The Experts below are selected from a list of 186 Experts worldwide ranked by ideXlab platform
Joseph W Lynch - One of the best experts on this subject based on the ideXlab platform.
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a Picrotoxin specific conformational change in the glycine receptor m2 m3 loop
Journal of Biological Chemistry, 2005Co-Authors: Rebecca L Hawthorne, Joseph W LynchAbstract:Abstract The external loop linking the M2 and M3 transmembrane domains is crucial for coupling agonist binding to channel gating in the glycine receptor chloride channel (GlyR). A substituted cysteine accessibility scan previously showed that glycine activation increased the surface accessibility of 6 contiguous residues (Arg271– Lys276) toward the N-terminal end of the homomeric α1 GlyR M2–M3 loop. In the present study we used a similar approach to determine whether the allosteric antagonist, Picrotoxin, could impose conformational changes to this domain that cannot be induced by varying agonist concentrations alone. Picrotoxin slowed the reaction rate of a sulfhydryl-containing compound (MTSET) with A272C, S273C, and L274C. Before interpreting this as a Picrotoxin-specific conformational change, it was necessary to eliminate the possibility of steric competition between Picrotoxin and MTSET. Accordingly, we showed that Picrotoxin and the structurally unrelated blocker, bilobalide, were both trapped in the R271C GlyR in the closed state and that a point mutation to the pore-lining Thr6′ residue abolished inhibition by both compounds. We also demonstrated that the Picrotoxin dissociation rate was linearly related to the channel open probability. These observations constitute a strong case for Picrotoxin binding in the pore. We thus conclude that the Picrotoxin-specific effects on the M2–M3 loop are mediated allosterically. This suggests that the M2–M3 loop responds differently to the occupation of different binding sites.
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A Picrotoxin-specific Conformational Change in the Glycine Receptor M2–M3 Loop
Journal of Biological Chemistry, 2005Co-Authors: Rebecca L Hawthorne, Joseph W LynchAbstract:Abstract The external loop linking the M2 and M3 transmembrane domains is crucial for coupling agonist binding to channel gating in the glycine receptor chloride channel (GlyR). A substituted cysteine accessibility scan previously showed that glycine activation increased the surface accessibility of 6 contiguous residues (Arg271– Lys276) toward the N-terminal end of the homomeric α1 GlyR M2–M3 loop. In the present study we used a similar approach to determine whether the allosteric antagonist, Picrotoxin, could impose conformational changes to this domain that cannot be induced by varying agonist concentrations alone. Picrotoxin slowed the reaction rate of a sulfhydryl-containing compound (MTSET) with A272C, S273C, and L274C. Before interpreting this as a Picrotoxin-specific conformational change, it was necessary to eliminate the possibility of steric competition between Picrotoxin and MTSET. Accordingly, we showed that Picrotoxin and the structurally unrelated blocker, bilobalide, were both trapped in the R271C GlyR in the closed state and that a point mutation to the pore-lining Thr6′ residue abolished inhibition by both compounds. We also demonstrated that the Picrotoxin dissociation rate was linearly related to the channel open probability. These observations constitute a strong case for Picrotoxin binding in the pore. We thus conclude that the Picrotoxin-specific effects on the M2–M3 loop are mediated allosterically. This suggests that the M2–M3 loop responds differently to the occupation of different binding sites.
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a single β subunit m2 domain residue controls the Picrotoxin sensitivity of αβ heteromeric glycine receptor chloride channels
Journal of Neurochemistry, 2001Co-Authors: Qiang Shan, Justine L Haddrill, Joseph W LynchAbstract:This study investigated the residues responsible for the reduced Picrotoxin sensitivity of the alpha beta heteromeric glycine receptor relative to the alpha homomeric receptor. By analogy with structurally related receptors, the beta subunit M2 domain residues P278 and F282 were considered the most likely candidates for mediating this effect. These residues align with G254 and T258 of the alpha subunit. The T258A, T258C and T258F mutations dramatically reduced the Picrotoxin sensitivity of the alpha homomeric receptor. Furthermore, the converse F282T mutation in the beta subunit increased the Picrotoxin sensitivity of the alpha beta heteromeric receptor. The P278G mutation in the beta subunit did not affect the Picrotoxin sensitivity of the alpha beta heteromer. Thus, a ring of five threonines at the M2 domain depth corresponding to alpha subunit T258 is specifically required for Picrotoxin sensitivity. Mutations to alpha subunit T258 also profoundly influenced the apparent glycine affinity. A substituted cysteine accessibility analysis revealed that the T258C sidechain increases its pore exposure in the channel open state. This provides further evidence for an allosteric mechanism of Picrotoxin inhibition, but renders it unlikely that Picrotoxin las an allosterically acting 'competitive' antagonist) binds to this residue.
