrin and other cytoskeletal proteins produces substantial changes in the shape of blood-borne cells and the distribution of their surface receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Spatial learning in the rat: impairment induced by the thiol-proteinase inhibitor, leupeptin, and an analysis of [3H]glutamate receptor binding in relation to learning.

Rats were given continuous intraventricular infusion of saline or the thiol-proteinase inhibitor leupeptin, via subcutaneously implanted osmotic minipumps, while being trained on a spatial learning water task using spaced trials. Leupeptin caused overnight forgetting during training, but performance eventually reached asymptote in both groups. A retention test conducted 48 h later to assess spatial memory revealed no significant group differences, but did cause, in saline-treated rats only, a disruption of subsequent retraining back to the correct spatial location. The groups showed no differences in Cl-dependent [3H]glutamate receptor binding to hippocampal or entorhinal cortex membranes subsequent to training. In a second experiment, normal rats trained on the same task also showed no differences in Cl-dependent [3H]glutamate binding relative to rats exposed to the water task but given random spatial position training and handled controls. The results are discussed in relation to the hypothesis of Lynch and Baudry (Science (1984) 224, 1057-1063) that a calcium-dependent thiol proteinase is involved in memory formation through its ability to modify glutamate receptor distribution and dendritic spine shape.

Animals↗
PubMed1987

Polyamines stimulate mitochondrial calcium transport in rat brain.

The effects of the polyamines spermine and spermidine on rat brain mitochondrial calcium transport were examined using a variety of techniques for measuring the kinetics of calcium uptake and the buffering capabilities of isolated mitochondria. Spermine both increased the rate of calcium accumulation and decreased the set-point to which isolated mitochondria buffer free calcium concentration. In the presence of physiological concentrations of sodium and magnesium, spermine lowered the extramitochondrial calcium level to approximately 0.3 microM, a value close to the resting intracellular calcium concentration. The effect of polyamines was concentration dependent, with a half-maximal effect of spermine observed at approximately 0.1-0.4 mM (respiratory substrate dependent), whereas spermidine was approximately 10 times less potent. Calcium transport by hippocampal mitochondria was stimulated markedly more by spermine than was calcium transport by mitochondria isolated from brainstem. The stimulatory effect of spermine was not due to an increase in the transport of respiratory substrates inside the mitochondria nor to an effect on the enzymes using these respiratory substrates. An examination of the effect of spermine on the kinetics of calcium uptake indicated that spermine increased calcium uptake maximally at low calcium concentrations. Beyond that level, the stimulatory effect of spermine decreases, and spermine can even inhibit calcium uptake. These results are in good agreement with previous reports on the effects of polyamines on calcium transport in mitochondria from peripheral tissue. They support the hypothesis that spermine increases the rate of calcium uptake by mitochondria by increasing the affinity of the uniporter for calcium.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

L-phenylalanyl-L-glutamate-stimulated, chloride-dependent glutamate binding represents glutamate sequestration mediated by an exchange system.

Stimulation of glutamate binding by the dipeptide L-phenylalanyl-L-glutamate (Phe-Glu) was inhibited by the peptidase inhibitor bestatin, suggesting that the stimulation was caused by glutamate liberated from the dipeptide and not by the dipeptide itself. It further suggests that this form of glutamate binding should be reinterpreted as glutamate sequestration and that stimulation of binding both by dipeptides and after preincubation with high concentrations of glutamate is likely to be due to counterflow accumulation. Several other criteria indicate that most of glutamate binding stimulated by chloride represents glutamate sequestration: Binding is reduced when the osmolarity of the incubation medium is increased, when membranes incubated with [3H]glutamate are lysed before filtration, and when membranes are made permeable by transient exposure to saponin. Moreover, dissociation of bound glutamate after a 100-fold dilution of the incubation medium is accelerated about 50 times by the addition of glutamate to the dilution medium. This result would be anomalous if glutamate were bound to a receptor site; it suggests instead that glutamate is transported in and out of membrane vesicles by a transport system that preferentially mediates exchange between internal and external glutamate. Glutamate binding contains a component of glutamate sequestration even when measured in the absence of chloride. Sequestration is adequately abolished only after treating membranes with detergents; even extensive lysis, sonication, and freezing/thawing may be insufficient.

Aminopeptidases↗
PubMed1987

[Adrenaline activates oxidative phosphorylation of rat liver mitochondria through alpha 1-receptors].

