Does lead damage motor neurons?

It has been suggested that lead (Pb) may damage motor neurons selectively after retrograde axonal transport from the neuromuscular junction. This has reinforced suspicions that Pb could be a cause of some sporadic motor neuron diseases. However, the long-term effect of Pb on spinal motor neurons is not known. To investigate this, we injected mice in the right hindlimb with 0.1 ml of 2.5% Pb nitrate. Nine months later we measured the sizes and counted the numbers of motor neuron cell bodies in the anterior horns of the L4 spinal cord. There was no significant difference in sizes or numbers of motor neuron cell bodies between the left and right sides of the spinal cord in either group or between groups. These data do not therefore support the hypothesis that Pb transported from muscle damages spinal motor neurons.