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Enflurane directly depresses glutamate AMPA and NMDA currents in mouse spinal cord motor neurons independent of actions on GABAA or glycine receptors.
Anesthesiology. 2000 Oct; 93(4):1075-84.A

Abstract

BACKGROUND

The spinal cord is an important anatomic site at which volatile agents act to prevent movement in response to a noxious stimulus. This study was designed to test the hypothesis that enflurane acts directly on motor neurons to inhibit excitatory synaptic transmission at glutamate receptors.

METHODS

Whole-cell recordings were made in visually identified motor neurons in spinal cord slices from 1- to 4-day-old mice. Excitatory postsynaptic currents (EPSCs) or potentials (EPSPs) were evoked by electrical stimulation of the dorsal root entry area or dorsal horn. The EPSCs were isolated pharmacologically into glutamate N-methyl-d-aspartate (NMDA) receptor- and non-NMDA receptor-mediated components by using selective antagonists. Currents also were evoked by brief pulse pressure ejection of glutamate under various conditions of pharmacologic blockade. Enflurane was made up as a saturated stock solution and diluted in the superfusate; concentrations were measured using gas chromatography.

RESULTS

Excitatory postsynaptic currents and EPSPs recorded from motor neurons by stimulation in the dorsal horn were mediated by glutamate receptors of both non-NMDA and NMDA subtypes. Enflurane at a general anesthetic concentration (one minimum alveolar anesthetic concentration) reversibly depressed EPSCs and EPSPs. Enflurane also depressed glutamate-evoked currents in the presence of tetrodotoxin (300 nm), showing that its actions are postsynaptic. Block of inhibitory gamma-aminobutyric acid A and glycine receptors by bicuculline (20 micrometer) or strychnine (2 micrometer) or both did not significantly reduce the effects of enflurane on glutamate-evoked currents. Enflurane also depressed glutamate-evoked currents if the inhibitory receptors were blocked and if either D,L-2-amino-5-phosphonopentanoic acid (50 micrometer) or 6-cyano-7-nitroquinoxaline-2,3-dione disodium (10 micrometer) was applied to block NMDA or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-kainate receptors respectively.

CONCLUSIONS

Enflurane exerts direct depressant effects on both alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and NMDA glutamate currents in motor neurons. Enhancement of gamma-aminobutyric acid A and glycine inhibition is not needed for this effect. Direct depression of glutamatergic excitatory transmission by a postsynaptic action on motor neurons thus may contribute to general anesthesia as defined by immobility in response to a noxious stimulus.

Authors+Show Affiliations

Department of Anesthesia, Stanford University School of Medicine, Stanford, California, USA.No affiliation info available

Pub Type(s)

Journal Article
Research Support, U.S. Gov't, P.H.S.

Language

eng

PubMed ID

11020764

Citation

Cheng, G, and J J. Kendig. "Enflurane Directly Depresses Glutamate AMPA and NMDA Currents in Mouse Spinal Cord Motor Neurons Independent of Actions On GABAA or Glycine Receptors." Anesthesiology, vol. 93, no. 4, 2000, pp. 1075-84.
Cheng G, Kendig JJ. Enflurane directly depresses glutamate AMPA and NMDA currents in mouse spinal cord motor neurons independent of actions on GABAA or glycine receptors. Anesthesiology. 2000;93(4):1075-84.
Cheng, G., & Kendig, J. J. (2000). Enflurane directly depresses glutamate AMPA and NMDA currents in mouse spinal cord motor neurons independent of actions on GABAA or glycine receptors. Anesthesiology, 93(4), 1075-84.
Cheng G, Kendig JJ. Enflurane Directly Depresses Glutamate AMPA and NMDA Currents in Mouse Spinal Cord Motor Neurons Independent of Actions On GABAA or Glycine Receptors. Anesthesiology. 2000;93(4):1075-84. PubMed PMID: 11020764.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Enflurane directly depresses glutamate AMPA and NMDA currents in mouse spinal cord motor neurons independent of actions on GABAA or glycine receptors. AU - Cheng,G, AU - Kendig,J J, PY - 2000/10/6/pubmed PY - 2001/2/28/medline PY - 2000/10/6/entrez SP - 1075 EP - 84 JF - Anesthesiology JO - Anesthesiology VL - 93 IS - 4 N2 - BACKGROUND: The spinal cord is an important anatomic site at which volatile agents act to prevent movement in response to a noxious stimulus. This study was designed to test the hypothesis that enflurane acts directly on motor neurons to inhibit excitatory synaptic transmission at glutamate receptors. METHODS: Whole-cell recordings were made in visually identified motor neurons in spinal cord slices from 1- to 4-day-old mice. Excitatory postsynaptic currents (EPSCs) or potentials (EPSPs) were evoked by electrical stimulation of the dorsal root entry area or dorsal horn. The EPSCs were isolated pharmacologically into glutamate N-methyl-d-aspartate (NMDA) receptor- and non-NMDA receptor-mediated components by using selective antagonists. Currents also were evoked by brief pulse pressure ejection of glutamate under various conditions of pharmacologic blockade. Enflurane was made up as a saturated stock solution and diluted in the superfusate; concentrations were measured using gas chromatography. RESULTS: Excitatory postsynaptic currents and EPSPs recorded from motor neurons by stimulation in the dorsal horn were mediated by glutamate receptors of both non-NMDA and NMDA subtypes. Enflurane at a general anesthetic concentration (one minimum alveolar anesthetic concentration) reversibly depressed EPSCs and EPSPs. Enflurane also depressed glutamate-evoked currents in the presence of tetrodotoxin (300 nm), showing that its actions are postsynaptic. Block of inhibitory gamma-aminobutyric acid A and glycine receptors by bicuculline (20 micrometer) or strychnine (2 micrometer) or both did not significantly reduce the effects of enflurane on glutamate-evoked currents. Enflurane also depressed glutamate-evoked currents if the inhibitory receptors were blocked and if either D,L-2-amino-5-phosphonopentanoic acid (50 micrometer) or 6-cyano-7-nitroquinoxaline-2,3-dione disodium (10 micrometer) was applied to block NMDA or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-kainate receptors respectively. CONCLUSIONS: Enflurane exerts direct depressant effects on both alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and NMDA glutamate currents in motor neurons. Enhancement of gamma-aminobutyric acid A and glycine inhibition is not needed for this effect. Direct depression of glutamatergic excitatory transmission by a postsynaptic action on motor neurons thus may contribute to general anesthesia as defined by immobility in response to a noxious stimulus. SN - 0003-3022 UR - https://www.unboundmedicine.com/medline/citation/11020764/Enflurane_directly_depresses_glutamate_AMPA_and_NMDA_currents_in_mouse_spinal_cord_motor_neurons_independent_of_actions_on_GABAA_or_glycine_receptors_ L2 - https://pubs.asahq.org/anesthesiology/article-lookup/doi/10.1097/00000542-200010000-00032 DB - PRIME DP - Unbound Medicine ER -