No abstract

Methylmercury chloride (MMC) was given to pregnant rats on the 6th, 7th, 8th, and 9th day after conception in doses of 0.05 and 2.0 mg/kg/day. The female offspring of these animals were tested 90 days after birth for learning ability using operant conditioning procedures. The rats were kept at 90% of their normal body weight and trained in a lever-box to press a bar in order to obtain a food pellet. Significant differences in the acquisition speed became apparent when the ratio of bar presses to reward was increased in a classical contingency of differential reinforcement of high rates even at MMC-doses of 4 X 0.05 mg/kg. These differences were not found in the general motility level nor in motor coordination.