We examined the acute toxicity of dieldrin, a possible environmental risk factor of Parkinson's disease, in a dopaminergic cell model, PC12 cells, to determine early cellular events underlying the pesticide-induced degenerative processes. EC(50) for 1 h dieldrin exposure was 143 microM for PC12 cells, whereas EC(50) for non-dopaminergic cells was 292-351 microM, indicating that dieldrin is more toxic to dopaminergic cells. Dieldrin also induced rapid, dose-dependent releases of dopamine and its metabolite, DOPAC, resulting in depletion of intracellular dopamine. Additionally, dieldrin exposure caused depolarization of mitochondrial membrane potential in a dose-dependent manner. Flow cytometric analysis showed generation of reactive oxygen species (ROS) within 5 min of dieldrin treatment, and significant increases in lipid peroxidation were also detected following 1 h exposure. ROS generation was remarkably inhibited in the presence of SOD. Dieldrin-induced apoptosis was significantly attenuated by both SOD and MnTBAP (SOD mimetic), suggesting that dieldrin-induced superoxide radicals serve as important signals in initiation of apoptosis. Furthermore, pretreatment with deprenyl (MAO-inhibitor) or alpha-methyl-L-p-tyrosine (TH-inhibitor) also suppressed dieldrin-induced ROS generation and DNA fragmentation. Taken together, these results suggest that rapid release of dopamine and generation of ROS are early cellular events that may account for dieldrin-induced apoptotic cell death in dopaminergic cells.