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Neurotoxicity of methylmercury in the pigeon
Abstract:
Pigeons repeatedly exposed to sublethal doses of methylmercury (5-10 mg Hg/kg/wk, po, for 34-77 days) exhibited marked behavioral changes that were accompanied by only minor evidence of neuropathologic changes at the light microscopic level. Accuracy and rate of pecking for grain declined while food intake remained unchanged. Methylmercury produced permanent changes in posture and in motor coordination. The regional distribution of methylmercury within the nervous system was poorly correlated with the distribution of pathologic changes. Overt behavioral signs appeared after the brain accumulated more than about 12 to 16 ppm Hg. Data with pigeons support earlier evidence that the dose-response function for methylmercury is modulated by dose rate and duration of exposure, since the pattern of blood and tissue distribution of Hg is established in advance of the appearance of signs. The pigeon is more sensitive to methylmercury than are mice and rats, but less sensitive than primates.
Insights
Sublethal methylmercury exposure in pigeons caused significant behavioral changes, including impaired motor skills, despite minimal microscopic brain damage. These effects highlight methylmercury
Area of Science:
- Neurotoxicology
- Avian toxicology
- Environmental health
Background:
- Methylmercury is a potent neurotoxin with significant environmental and health implications.
- Understanding the dose-response relationship and species-specific sensitivity is crucial for risk assessment.
Purpose of the Study:
- To investigate the behavioral and neuropathological effects of chronic, sublethal methylmercury exposure in pigeons.
- To correlate mercury accumulation in the brain with observed clinical signs and pathological changes.
Main Methods:
- Pigeons were administered methylmercury (5-10 mg Hg/kg/wk, po) for 34-77 days.
- Behavioral assessments included pecking accuracy, rate, and motor coordination.
- Neuropathological changes were examined at the light microscopic level.
Main Results:
- Sublethal methylmercury exposure induced marked behavioral deficits, including reduced pecking accuracy and impaired motor coordination.
- Neuropathological changes were minimal at the light microscopic level, despite significant behavioral alterations.
- Overt signs of toxicity appeared when brain mercury levels exceeded approximately 12-16 ppm.
- Mercury distribution in the nervous system did not strongly correlate with pathological findings.
Conclusions:
- Pigeons exhibit high sensitivity to methylmercury, showing significant behavioral impairment with minimal detectable neuropathology.
- The dose-response relationship for methylmercury is influenced by dose rate and exposure duration.
- Pigeons serve as a valuable model for studying methylmercury neurotoxicity, displaying greater sensitivity than rodents but less than primates.