[Effects of methylmercury exposure on the locomotor activity of rats].

The present study was undertaken to investigate the precursory effects of methylmercury poisoning by measuring the locomotor activity of rats. Methylmercury was administered to male rats mixed in the rat food. The period of administration was 30 days. The effects on the rats exposed to a level of 100 ppm of methylmercury were evaluated from the 6th week to the time of death, based on the locomotor activity, body weight and food intake. Methylmercury-fed rats showed decreased weight gain and food intake compared with the controls for the first 7 days. When the animals were given methylmercury, the rats began to die at 21 days, 4/ 4 of rats dying by the 28 days therafter. At the time when all of the experimental rats died, the average body weight had decreased to 52.6% of that of age-matched controls. The mercury concentration in the