MERCURY CONTAMINATION OF FISH IN THE OJIBWAY DIET .2. SENSORY EVOKED-RESPONSES IN RATS FED WALLEYE

The Ojibwa people of the upper Great Lakes in the United States have a long history of utilizing walleye caught by spear fishing as a major part of their diets. Walleye (Stizostedion vitreum) have been collecte d and prepared into fillets using traditional methods, submitted for t otal mercury (Hg) analysis, and fed to laboratory rats in standard neu rotoxicity protocols to determine the human health risks associated wi th consuming these fish. Wisconsin officials recommend avoiding the co nsumption of fish containing more than 0.5 ppm Hg Laboratory rodent ne urotoxicity bioassays included blending composite fish samples of 0.8, 0.4, and 0.2 ppm total mercury and feeding it to 48 young adult femal e Long Evans rats for 90 days. Standard behavioral assessments include d: clinical neurologic observations, motor activity, and accelerating rotarod Twelve of the 48 rats were surgically implanted for electrodia gnostic evaluations using sensory evoked potentials with auditory and visual stimuli. Auditory (clicks) responses were relatively stable and unaffected by Hg laden diets. However, visual evoked responses at low flash intensities demonstrated a dose related slowing of brain visual processing activity. Methylmercury contamination is known to affect v isual systems, and visual evoked brain potentials are apparently sensi tive indicators of dietary Hg.