Effect of an hyperbaric nitrogen narcotic ambience on arginine and citrulline levels, the precursor and co-product of nitric oxide, in rat striatum

Considering motor and locomotor dysfunctions occurring under the effect of nitrogen narcosis [1], also known as diver's staggers, previous studies conducted at the end of the 1990s logically focused on the dopaminergic transmission in the rat striatum. A decrease in striatal dopamine levels was highlighted [1,2]. And yet, the control of motor and locomotor activity by the striatum requires dopaminergic as much as glutamate receptors. Hence, the logical follow-on from the earlier work was to extend the research to this other main neurotransmitter-glutamate-and its regulatory pathways, particularly as Abraini [3] had early suggested that inert gases under pressure may act on protein receptors such as the NMDA (N-methyl D-Aspartate) Receptor, a glutamate receptor. Hence our investigation described a decrease in striatal glutamate levels in rats subjected to nitrogen under pressure [4]. The logical consequence was to test proximal and distal stimulation of the striatal glutamate release (Figure 1), but no improvement was observed in relation to rat behavioural disorders. In fact, neither the intrastriatal NMDA infusion nor the KCl-mPFC (motor Prefrontal Cortex area) stimulation was effective in rectifying the nitrogen-induced glutamate reduction in the striatum [5,6]. Nevertheless, we demonstrated that the NMDA-receptor remains functional in the striatum, like in the substantia nigra [7,8], under the effect of nitrogen narcosis, as it increases extracellular dopamine levels. Even so, the increased effect on glutamate release noted under atmospheric pressure disappeared under pressurized nitrogen. We suspected a disturbance close to the plasma membrane on the intracellular side, behind the NMDA-receptor and we decided to focus on Nitric Oxide (NO). In fact, nitrogen under pressure has even been suggested by Vjotosh et al. in 1999 [9] to affect nitric oxide (NO) synthesis. We are the first to describe NO development under nitrogen narcosis.Actually, the retrograde action