Influence of maternal stress on the effects of prenatal exposure to methylmercury and arsenic on postnatal development and behavior in mice: a preliminary evaluation.

The present study combined maternal restraint stress with exposure to 2 environmental toxic elements, mercury and arsenic, given to mice concurrently with the restraint period (1000-1200 h, gestational days 15-18). Two groups of animals were given, by gavage, methylmercury chloride (MMC) (2 mg/kg/day), and 2 additional groups received sodium arsenite (10 mg/kg/day) on days 15-18 of gestation. Immediately after MMC or arsenite exposure, 1 group of MMC-treated mice and 1 group of arsenite-treated animals were restrained for 2 h/day. Control groups included restrained and unrestrained pregnant mice nonexposed to MMC or arsenite. All animals were allowed to deliver and wean their offspring. Pups were evaluated for physical development, as well as for behavioral effects. Except for a significant decrease in pivoting on postnatal day 9 in the group exposed to arsenite plus restraint, no other MMC- or arsenite-induced behavioral changes were noted in unrestrained or restrained groups. Although a significant delay in pinna detachment and in eye opening was observed in pups of the group exposed to arsenite and restraint, the development landmarks were not affected by restraint in the MMC-treated animals. Although maternal stress reduced body weight gain in the dams exposed to MMC plus restraint, a significant interaction between maternal stress and MMC could not be established for developmental toxicity. These preliminary results, combined with those of previous investigations, show that stress can significantly exacerbate the adverse effects of environmental toxic elements.