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

3L-Phosphinothricin modulation of inwardly rectifying K+ channels increased excitability in striatal medium-sized spiny neurons

International audiencePhosphinotricin (L-PPT) is the active compound of a broad-spectrum herbicide. Acute poisoning with L-PPT has various clinical manifestations, including seizures and convulsions. However, the exact mechanism of L-PPT toxicity remains unclear. The present study addressed the role of L-PPT, in the excitability of striatal medium-sized spiny neurons (MSNs). In whole-cell current-clamp experiments, L-PPT increased the input resistance (Ri), decreased the rheobase and increased the firing frequency of action potentials. In voltage-clamp experiments, L-PPT inhibited the inward-rectifying potassium (Kir) currents. Finally, the effects of L-PPT mimicked the inhibition of Kir channels with Ba2+ on neuronal excitability. Altogether, these results suggest that the herbicide L-PPT is a modulator of Kir channels in MSNs. Thereby, Kir channels are potent regulators of the excitability of MSNs and reduced open probability of these channels would generate a powerful upregulation of neuronal output. This effect may represent a possible mechanism for L-PPT dependent neuronal toxicity

Changes in voltage activation of contraction in frog skeletal muscle fibres as a result of sarcoplasmic reticulum Ca2+-ATPase activity

International audienceThe effects of cyclopiazonic acid, a specific sarcoplasmic reticulum Ca2+-ATPase inhibitor, on isometric tension were studied in response to prolonged steady-state depolarization induced by a rapid change in extracellular potassium concentration (potassium contractures) in frog semitendinosus muscle fibres. Cyclopiazonic acid (1-10 microM) enhanced the amplitude and time-course of relaxation of 146 mM potassium contracture. In the presence of cyclopiazonic acid 0.5 microM, the relationship between the amplitude of potassium contractures and the membrane potential shifted to more negative potentials, whereas the steady-state inactivation curve was unchanged. These observations suggest that cyclopiazonic acid has no effect on voltage sensors. The difference between potassium contractures in the absence and presence of cyclopiazonic acid in skeletal muscle fibres implies that the amplitude and slow relaxation of tension during prolonged steady-state depolarization may be expected to depend not only on inactivation of the process regulating calcium release from the sarcoplasmic reticulum but also on the ability of the sarcoplasmic reticulum to pump calcium

Na(+)-Ca2+ exchange induces low Na+ contracture in frog skeletal muscle fibers after partial inhibition of sarcoplasmic reticulum Ca(2+)-ATPase.

International audienceContractile responses due to reduction in external sodium concentration ([Na+]o) were investigated in twitch skeletal muscle fibers of frog semitendinosus. Experiments were conducted after partial inhibition of sarcoplasmic reticulum Ca(2+)-ATPase by cyclopiazonic acid (CPA). In the absence of CPA, Na+ withdrawal failed to produce any change in resting tension. In the presence of CPA (2-10 microM), [Na+]o reduction induced a transient contracture without a significant change in the resting membrane potential. The amplitude of the contracture displayed a step dependence on [Na+]o, was increased by K(+)-free medium and was prevented in Ca(2+)-free medium. This contracture was inhibited by various blockers of the Na(+)-Ca2+ exchange but was little affected by inhibitors of sarcolemmal Ca(2+)-ATPase or mitochondria. When sarcoplasmic reticulum function was impaired, low-Na+ solutions caused no contracture. These results provide evidence that skeletal muscle fibers possess a functional Na(+)-Ca2+ exchange which can mediate sufficient Ca2+ entry to activate contraction by triggering Ca2+ release from sarcoplasmic reticulum when the sodium electrochemical gradient is reduced, and sarcoplasmic reticulum Ca(2+)-ATPase is partially inhibited. This indicates that when the sarcoplasmic reticulum Ca(2+)-ATPase is working (no CPA), Ca2+ fluxes produced by the exchanger are buffered by the sarcoplasmic reticulum. Thus the Na(+)-Ca2+ exchange may be one of the factors determining sarcoplasmic reticulum Ca2+ content and thence the magnitude of the release of Ca2+ from the sarcoplasmic reticulum

Impact of TIEG1 on the structural properties of fast- and slow-twitch skeletal muscle

International audienceIntroductionTransforming growth factor-beta (TGF-β)–inducible early gene-1 (TIEG1) is a transcription factor that is highly expressed in skeletal muscle. The purpose of this study was to characterize the structural properties of both fast-twitch (EDL) and slow-twitch (soleus) muscles in the hindlimb of TIEG1-deficient (TIEG1−/−) mice.MethodsTen slow and 10 fast muscles were analyzed from TIEG1−/− and wild-type (WT) mice using MRI texture (MRI-TA) and histological analyses.ResultsMRI-TA could discriminate between WT slow and fast muscles. Deletion of the TIEG1 gene led to changes in the texture profile within both muscle types. Specifically, muscle isolated from TIEG1−/− mice displayed hypertrophy, hyperplasia, and a modification of fiber area distribution.ConclusionsWe demonstrated that TIEG1 plays an important role in the structural properties of skeletal muscle. This study further implicates important roles for TIEG1 in the development of skeletal muscle and suggests that defects in TIEG1 expression and/or function may be associated with muscle disease

