Alterations in nigral NMDA and GABAA receptor control of the striatal dopamine level after repetitive exposures to nitrogen narcosis.
Nitrogen pressure exposure in rats results in decreased dopamine (DA) release at the striatal terminals of the substantia nigra pars compacta (SNc) dopaminergic neurons, demonstrating the narcotic potency of nitrogen. This effect is attributed to decreased excitatory and increased inhibitory inputs to dopaminergic neurons, involving a change in NMDA and GABA(A) receptor function. We investigated whether repetitive exposures to nitrogen modify the excitatory and inhibitory control of the dopaminergic nigro-striatal pathway. We used voltammetry to measure dopamine levels in freely-moving rats, implanted with dopamine-sensitive electrodes in the striatum. NMDA/GABA(A) receptor agonists (NMDA/muscimol) and antagonists (AP7/gabazine) were administered through a guide-cannula into the SNc, and their effects on striatal dopamine levels were measured under normobaric conditions, before and after five repetitive exposures to 1 MPa nitrogen. NMDA-mediated dopamine release was greater following repetitive exposures, AP7-mediated inhibition of glutamatergic input was blocked, suggesting that NMDA receptor sensitivity was increased and glutamate release reduced. Muscimol did not modify dopamine levels following repetitive exposures, whereas the effect of gabazine was greater after exposures than before. This suggested that interneuronal GABA(A) receptors were desensitized, leading to an increased GABAergic input at dopaminergic cells. Thus, repetitive nitrogen exposure induced persistent changes in glutamatergic and GABAergic control of dopaminergic neurons, resulting in decreased activity of the nigrostriatal pathway.
Lavoute
Cécile
C
Université de la Méditerranée et Institut de Médecine Navale du Service de Santé des Armées, UPRES EA 3280, Physiopathologie et Action Thérapeutique des Gaz Sous Pression, IFR Jean-Roche, Faculté de Médecine Nord, 13015 Marseille, France.
Weiss
Michel
M
Rostain
Jean-Claude
JC
D000399:Air Pressure; D000818:Animals; D001273:Atmosphere Exposure Chambers; D001480:Basal Ganglia Diseases / Q000209:etiology / Q000378:metabolism / Q000503:physiopathology; D003342:Corpus Striatum / Q000378:metabolism* / Q000503:physiopathology; D004195:Disease Models, Animal; D004298:Dopamine / Q000378:metabolism*; D004334:Drug Administration Schedule; D018755:GABA Agonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D058785:GABA-A Receptor Agonists; D058787:GABA-A Receptor Antagonists; D018698:Glutamic Acid / Q000378:metabolism; D007222:Inert Gas Narcosis / Q000150:complications / Q000378:metabolism* / Q000503:physiopathology; D008297:Male; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism / Q000633:toxicity; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000378:metabolism*; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D013378:Substantia Nigra / Q000378:metabolism* / Q000503:physiopathology; D013569:Synapses / Q000187:drug effects / Q000378:metabolism; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D018755:GABA Agonists; D018756:GABA Antagonists; D058785:GABA-A Receptor Agonists; D058787:GABA-A Receptor Antagonists; D011963:Receptors, GABA-A; D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D009584:Nitrogen; D004298:Dopamine