Chronic exposure to mercuric chloride during gestation affects sensorimotor development and later behaviour in rats

The current study was performed to assess the effects of inorganic mercury (mercuric chloride - HgCl(2)) on the development of offsprings from intoxicated-mother during pregnancy. In this respect, pregnant rats were chronically treated with HgCl(2) at 50 ppm (Hg50) and 100 ppm (Hg100) in drinking water. After parturition, maternal behaviour was recorded during 30 min at 1st to 6th postnatal day (Pnd). The development of their offspring was studied during the first 17 days after birth. Sensorimotor development of pups was measured by different tests: rooting reflex, vibrissae placing response, righting reflex, negative geotaxis, suspension test and rotating grid. Two month after birth, the anxiety of offspring was tested using the elevated plus maze test. Our results indicate that mercury treatment significantly reduced the nursing and increased the time out the nest or drinking and eating. We also showed that prenatal exposure to HgCl(2) decreased weight gain. Importantly, the rooting reflex, the development of the vibrissae placing response, the righting reflex, the grip strength and the negative geotaxis behaviour were delayed in the offspring of dams treated with Hg50, the delay being more severe with Hg100. We also found a decrease in anxiety in adulthood. Cross-fostering test support the direct toxic effects of mercury.