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mutations affecting the glycine receptor agonist transduction mechanism convert the competitive antagonist Picrotoxin into an allosteric potentiator
Journal of Biological Chemistry, 1995Co-Authors: Joseph W Lynch, Sundran Rajendra, Peter H Barry, Peter R SchofieldAbstract:Abstract Contrary to its effects on the -aminobutyric acid type A receptor, Picrotoxin antagonism of the α1 subunit of the human glycine receptor is shown to be competitive, not use-dependent, and nonselective between the Picrotoxin components, picrotin, and Picrotoxinin. Competitive antagonism and non-use dependence are consistent with Picrotoxin binding to a site in the extracellular domain. The mutations Arg Leu or Arg Gln at residue 271 of the glycine receptor α1 subunit, which are both associated with human startle disease, have previously been demonstrated to disrupt the transduction process between agonist binding and channel activation. We show here that these mutations also transform Picrotoxin from an allosterically acting competitive antagonist to an allosteric potentiator at low (0.01-3 μM) concentrations and to a noncompetitive antagonist at higher (≥3 μM) concentrations. This demonstrates that arginine 271 is involved in the transduction process between Picrotoxin binding and its mechanism of action. Thus, the allosteric transduction pathways of both agonists and antagonists converge at a common residue prior to the activation gate of the channel, suggesting that this residue may act as an integration point for information from various extracellular ligand binding sites.
F Arespena - One of the best experts on this subject based on the ideXlab platform.
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a study of neurotoxic biomarkers c fos and gfap after acute exposure to gsm radiation at 900 mhz in the Picrotoxin model of rat brains
Neurotoxicology, 2011Co-Authors: M Carballoquintas, Isabel Maria Martinezsilva, Carmen Cadarsosuarez, M Alvarezfigueiras, F Arespena, E LopezmartinAbstract:Abstract The acute effects of microwave exposure from the Global System for Mobile Communication (GSM) were studied in rats, using 900 MHz radiation at an intensity similar to mobile phone emissions. Acute subconvulsive doses of Picrotoxin were then administered to the rats and an experimental model of seizure-proneness was created from the data. Seventy-two adult male Sprague-Dawley rats underwent immunochemical testing of relevant anatomical areas to measure induction of the c-fos neuronal marker after 90 min and 24 h, and of the glial fibrillary acidic protein (GFAP) 72 h after acute exposure to a 900 MHz electromagnetic field (EMF). The experimental set-up facilitated measurement of absorbed power, from which the average specific absorption rate was calculated using the finite-difference time-domain (FDTD) 2 h after exposure to EMF radiation at 1.45 W/kg in Picrotoxin-treated rats and 1.38 W/kg in untreated rats. Ninety minutes after radiation high levels of c-fos expression were recorded in the neocortex and paleocortex along with low hippocampus activation in Picrotoxin treated animals. Most brain areas, except the limbic cortical region, showed important increases in neuronal activation 24 h after Picrotoxin and radiation. Three days after Picrotoxin treatment, radiation effects were still apparent in the neocortex, dentate gyrus and CA3, but a significant decrease in activity was noted in the piriform and entorhinal cortex. During this time, glial reactivity increased with every seizure in irradiated, Picrotoxin-treated brain regions. Our results reveal that c-fos and glial markers were triggered by the combined stress of non-thermal irradiation and the toxic effect of Picrotoxin on cerebral tissues.
