Comparison of Nitrogen Narcosis and Helium Pressure Effects on Striatal Amino Acids: A Microdialysis Study in Rats |
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Authors: | Nicolas Vallée Jean-Claude Rostain Alain Boussuges Jean-Jacques Risso |
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Institution: | (1) Faculté de Médecine Nord, IFR de Neurosciences Jean-Roche, Université de la Méditerranée et Institut de Médecine Navale du Service de Santé des Armées (IMNSSA), UMR – MD2, Physiologie et Physiopathologie en Conditions d’Oxygénation Extrêmes, 13916 Marseille cedex 20, France;(2) IMNSSA, BP 610, 83800 Toulon Armees, France |
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Abstract: | Exposure to nitrogen–oxygen mixture at high pressure induces narcosis, which can be considered as a first step toward general
anaesthesia. Narcotic potencies of inert gases are attributed to their lipid solubility. Nitrogen narcosis induces cognitive
and motor disturbances that occur from 0.3 MPa in man and from 1 MPa in rats. Neurochemical studies performed in rats up to
3 MPa have shown that nitrogen pressure decreases striatal dopamine release like argon, another inert gas, or nitrous oxide,
an anaesthetic gas. Striatal dopamine release is under glutamatergic and other amino acid neurotransmission regulations. The
aim of this work was to study the effects of nitrogen at 3 MPa on striatal amino acid levels and to compare to those of 3 MPa
of helium which is not narcotic at this pressure, by using a new technique of microdialysis samples extraction under hyperbaric
conditions, in freely moving rats. Amino acids were analysed by HPLC coupled to fluorimetric detection in order to appreciate
glutamate, aspartate, glutamine and asparagine levels. Nitrogen–oxygen mixture exposure at 3 MPa decreased glutamate, glutamine
and asparagine concentrations. In contrast, with helium–oxygen mixture, glutamate and aspartate levels were increased during
the compression phase but not during the stay at maximal pressure. Comparison between nitrogen and helium highlighted the
narcotic effects of nitrogen at pressure. As a matter of fact, nitrogen induces a reduction in glutamate and in other amino
acids that could partly explain the decrease in striatal dopamine level as well as the motor and cognitive disturbances reported
in nitrogen narcosis. |
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Keywords: | Basal ganglia Glutamate Aspartate Dopamine Neurotransmitters Narcosis Inert gases Anaesthesia |
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