We studied the effects and mode of action of epinephrine on the oxidative phosphorylation of rat liver mitochondria. With either succinate or beta-hydroxybutyrate as substrate, i.v. injection of 1.5 microgram/100 g epinephrine increased the respiratory rates by 30-40% in state 3 (with ADP), and by 20-30% in state 4 (after ADP phosphorylation), so that the respiratory control ratio (state 3/state 4) changed little. The respiratory stimulation by epinephrine was maximal 20 minutes after its injection. The action of epinephrine on mitochondria was blocked by pretreatment of the animals with the alpha 1-antagonist prazosin but not by treatment with the beta-antagonist propranolol. I. v. injection of 10 micrograms/100 g phenylephrine evoked the same mitochondrial response as epinephrine. I. v. administration of 50 micrograms/100 g dibutyryl cyclic AMP enhanced glycaemia but did not affect mitochondrial respiration. Epinephrine therefore has an alpha 1-type of action on mitochondrial oxidative phosphorylation.

Adrenergic alpha-Antagonists↗
PubMed1986

A comparative study of soluble calcium-dependent proteolytic activity in brain.

Recent studies have shown that soluble calcium activated proteases (calpains) in brain degrade proteins associated with the cytoskeleton and vary markedly in activity across regions and as a function of development. It was suggested that the observed differences in calpain activity reflect differences in the turnover rate of structural elements. The present study extends this analysis by measuring the properties and activity of calpain in representatives of the five classes of vertebrates with particular emphasis on the mammals. No evidence for proteolysis was found in soluble fractions of fish brains at neutral pH in the presence or absence of added calcium. A substantial calcium-independent proteolytic activity was found in amphibian brains--the effects of a variety of protease inhibitors indicated that it is also a neutral thiol (cysteine) protease. Reptilian brains exhibited both calcium-independent and calcium-dependent proteolytic activity. Virtually all proteolytic activity in birds (5 species) and mammals (9 species) measured at neutral pH was calcium-dependent. The endogenous substrates for the calcium activated proteases were very similar in several species of birds and mammals as were the effects of a variety of protease inhibitors. However, the activity of the enzyme, expressed per mg of soluble protein, was highly and negatively correlated with brain size in the mammals. The allometric expression for this relationship was similar to that found for the density of neurons in cerebral cortex as a function of absolute brain size. These results indicate that soluble proteolytic enzymes in brain are differentially expressed among classes of vertebrates and suggest that the turnover of cytoskeletal elements in birds and mammals differs in important ways from that found in fish and amphibians. The results obtained for mammals raise the possibility of a relationship between brain size and the rate at which structural elements are broken down and replaced in this vertebrate class.

Amphibians↗
PubMed1986

Induction of glutamate binding sites in hippocampal membranes by transient exposure to high concentrations of glutamate or glutamate analogs.

The number of Na+-independent, Cl--dependent glutamate binding sites in rat hippocampal membranes is increased two- to fourfold after pre-exposing isolated membranes or hippocampal slices to high concentrations (0.1-10 mM) of L-glutamate or of glutamate analogs with high affinity for this binding site, such as quisqualate, homocysteate, or aminoadipate. N-Methylaspartate and kainate are ineffective. A similar binding increase is induced by transient exposure to the dipeptide tyrosylglutamate. The newly induced binding sites appear to be identical with pre-existing Cl--dependent binding sites by several criteria: They have a similar pharmacological profile, they are sensitive to low concentrations of Na+, and the number of sites can be further increased by transient exposure to micromolar calcium concentrations. Moreover, binding of [3H]APB, a ligand selective for the Cl--dependent glutamate binding sites, is also increased after glutamate preincubation. The induction of binding sites by high glutamate concentrations, described herein, is calcium-independent, not inhibited by leupeptin and, therefore, different from the previously described activation of binding sites by a calcium-sensitive protease. The high concentration of ligand needed to induce increased binding suggests the presence in hippocampal membranes of a binding site with low, millimolar affinity that is functionally related to the known high-affinity binding sites. Several interpretations of the observed effects and their implications for the possible relationship between the binding site and the synaptic receptor are discussed.

2-Amino-5-phosphonovalerate↗
PubMed1986

[Effects of glucagon and epinephrine on the rat liver: oxidative phosphorylation and ultrastructure].

