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140. Axonal neurotoxicity of local anesthetics in compartmented rat dorsal root ganglion cell cultures
141. Neurotoxic properties of the investigational local anesthetic adjuvant ephedrine
I. Haller1, L. Klimaschewski2, P. Gerner3, P. Lirk1 [email protected] 1Department of Anesthesiology, Innsbruck Medical University, Innsbruck, Austria, 2Division of Neuroscience, Innsbruck Medical University, Innsbruck, Austria, 3Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA
I. Haller1, L. Klimaschewski2, P. Gerner3, P. Lirk1 [email protected] 1Dept. of Anesthesiology, Innsbruck Medical University, Innsbruck, Austria, 2Division of Neuroanatomy, Innsbruck Medical University, Innsbruck, Austria, 3Dept. of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA
Background: Direct neurotoxicity of local anesthetics (LA) is a frequent problem, and may cause transient and even permanent neurologic complications, such as radicular irritation or cauda equina syndrome. Thus far, all investigations about LA neurotoxicity have been carried out in dissociated neuron cultures, immersing both soma and axon with local anesthetic. We used compartmented adult rat dorsal root ganglion neuron cultures, which facilitate selective incubation of axon, or soma, to determine whether local anesthetic-induced axonal neurotoxicity is a process that is confined to the neuron’s axon, or whether it involves the neuronal soma, as well.
Background: Because ephedrine may be a useful adjuvant to local anesthetics, we investigated its neurotoxicity in an adult rat dorsal root ganglion cell culture model.
Methods: Lidocaine (40 mM / ⬃1%) was added to the central and/or the peripheral compartment of three-chambered dishes. Additionally, we co-applied an inhibitor of the p38 Mitogen-Activated Protein Kinase (MAPK) to determine their effect both locally at the axon, and the neuron’s soma. Neuronal survival, axonal length and morphology were used as outcome measures. Results: Central incubation with lidocaine resulted in a reduction in soma number (from 100% to 60 ⫾ 8%), and axonal outgrowth length (from 100% to 43 ⫾ 10%). Incubation in the peripheral (axon) compartment caused severe axonal “dying-back” degeneration, decreasing maximal axonal distances to 53 ⫾ 6 %, without affecting survival of somata. During axonal incubation with lidocaine, peripheral application of p38 MAPK inhibitor significantly decreased neurotoxicity. Conclusion: We describe compartmental primary sensory neuron cultures as a potentially useful in vitro model to determine in detail mechanisms involved in local anesthetic-induced neurotoxicity. Incubation of somata or axons with lidocaine and/or MAPK inhibitor showed distinctly different responses concerning survival, and it appears that local anesthetic-induced axonal neurotoxicity mediated by activation of the p38 MAPK is a localized process.
Material and Methods: Primary sensory neuron cultures were employed to determine dose-dependency and potential selectivity of ephedrine neurotoxicity on specific neuron categories, grouped according to cell size, or phenotype (IB4- and CGRP-positive neurons). Moreover, we pharmacologically inhibited mitogen-activated protein kinases (MAPK), p38, p42/44 and c-jun N-terminal kinases, assessing neuron survival, and performed ELISAs to detect MAPK activation. Results: Ephedrine demonstrated neurotoxic effects on adult rat DRG neurons at concentrations of 0.1 % and higher, as shown by a significant reduction of neuron survival (P ⬍ 0.001). At a concentration of 0.25 % it caused LDH release and induced specific activation of p38 MAPK. Pharmacologic inhibition of MAPKs (p38, p42/44 and JNK), however, had no protective effect on neuron survival. Moreover, ephedrine predominantly affected small-sized (0-35 m) neurons, including both IB4- and CGRP-positive neurons, as compared to controls (P ⬍ 0.001). Conclusion: Ephedrine shows a significant potential for neurotoxicity, which has to be taken into consideration regarding its possible use as adjuvant for local anesthesia. Furthermore, it specifically activates p38 MAPK, similar to the conventional local anesthetic lidocaine, suggesting a common mechanism of toxicity. However, inhibition of MAPK did not alleviate neurotoxicity, suggesting that this pathway is not exclusively responsible for toxicity. Finally, ephedrine has a predominant neurotoxic effect upon small-sized neurons, most of which are involved in nociception. 1. Hung YC, Kau YC, Zizza AM et al. Ephedrine Blocks Rat Sciatic Nerve In Vivo and Sodium Channels In Vitro. Anesthesiology 2005; 103: 124652.
