title: How can an inert gas counterbalance a NMDA-induced glutamate release?
abstract: Previous neurochemical studies performed in rats have revealed a decrease of striatal dopamine and glutamate induced by inert gas narcosis. We sought to establish the hypothetical role of glutamate and its main receptor, the N-methyl-d-aspartate (NMDA) receptor, in this syndrome. We aimed to counteract the nitrogen narcosis-induced glutamate and dopamine decreases by stimulating the NMDA receptor in the striatum. We used bilateral retrodialysis on awake rats, submitted to nitrogen under pressure (3 MPa). Continuous infusion of 2 mM of NMDA under normobaric conditions (0.01 MPa) (n = 8) significantly increased extracellular average levels of glutamate, aspartate, glutamine, and asparagine by 241.8%, 292.5%, 108.3%, and 195.3%, respectively. The same infusion conducted under nitrogen at 3 MPa (n = 6) revealed significant lower levels of these amino acids (n = 8/6, P > 0.001). In opposition, the NMDA-induced effects on dopamine, dihydrophenylacetic acid (DOPAC), and homovanillic acid (HVA) levels were statistically not affected by the nitrogen at 3 MPa exposure (n = 8/6, P > 0.05). Dopamine was increased by >240% on average. HVA was decreased (down to 40%), and there was no change in DOPAC levels, in both conditions. Results highlight that the NMDA receptor is not directly affected by nitrogen under pressure as indicated by the elevation in NMDA-induced dopamine release under hyperbaric nitrogen. On the other hand, the NMDA-evoked glutamate increase is counteracted by nitrogen narcosis. No improvement in motor and locomotor disturbances was observed with high striatal concentration in dopamine. Further experiments have to be done to specify why the striatal glutamate pathways, in association with the inhibition of its metabolism, only are affected by nitrogen narcosis in this study.
authors.affiliation: Department of Marine and Underwater Research, UMR-MD2, Institut de Médecine Navale du Service de Santé des Armées, IRBA Toulon, Toulon Cedex 9, France. n.vallee@imnssa.net
authors.forename: Nicolas
authors.initials: N
authors.lastname: Vallee
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Rostain
authors.forename: Jean-Jacques
authors.initials: JJ
authors.lastname: Risso
mesh_terms: D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism; D000818:Animals; D001216:Asparagine / Q000378:metabolism; D001224:Aspartic Acid / Q000378:metabolism; D002408:Catheters, Indwelling; D002851:Chromatography, High Pressure Liquid; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism*; D004298:Dopamine / Q000378:metabolism; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism*; D005973:Glutamine / Q000378:metabolism; D006719:Homovanillic Acid / Q000378:metabolism; D007222:Inert Gas Narcosis / Q000378:metabolism*; D008297:Male; D017551:Microdialysis; D016202:N-Methylaspartate / Q000494:pharmacology*; D009584:Nitrogen / Q000008:administration & dosage*; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D018709:Statistics, Nonparametric
chemical_list: D018690:Excitatory Amino Acid Agonists; D016194:Receptors, N-Methyl-D-Aspartate; D005973:Glutamine; D015102:3,4-Dihydroxyphenylacetic Acid; D001224:Aspartic Acid; D018698:Glutamic Acid; D016202:N-Methylaspartate; D001216:Asparagine; D009584:Nitrogen; D004298:Dopamine; D006719:Homovanillic Acid