The Expression and Significance of Metallothioneins in Murine Organs and Tissues Following Mercury Vapour Exposure

The fate of inspired mercury vapour (Hg0) is critical in the central nervous system (CNS) where it can circumvent the blood–brain barrier (BBB) at the neuromuscular junction (NMJ) and accumulate indefinitely in motor neurons by retrograde transport. The detoxification of systemic Hg0 by lung and liver requires investigation. We exposed 129/Sv wild-type (Wt) and 129/Sv MT-I, II double knockout (KO) mice to 500 µg Hg0/m3 for 4 hours to investigate the expression of MT in the lung, liver, and spinal cord following Hg0 exposure using unexposed groups as controls. There were congestive changes in liver and lung of both Wt and MT-KO groups of Hg0-treated mice; these changes appeared more pronounced in the MT-KO group. Motor neurons in the spinal cord did not show any pathological changes. Based on expression of MT, liver appears to have a major role in trapping and stabilising mercury. In the spinal cord, MT was expressed in all white matter astrocytes and in some grey matter astrocytes. Notably, motor neurons did not express MT, and the presence of MT could not be demonstrated in the axons of the ventral root. The absence of MT expression in motor neurons and their axons suggests the dependence of the motor system on the detoxifying capacity of liver MTs. Keywords. Mercury vapour; dental amalgam; metallothionein; metallothionein knockout mice; lung; liver; motor neurons; motor neuron disease