Effect of nitrogen narcosis on extracellular levels of dopamine and its metabolites in the rat striatum, using intracerebral microdialysis.

In man, nitrogen narcosis is characterized by euphoria, impaired cognitive function, neuromuscular incoordination and, ultimately, loss of consciousness. Because of the motor movement disorders, we chose to study the nigrostriatal system, whose major function is to regulate the extrapyramidal nervous system. The purpose of this investigation was to monitor changes in extracellular levels of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the striatum of conscious rats, using intracerebral microdialysis. Results show a 40% decrease in extracellular DA concentration, a 59% increase in extracellular DOPAC and an increase in HVA starting with exposure to the nitrogen mixture. Thirty minutes after the beginning of the exposure, a compensation phase took place. HVA returns to its initial basal value, and levels of DOPAC and DA returned towards normal but never reached their initial values. These results contrast with those observed during the High Pressure Neurological Syndrome (HPNS, 5.1 MPa of helium pressure) in which there is a significant increase in extracellular DA. Therefore, some of the symptoms of nitrogen narcosis may be linked with the decrease in the extracellular DA levels.