Neurotoxicity produced by intracranial administration of methylmercury in rats

Abstract

Methylmercuric chloride administered as a single intracranial injection in μg quantities produced a neurological syndrome in rats within 24 hr that resembled the effects produced by repeated sc injections of 10 mg/kg over a period of 7–14 days. Neuromuscular function evaluated semiquantitatively by graded performance in simple strength and coordination tests showed severe impairment at 24 hr in intracranially methylmercury-treated animals, with recovery taking place by 72 hr. Body weight decreased and recovered during a similar time course. Incorporation of tritiated leucine into brain protein was increased significantly at 24 hr as measured in vitro in brain homogenates and in vivo by administering the labeled amino acid ip. Incorporation returned to control values by 72 hr after the methylmercury injection. Residual brain mercury concentrations at 24 hr were about 5-fold lower than those accompanying overt neurological signs in rats produced by sc administration. Histological examination of brains from intracranially and subcutaneously dosed rats revealed that the lesions produced by the 2 methods were substantially different. Intracranial injection of methylmercury was found to produce an isolated neurotoxic syndrome similar in some respects to the neurotoxicity seen in systemic intoxications but dissimilar histopathologically.