Chronic exposure to glufosinate-ammonium induces spatial memory impairments, hippocampal MRI modifications and glutamine synthetase activation in mice

International audienceGlufosinate-ammonium (GLA), the active compound of a worldwide-used herbicide, acts by inhibiting the plant glutamine synthetase (GS) leading to a lethal accumulation of ammonia. GS plays a pivotal role in the mammalian brain where it allows neurotransmitter glutamate recycling within astroglia. Clinical studies report that an acute GLA ingestion induces convulsions and memory impairment in humans. Toxicological studies performed at doses used for herbicidal activity showed that GLA is probably harmless at short or medium range periods. However, effects of low doses of GLA on chronically exposed subjects are not known. In our study, C57BL/6J mice were treated during 10 weeks three times a week with 2.5, 5 and 10 mg/kg of GLA. Effects of this chronic treatment were assessed at behavioral, structural and metabolic levels by using tests of spatial memory, locomotor activity and anxiety, hippocampal magnetic resonance imaging (MRI) texture analysis, and hippocampal GS activity assay, respectively. Chronic GLA treatments have effects neither on anxiety nor on locomotor activity of mice but at 5 and 10 mg/kg induce (1) mild memory impairments, (2) a modification of hippocampal texture and (3) a significant increase in hippocampal GS activity. It is suggested that these modifications may be causally linked one to another. Since glutamate is the main neurotransmitter in hippocampus where it plays a crucial role in spatial memory, hippocampal MRI texture and spatial memory alterations might be the consequences of hippocampal glutamate homeostasis modification revealed by increased GS activity in hippocampus. The present study provides the first data that show cerebral alterations after chronic exposure to GLA

Neurotoxicité du principe actif d'un herbicide à large spectre, le glufosinate d'ammonium, chez la souris

Le glufosinate d ammonium (GLA) est le principe actif d un herbicide à large spectre. Son utilisation tend à s accroître avec le développement des cultures transgéniques résistantes à cet herbicide, entraînant une augmentation de l'exposition des agriculteurs au GLA, à de faibles doses mais sur des périodes prolongées. L action herbicide du GLA s effectue par inhibition de la glutamine synthétase (GS) végétale. Cette enzyme, est également présente dans le système nerveux central des mammifères où elle joue un rôle primordial dans l homéostasie du principal neurotransmetteur excitateur, le glutamate. Dans le cas d intoxication aiguë chez l Homme, le GLA induit des convulsions. Au cours de ce travail, nous avons tenté d établir, sur le modèle souris, l origine de ces convulsions et les autres conséquences cérébrales du traitement. L évolution spatio-temporelle de l activation de la protéine Fos semble attribuer l origine des convulsions induites par le GLA (75 mg/kg) au gyrus denté. Les crises d épilepsie induites par le GLA sont suivies de dégénérescence neuronale et d une réaction microgliale 24 h après l injection de GLA ainsi que d une astrogliose à 15 j. Le diazepam arrête les crises d épilepsie et prévient la neurodégénérescence mais n empêche par la réaction gliale. Dans la deuxième partie de mes travaux de thèse, nous nous sommes intéressé au GLA en tant qu herbicide pouvant présenter un risque en termes de santé publique. Nous avons évalué les effets neurotoxiques d un traitement chronique à faibles doses de GLA. Un tel traitement induit chez les souris un léger déficit d apprentissage spatial observé dans le test du labyrinthe radiaire. Par ailleurs, l étude IRM associée à une analyse de texture montre que la structure de l hippocampe est altérée. Cette altération peut être corrélée avec les changements métaboliques observés tels que l activation de la GS. Ces résultats plaident en faveur d un effet neuroactif du GLA.ORLEANS-BU Sciences (452342104) / SudocSudocFranceF

Respiratory failure triggered by cholinesterase inhibitors may involve activation of a reflex sensory pathway by acetylcholine spillover

