This study was carried out to clarify the effects of methylmercury intoxication on the ethanolinduced sleeping time of mice. The mice were injected with methylmercury chloride (MMC) (10mgMMC/kg body weight) subcutaneously for 1, 5 and 10 successive days (1, 5 and 10inj.), and control mice received only saline. Twenty-four hours, after the last injection, these mice were treated with ethanol (4.5mgEtOH/kg body weight) intraperitoneally and subsequent sleeping time was observed. After 24 hours, mice were sacrificed to measure the concentration of MMC in various brain regions and liver. A similar experiment without ethanol treatment was also performed to assay the biogenic monoamines in various brain regions and alcohol dehydrogenase (ADH) activity in liver. The results can be summarized as follows:
1) Ethanol-induced sleeping time was 170min. in the 10inj. and it was significantly longer than saline, 1 and 5inj. However, other experimental groups showed no change when compared with saline.
2) Norepinephrine levels increased in white matter and pons + medulla after 1inj.
3) Dopamine levels increased only in white matter of the 10inj. when compared with saline. No changes were shown in the other groups.
4) Serotonin levels increased in all the regions after 1inj.
5) ADH activity in liver did not show any alteration during the experimental period when compared with saline.
6) MMC in brain and liver increased with time and finally reached 15-16ppm in the cerebrum and 11ppm in pons + medulla; however, we could not recognize paralysis of hind leg crossing in mice.
Thus, it may be suggested that changes in ethanol-induced sleeping time of the MMC-administered mice were dependent on the alteration of biogenic monoamines and the concentration of MMC in the brain.
