Abstract: Purpose : To detect the neurobehavioral teratogenic effect of methylmercury exposure at early embryonic stage on off spring. Methods : Methylmercury chloride was force2fed to the Wistar rat s during the 6th～9th day after conception at doses of 0. 00 mg/ (kg·bw·d) , 0. 01 mg/ (kg·bw·d) , 0. 05 mg/ (kg·bw·d) and 2. 00mg/ (kg·bw·d) . The toxicity in the embryos , developmental landmarks of 201 off spring and operant behavior test of 32 off spring were measured. The brain morphology and the levels of monamine neurot ransmitters (NA ,DA , 52HT) were tested in 24 off spring at 10 weeks old. Double blind was used in whole experiment . Results :In 3 exposure groups , the body weight and tail development of embryos were slower ( P < 0. 01) , the early developmental landmarks and neurobehavioral development of off spring were delayed ( P < 0. 05) , and their performances in operant behavior were worse than those of the cont rol group ( P < 0. 05) . No histomorphological alteration in the off spring brains was observed in all groups. The levels of monamine neurot ransmitters in brains of 3 exposure groups were increased ( P < 0. 05) . Some result s showed a dose2effect relationship. Conclusion : Early pregnant exposure to methylmercury at a low dose showed some embryotoxicity and adverse effect s on the developing nervous system of the rat off spring and also resulted in neurobehavioral changes.

Key words: methylmercury, behavioral teratogenicity, off spring, Wistar rat