DISTURBANCES OF ACCOMMODATION IN MINAMATA DISEASE - A NEUROPATHOLOGICAL STUDY OF METHYLMERCURY TOXICITY IN COMMON MARMOSET MONKEYS

Disturbances of accommodation are part of the spectrum of neuro-ophtha lmological findings in patients with Minamata disease. The authors con ducted a study in an animal model of mercury toxicity to identify the anatomical lesions underlying these defects. Three common marmosets re ceived 1.0 mg/kg of methylmercury chloride (MMC) twice weekly for seve n to ten weeks until signs of mercury toxicity evolved. Histopathologi cal analysis revealed severe neuronal loss and proliferation of astrog lia in the Edinger-Westphal (EW) and anteromedian (AM) nuclei of the m idbrain. Less severe neuronal degeneration was observed in the cerebra l cortex surrounding the lateral sulcus. In addition, a single animal showed gliosis in the region of the fastigial nucleus of the cerebellu m. Among cortical and subcortical structures involved in accommodation the EW and AM nuclei were the most severely affected. The authors' re sults suggest that impaired accommodation in patients with methylmercu ry intoxication arises mainly from lesions in the visceral nuclei of t he midbrain.