Biomedical subjects

Michel Vignes

Publications and source records attributed to Michel Vignes.

7 recordsLinked to original sources

PubMed2006

Anxiolytic properties of green tea polyphenol (-)-epigallocatechin gallate (EGCG).

Naturally occurring polyphenols are potent antioxidants. Some of these compounds are also ligands for the GABA(A) receptor benzodiazepine site. This feature endows them with sedative properties. Here, the anxiolytic activity of the green tea polyphenol (-)-epigallocatechin gallate (EGCG) was investigated after acute administration in mice, using behavioral tests (elevated plus-maze and passive avoidance tests) and by electrophysiology on cultured hippocampal neurons. Patch-clamp experiments revealed that EGCG (1-10 muM) had no effect on GABA currents. However, EGCG reversed GABA(A) receptor negative modulator methyl beta-carboline-3-carboxylate (beta-CCM) inhibition on GABA currents in a concentration dependent manner. This was also observed at the level of synaptic GABA(A) receptors by recording spontaneous inhibitory synaptic transmission. In addition, EGCG consistently inhibited spontaneous excitatory synaptic transmission. Behavioral tests indicated that EGCG exerted both anxiolytic and amnesic effects just like the benzodiazepine drug, chlordiazepoxide. Indeed, EGCG in a dose-dependent manner both increased the time spent in open arms of the plus-maze and decreased the step-down latency in the passive avoidance test. GABA(A) negative modulator beta-CCM antagonized EGCG-induced amnesia. Finally, state-dependent learning was observable after chlordiazepoxide and EGCG administration using a modified passive avoidance procedure. Optimal retention was observed only when animals were trained and tested in the same state (veh-veh or drug-drug) and significant retrieval alteration was observed in different states (veh-drug or drug-veh). Moreover, EGCG and chlordiazepoxide fully generalized in substitution studies, indicating that they induced indistinguishable chemical states for the brain. Therefore, our data support that EGCG can induce anxiolytic activity which could result from an interaction with GABA(A) receptors.

Animals↗

PubMed2006

Low-frequency stimulation induces a new form of LTP, metabotropic glutamate (mGlu5) receptor- and PKA-dependent, in the CA1 area of the rat hippocampus.

Low frequency-induced short-term synaptic plasticity was investigated in hippocampal slices with 60-electrode recording array. Remarkably, the application of low-frequency stimulation (1 Hz) for a short duration (3-5 min) resulted in the induction of a slow-onset long-term potentiation (LTP) in the immediate vicinity of the stimulated electrode. This phenomenon was observed exclusively in the CA1 subfield, neither in the CA3 area nor in the dentate gyrus. The induction of this slow-onset LTP required neither N-methyl-D-aspartate (NMDA) nor non-NMDA ionotropic receptor activation but was strongly dependent on metabotropic glutamate mGlu(5) receptor stimulation and [Ca(2+)]i increase. In addition, this form of synaptic plasticity was associated with an increase in cAMP concentration and required protein kinase A activation. Paired-pulse facilitation ratio and presynaptic fiber volley amplitude were unaffected when this LTP was triggered, suggesting the involvement of postsynaptic modifications. Although mitogen activated protein kinase pathway was stimulated after the application of low frequency, the induction and maintenance of this slow-onset LTP were not dependent on the activation of this intracellular pathway. The direct activation of adenylyl cyclase with forskolin also induced a synaptic enhancement displaying similar features. This new form of LTP could represent the mnesic engram of mild and repetitive stimulation involved in latent learning.

Adenylyl Cyclases↗

PubMed2006

Developmental switch from LTD to LTP in low frequency-induced plasticity.

