Behavioral effects of chronic manganese administration in rats: locomotor activity studies.

Manganese (Mn) is an industrially important metal which, when given in excess, produces lesions in the basal ganglia of rats and humans. Humans poisoned with Mn often exhibit an initial hyperactivity ("manganese madness") followed by a parkinsonian-like syndrome. The present studies examined the effects of chronic Mn exposure on locomotor activity in rats maintained on 0.0 or 1.0 mg Mn(Cl)2 X 4H2O/ml drinking water. No differences in mean body weights were observed from 0-65 weeks of treatment. Locomotor activity was tested in 15 min sessions at weekly intervals (Weeks 1-13), then at 4 or 14 week intervals thereafter. Mn treatment produced a significant increase in activity on weeks 5-7 before returning to control values at 8 weeks. Habituation measured within a test session was not affected at any time. At 14 and, to a lesser extent, 29 weeks, Mn animals were found to be more responsive to the effects of 1.25 mg/kg d-amphetamine (d-A) than controls. This increased responsiveness was gone at Weeks 41 and 65. Consistent with clinical reports, these results suggest that Mn may produce a transient increase in dopaminergic function, as measured by both spontaneous and d-A-stimulated locomotor activity.