Interestingly, the MPTP neurotoxin is often presented as being “selective of DA neurons.” Hence, few studies have investigated either the DA loss outside the nigrostriatal system or the loss of other neurotransmitters. Pifl and collaborators executed an insightful study (Pifl et al. 1991) in which they measured the tissue concentration of the monoamines DA, noradrenaline and serotonin in 45 brain regions in macaques monkeys chronically intoxicated with systemic MPTP over few weeks. None of the three major brain monoamine neuron systems was completely resistant to the neurotoxin. In addition, each brain monoamine had a characteristic regional pattern of MPTP-induced changes. The most significant alterations were found within the nigrostriatal dopamine system, i.e., profound DA loss in caudate nucleus, putamen and SNc.