Protective effect of melatonin on methylmercury-induced mortality in mice

Effect of melatonin on the mortality in methylmercury chloride (MMC)-intoxi cated mice was evaluated. Mice were given MMC in the diet (40 mgHg/g) with or without melatonin in drinking water (20 mg/ml) for 5 weeks. In the contr ol group, given MMC alone, 4 of 10 mice began to show neurological signs (e .g., abnormal righting reflex, staggering gaitfallen and posture on its sid e) concomitant with loss of body weight 4-7 days before death. This group a lso showed 60% of survival rate on the 35th day. However, the treated group , concomitantly given melatonin, showed a 100% of survival rate on the 35th day, although 1 of 10 mice began to show the neurological signs on the 33r d day. The level of thiobarbituric acid reactive substance in the brain, as an indication of oxidative damage, showed a significant decrease in the tr eated group compared with the control group. Thus, the 100% survival rate i n the treated group may be partly due to antioxidative effect of melatonin on the MMC induced neurotoxicity.