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the action of pulse modulated gsm radiation increases regional changes in brain activity and c fos expression in cortical and subcortical areas in a rat model of Picrotoxin induced seizure proneness
Journal of Neuroscience Research, 2009Co-Authors: E Lopezmartin, Carmen Cadarsosuarez, J Bregains, J L Relovaquinteiro, F J Jorgebarreiro, F ArespenaAbstract:The action of the pulse-modulated GSM radiofrequency of mobile phones has been suggested as a physical phenomenon that might have biological effects on the mammalian central nervous system. In the present study, GSM-exposed Picrotoxin-pretreated rats showed differences in clinical and EEG signs, and in c-Fos expression in the brain, with respect to Picrotoxin-treated rats exposed to an equivalent dose of unmodulated radiation. Neither radiation treatment caused tissue heating, so thermal effects can be ruled out. The most marked effects of GSM radiation on c-Fos expression in Picrotoxin-treated rats were observed in limbic structures, olfactory cortex areas and subcortical areas, the dentate gyrus, and the central lateral nucleus of the thalamic intralaminar nucleus group. NonPicrotoxin-treated animals exposed to unmodulated radiation showed the highest levels of neuronal c-Fos expression in cortical areas. These results suggest a specific effect of the pulse modulation of GSM radiation on brain activity of a Picrotoxin-induced seizure-proneness rat model and indicate that this mobile-phone-type radiation might induce regional changes in previous preexcitability conditions of neuronal activation. © 2008 Wiley-Liss, Inc.
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gsm radiation triggers seizures and increases cerebral c fos positivity in rats pretreated with subconvulsive doses of Picrotoxin
Neuroscience Letters, 2006Co-Authors: E Lopezmartin, Jose L Relovaquinteiro, Rosalia Gallegogomez, Manuel Peleteirofernandez, Francisco Barreiro, F ArespenaAbstract:This study investigated the effects of mobile-phone-type radiation on the cerebral activity of seizure-prone animals. When rats transformed into an experimental model of seizure-proneness by acute subconvulsive doses of Picrotoxin were exposed to 2 h GSM-modulated 900 MHz radiation at an intensity similar to that emitted by mobile phones, they suffered seizures and the levels of the neuronal activity marker c-Fos in neocortex, paleocortex, hippocampus and thalamus increased markedly. Non-irradiated Picrotoxin-treated rats did not suffer seizures, and their cerebral c-Fos counts were significantly lower. Radiation caused no such differences in rats that had not been pretreated with Picrotoxin. We conclude that GSM-type radiation can induce seizures in rats following their facilitation by subconvulsive doses of Picrotoxin, and that research should be pursued into the possibility that this kind of radiation may similarly affect brain function in human subjects with epileptic disorders.
E Lopezmartin - One of the best experts on this subject based on the ideXlab platform.
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a study of neurotoxic biomarkers c fos and gfap after acute exposure to gsm radiation at 900 mhz in the Picrotoxin model of rat brains
Neurotoxicology, 2011Co-Authors: M Carballoquintas, Isabel Maria Martinezsilva, Carmen Cadarsosuarez, M Alvarezfigueiras, F Arespena, E LopezmartinAbstract:Abstract The acute effects of microwave exposure from the Global System for Mobile Communication (GSM) were studied in rats, using 900 MHz radiation at an intensity similar to mobile phone emissions. Acute subconvulsive doses of Picrotoxin were then administered to the rats and an experimental model of seizure-proneness was created from the data. Seventy-two adult male Sprague-Dawley rats underwent immunochemical testing of relevant anatomical areas to measure induction of the c-fos neuronal marker after 90 min and 24 h, and of the glial fibrillary acidic protein (GFAP) 72 h after acute exposure to a 900 MHz electromagnetic field (EMF). The experimental set-up facilitated measurement of absorbed power, from which the average specific absorption rate was calculated using the finite-difference time-domain (FDTD) 2 h after exposure to EMF radiation at 1.45 W/kg in Picrotoxin-treated rats and 1.38 W/kg in untreated rats. Ninety minutes after radiation high levels of c-fos expression were recorded in the neocortex and paleocortex along with low hippocampus activation in Picrotoxin treated animals. Most brain areas, except the limbic cortical region, showed important increases in neuronal activation 24 h after Picrotoxin and radiation. Three days after Picrotoxin treatment, radiation effects were still apparent in the neocortex, dentate gyrus and CA3, but a significant decrease in activity was noted in the piriform and entorhinal cortex. During this time, glial reactivity increased with every seizure in irradiated, Picrotoxin-treated brain regions. Our results reveal that c-fos and glial markers were triggered by the combined stress of non-thermal irradiation and the toxic effect of Picrotoxin on cerebral tissues.
