Effect of manganese on biogenic amine metabolism in regions of the rat brain

Abstract

The effect of prolonged exposure to low-level manganese (Mn) on regional levels of biogenic amines in the rat brain was studied. Rats were given Mn in drinking-water for 90 days, which resulted in a two- to three-fold accumulation of Mn in all regions of the brain. After exposure, dopamine β-hydroxylase (DBH), monoamine oxidase (MAO), dopamine (DA) and serotonin (5-HT) were measured in regions of the brain. There was a significant inhibition of DBH in the striatum ( P < 0.01), hypothalamus ( P < 0.01), mid-brain ( P < 0.001) and cortex ( P < 0.01). MAO was also decreased significantly in the cerebellum and cortex (both P < 0.01). The striatum showed a decrease in DA content, but this was not significant. However, the hippocampus showed a significant decrease ( P < 0.01) and the mid-brain showed a significant increase ( P < 0.01) in DA levels. No significant changes were observed in 5-HT levels in any region, except for an increase in the cortex ( P < 0.01). It was observed that prolonged exposure of rats to low-level Mn affects both DBH and MAO, and that this effect is region-specific. However, the effect of Mn on biogenic amines seems to be variable, and this might explain the variable signs and symptoms observed in the various phases of Mn toxicity in humans.