Twenty minutes after i.v. injection of 1.5 micrograms/100 g epinephrine, the phosphorylation rates of rat liver mitochondria were increased by 30-40%. Treatment with cycloheximide or actinomycin D 20 min before epinephrine or glucagon (10 micrograms/100 g, i.v.) injection blocked much of the respiratory activation by these hormones. The treatment with glucagon or epinephrine (20 min) provoked an important development of rough endoplasmic reticulum of which cisternae were closely associated with the mitochondria, and an appearance of abundant ribosomes. We observed close structural contact between mitochondria, and also between smooth endoplasmic reticulum membranes and mitochondria. Thus, glucagon and epinephrine provoked an early stimulation of mRNA and protein synthesis which could be involved in the activation of mitochondrial energy metabolism.

Adenosine Diphosphate↗
PubMed1986

Long-term potentiation and kindling: similar biochemical mechanisms?

For years, the hypotheses concerning the physiological mechanisms of epilepsy and spreading depression have implicated failures in inhibitory mechanisms and, in particular, GABA-mediated responses. More recent experiments have focused on the participation of excitatory neurotransmitters and especially on glutamate-mediated responses in order to account for the long-lasting changes in the excitability of neurons found in epilepsy. Evidence supporting this view has been provided by the fact that two different types of manipulation resulting in long-lasting changes in synaptic excitability, namely kindling and long-term potentiation (LTP) of synaptic transmission, result in modification of excitatory amino acid receptors. Kindling represents the progressive development of generalized seizures generated by repeated low levels of electrical stimulation of various limbic structures, and is generally accepted as a good model of epilepsy; it is associated with an increase in excitatory mechanisms and, in particular, with an increase in the number of glutamate binding sites that are presumed to represent a category of glutamate receptors. Similarly, LTP is elicited by brief bursts of electrical stimulation in monosynaptic excitatory pathways and is also associated with an increase in the number of the same type of glutamate binding sites. The present review compares the similarities between these two long-lasting forms of synaptic plasticity, and proposes that similar biochemical mechanism might underlie the changes in glutamate receptors. In addition, it describes a molecular mechanism that involves a calcium-dependent protease associated with postsynaptic membranes, the activation of which results in the unmasking of glutamate receptors. Moreover, since this mechanism has been recently implicated in the storage of some types of information in the mammalian telencephalon, these studies raise the possibility that epilepsy may represent a dangerous side-effect of an efficacious learning mechanism.

Animals↗
PubMed1986

Induction of ornithine decarboxylase as a possible mediator of seizure-elicited changes in genomic expression in rat hippocampus.

Small electrolytic lesions placed in the hilus of the dentate gyrus have been shown to induce behavioral seizures, an elevation in the concentration of the opioid peptide enkephalin, and an increase in the transcription of the gene coding for the peptide precursor of enkephalin. Since polyamines and ornithine decarboxylase (ODC), the rate-limiting enzyme in their synthesis, have been shown to play critical roles in the growth and differentiation of several types of tissue, we tested for changes in ODC activity at various times following the initiation of seizures. ODC activity is significantly increased 3 hr after the lesions, reaches maximal (50-fold) levels about 12 hr later, and returns to control values after 48 hr. The increase occurs in both hippocampi following unilateral electrolytic lesions, is blocked by treatments that suppress limbic seizures, and does not occur after lesions that fail to elicit seizures; accordingly, we conclude that the increase in ODC activity results from epileptiform activity rather than some other consequence of the hilar lesion (e.g., deafferentation). The increase in ODC activity precedes the increase in the amount of mRNA coding for the enkephalin prohormone, which, in turn, precedes the increase in enkephalin levels. These results are consistent with the hypothesis that the early induction of ODC following the initiation of seizures leads to an alteration in genomic expression, which, in turn, changes neuropeptide levels. Adult brains thus appear to possess trophic responses of a type found in a variety of developing cell types and organs, and the possibility exists that these are involved in the control of seizure susceptibility.

Adrenalectomy↗
PubMed1985

Distribution of calpain I, an enzyme associated with degenerative activity, in rat brain.

The calcium-activated protease calpain I was localized in rat brain by immunocytochemistry. Calpain I-like immunoreactivity (CLI) was prominent in several structures in which degeneration is an ongoing feature, e.g. spinal motoneurons, olfactory nerve. Also noteworthy was the presence of CLI in regions susceptible to age-related pathologies, e.g. cerebellar Purkinje cells, substantia nigra and subiculum. This distribution suggests that calpain I may be involved with both normal and pathological neuronal degeneration.

Animals↗