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 in vestigated the production of the hydroxyl free radical (OH.) in the substan tia nigra (SN) and the striatum (CS) several moments after intranigral inje ction of the neurotoxin, with or without an added episode of hypoxia (30 mi n, 95% N-2, 5% O-2). We utilized the hydroxylation of salicylate to 2,3 dih ydroxybenzoic acid (2,3 DHBA) as indication of OH. production. When 2.3 DHB A levels were not modified, the levels of 2,5 DHBA were taken as an indicat ion 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 afte r 120 min and was high up to 24 h. An episode of hypoxia (60 min after 6-OH DA injection) significantly worsened the decrease of dopamine (DA) in the s triatum assessed 8 days after injection of 6-OHDA in the SN. Hypoxia perfor med 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 al one, 2,3 DHBA increased significantly 120 min after the injection, when the hypoxia-reoxygenation was added to the 6-OHDA treatment. Our data are show ing a relationship between the increase in OH. production and a concomitant worsening of neuronal degeneration. As a whole, the results support the id ea that neurons undergoing 6-OHDA neurotoxicity have their antioxidant defe nces affected and that oxidative stress is actually an important eliciting factor in 6-OHDA dependant neurodegeneration. However, OH. may not be the m ain radical species involved in this process. Additionally, 6-OHDA also app eared to provoke a long-term increase in CYP 450 activity. (C) 1998 Elsevie r Science B.V. All rights reserved.