Effects of the high methylmercury dose used in the collaborative behavioral teratology study on brain anatomy.

Pregnant rats were injected with 0, 6 or 10 mg/kg of methylmercuric chloride on Days 6-9 of gestation. Dams given the 10 mg/kg dose failed to deliver young or produced stillborn. External morphology was normal for rats given either the 0 or 6 mg/kg dose. Whole brains were examined from male and female rats, 21 or 90 days old. External brain dimensions were measured with calipers. Brains were sectioned at three criterion locations. A microprojector was used to project brain sections in order to measure intrastructural distances. Sections were examined with a light microscope to look for abnormalities. Various expected age-related changes were noted showing the sensitivity of the anatomical methods. Methylmercury produced hydrocephalus, decreased thickness of cerebral cortex in the parietal section and increased thickness of hippocampus in the occipital section. With these exceptions, the brains of mercury-treated rats showed normal development.