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the action of pulse modulated gsm radiation increases regional changes in brain activity and c fos expression in cortical and subcortical areas in a rat model of Picrotoxin induced seizure proneness
Journal of Neuroscience Research, 2009Co-Authors: E Lopezmartin, Carmen Cadarsosuarez, J Bregains, J L Relovaquinteiro, F J Jorgebarreiro, F ArespenaAbstract:The action of the pulse-modulated GSM radiofrequency of mobile phones has been suggested as a physical phenomenon that might have biological effects on the mammalian central nervous system. In the present study, GSM-exposed Picrotoxin-pretreated rats showed differences in clinical and EEG signs, and in c-Fos expression in the brain, with respect to Picrotoxin-treated rats exposed to an equivalent dose of unmodulated radiation. Neither radiation treatment caused tissue heating, so thermal effects can be ruled out. The most marked effects of GSM radiation on c-Fos expression in Picrotoxin-treated rats were observed in limbic structures, olfactory cortex areas and subcortical areas, the dentate gyrus, and the central lateral nucleus of the thalamic intralaminar nucleus group. NonPicrotoxin-treated animals exposed to unmodulated radiation showed the highest levels of neuronal c-Fos expression in cortical areas. These results suggest a specific effect of the pulse modulation of GSM radiation on brain activity of a Picrotoxin-induced seizure-proneness rat model and indicate that this mobile-phone-type radiation might induce regional changes in previous preexcitability conditions of neuronal activation. © 2008 Wiley-Liss, Inc.
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gsm radiation triggers seizures and increases cerebral c fos positivity in rats pretreated with subconvulsive doses of Picrotoxin
Neuroscience Letters, 2006Co-Authors: E Lopezmartin, Jose L Relovaquinteiro, Rosalia Gallegogomez, Manuel Peleteirofernandez, Francisco Barreiro, F ArespenaAbstract:This study investigated the effects of mobile-phone-type radiation on the cerebral activity of seizure-prone animals. When rats transformed into an experimental model of seizure-proneness by acute subconvulsive doses of Picrotoxin were exposed to 2 h GSM-modulated 900 MHz radiation at an intensity similar to that emitted by mobile phones, they suffered seizures and the levels of the neuronal activity marker c-Fos in neocortex, paleocortex, hippocampus and thalamus increased markedly. Non-irradiated Picrotoxin-treated rats did not suffer seizures, and their cerebral c-Fos counts were significantly lower. Radiation caused no such differences in rats that had not been pretreated with Picrotoxin. We conclude that GSM-type radiation can induce seizures in rats following their facilitation by subconvulsive doses of Picrotoxin, and that research should be pursued into the possibility that this kind of radiation may similarly affect brain function in human subjects with epileptic disorders.
Rebecca L Hawthorne - One of the best experts on this subject based on the ideXlab platform.
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a Picrotoxin specific conformational change in the glycine receptor m2 m3 loop
Journal of Biological Chemistry, 2005Co-Authors: Rebecca L Hawthorne, Joseph W LynchAbstract:Abstract The external loop linking the M2 and M3 transmembrane domains is crucial for coupling agonist binding to channel gating in the glycine receptor chloride channel (GlyR). A substituted cysteine accessibility scan previously showed that glycine activation increased the surface accessibility of 6 contiguous residues (Arg271– Lys276) toward the N-terminal end of the homomeric α1 GlyR M2–M3 loop. In the present study we used a similar approach to determine whether the allosteric antagonist, Picrotoxin, could impose conformational changes to this domain that cannot be induced by varying agonist concentrations alone. Picrotoxin slowed the reaction rate of a sulfhydryl-containing compound (MTSET) with A272C, S273C, and L274C. Before interpreting this as a Picrotoxin-specific conformational change, it was necessary to eliminate the possibility of steric competition between Picrotoxin and MTSET. Accordingly, we showed that Picrotoxin and the structurally unrelated blocker, bilobalide, were both trapped in the R271C GlyR in the closed state and that a point mutation to the pore-lining Thr6′ residue abolished inhibition by both compounds. We also demonstrated that the Picrotoxin dissociation rate was linearly related to the channel open probability. These observations constitute a strong case for Picrotoxin binding in the pore. We thus conclude that the Picrotoxin-specific effects on the M2–M3 loop are mediated allosterically. This suggests that the M2–M3 loop responds differently to the occupation of different binding sites.
