Methylmercury induced alterations in brain amine syntheses in rats.

Male Sprague-Dawley rats were treated with a cumulative dose of 0, 5, 15 and 50 mg methylmercury/kg body weight. The doses were adequate to provide a clinical neuromuscular dysfunction at the highest dose whereas no toxicity was observed at the lowest treatment level. Whole brain concentrations of tyrosine but not tryptophan were slightly reduced by the treatment. No effect of methylmercury was observed in the levels of norepinephrine (NE), dopamine (DA), serotonin (5-HT), dihydroxyphenylacetic acid (DOPAC), or 5-hydroxyindoleacetic acid (5-HIAA). The synthesis rate for DA, but not the other biogenic amines, was decreased at all treatment levels of methylmercury. The results suggested a sensitivity of dopaminergic pathways to methylmercury toxicity in the central nervous system and are consistent with interference with cholinergic mechanisms and neurotransmitter enzymes by methylmercury as previously reported.