MPP+ exhibits its toxicity mainly by promoting the formation of reactive free radicals in the mitochondria of dopaminergic neurons in the substantia nigra.[1][10] MPP+ can siphon electrons from the mitochondrial electron transport chain at complex I and be reduced, in the process forming radical reactive oxygen species which go on to cause further, generalized cellular damage.[9][10] In addition, the overall inhibition of the electron transport chain eventually leads to stunted ATP production and eventual death of the dopaminergic neurons, which ultimately displays itself clinically as symptoms of Parkinson's disease.[3][9][10]