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Effects of low dose methylmercury administration during the postnatal brain growth spurt in rats
Addolorata Coluccia1, Pietro Borracci, Arcangela Giustino
1Department of Pharmacology and Human Physiology, Medical School, University of Bari, Policlinico, Piazza G. Cesare 11, 70124 Bari, Italy.
Insights
Low-level methylmercury (MeHg) exposure in young rats caused lasting motor and learning problems. This highlights the risks of mercury exposure during critical brain development periods.
Area of Science:
- Neuroscience
- Toxicology
- Developmental Biology
Background:
- Methylmercury (MeHg) is a potent neurotoxin.
- Prenatal and early postnatal exposure can lead to developmental neurotoxicity.
- Understanding the long-term effects of low-level exposure is crucial for public health.
Purpose of the Study:
- To investigate the persistent neurobehavioral effects of low-level methylmercury exposure during a critical brain development period in rats.
- To assess motor function and learning capabilities following early-life MeHg exposure.
Main Methods:
- Male Sprague-Dawley rats were orally administered 0.75 mg/kg/day methylmercury chloride from postnatal day 14 to 23.
- Locomotor activity was assessed weekly from postnatal day 24 to 45 using the Opto-Varimex apparatus.
- Learning performance was evaluated on postnatal day 90 using a conditioned avoidance task.
Main Results:
- Methylmercury exposure resulted in significantly reduced rearing behavior without affecting distance traveled, resting time, or central arena time.
- Treated rats exhibited impaired learning in the conditioned avoidance task, failing to show improvement over time.
- Brain mercury concentrations in MeHg-treated rats were 0.82+/-0.05 microg/g tissue.
Conclusions:
- Low-level methylmercury exposure during late brain development induces subtle yet persistent motor and learning deficits.
- These findings underscore the potential hazards of methylmercury exposure for developing children.
- Early-life exposure to neurotoxins can have long-lasting consequences on cognitive and motor functions.
Abstract:
Male Sprague-Dawley rats from eight litters were orally administered 0.75 mg/kg/day methylmercury (MeHg) chloride from postnatal day (PD) 14 to PD 23. One male pup per litter from eight different litters per treatment group was used. Each pup was used only for a single behavioral test and tested once. The MeHg dose level resulted in Hg brain concentrations of 0.82+/-0.05 microg/g tissue (n=4). Locomotor behavior was studied in the Opto-Varimex apparatus by testing rats (n=8) weekly from PD 24 to PD 45. Performance of rats (n=8) on learning paradigm was analysed on PD 90. MeHg treatment induced a significant reduction in the number of rearings without altering the distance travelled, the resting time and the time spent in the central part of the arena. Results of conditioned avoidance task showed that, unlike control rats, MeHg-treated animals did not show improvement over blocks and never reached a level of performance that would indicate significant learning had taken place. The present results show that low level exposure to MeHg during late brain growth spurt induces subtle and persistent motor and learning deficits, further underlining the serious potential hazard for the exposed children.
