Abstract
It is well known that high concentrations of hydrogen sulfide (approximately 1500 ppm) are exceedingly toxic. However, few studies have been done on the response of the living body exposed to this substance at a sublethal concentration (under 500 ppm). We analyzed the effect of hydrogen sulfide at various concentrations (100 ?? 500 ppm) in Wistar strain rats which were well trained on conditioned avoidance response, and we found that discriminated avoidance response was significantly inhibited immediately after exposure to 200 ppm at the minimum, but significant inhibition of Sidman-type avoidance response was observed after exposure to 300 ppm. There was no correlation between the inhibitory intensity and the response rate on the behavioral baseline. The extinction of Sidman-type avoidance response was significantly accelerated only when the animal was exposed to a concentration over 500 ppm. In case of exposure to 300 ?? 500 ppm of hydrogen sulfide, both the discriminated and Sidman-type avoidance responses were inhibited at a rate and intensity which paralleled the concentrations. At one hour after forced ventilation, however, the initial response level was restored, but in case of exposure to higher concentrations, the inhibitory effect sometimes persisted until the next day. With other rats placed under almost the same conditions, blood pressure, respiration and heart rates were determined without anesthesia, following the exposure to 100 ?? 500 ppm of hydrogen sulfide. It was found that these values showed only transient deflections for about 5 min immediately after the exposure, but thereafter remained relatively stable for one hour. It was consequently assumed that inhibition of conditioned avoidance responses after exposure to hydorgen sulfide might be due to a depressive effect on the central nervous system.