Perinatal exposure to dichloro-bisphenol A alters hepatic lipid composition in mouse: a study by MRI and 1H MRS

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Perinatal exposure to dichloro-bisphenol A alters lipid composition of mouse liver

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Gestational and lactational exposure to dichlorinated bisphenol A induces early alterations of hepatic lipid composition in mice

International audienceObjectiveUsing non-invasive magnetic resonance (MR) techniques and a histological approach, we assessed the outcomes of perinatal exposure at a low dose of 3,3′-DCBPA (2-chloro-4-[1-(3-chloro-4-hydroxyphenyl)-1-methylethyl]phenol) and/or 3,5-DCBPA (2,6-dichloro-4-[1-(4-hydroxyphenyl)-1-methylethyl]phenol) on mice livers.Materials and methodsFertilized female Swiss mice were injected intraperitoneally during gestation and lactation with either vehicle control, 20 μg/kg/day of BPA, 3,5-DCBPA, 3,3′-DCBPA or a mixture (mix-DCBPA). Complementary methods were used to evaluate, in male and female pups, (1) liver structure by texture analysis of images obtained through MR imaging (MRI) and histology, (2) hepatic lipid composition through in vivo 1H MR spectroscopy (1H MRS).ResultsPrincipal component analysis of texture parameters showed no structural modification of the liver with BPA and DCBPA treatments. Accordingly, no hepatic microvesicular steatosis was observed through hematoxylin–eosin staining. Compared to control, MRS revealed no difference in lipid composition for BPA, 3,5-DCBPA or 3,3′-DCBPA groups. However, MRS detected a significant increase in the mix-DCBPA groups for the saturated component of fatty acids (FA), total unsaturated FA bond index and polyunsaturated FA bond index.ConclusionPrior to any structural changes, polyunsaturated fatty acids significantly increased in young male and female mice exposed perinatally at a low dose to a mixture of dichlorinated BPA

Cyclopiazonic acid-induced changes in the contraction and Ca 2+ transient of frog fast-twitch skeletal muscle

International audienceThe effects of cyclopiazonic acid (CPA) were investigated on isolated skeletal muscle fibers of frog semitendinosus muscle. CPA (0.5-10 microM) enhanced isometric twitch but produced little change in resting tension. At higher concentrations (10-50 microM), CPA depressed twitch and induced sustained contracture without affecting resting and action potentials. In Triton-skinned fibers, CPA had no significant effect on myofibrillar Ca2+ sensitivity but decreased maximal activated force at concentrations > 5 microM. In intact cells loaded with the Ca2+ fluorescence indicator indo 1, CPA (2 microM) induced an increase in Ca(2+)-transient amplitude (10 +/- 2.5%), which was associated with an increase in time to peak and in the time constant of decay. Consequently, peak force was increased by 35 +/- 4%, and both time to peak and the time constant of relaxation were prolonged. It is concluded that CPA effects, at a concentration of up to 2 microM, were associated with specific inhibition of sarcoplasmic reticulum Ca(2+)-adenosinetriphosphatase in intact skeletal muscle and that inhibition of the pump directly affected the handling of intracellular Ca2+ and force production

Methyl jasmonate-induced stimulation of sarcoplasmic reticulum Ca(2+)-ATPase affects contractile responses in rat slow-twitch skeletal muscle.

International audienceThe purpose of this study was to determine whether methyl jasmonate, a stimulator of Ca(2+)-adenosine triphosphatase (ATPase) activity of the purified ATPase from fast-twitch skeletal muscle, could affect contractile responses in small bundles of rat isolated slow-twitch (soleus) fibers. In saponin-skinned fibers, sarcoplasmic reticulum (SR) Ca(2+) loading was performed in pCa 7.0 solution. The amount of Ca(2+) taken up was monitored by use of the amplitude of contraction following application of 10 mM caffeine. Results indicate that the increased loading rate in the presence of methyl jasmonate is likely due to stimulation of the SR Ca(2+)-ATPase. In Triton-skinned fibers, the myofibrillar Ca(2+) sensitivity was not changed by methyl jasmonate (50-200 microM). In intact fibers, the amplitude and the time constant of relaxation of twitch and potassium contracture were reversibly reduced after 2 min of application of methyl jasmonate at a concentration of up to 125 microM. At higher concentrations (>150 microM), effects were not reversible. In the presence of methyl jasmonate (100 microM), the relationship between the amplitude of potassium contractures and the membrane potential shifted to more positive potentials, whereas the steady-state inactivation curve was unchanged. These observations suggest that methyl jasmonate has no effect on voltage sensors. Taken together, our results show that methyl jasmonate is a potent, reversible, and specific stimulator of the SR Ca(2+) pump in slow-twitch skeletal muscle and is an extremely valuable pharmacological tool for improving relaxation and studying calcium-signaling questions