Research On Toxicology Of The Visual System Effected By Mercury

Many studies have shown that mercury (Hg) is a toxic heavy metal in a wide range of hazards, and it is one of the most common harm for human environmental pollution. It is shown that mercury has harmful effects on the visual system by early researchs, additionally, retinal nerve fibers and photoreceptor cells get risk before mercury poisoning, so further studies on the toxicology of the visual system effected by mercury is signficantly important.Objectives:The animal models of mercury poisoning for susceptible mice is created, then the changes of waves a and b from ERG (electroretinogram) test and the changes of the microstructure of the retina between normal mice and susceptible mice are obtained and constrasted, in the last, the harm of mercury for the visual system and its mechanism is studied preliminarily.Methods:First,48healthy and clean SD mice were randomly divided into3groups:compared group, treated group with low concentrations of mercury vapor0.01mg/m3, treated group with high concentrations of mercury vapor3mg/m3. Then, the right eyes of mice in each group were done with ERG test respectively before staining mercury vapor and after1week,2weeks,3weeks and4weeks, totally5times for one eye. Afterward, some mice in each group were killed respectively after1week,2weeks,3weeks and4weeks. The eyes of killed mice were collected, and their retinal tissues were picked under a microscope, and the transmission electron microscopy (TEM) took radiography under the same conditions. At last, ultrastructures of retinal nerve Ganglion cells and bipolar cell were observed, and their changing processes are compared.Results:1. ERG test:Before staining mercury vapor, no significant differences were found in the amplitudes and latencies of waves a and b between the compared group and the treated groups. In treated group with low concentrations of mercury vapor, after1and2weeks, no significant differences were found in the amplitudes and latencies of wave a yet, but the amplitudes of wave b decreased and the latencies extended. Afer3and4weeks, the amplitudes of both waves a and b decreased and the latencies extended, especially after4weeks, where the shapes of waves a and b were low and smooth. In treated group with high concentrations of mercury vapor, after1week, no significant differences were found in the amplitudes and latencies of wave a yet, but the amplitudes of wave b decreased and the latencies extended. Afer2weeks, the amplitudes of both waves a and b decreased and the latencies extended, and these differences are obvious. Afer3and4weeks, the shapes of both waves a and b became not identifiable, expressed as no wave shapes.2. Retinal ultrastructure observation:retinal changed under electronic microscopy. The results showed that:(1) With the extension of staining mercury vapor, retinal ganglion cells, bipolar cells and Muller cells pathologically changed in turn, as follows:mitochondria and endoplasmic reticulum edema, nucleus notch edema, nucleus dissolved and disappeared, apoptotic bodies, and so on.(2) The level retinal ultrastructural changes of the two treated groups are always significantly different from the control group after one, two, three and four weeks (P<0.01). The level retinal ultrastructural changes of the treated group with high concentrations of mercury vapor is always significantly different from the treated group with low concentrations of mercury vapor after one, two, three and four weeks (P<0.05).Conclusions:1. Mercury can cause ultrastructures of retinal nerve cells’bodies and penetrations change, so that mercury does damage to the visual system.2. Hazards of mercury on the ultrastructures of visual systems were related in the same direction with the concentration of mercury vapor in the air and its exposure time.3. Results from ERG test and changes of retinal ultrastructures under TEM are consistent.