EFFECTS OF REPEATED EXPOSURES OF HYDROGEN-SULFIDE ON RAT HIPPOCAMPAL EEG

Exposure to high levels of hydrogen sulphide (H2S) in humans has been associated with a number of respiratory and neurological symptoms Acut e toxicity following exposure to high concentrations is well-documente d, however, there is little scientific information concerning the effe cts of exposure to low concentrations, The effects of low levels of H2 S on electroencephalographic (EEG) activity in the hippocampus and neo cortex were investigated on the freely moving rat (Sprague-Dawley). Hi ppocampal electrodes were implanted in the dentate gyrus (DG) and CA1 region. Activity was recorded for 10 min just prior to H2S exposure in the presence of air (pre-exposure). Rats were exposed to H2S (25, 50, 75 or 100 ppm) for 3 h/day; data was collected during the final 10 mi n of each exposure. The total power of hippocampal theta activity incr eased in a concentration-dependent manner in both DG and CA1; repeated exposures for 5 consecutive days resulted in a cumulative effect that required 2 weeks for complete recovery. The effects were found to be highly significant at all concentrations within subjects. Neocortical EEG and LIA (Large Amplitude Irregular Activity) were unaffected. The results demonstrate that repeated exposure to low levels of H2S can pr oduce cumulative changes in hippocampal function and suggest selectivi ty of action of this toxicant.