A study of startle and locomotor activity in rats exposed prenatally to methylmercury.

The permanence of developmental abnormalities from prenatal methylmercuric chloride (MMC) was examined in the offspring of Sprague-Dawley rats exposed on Days 6-15 of gestation to 0.00, 0.25, 1.25, 2.50, or 5.0 mg/kg MMC. The effects of MMC on reproduction and early physical development were examined together with tests of negative geotaxis, righting, pivoting, swimming, locomotor activity in an open field, and startle responses to either tactile or acoustic stimuli. No live offspring were produced by females treated with 5.0 mg/kg MMC. Offspring from the 2.50 mg/kg dose group displayed impaired performance on almost all pre-weaning measures and continuing abnormalities on longitudinal tests of locomotor activity in an open field and startle response performance.