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The purpose of this study was to investigate the change in the striatal dopamine (DA) level in freely-moving rat exposed to different partial pressure of oxygen (from 1 to 5 ATA). Some works have suggested that DA release by the substantia nigra pars compacta (SNc) neurons in the striatum could be disturbed by hyperbaric oxygen (HBO) exposure, altering therefore the basal ganglia activity. Such changes could result in a change in glutamatergic and GABAergic control of the dopaminergic neurons into the SNc. Such alterations could provide more information about the oxygen-induced seizures observed at 5 ATA in rat. DA-sensitive electrodes were implanted into the striatum under general anesthesia. After 1 week rest, awaked rats were exposed to oxygen-nitrogen mixture at a partial pressure of oxygen of 1, 2, 3, 4 and 5 ATA. DA level was monitored continuously (every 3 min) by in vivo voltammetry before and during HBO exposure. HBO induced a decrease in DA level in relationship to the increase in partial pressure of oxygen from 1 ATA to 4 ATA (-15 % at 1 ATA, -30 % at 2 ATA, -40 % at 3 ATA, -45 % at 4 ATA), without signs of oxygen toxicity. At 5 ATA, DA level strongly decreases (-75 %) before seizure which occurred after 27 min ± 7 HBO exposure. After the epileptic seizure the decrease in DA level disappeared. These changes and the biphasic effect of HBO were discussed in function of HBO action on neurochemical regulations of the nigro striatal pathway.

In rats, a single exposure to 3 MPa nitrogen induces change in motor processes, a sedative action and a decrease in dopamine release in the striatum. These changes due to a narcotic effect of nitrogen have been attributed to a decrease in glutamatergic control and the facilitation of GABAergic neurotransmission involving NMDA and GABA(A) receptors, respectively. After repeated exposure to nitrogen narcosis, a second exposure to 3 MPa increased dopamine levels suggesting a change in the control of the dopaminergic pathway. We investigated the role of the nigral NMDA and GABA(A) receptors in changes in the striatal dopamine levels. Dopamine-sensitive electrodes were implanted into the striatum under general anesthesia, together with a guide-cannula for drug injections into the SNc. Dopamine level was monitored by in vivo voltammetry. The effects of NMDA/GABA(A) receptor agonists (NMDA/muscimol) and antagonists (AP7/gabazine) on dopamine levels were investigated. Rats were exposed to 3 MPa nitrogen before and after five daily exposures to 1 MPa. After these exposures to nitrogen narcosis, gabazine, NMDA and AP7 had no effect on the nitrogen-induced increase in dopamine levels. By contrast, muscimol strongly enhanced the increase in dopamine level induced by nitrogen. Our findings suggest that repeated nitrogen exposure disrupted NMDA receptor function and decreased GABAergic input by modifying GABA(A) receptor sensitivity. These findings demonstrated a change in the mechanism of action of nitrogen at pressure.