[Methylmercury toxicosis. I. Relationship between the onset of motor incoordination and mercury contents in the brain (author's transl)]

Mice were given one or repeated administrations of methylmercury chloride (MMC) in an attempt to determine the sexual differences as related to toxic signs, particularly, motor incoordination and the period to evolvement of toxicity. Male and female mice were given 50.6 mg/kg of MMC (about equal to the LD50 in female mice) orally only once, and changes in general behavior and mortality were observed for the following 13 days. Another group of male and female mice was fed food containing 50 and 100 ppm of MMC for 30 days, respectively. The rotarod performance test was carried out daily during the application period, to compare the onset stages of toxic signs and motor incoordination between the groups. The mercury content of the brain was measured at 1- to 2-day intervals during the application period. When the animals were given MMC only once, the males began to die at 3 days, 7/8 of the group dying by the 7th day, while the females began to die at 8 days, with 5/8 of the group dying thereafter: there was thus an obvious sexual difference in the toxicity. When the animals were given MMC admixed with food, however, the females proved more sensitive to the compound both in onset and severity of toxic signs. The onset was seen in the females at the stage when they had ingested about half the amount of the toxic food ingested by the males. The onset and the period in days to the onset of suppressed rotarod performance both in the groups on 50 and 100 ppm were correlated to the daily intake of MMC, the total MMC intake to the onset in the 2 groups being similar. The accumulation of mercury in the brain increased linearly in both groups, with the MMC content of the brain at the onset was about 20 microgram Hg per g of brain (on the wet basis), i.e., about twice that of the human brain. The mercury content in the brain of the female mice tended to reach the toxicity threshold earlier than that in the brain of the males.