Pathology of subacute methylmercurialism in cats

Clinical signs of toxicosis, neurologic lesions, and increased tissue residues of methylmercury (MM)were produced in 9 cats by oral administration of 1.29 and 0.86 mg of Hg/kg of body weight/day as methylmercuric hydroxide. Clinical signs, which began after 15 days of exposure, included anorexia, ataxia, hypermetria, proprioceptive impairment, blindness, vertical nystagmus, and grand mal convulsions. Significant lesions occurred in cerebrum, brainstem, and cerebellum and correlated well with clinical signs. Microscopic central nervous system lesions consisted of neuronal degeneration, necrosis and loss of neurons, swollen axons, demyelination, loss of nerve cell processes, vacuolation of neuropil, gliosis, neuronophagia, perivascular cuffs, endothelial hypertrophy and hyperplasia, leptomeningitis, and infrequent vascular necrosis. Overall distribution of central nervous system lesions was unrelated to daily dose, but more advanced lesions were produced by the smaller daily dose. Mean tissue residues of MM were generally directly related to daily dose, and the average distribution among tissues was constant, with highest concentrations in liver, followed by kidney, spleen, muscle, and brain. In utero exposure of kittens to MM, revealed transplacental accumulation.