Behavioral and neuropathological effects of prenatal methylmercury exposure in mice.

Pregnant C3H/HeN mice were orally administered a single dose of 20 mg/kg methylmercuric chloride on one of days 13 through 17 of pregnancy. They were allowed to give birth and the newborn mice were foster mothered, but the weaning rate was low. Long-term behavioral impairment was manifest in mice of every treated group. The righting movement was mildly disturbed when animals were dropped from about 40 cm high. The tail position was low during walking. Some animals showed strong flexion of the hind limbs when held by the tail. Spontaneous locomotor activity was reduced. At 10-12 weeks of age, the animals were sacrificed and the brain was histologically examined. The brain weight was reduced. The nucleus caudatus putamen was slightly reduced in size leaving the lateral ventricles dilated. Cerebellar folial patterns were slightly simplified. These neurobehavioral symptoms and pathological changes tended to be comparatively more severe in animals treated on days 13 and 14 of pregnancy than those of the other groups, but the differences were small.