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A Picrotoxin-specific Conformational Change in the Glycine Receptor M2–M3 Loop
Journal of Biological Chemistry, 2005Co-Authors: Rebecca L Hawthorne, Joseph W LynchAbstract:Abstract The external loop linking the M2 and M3 transmembrane domains is crucial for coupling agonist binding to channel gating in the glycine receptor chloride channel (GlyR). A substituted cysteine accessibility scan previously showed that glycine activation increased the surface accessibility of 6 contiguous residues (Arg271– Lys276) toward the N-terminal end of the homomeric α1 GlyR M2–M3 loop. In the present study we used a similar approach to determine whether the allosteric antagonist, Picrotoxin, could impose conformational changes to this domain that cannot be induced by varying agonist concentrations alone. Picrotoxin slowed the reaction rate of a sulfhydryl-containing compound (MTSET) with A272C, S273C, and L274C. Before interpreting this as a Picrotoxin-specific conformational change, it was necessary to eliminate the possibility of steric competition between Picrotoxin and MTSET. Accordingly, we showed that Picrotoxin and the structurally unrelated blocker, bilobalide, were both trapped in the R271C GlyR in the closed state and that a point mutation to the pore-lining Thr6′ residue abolished inhibition by both compounds. We also demonstrated that the Picrotoxin dissociation rate was linearly related to the channel open probability. These observations constitute a strong case for Picrotoxin binding in the pore. We thus conclude that the Picrotoxin-specific effects on the M2–M3 loop are mediated allosterically. This suggests that the M2–M3 loop responds differently to the occupation of different binding sites.
German Sierramarcuno - One of the best experts on this subject based on the ideXlab platform.
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anticonvulsant effect of the calcineurin inhibitor ascomycin on seizures induced by Picrotoxin microperfusion in the rat hippocampus
Pharmacology Biochemistry and Behavior, 2006Co-Authors: Araceli Vazquezlopez, German Sierraparedes, German SierramarcunoAbstract:Abstract The potential in vivo anticonvulsant effect of calcineurin (protein phosphatase 2B) inhibitor ascomycin against seizures induced by intrahippocampal microdialysis of Picrotoxin was examined in the present study. After establishing individual Picrotoxin seizure thresholds, ascomycin was continually microperfused into the rat hippocampus through microdialysis probes at concentrations 10, 50 and 100 μM. No behavioral or electroencephalographic effects were observed during microperfusion of ascomycin alone. Low concentrations (10 μM) of ascomycin did not prevent Picrotoxin seizures, however, 50 and 100 μM ascomycin showed antiepileptic effect, completely suppressing seizures in 41.7% and 75% of the animals studied respectively. Mean seizure duration and mean number of seizures were significantly reduced ( P
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role of camp dependent protein kinase on acute Picrotoxin induced seizures
Neurochemical Research, 2005Co-Authors: Araceli Vazquezlopez, German Sierraparedes, German SierramarcunoAbstract:cAMP-dependent protein kinase (PKA) is a major modulator of synaptic transmission likely to be involved in molecular and cellular events leading to epileptogenesis, but little is known about how it affects the onset of acute epileptic seizures. In this study, we determined PKA enzymatic activity in the rat hippocampus during Picrotoxin-induced seizures, using H-9 dihydrochloride, a PKA inhibitor, to investigate the in vivo effects of this enzyme on seizures induced by Picrotoxin microdialysis in the rat hippocampus. No significant modifications were found in PKA activity during seizures as compared to control rats, but H-9 dihydrochloride microperfusion (100 μM) prevented Picrotoxin seizures in 50% of the animals and significantly reduced the mean number of seizures and mean seizure duration. These results suggest that acute Picrotoxin-induced seizures occur without an increase in hippocampal PKA activity, but reduced PKA-mediated phosphorylation protects against Picrotoxin seizures, probably by increasing the inhibitory potential of GABAA receptors. The possibility of other targets for H-9 dihydrochloride, such as PKC, PKG or CAMKII, however, cannot be ruled out.