The document discusses the relationship between mitochondrial dysfunction and Parkinson's disease (PD). It summarizes that neurotoxins like MPTP can induce PD by decreasing the activity of mitochondrial Complex I, which is involved in cellular respiration. This reduction in Complex I activity leads to increased oxidative stress and apoptosis of dopaminergic neurons. While certain genetic polymorphisms and calcium accumulation may also contribute to mitochondrial dysfunction, neurotoxins appear to be a primary factor in reducing Complex I activity and inducing PD.