MERCURY IN HUMAN SPINAL MOTOR-NEURONS

Inorganic mercury has been proposed as a neurotoxin that could cause s poradic motor neuron disease (SMND). We were therefore interested to s ee if mercury could be detected in the upper and lower motor neurons o f SMND patients, and if mercury accumulated within motor neurons durin g life. Paraffin sections of formalin-fixed spinal cord (22 control ad ults, 20 SMND adults, 25 infants) and frontal primary motor col-tex (9 control adults, 18 SMND adults, 30 infants) were stained with silver nitrate autometallography to detect ionic mercury. Mercury was found i n the spinal motor neurons of 36% of adult control cases and 45% of ad ult SMND cases, with no significant difference between groups. No merc ury was seen in infant spinal motor neurons, or in any adult or infant corticomotoneurons. In conclusion, many humans appear to accumulate m ercury in their spinal motor neurons by the time they are adults, but mercury does not appear to play a major role in the loss of upper or l ower motor neurons in SMND.