Best Free Papers
140. Axonal neurotoxicity of local anesthetics in compartmented rat dorsal root ganglion cell cultures
141. Neurotoxic properties of the investigational local anesthetic adjuvant ephedrine
I. Haller1, L. Klimaschewski2, P. Gerner3, P. Lirk1 [email protected] 1Department of Anesthesiology, Innsbruck Medical University, Innsbruck, Austria, 2Division of Neuroscience, Innsbruck Medical University, Innsbruck, Austria, 3Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA
I. Haller1, L. Klimaschewski2, P. Gerner3, P. Lirk1 [email protected] 1Dept. of Anesthesiology, Innsbruck Medical University, Innsbruck, Austria, 2Division of Neuroanatomy, Innsbruck Medical University, Innsbruck, Austria, 3Dept. of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA
Background: Direct neurotoxicity of local anesthetics (LA) is a frequent problem, and may cause transient and even permanent neurologic complications, such as radicular irritation or cauda equina syndrome. Thus far, all investigations about LA neurotoxicity have been carried out in dissociated neuron cultures, immersing both soma and axon with local anesthetic. We used compartmented adult rat dorsal root ganglion neuron cultures, which facilitate selective incubation of axon, or soma, to determine whether local anesthetic-induced axonal neurotoxicity is a process that is confined to the neuron’s axon, or whether it involves the neuronal soma, as well.
Background: Because ephedrine may be a useful adjuvant to local anesthetics, we investigated its neurotoxicity in an adult rat dorsal root ganglion cell culture model.
Methods: Lidocaine (40 mM / ⬃1%) was added to the central and/or the peripheral compartment of three-chambered dishes. Additionally, we co-applied an inhibitor of the p38 Mitogen-Activated Protein Kinase (MAPK) to determine their effect both locally at the axon, and the neuron’s soma. Neuronal survival, axonal length and morphology were used as outcome measures. Results: Central incubation with lidocaine resulted in a reduction in soma number (from 100% to 60 ⫾ 8%), and axonal outgrowth length (from 100% to 43 ⫾ 10%). Incubation in the peripheral (axon) compartment caused severe axonal “dying-back” degeneration, decreasing maximal axonal distances to 53 ⫾ 6 %, without affecting survival of somata. During axonal incubation with lidocaine, peripheral application of p38 MAPK inhibitor significantly decreased neurotoxicity. Conclusion: We describe compartmental primary sensory neuron cultures as a potentially useful in vitro model to determine in detail mechanisms involved in local anesthetic-induced neurotoxicity. Incubation of somata or axons with lidocaine and/or MAPK inhibitor showed distinctly different responses concerning survival, and it appears that local anesthetic-induced axonal neurotoxicity mediated by activation of the p38 MAPK is a localized process.
Material and Methods: Primary sensory neuron cultures were employed to determine dose-dependency and potential selectivity of ephedrine neurotoxicity on specific neuron categories, grouped according to cell size, or phenotype (IB4- and CGRP-positive neurons). Moreover, we pharmacologically inhibited mitogen-activated protein kinases (MAPK), p38, p42/44 and c-jun N-terminal kinases, assessing neuron survival, and performed ELISAs to detect MAPK activation. Results: Ephedrine demonstrated neurotoxic effects on adult rat DRG neurons at concentrations of 0.1 % and higher, as shown by a significant reduction of neuron survival (P ⬍ 0.001). At a concentration of 0.25 % it caused LDH release and induced specific activation of p38 MAPK. Pharmacologic inhibition of MAPKs (p38, p42/44 and JNK), however, had no protective effect on neuron survival. Moreover, ephedrine predominantly affected small-sized (0-35 m) neurons, including both IB4- and CGRP-positive neurons, as compared to controls (P ⬍ 0.001). Conclusion: Ephedrine shows a significant potential for neurotoxicity, which has to be taken into consideration regarding its possible use as adjuvant for local anesthesia. Furthermore, it specifically activates p38 MAPK, similar to the conventional local anesthetic lidocaine, suggesting a common mechanism of toxicity. However, inhibition of MAPK did not alleviate neurotoxicity, suggesting that this pathway is not exclusively responsible for toxicity. Finally, ephedrine has a predominant neurotoxic effect upon small-sized neurons, most of which are involved in nociception. 1. Hung YC, Kau YC, Zizza AM et al. Ephedrine Blocks Rat Sciatic Nerve In Vivo and Sodium Channels In Vitro. Anesthesiology 2005; 103: 124652.