Alterations in brain dopamine and GABA following inorganic or organic manganese administration.

Administration of manganese to mice in the form of MnCl2 (4%) in the diet for 6 months or injections of the organic fuel-additive methylcyclopentadienyl manganese tricarbonyl (MMT) for 3 weeks resulted in a decrease in dopamine concentrations in the striatum and olfactory tubercles. The GABA content of the striatum was elevated after either treatment while the cerebellar GABA content did not change; GABA in the substantia nigra of MMT-treated mice was also increased. Choline acetyltransferase activity remained unchanged in response to either manganese treatment. These results are in general agreement with previous studies of inorganic manganese toxicity in other animal species. These changes in neurotransmitter concentrations were observed after longterm manganese administration but were not seen in mice injected acutely with MMT or exposed to MnCl2 for 1-2 months.