Hydroxyl radical production in the substantia nigra after 6-hydroxydopamine and hypoxia-reoxygenation.

To study the involvement of oxidative stress in 6-OHDA neurotoxicity, we investigated the production of the hydroxyl free radical (OH.) in the substantia nigra (SN) and the striatum (CS) several moments after intranigral injection of the neurotoxin, with or without an added episode of hypoxia (30 min, 95% N2, 5% O2). We utilized the hydroxylation of salicylate to 2,3 dihydroxybenzoic acid (2,3 DHBA) as indication of OH. production. When 2.3 DHBA levels were not modified, the levels of 2,5 DHBA were taken as an indication of cytochrome P450 (CYP 450) metabolism. 6-OHDA alone did not increase the production of 2,3 DHBA in the SN. 2,5 DHBA increased significantly after 120 min and was high up to 24 h. An episode of hypoxia (60 min after 6-OHDA injection) significantly worsened the decrease of dopamine (DA) in the striatum assessed 8 days after injection of 6-OHDA in the SN. Hypoxia performed 60 min and 24 h before or 24 h after 6-OHDA did not show any additional effect on striatal DA levels. Contrary to results obtained after 6-OHDA alone, 2,3 DHBA increased significantly 120 min after the injection, when the hypoxia-reoxygenation was added to the 6-OHDA treatment. Our data are showing a relationship between the increase in OH. production and a concomitant worsening of neuronal degeneration. As a whole, the results support the idea that neurons undergoing 6-OHDA neurotoxicity have their antioxidant defences affected and that oxidative stress is actually an important eliciting factor in 6-OHDA dependant neurodegeneration. However, OH. may not be the main radical species involved in this process. Additionally, 6-OHDA also appeared to provoke a long-term increase in CYP 450 activity.