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Mercury is a neurotoxin that exists in a number of physical and chemical forms, producing different effects in the brain. In the present work, we have studied the effects of intrastriatal administration of different doses (40 microM, 400 microM, and 4 mM) of organic mercury (methyl-mercury, MeHg) on the dopaminergic system of rat striatum, in conscious and freely-moving animals, using microdialysis coupled to Liquid Chromatography. In previous works, we have discussed the effects of chronic and acute administration of MeHg on striatal dopaminergic system assessing changes in both release and metabolism of striatal dopamine (DA). In the present study we report that the intrastriatal administration of different doses of MeHg (40 microM, 400 microM, and 4 mM) produced significant increases (907 +/- 31%, 2324 +/- 156%, and 9032 +/- 70% of basal levels, respectively for the different doses) in DA release from rat striatal tissue associated with significant decreases in extracellular levels of its main metabolites dihydroxyphenylacetic acid (DOPAC) and homovallinic acid (HVA) using the dose of 4 mM MeHg (35 +/- 3% and 48 +/- 1%, respectively), whereas non-significant changes in metabolite levels were observed with the doses of 40 microM and 400 microM MeHg. We explain these effects as a result of stimulated DA release and/or decreased DA intraneuronal degradation.