Accumulation of inorganic mercury in lower motoneurons of mice

The distribution of mercury within the lower brain stem and spinal cord of mice was investigated at various intervals after a single intramuscular injection of mercuric chloride. The autometallographic technique was used to demonstrate the presence of mercury deposits in tissue sections. Accumulation of mercury was observed in motoneurons of the anterior horns and in motor nuclei of the brainstem. In addition, mercury was present in the neuropil of the area postrema and within renal tubular cells. At the ultrastructural level, mercury was localized to neuronal lysosomes. The preferential accumulation of mercury in motoneurons within the spinal cord and brain stem is most probably due to an uptake of mercury in motor nerve terminals followed by retrograde axonal transport to the cell bodies.