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The efficacy of physiological and pharmacological N-methyl-D-aspartate receptor block is greatly reduced under hyperbaric conditions.

Abstract
Human divers exposed to hyperbaric pressure may suffer from cognitive and motor impairments thought to be related to high pressure effects per ce. These effects, termed high pressure neurological syndrome (HPNS), appear at pressure above 1.1 MPa. HPNS involves CNS hyperexcitability that is partially attributed to augmented responses of the glutamatergic N-methyl-d-aspartate receptor (NMDAR). NMDAR is blocked by Mg(2+) (physiologically) and by dl-2-Amino-5-phosphonopentanoic acid (AP5, pharmacologically). We have recently reported that hyperbaric pressure augments rat hippocampus NMDAR synaptic response and generates hyperexcitability. We now test pressure effects on the blockade efficacy of Mg(2+)and AP5. Under high pressure conditions more than double [Mg(2+)](o) and [AP5](o) were needed to achieve similar effects on NMDAR synaptic response's amplitude, decay time, and time integral comparable to control conditions. [Mg(2+)](o) and [AP5](o) concentration-response curves and the concentration for 50% responses' inhibition (IC(50)s) showed similar normalized pattern at control and pressure for each parameter. We conclude that hyperbaric pressure reduces the efficacy of these NMDAR blockers that may be associated with the receptor conformational change(s). This provides additional mechanism for pressure over activation of NMDAR. Taken together with our previous reports, high pressure modification of NMDAR activity significantly contributes to CNS hyperexcitability and possibly for long term vulnerability.
AuthorsA Mor, Y Grossman
JournalNeuroscience (Neuroscience) Vol. 169 Issue 1 Pg. 1-7 (Aug 11 2010) ISSN: 1873-7544 [Electronic] United States
PMID20457226 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
CopyrightCopyright (c) 2010 IBRO. Published by Elsevier Ltd. All rights reserved.
Chemical References
  • Excitatory Amino Acid Antagonists
  • Receptors, N-Methyl-D-Aspartate
  • 2-amino-5-phosphono-3-pentenoic acid
  • 2-Amino-5-phosphonovalerate
  • Magnesium
Topics
  • 2-Amino-5-phosphonovalerate (analogs & derivatives, pharmacology)
  • Animals
  • Atmosphere Exposure Chambers
  • Dose-Response Relationship, Drug
  • Excitatory Amino Acid Antagonists (pharmacology)
  • Excitatory Postsynaptic Potentials (drug effects)
  • High Pressure Neurological Syndrome (physiopathology)
  • Hippocampus (metabolism)
  • In Vitro Techniques
  • Magnesium (pharmacology)
  • Pressure
  • Pyramidal Cells (drug effects, physiology)
  • Rats
  • Receptors, N-Methyl-D-Aspartate (antagonists & inhibitors, chemistry)
  • Synaptic Transmission (drug effects, physiology)

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