Mercury accumulation and its distribution to metallothionein in mouse brain after sub-chronic pulse exposure to mercury vapor.
Previously we found that exposure to mercury vapor effectively induced metallothionein (MT) biosynthesis in rat brain. Although the induction of not only MT-I/II but also MT-III was evident, the induction rate of the latter was much lower than that of the former. The brain of an MT-null mouse lacks MT-I/II, but has MT-III. Here we examined the effects of sub-chronic pulse exposure to mercury vapor on the brain MT in MT-null mice and their wild type controls. MT-null and wild type mice were preliminarily exposed to mercury vapor for 2 weeks at 0.1 mg Hg/m(3) for 1 h/day for 3 days a week, and then exposed for 11 weeks at 4.1 mg Hg/m(3) for 30 min/day for 3 days a week. This exposure caused no toxic signs such as abnormal behavior or loss of body weight gain in the mice of either strain throughout the experimental period. Twenty-four hours after the termination of the exposure, mice were sacrificed and brain samples were subjected to mercury analysis, MT assay, and pathological examination. The MT-null mice showed lower accumulation of mercury in the brain than the wild type mice. Mercury exposure resulted in a 70% increase of brain MT in the wild type mice, which was mostly accounted for by the increase in MT-I/II. On the other hand, the brain MT in the MT-null mice increased by 19%, suggesting less reactivity of the MT-III gene to mercury vapor. Although histochemical examination revealed silver-mercury grains in the cytoplasm of nerve cells and glial cells throughout the brains of both strains, no significant difference was observed between the two strains.
Yasutake
A
A
Biochemistry Section, National Institute for Minamata Disease, Minamata, Kumamoto 867-0008, Japan. yasutake@nimd.go.jp
Sawada
M
M
Shimada
A
A
Satoh
M
M
Tohyama
C
C
D000280:Administration, Inhalation; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D008628:Mercury / Q000493:pharmacokinetics* / Q000633:toxicity; D008668:Metallothionein / Q000096:biosynthesis* / Q000235:genetics; D051379:Mice; D018345:Mice, Knockout; D013997:Time Factors; D014018:Tissue Distribution; D014835:Volatilization
D008668:Metallothionein; D008628:Mercury