It is a monoaminergic neurotoxin that acts by interfering with oxidative phosphorylation in mitochondria by inhibiting complex I, leading to the depletion of ATP and eventual cell death.

MPTP is converted in the brain into MPP+ by the enzyme MAO-B, ultimately causing parkinsonism in primates by killing certain dopamine-producing neurons in the substantia nigra.

[3] Though no longer in use as an herbicide, cyperquat's closely related structural analog paraquat still finds widespread usage, raising some safety concerns.

[5] This paper followed a string of poisonings that took place in San Jose, California in 1982 in which users of an illicitly synthesized analog of meperidine were presenting to hospital emergency rooms with symptoms of Parkinson's.

[9] MPP+ exhibits its toxicity mainly by promoting the formation of reactive free radicals in the mitochondria of dopaminergic neurons in the substantia nigra.

[1][9][10] MPP+ also displays toxicity by inhibiting the synthesis of catecholamines, reducing levels of dopamine and cardiac norepinephrine, and inactivating tyrosine hydroxylase.

MPP+ injected as an aqueous solution into the bloodstream causes no symptoms of Parkinsonism in test subjects, since the highly charged molecule is unable to diffuse through the blood-brain barrier.

[11] Studies in rats and mice show that various compounds, including nobiletin, a flavonoid found in citrus, can rescue dopaminergic neurons from degeneration caused by treatment with MPP+.

[12] MPP+, sold as the chloride salt under the brand name cyperquat, was used briefly in the 1970s as an herbicide to protect crops against nutsedge, a member of the cyperus genus of plants.

[3] MPP+ as a salt has much lower acute toxicity than its precursor MPTP due to the inability of the former to pass through the blood-brain barrier and ultimately access the only cells that will permit its uptake, the dopaminergic neurons.

[14] MPP+ encountered in the salt form is far less toxic by ingestion, inhalation, and skin exposure than its biological precursor MPTP, due to the inability of MPP+ to cross the blood-brain barrier and freely diffuse across cellular membranes.