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Comparative Neurotoxicity of Methylmercury and Mercuric Chloride In Vivo and In Vitro

It is impossible to remove methylmercury (MeHg) from biological systems
because MeHg is found throughout our environment in many fresh and salt water fish.
The consumption of fish is important to human nutrition and health. The mechanism of
MeHg neurotoxicity must be understood to minimize adverse exposure consequences.
The dissertation objective was to: 1) compare mechanisms of MeHg neurotoxicity
between animals exposed as adults and those exposed during gestation, and 2) develop
an in vitro test model of in vivo MeHg exposure.
Total mercury (Hg) levels in tissue / cells were determined by combustion /
trapping / atomic absorption. Cell death was determined by Fluoro-Jade histochemical
staining and activated caspase 3 immunohistochemistry for in vivo studies, and Trypan
blue exclusion, lactate dehydrogenase activity, and cytotoxicity assays for in vitro
studies. Mitochondrial membrane potential (MMP), intracellular calcium ion
concentration ([Ca2+]i), and production of reactive oxygen species (ROS) were
determined using fluorescence microscopy or microplate reader assays. Young adult
C57Bl/6 mice were exposed to a total dose of 0, 1.0, or 5.0 mg/kg body weight MeHg
divided over postnatal days (P)35 to 39. Pregnant female mice were exposed to a total
does of 0, 0.1, or 1.0 mg/kg body weight MeHg divided over gestational days (G)8 to 18.
SY5Y cells were exposed to 0, 0.01, 0.1, or 1.0 ?M MeHg or HgCl2 for 24, 48, or 72
hours. Total Hg in brains of young adult mice, mouse pups, and SY5Y cells accumulated
in a dose-dependent manner. Cell death increased in SY5Y cells exposed to the highest
concentrations of MeHg and HgCl2 used in this study. Cell death increased in the
molecular and granule cerebellar cell layers of young adult mice exposed to the highest
doses of MeHg used in this study. P0 mouse pups showed no increase in cell death
within the cerebellum following MeHg exposure. Cerebella of mice at P10 exhibited
decreased dying cells only in the external germinal layer.
Low concentrations of MeHg affected MMP in both in vivo and in vitro studies,
but did not result in decreased MMP typically associated with higher MeHg
concentrations. [Ca2+]i was increased throughout the in vivo experiments in an age- , sexand
brain region-dependent manner. Generation of ROS was decreased in both in vivo
and in vitro studies with both the MeHg and HgCl2
(in vitro) treatments.
In summary, low and moderate MeHg exposure, both in vivo and in vitro, altered
mitochondrial function, Ca2+ homeostasis, and ROS differently than what is reported in
the literature for higher MeHg exposure concentrations. SY5Y cells were sensitive to
low-levels of MeHg and HgCl2 and responded similarly to cells in the whole animal
studies, thus making SY5Y cells realistic candidates for mechanistic MeHg studies.
Cell culture and whole animal neuronal functional studies at chronic low-level
MeHg exposure are limited. These data suggest that low-levels of MeHg may affect
neuronal function. Therefore, further chronic low-level MeHg neuronal functional
studies are warranted.

Identiferoai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-08-3232
Date2009 August 1900
CreatorsThuett, Kerry A.
ContributorsAbbott, Louise C., Tiffany-Castiglioni, Evelyn
Source SetsTexas A and M University
Languageen_US
Detected LanguageEnglish
TypeBook, Thesis, Electronic Dissertation, text
Formatapplication/pdf

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