The stimulation of the Schaffer collateral/commissural fibers at low frequency (1 Hz) for 3-5 min can trigger a slow-onset form of low-frequency stimulation (LFS)-long-term potentiation (LTP) (LFS-LTP) in the CA1 area of the adult rat hippocampus. Here we have examined the developmental profile of this plasticity. In 9-15 day-old rats, the application of 1 Hz for 5 min induced long-term depression (LFS-LTD). In 17-21 day-old rats, 1 Hz stimulation had no effect when applied for 5 min but mediated LTD when stimulus duration was increased to 15 min. Over 25 day-old, 1 Hz stimulation mediated LFS-LTP. LFS-LTD was dependent on both N-methyl-D-aspartate (NMDA) and mGlu5 receptor activation. Antagonists of mGlu1alpha and cannabinoid type 1 receptor were ineffective to block LTD induction. LFS-LTD was not associated with a change in paired-pulse facilitation ratio, suggesting a postsynaptic locus of expression of this plasticity. Next, we examined whether LFS-LTD was related to 'chemical' LTDs obtained by the direct stimulation of mGlu5 and NMDA receptors. The saturation of LFS-LTD completely occluded NMDA- and (RS)-2-Chloro-5-hydroxyphenylglycine (CHPG)-induced LTD. CHPG-LTD and NMDA-LTD occluded each other. In addition, we observed that NMDA-LTD was dependent on mGlu5 receptor activation in 9-12 day old rats while it was not in animals older than 15 day-old. Therefore we postulate that during LFS application, NMDA and mGlu5 receptor could interact to trigger LTD. Low-frequency-mediated synaptic plasticity is subject to a developmental switch from NMDA- and mGlu5 receptor-dependent LTD to mGlu5 receptor-dependent LTP with a transient period (17-21 day-old) during which LFS is ineffective.

Age Factors↗

PubMed2005

A transient treatment of hippocampal neurons with alpha-tocopherol induces a long-lasting protection against oxidative damage via a genomic action.

Neuroprotection exerted by alpha-tocopherol against oxidative stress was investigated in cultured rat hippocampal neurons. In addition to its direct action as a radical scavenger revealed at concentrations above 10 microM, a transient application of 1 microM alpha-tocopherol phosphate (alpha-TP) to neurons induced a complete delayed long-lasting protection against oxidative insult elicited by exposure to Fe2+ ions, but not against excitotoxicity. A minimal 16-h application of alpha-TP was required to observe the protection against subsequent oxidative stress. This delayed protection could last up to a week after the application of alpha-TP, even when medium was changed after the alpha-TP treatment. Cycloheximide, added either 2 h before or together with alpha-TP, prevented the delayed neuroprotection, but not the acute. However, cycloheximide applied after the 16-h alpha-TP pretreatment did not alter the delayed neuroprotection. Neither Trolox, a cell-permeant analogue of alpha-tocopherol, nor other antioxidants, such as epigallocatechin-gallate and N-acetyl-L-cysteine, elicited a similar long-lasting protection. Only tert-butylhydroquinone could mimic the alpha-TP effect. Depletion of glutathione (GSH) by L-buthionine sulfoximine did not affect the delayed alpha-TP protection. Thus, in addition to its acute anti-radical action, alpha-TP induces a long-lasting protection of neurons against oxidative damage, via a genomic action on antioxidant defenses apparently unrelated to GSH biosynthesis.

Animals↗

PubMed2005

Gliotoxicity in hippocampal cultures is induced by transportable, but not by nontransportable, glutamate uptake inhibitors.

Extracellular glutamate is kept below a toxic level by glial and neuronal glutamate transporters. Here we show that the transportable glutamate uptake inhibitor L-trans-pyrrolidine-2,4-dicarboxylate (t-PDC) induced cell death in mature, but not in immature, hippocampal neuron-enriched cultures. The cell death produced by a 24-hr treatment with t-PDC was dose-dependent and reached 85% of the cell population at a 250 microM concentration at 23 days in vitro (DIV). Immunocytochemistry experiments showed that, under these experimental conditions, t-PDC killed not only neurons as expected but also glial cells. The N-methyl-D-aspartate (NMDA) antagonist D-2-aminophosphonovalerate (D-APV; 250 microM) only partially reversed this toxicity, completely protecting the neuronal cell population but not the glial population. The antioxidant compounds alpha-tocopherol or Trolox, used at concentrations that reverse the oxidative stress-induced toxicity, did not block the gliotoxicity specifically produced by t-PDC in the presence of D-APV. The nontransportable glutamate uptake inhibitor DL-threo-beta-benzyloxyaspartate (TBOA) elicited cell death only in mature, but not in immature, hippocampal cultures. The TBOA toxic effect was dose dependent and reached a plateau at 100 microM in 23-DIV cultures. About 50% of the cell population died. TBOA affected essentially the neuronal population. D-APV (250 microM) completely reversed this toxicity. It is concluded that nontransportable glutamate uptake inhibitors are neurotoxic via overactivation of NMDA receptors, whereas transportable glutamate uptake inhibitors induce both an NMDA-dependent neurotoxicity and an NMDA- and oxidative stress-independent gliotoxicity, but only in mature hippocampal cultures.

