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Behavioral effects of chronic manganese administration in rats: locomotor activity studies
Abstract:
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.
Insights
Chronic manganese (Mn) exposure in rats caused a temporary increase in locomotor activity and heightened responsiveness to amphetamine. These findings suggest a transient impact on dopaminergic function, mirroring human manganese poisoning symptoms.
Area of Science:
- Neuroscience
- Toxicology
- Environmental Health
Background:
- Manganese (Mn) is an essential trace element with industrial applications.
- Excessive Mn exposure can lead to neurological damage, particularly in the basal ganglia.
- Human Mn poisoning presents with hyperactivity and parkinsonian symptoms.
Purpose of the Study:
- To investigate the effects of chronic manganese exposure on locomotor activity in rats.
- To assess the impact of manganese on behavioral responses to amphetamine stimulation.
- To explore the transient nature of manganese-induced neurological changes.
Main Methods:
- Rats were exposed to 0.0 or 1.0 mg Mn(Cl)2 X 4H2O/ml drinking water chronically.
- Locomotor activity was measured weekly for 13 weeks, then at extended intervals.
- Responsiveness to d-amphetamine (d-A) was tested at specific time points during the exposure period.
Main Results:
- Manganese exposure led to a significant, transient increase in spontaneous locomotor activity between weeks 5-7.
- Mn-exposed rats showed increased responsiveness to d-amphetamine at 14 and 29 weeks, which diminished by week 41.
- No significant differences in body weight or habituation were observed between groups.
Conclusions:
- Chronic manganese exposure can transiently enhance dopaminergic function in rats, as indicated by increased locomotor activity.
- The observed behavioral changes partially mimic the initial hyperactivity seen in human manganese poisoning.
- These findings support the hypothesis of a temporary alteration in dopaminergic pathways following manganese overexposure.