International audienceRespiration failure during exposure by cholinesterase inhibitors has been widely assumed to be due to inhibition of cholinesterase in the brain. Using a double chamber plethysmograph to measure various respiratory parameters , we observed long "end inspiratory pauses" (EIP) during most exposure that depressed breathing. Surprisingly, Colq KO mice that have a normal level of acetylcholinesterase (AChE) in the brain but a severe deficit in muscles and other peripheral tissues do not pause the breathing by long EIP. In mice, long EIP can be triggered by a nasal irritant. Eucalyptol, an agonist of cold receptor (TRPM8) acting on afferent sensory neurons and known to reduce the EIP triggered by such irritants, strongly reduced the EIP induced by cholinesterase inhibitor. These results suggest that acetylcholine (ACh) spillover from the neuromuscular junction, which is unchanged in Colq KO mice, may activate afferent sensory systems and trigger sensory reflexes, as reversed by eucalyptol. Indeed, the role of AChE at the cholinergic synapses is not only to accurately control the synaptic transmission but also to prevent the spillover of ACh. In the peripheral tissues, the ACh flood induced by cho-linesterase inhibition may be very toxic due to interaction with non-neuronal cells that use ACh at low levels to communicate with afferent sensory neurons

Immunomodulatory influence of bone marrow-derived mesenchymal stem cells on neuroinflammation in astrocyte cultures.

The therapeutic benefits associated with mesenchymal stem cells (MSCs) largely result from their immunomodulatory and neurotrophic properties. In this study, we evaluated the effects of MSCs on astrocyte cultures exposed to lipopolysaccharide. In response to this inflammatory trigger, astrocytes showed an increased expression of pro-inflammatory genes (IL-1β, TNFα, IL-6), which was attenuated by pre-exposure to MSC conditioned medium. Furthermore, mediators released by MSCs increased cell proliferation and altered the regulation of intermediate filaments (GFAP, vimentin), pro-inflammatory enzymes (iNOS, COX-2) and receptors (TLR4, CD14, mGluR3, mGluR5). These data demonstrate that MSCs influence diverse cell types participating in the response to neuroinflammation

Expression of tyrosine hydroxylase and vasopressin in magnocellular neurons of salt-loaded aged rats

Tyrosine hydroxylase (TH) is expressed in catecholaminergic neurons. However, under certain conditions it is also ectopically expressed in magnocellular neurons of the hypothalamus. To test the hypothesis that this expression of TH is related to the cellular activation of these neurons and/or to the vasopressin (VP) expression, we studied the expression of both TH and VP in control and salt-loaded aged rats. Our results demonstrate that aged rats show a marked TH expression in VP cells which is further increased by osmotic stimulation in the absence of increase in VP synthesis in the supraoptic nucleus. The presence of TH-immunopositive dendritic swellings in the ventral part of this nucleus reveals the high state of plasticity of these neurons. Furthermore, the lack of several actors of catecholamine biosynthesis in these neurons suggests a different role for TH. This study further demonstrates an ectopic expression of TH in hypothalamic neurons of aged rats and a TH expression linked to the activation of VP neurons but unrelated to VP synthesis. Microsc. Res, Tech. 56:81-91, 2002. (C) 2002 Wiley-Liss, Inc

Chronic exposure at low dose, to the organophosphorus herbicide phosphinothricin (PPT), induces astrocytosis and hyperlocomotion in mouse

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Opposite regulation of metabotropic glutamate receptor 3 and metabotropic glutamate receptor 5 by inflammatory stimuli in cultured microglia and astrocytes.

