EARLY EFFECTS OF METHYLMERCURY ON THE VISUAL EVOKED-RESPONSE OF THE DOG

  • 1 January 1981
    • journal article
    • research article
    • Vol. 2  (3) , 499-514
Abstract
A disturbing characteristic of methylmercury (MeHg) intoxication is the preclinical silent stage. This stage is followed by the sometimes rapid onset of clinical signs such as peripheral sensory loss, motor difficulties and visual and auditory impairment. The objective of this study was to search for preclinical changes in the elctrophysiological activity of the CNS of dogs exposed to methylmercury chloride. Because of the prominence of the visual system in the MeHg literature, the visual evoked response (VER) was selected for evaluation. A dose rate of 500 .mu.g/kg per day orally was expected to cause clinically apparent toxicosis in .apprx. 2 mo. After 1 wk of exposure, a subtle distortion of the VER occurred. In a parallel group of dogs, blood Hg was 0.74 .mu.g/ml at this time and brain Hg content was 1.28 .mu.g/g at the occipital cortex. Although the dogs continued to receive MeHg, VER remained remarkably stable for the next 5-8 wk and then rapidly degraded during the next few days as the dogs exhibited visual and motor distabilities. In many species of animals, when brain Hg is .apprx. 15 .mu.g/g, clinical and histopathologic changes are present and may be detected at 8 .mu.g/g. Distortion of the VER at 1.28 .mu.g/g Hg at the visual cortex demonstrated that CNS changes existed during the silent stage of toxicosis and at a brain Hg content suggesting physiologic dysfunction of neurons rather than neuronal death.

This publication has 1 reference indexed in Scilit: