Brain regional manganese levels and monoamine metabolism in manganese-treated neonatal rats.

The brain distribution of manganese (Mn) and the regional steady state levels of monoamines and their metabolites in normal and Mn-treated neonatal rats have been investigated. Neonatal rats were intubated daily with distilled water, 25 or 50 micrograms manganous chloride/g/day for 14 or 21 days. Manganese levels in brain regions and liver were analyzed by flameless atomic absorption spectroscopy. Norepinephrine, dopamine, serotonin and their metabolites in the striatum, hypothalamus, and nucleus accumbens were analyzed by HPLC. The levels of Mn in Mn-treated animals were increased at 14 and 21 days of age although brain levels at 21 days were lower than those at 14 days. Monoamine and metabolite levels were not altered by Mn treatment in any region at either age. Thus, increases in brain Mn levels do not necessarily result in alterations in steady state neurotransmitter and metabolite levels. These results suggest that the neurotoxic effects of these doses of Mn administered to neonatal animals are not expressed as alterations in steady state levels of monoamines and metabolites. The developing nervous system may be able to compensate for neurochemical changes caused by Mn exposure.