Platelet activating factor (PAF) has been suggested to play a critical role in the pathogenesis of neurological disorders. We assessed the effect of PAF against the toxicity of 1-methyl-4-phenylpyridinium (MPP(+)), a parkinsonian toxin, in relation to apoptotic process. PAF exhibited differential effect against the MPP(+) toxicity in differentiated PC12 cells depending on concentration. Treatment with 0.75 microM PAF significantly attenuated the MPP(+)-induced increase in Bax levels, decrease in Bid and Bcl-2 levels, and mitochondrial membrane potential loss that lead to the release of cytochrome c and subsequent caspase-3 activation. The inhibitory effect of PAF was not associated with nuclear factor-kappaB activation. In contrast, PAF at the concentrations greater than 2.5 microM exhibited a toxicity and additive effect on the MPP(+) toxicity. The results show that PAF at low concentrations, which does not induce a significant toxicity, may prevent the MPP(+) toxicity by suppressing the apoptosis-related protein activation and mitochondrial membrane permeability change that lead to the cytochrome c release and caspase-3 activation. The preventive effect seems to be associated with the inhibitory effect on the formation of reactive oxygen species and depletion of GSH. In contrast, PAF at higher concentrations may exhibit an additive toxic effect against the MPP(+) toxicity by increasing apoptosis-related protein activation.