Metabotropic glutamate receptors (mGluRs) were previously shown to modulate several essential functions in glial cells, including cell proliferation, glutamate uptake, neurotrophic support, and inflammatory responses. As these receptors are regularly proposed as promising targets for the treatment of a wide range of neurological disorders, we herein examined the reciprocal modulation of glial mGluRs by inflammation. Such regulation of mGluRs was also studied in cultures from an experimental model of amyotrophic lateral sclerosis (ALS). Indeed, ALS is characterized by increased neuroinflammation, and glial cell cultures derived from the animal model (rat expressing hSOD1(G93A)) show enhanced glial reactivity. Within 72 h, the pro-inflammatory cytokines tumor necrosis factor α (TNFα) and interleukin 1β (IL-1β) induced an increase in mGluR3 and a decrease in mGluR5 gene expression. A similar regulation of these receptors was observed in microglia 48 h after an initial 4-h exposure to lipopolysaccharide. In hSOD1(G93A)-derived glial cultures, the gene up-regulation of mGluR3 (but not the gene down-regulation of mGluR5) was found to be enhanced in both astrocytes and microglia. Together, these results indicate that an inflammatory environment triggers an opposite regulation in the gene expression of the two predominant mGluR subtypes found in glial cells, and that these regulations were particularly robust in hSOD1(G93A) glial cultures. As neuroinflammation commonly occurs in several nervous diseases, its influence on mGluR expression should be taken into account when considering these receptors as future drug targets

Pharmacological blockade of dopamine D(2) receptors by aripiprazole is not associated with striatal sensitization.

The partial agonist profile of novel antipsychotics such as aripiprazole has hardly been demonstrated in biochemical assays on animal tissues. As it is established that responses induced by dopamine D(2) receptor agonists are increased in models of dopaminergic sensitization, this paradigm was used in order to facilitate the detection of the partial agonist properties of aripiprazole. At variance with all other partial and full agonists tested, the partial agonist properties of aripiprazole were not revealed in guanosine 5'-O-(γ-[(35)S]thiotriphosphate ([(35)S]GTPγS) binding assays on striatal membranes from haloperidol-treated rats. Hence, aripiprazole behaved as an antagonist, efficiently inhibiting the functional response to dopamine. Similarly, in behavioural assays, aripiprazole dose-dependently inhibited the stereotypies elicited by apomorphine. However, at variance with haloperidol, repeated administrations of aripiprazole (3 weeks) at the doses of 10 and 30 mg/kg did not induce any up-regulation or hyperfunctionality of the dopamine D(2) receptors in the striatum. These data highlight the putative involvement of other pharmacological targets for aripiprazole that would support in the prevention of secondary effects commonly associated with the blockade of striatal dopamine D(2) receptors. Hence, in additional experiments, aripiprazole was found to efficiently promote [(35)S]GTPγS binding in hippocampal membranes through the activation of 5-HT(1A) receptors. Further experiments investigating the second-messenger cascades should be performed so as to establish the functional properties of aripiprazole and understand the mechanism underlying the prevention of dopamine receptor regulation in spite of the observed antagonism

MRI texture analysis as a non invasive tool to show cerebral structural changes after herbicide treatment in mice

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An easy method for the determination of active concentrations of cholinesterase reactivators in blood samples: Application to the efficacy assessment of non quaternary reactivators compared to HI-6 and pralidoxime in VX-poisoned mice

International audienceOrganophosphorus nerve agents, like VX, are highly toxic due to their strong inhibition potency against acetylcholinesterase (AChE). AChE inhibited by VX can be reactivated using powerful nucleophilic molecules, most commonly oximes, which are one major component of the emergency treatment in case of nerve agent intoxication. We present here a comparative in vivo study on Swiss mice of four reactivators: HI-6, pralidoxime and two uncharged derivatives of 3-hydroxy-2-pyridinaldoxime that should more easily cross the blood-brain barrier and display a significant central nervous system activity. The reactivability kinetic profile of the oximes is established following intraperitoneal injection in healthy mice, using an original and fast enzymatic method based on the reactivation potential of oxime-containing plasma samples. HI-6 displays the highest reactivation potential whatever the conditions, followed by pralidoxime and the two non quaternary reactivators at the dose of 50 mg/kg bw. But these three last reactivators display equivalent reactivation potential at the same dose of 100 μmol/kg bw. Maximal reactivation potential closely correlates to surviving test results of VX intoxicated mice