Mercury vapor uptake into the nervous system of developing mice.

The localisation of mercury in the developing nervous system following mercury vapor (Hg(0)) exposure is not clear. We therefore looked for mercury in the mouse nervous system following fetal or neonatal exposure to Hg(0). Mice were exposed to 50 or 500 microg/m(3) Hg(0) for 4 h a day for 5 days in late pregnancy, and pups sacrificed on postnatal day (P)1 or P40. Neonatal mice were exposed to 500 microg/m(3) Hg(0) for 2 h between P1 and P23, and were sacrificed 2 days later or at P40. Paraffin sections of the nervous system were stained with autometallography to detect inorganic mercury. No mercury was seen in the nervous system of pups after fetal exposure to the 50 microg/m(3) Hg(0) dose rate. After fetal exposure to the 500 microg/m(3) Hg(0) dose rate, mercury was seen in nervous system blood vessels and sensory ganglia. No mercury was seen in the nervous system after neonatal exposure to 500 microg/m(3) Hg(0) for 2 h between P1 and P10. From this exposure at P11 onwards, mercury was detected in motor neurons. The lack of stainable mercury in early developing central neurons suggests that the fetal and neonatal nervous systems are somehow protected from Hg(0) uptake.