Amino Acid Transport System X-AG↗

PubMed2003

Opposite effects of alpha 1- and beta-adrenoceptor stimulation on both glutamate- and gamma-aminobutyric acid-mediated spontaneous transmission in cultured rat hippocampal neurons.

The effects of adrenergic receptor stimulation on spontaneous synaptic transmission were investigated in cultured rat hippocampal neurons by recording spontaneous excitatory and inhibitory postsynaptic currents (sEPSC and sIPSC). Noradrenaline (NA) inhibited sEPSC in a concentration-dependent manner, with maximal effect at 10 microM. The alpha(1)- and alpha(2)-adrenoceptor-selective agonists cirazoline and clonidine induced an inhibition of sEPSC appearance, whereas the beta-adrenoceptor agonist isoproterenol elicited an increase. The inhibitory effect of NA was reversed by alpha(1)-adrenoceptor blockade. The participation of gamma-aminobutyric acid (GABA)(B)-receptor stimulation in the inhibitory effect of NA was further examined. GABA(B)-receptor stimulation with baclofen induced a strong inhibition of bursting activity, which was fully reversed by the GABA(B) antagonist CGP 55845. By itself, CGP 55845 exerted a stimulatory effect on sEPSC frequency. In the presence of CGP 55845, the inhibitory effects of cirazoline and clonidine were maintained. NA (1, 10, and 100 microM) and alpha-adrenoceptor agonists decreased miniature EPSC and IPSC occurrence, whereas beta-adrenergic stimulation increased it. In 50% of the cells examined, NA (1, 10 microM) had a stimulatory effect on sIPSC, whereas, in the remaining 50% of cells, NA (1, 10 microM) had an inhibitory effect. In all the cells, 100 microM NA induced an inhibition of sIPSC. The inhibitory effect of NA was due to alpha(1)-receptor stimulation, whereas the excitatory effect was due to beta-receptor stimulation. In cultured hippocampal neurons, spontaneous excitatory and inhibitory synaptic transmissions are both similarly altered by adrenoceptor stimulation. However, in a subset of cells, low concentrations of NA mediate an increase of sIPSC via beta-adrenoceptor activation.

Adrenergic alpha-1 Receptor Agonists↗

PubMed2002

Xenorhabdus nematophila (enterobacteriacea) secretes a cation-selective calcium-independent porin which causes vacuolation of the rough endoplasmic reticulum and cell lysis.

Xenorhabdus nematophila and Photorhabdus luminescens are two related enterobacteriaceae studied for their use in biological control and for synthesis of original virulence factors and new kinds of antibiotics. X. nematophila broth growth exhibits different cytotoxic activities on insect (Spodoptera littoralis, lepidoptera) immunocytes (hemocytes). Here we report the purification of the flhDC-dependent cytotoxin, a 10,790-Da peptide we have called alpha-Xenorhabdolysin (alpha X). We show that plasma membrane of insect hemocytes and of mammal red blood cells is the first target of this toxin. Electrophysiological and pharmacological approaches indicate that the initial effect of alpha X on macrophage plasma membrane is an increase of monovalent cation permeability, sensitive to potassium channel blockers. As a consequence, several events can occur intracellularly, such as selective vacuolation of the endoplasmic reticulum, cell swelling, and cell death by colloid-osmotic lysis. These effects, inhibited by potassium channel blockers, are totally independent of Ca(2+). However, the size of the pores created by alpha X on macrophage or red blood cell plasma membrane increases with toxin concentration, which leads to a rapid cell lysis.

Animals↗