ABSTRACT
Administration of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) to adult (2-month to 4-month-old) male C57BL/6 mice (MPTP-sensitive) is a valuable Parkinson's disease model. At comparable age, other strains, such as BALB/c, are minimally affected by MPTP (MPTP-resistant). However, the maintenance of resistance to MPTP throughout aging in MPTP-resistant strains has not been studied. Here, we show that, as previously reported, 1-month and 18-month-old C57BL/6 mice are least and most sensitive to MPTP, respectively. MPTP, as expected, did not affect the younger (1-month and 3-month-old) BALB/c mice, but it markedly decreased striatal dopamine in the older (10-month and 18-month-old) BALB/c mice. These data suggest that the sensitivity to MPTP is age dependent and that mice from an MPTP-resistant strain lose their resistance as they age.
Subject(s)
1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine/pharmacology , Aging , Corpus Striatum/drug effects , Dopamine Agents/pharmacology , 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine/administration & dosage , Animals , Blotting, Western , Chromatography, High Pressure Liquid , Corpus Striatum/physiology , Dopamine/metabolism , Dopamine Agents/administration & dosage , Drug Resistance , Immunohistochemistry , Male , Mice , Mice, Inbred BALB C , Mice, Inbred C57BL , Species Specificity , Tyrosine 3-Monooxygenase/metabolismABSTRACT
A possible link between Parkinson's disease and pesticide exposure has been suggested, and recently it was shown that the herbicide atrazine (ATR) modulates catecholamine metabolism in PC12 cells and affects basal ganglia function in vivo. Hence, the objectives of this study were to: (i) determine if ATR is capable of modulating dopamine (DA) metabolism in striatal tissue slices in vitro and (ii) explore possible mechanisms of its effects. Striatal tissues from adult male Sprague-Dawley rats were incubated with up to 500 microM ATR in a metabolic shaker bath at 37 degrees C and an atmosphere of 95% O(2) and 5% CO(2) for 4h. At the end of incubation, samples were collected for both tissue and media levels of DA and its metabolites (3,4-dihydroxyphenylacetic acid, DOPAC and homovanillic acid, HVA), which were determined by high-performance liquid chromatography with electrochemical detection (HPLC-ECD). To gain some mechanistic insight in to the way ATR affects DA metabolism, several pharmacological manipulations were performed. Striata exposed to ATR at concentrations of 100 microM and greater had a dose-dependent decrease of tissue levels of DA. At doses of ATR 50 microM and greater, the DOPAC+HVA/DA ratio was dose-dependently increased. Tyrosine hydroxylase (TH, the rate-limiting enzyme in DA synthesis) protein levels and activity were not affected by ATR treatment. However, high potassium-induced DA release into the medium was decreased, whereas the increase in media DA observed in the presence of the DA uptake inhibitor nomifensine was increased even further by ATR in a dose-dependent manner. All of these effects of ATR were observed at levels that were not toxic to the tissue, as LDH release into the medium (lactate dehydrogenase, an index of non-specific cytotoxicity) was not affected by ATR. Taken together, results from this study suggest that ATR decreases tissue DA levels not by affecting TH activity, but possibly by interfering with the vesicular storage and/or cellular uptake of DA.
Subject(s)
Atrazine/toxicity , Brain Diseases/chemically induced , Corpus Striatum/drug effects , Dopamine/metabolism , Herbicides/toxicity , 3,4-Dihydroxyphenylacetic Acid/metabolism , Animals , Brain Diseases/metabolism , Dopamine Uptake Inhibitors/pharmacology , Enzyme Inhibitors/pharmacology , Homovanillic Acid/metabolism , Hydrazines/pharmacology , In Vitro Techniques , L-Lactate Dehydrogenase/metabolism , Male , Nomifensine/pharmacology , Random Allocation , Rats , Rats, Sprague-Dawley , Tyrosine 3-Monooxygenase/metabolismABSTRACT
Following combustion of fuel containing the additive methylcyclopentadienyl-manganese-tricarbonyl (MMT), manganese phosphate (MnPO(4)) and manganese sulfate (MnSO(4)) are emitted in the atmosphere. Manganese chloride (MnCl(2)), another Mn(2+) species, is widely used experimentally. Using rat striatal slices, we found that MnPO(4) decreased tissue and media dopamine (DA) and media Dopac (a DA metabolite) levels substantially more than either MnCl(2) or MnSO(4); antioxidants were partially protective. Also, both MnCl(2) and MnPO(4) (more potently) oxidized DA and Dopac even in the absence of tissue in the media, suggesting a direct interaction between Mn and DA/Dopac. Because aminochrome is a major oxidation product of DA, we next determined whether MnPO(4) will be more potent in forming aminochrome than MnCl(2) or MnSO(4) which, indeed, was the case. Thus, a potential additional mechanism for the neurotoxic effects of environmentally-relevant forms of Mn, MnPO(4) in particular, is the generation of reactive DA intermediates.
