Effects of pergolide treatment on in vivo hydroxyl free radical formation during infusion of 6-hydroxydopamine in rat striatum

This study focused on the early neurochemical events involved in 6-hydroxydopamine (6-OHDA) neurotoxicity and the putative neuroprotective effects of pergolide. 6-OHDA in 0.1% ascorbic acid/saline was delivered into rat striatum by means of microdialysis and 2,3-dihydroxybenzoic acid (2,3-DHBA) was measured as an index of hydroxyl free radical formation using salicylate trapping. Infusion of 6-OHDA (2–20 mM) via the dialysis probe for 15 min was associated with an immediate and striking increase in the extracellular levels of 2,3-DHBA and dopamine, and this effect was dose-dependent. An infusion of 10 mM 6-OHDA, equivalent to a direct injection of 4 μg free base, resulted in dopamine overflow with a maximum approx. 200-fold above the baseline. This massive overflow of toxic amounts of dopamine, much greater than expected of reuptake inhibition, seems to be the earliest response of nigrostriatal neurones to 6-OHDA. In rats treated with pergolide mesylate (7 days 0.5 mg/kg/day, i.p.), the average amount of 2,3-DHBA associated with 6-OHDA striatal infusion was significantly smaller than that in controls. This suggests that pergolide treatment leads to an increased ability of striatal tissue to quench hydroxyl radical formation in vivo.