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Published on: July 9, 2016
Assessment of mercury concentrations in mouse brain using different routes of administration and different tissue
Sairam Bellum1, Kerry A Thuett, Robert J Taylor
1Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University 4458 TAMU, College Station, TX, 77843-4458.
Abstract:
ABSTRACT The objective of this study was to determine the best method for preparing brain tissue for mercury analysis from mice exposed to methylmercury either through subcutaneous (SC) injection or through ingestion. C57BL/6 J mice at postnatal day 29 were exposed to 0.0 or 5.0 mg/kg methylmercuric chloride (MMC) given SC or through food containing MMC. Eighteen mice received vehicle (sodium bicarbonate; SC) and 18 additional mice received 5.0 mg/kg MMC (SC). Whole brain tissue was prepared using one of four tissue preparation methods: rapid freezing, saline perfusion, 4% paraformaldehyde perfusion fixation, or 4% paraformaldehyde immersion fixation. Brains from vehicle-treated mice exhibited minimal levels of mercury (0.0007 to 0.0018 ppm) in all preparation methods. Mercury content in rapidly frozen control brains differed statistically from immersion-fixed control brain tissue. There was no significant difference in mercury content from mice given 5.0 mg/kg MMC (SC) in all preparation methods (0.2660 to 0.3650 ppm). Additional mice were divided into groups of six mice each: single oral dose of 5.0 mg/kg MMC; total oral dose of 5.0 mg/kg MMC divided into five doses; and vehicle only. Forebrain (0.3243 ppm) and hindbrain (0.1908 ppm) mercury content in MMC-treated mice given multiple doses was 10 times higher than in brain tissue from mice given a single 5.0 mg/kg dose. Brain mercury content following administration of 5.0 mg/kg MMC via the oral route (0.5354 ppm) differed statistically from the SC route (0.3430 ppm). In conclusion, different tissue preparation methods do not significantly affect brain mercury content, but route of administration and dosing regimen can influence total brain mercury content.
Insights
This study found that while tissue preparation methods do not impact brain mercury levels, the route of administration and frequency of methylmercury dosing significantly affect mercury accumulation in mouse brains. This is crucial for accurate mercury analysis.
Area of Science:
- Toxicology
- Neuroscience
- Analytical Chemistry
Background:
- Methylmercury (MeHg) is a potent neurotoxin.
- Accurate quantification of mercury in brain tissue is essential for understanding its toxicokinetics and effects.
- Standardized methods for tissue preparation are needed to ensure reliable mercury analysis.
Purpose of the Study:
- To evaluate the impact of different tissue preparation methods on mercury analysis in mouse brain.
- To compare mercury levels in brain tissue following subcutaneous (SC) injection versus oral administration of methylmercury.
- To assess the influence of single versus multiple dosing regimens on brain mercury accumulation.
Main Methods:
- C57BL/6 J mice were exposed to methylmercuric chloride (MMC) via SC injection or oral ingestion.
- Four tissue preparation methods were employed: rapid freezing, saline perfusion, 4% paraformaldehyde perfusion fixation, and 4% paraformaldehyde immersion fixation.
- Mercury content in brain tissue was quantified using established analytical techniques.
Main Results:
- Tissue preparation methods (rapid freezing, saline perfusion, paraformaldehyde fixation) did not significantly alter brain mercury concentrations.
- Subcutaneous administration of MMC resulted in lower brain mercury levels (0.3430 ppm) compared to oral administration (0.5354 ppm).
- Multiple oral doses of MMC led to a tenfold increase in brain mercury content compared to a single oral dose.
Conclusions:
- Tissue preparation techniques have minimal impact on the accuracy of brain mercury measurements.
- The route of methylmercury administration (oral vs. SC) and the dosing regimen (single vs. multiple doses) are critical factors influencing mercury bioaccumulation in the brain.
- Findings highlight the importance of considering exposure route and dosing for accurate toxicological assessments of methylmercury.
