Intrastriatal administration of methylmercury increases in vivo dopamine release

Mercury is a neurotoxin that exists in a number of physical and chemical fo rms, producing different effects in the brain. In the present work, we have studied the effects of intrastriatal administration of different doses (40 mu M, 400 mu M, and 4 mM) of organic mercury (methyl-mercury, MeHg) on the dopaminergic system of rat striatum, in conscious and freely-moving animal s, 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 metab olism of striatal dopamine (DA). In the present study we report that the in trastriatal administration of different doses of MeHg (40 mu M, 400 mu M, a nd 3 mM) produced significant increases (907 +/- 31%, 2324 +/- 156%, and 90 32 +/- 70% of basal levels, respectively for the different doses) in DA rel ease from rat striatal tissue associated with significant decreases in extr acellular 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 mu M and 400 mu M MeHg. We explain thes e effects as a result of stimulated DA release and/or decreased DA intraneu ronal degradation.