Effects of methyl mercury in postnatal developing rats.

Rats on Postnatal Days 1 (PD 1), 14 (PD 14), and 35 (PD 35) were orally administered 0, 2.60, 3.64, 5.10, 7.14, and 10 mg/kg/day of methyl mercury chloride (MMC) for 10 consecutive days. Mercury (Hg) accumulation in the brain of the rats treated with 10 mg/kg/day of MMC for 10 consecutive days was highest in PD-14 rats, followed by PD-35 and PD-1 rats. Hg accumulations in the liver and kidney were lowest in PD-1 rats and increased markedly with development in postnatal phase. The effect of MMC treatment on body weight change was most severe in PD-35 rats. The body weight loss began on Day 5 in PD-35 rats and on Day 10 in PD-14 rats treated with 10 mg/kg/day of MMC, but not in PD-1 rates under the same treatment. The phenomenon of hindlimb-crossing was induced on Day 11 in PD-14 rats and on Day 14 in PD-35 rats treated with 10 mg/kg/day of MMC, but was not observed in PD-1 rats. The deficit of rotarod performance was apparent only at the dose of 7.14 mg/kg/day of MMC in PD-35 rats, whereas rotarod performance was dose-dependently inhibited by MMC treatment in PD-14 rats, and lowered even at the dose of 2.6 mg/kg/day of MMC. However, the performance was gradually restored to the control level by 1 month except in rats given 7.14 mg/kg/day of MMC. These findings indicated that the Hg distribution and the effects of MMC treatment on body weight gain and motor coordination were different among the rat postnatal developing phases.