The compound 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces an irreversible neurological syndrome in man and monkey which is similar to idiopathic Parkinson's disease in its clinical, pathological, neurochemical and pharmacological response properties. MPTP is selectively neurotoxic to the dopaminergic regions of the brain, destroying neurones in the substantia nigra (A8 and A9 cells, nigrostriatal system) but not the ventral tegmental area (A10 cells, mesolimbic system). Selective dopamine depletion and nigral cell loss after MPTP treatment has also been reported recently in the mouse. The mechanism by which a peripherally administered, low-molecular weight compound exerts permanent but selective toxic effects on dopamine systems in the brain may be relevant to parkinsonian syndromes induced by other toxins and to the disease process in idiopathic Parkinson's disease. We report here that MPTP is oxidized in the brain to a pyridinium species (a compound with potent herbicidal activity) and, in the monkey, is trapped intraneuronally. Furthermore, we demonstrate that this enzymatic oxidation is blocked in vivo in the mouse by a monoamine oxidase inhibitor, a condition which also blocks the neurotoxicity, indicating that the oxidative metabolism of MPTP is required for its neurotoxic effect.

BackgroundFrom January 2002 to May 2004, 28 puffer fish poisoning (PFP) cases in Florida, New Jersey, Virginia, and New York were linked to the Indian River Lagoon (IRL) in Florida. Saxitoxins (STXs) of unknown source were first identified in fillet remnants from a New Jersey PFP case in 2002.MethodsWe used the standard mouse bioassay (MBA), receptor binding assay (RBA), mouse neuroblastoma cytotoxicity assay (MNCA), Ridascreen ELISA, MIST Alert assay, HPLC, and liquid chromatography-mass spectrometry (LC-MS) to determine the presence of STX, decarbamoyl STX (dc-STX), and N-sulfocarbamoyl (B1) toxin in puffer fish tissues, clonal cultures, and natural bloom samples of Pyrodinium bahamense from the IRL.ResultsWe found STXs in 516 IRL southern (Sphoeroides nephelus), checkered (Sphoeroides testudineus), and bandtail (Sphoeroides spengleri) puffer fish. During 36 months of monitoring, we detected STXs in skin, muscle, and viscera, with concentrations up to 22,104 μg STX equivalents (eq)/100 g tissue (action level, 80 μg STX eq/100 g tissue) in ovaries. Puffer fish tissues, clonal cultures, and natural bloom samples of P. bahamense from the IRL tested toxic in the MBA, RBA, MNCA, Ridascreen ELISA, and MIST Alert assay and positive for STX, dc-STX, and B1 toxin by HPLC and LC-MS. Skin mucus of IRL southern puffer fish captive for 1-year was highly toxic compared to Florida Gulf coast puffer fish. Therefore, we confirm puffer fish to be a hazardous reservoir of STXs in Florida’s marine waters and implicate the dinoflagellate P. bahamense as the putative toxin source.ConclusionsAssociated with fatal paralytic shellfish poisoning (PSP) in the Pacific but not known to be toxic in the western Atlantic, P. bahamense is an emerging public health threat. We propose characterizing this food poisoning syndrome as saxitoxin puffer fish poisoning (SPFP) to distinguish it from PFP, which is traditionally associated with tetrodotoxin, and from PSP caused by STXs in shellfish.

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Unilateral intranigral administration of the oxidative metabolites of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 1-methyl-4-phenyl-dihydropyridine (MPDP+) or 1-methyl-4-phenylpyridine (MPP+) produced dose-dependently a depletion of dopamine in the ipsilateral striatum of rats two weeks following treatment. d-Amphetamine and apomorphine induced circling toward the lesioned side in these unilaterally treated animals. No contralateral circling behavior was observed after challenging with apomorphine. This dopamine lesioning effect of MPP+ was not blocked by pretreatment of animals with a dopamine uptake blocker, GBR 12909. Furthermore, MPP+ increased the 45Ca accumulation into cells at the site of injection and produced "nonspecific" cell membrane and/or cytotoxic damage seen by histological procedures. These results indicate that MPDP+ and MPP+ produced localized cytotoxic damage to nigrostriatal neurons, caused a decrease in striatal dopamine, and disrupted the nigrostriatal system's functioning following intranigral administration to rats. It is postulated that the cationic surfactant properties of MPDP+ and MPP+ might contribute to its neurotoxic effects.

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