The Experimental Study Of The Effects And The Mechanism Of Carbon Bisulfide On The Learning And Memory Ability Of Rats

Carbon disulfide (CS₂) is a kind of popular organic solvent. It is an intoxicant contributed to all over the body. Nervous system is the main target of CS₂ and the mechanism of toxic action is still unclear. Generous epidemiological investigation indicated that the memory ability could suffer different degree effect after long-term exposure to CS₂. Animal experiments also confirmed that CS₂ could change the behavior of toxic animals. However, at present, there is still no study involoved the mechanism of CS₂ on learning and memory ability. The goal of this study is to explore the effect and the mechanism of CS₂ on the learning and memory of rats by observing the learning and memory ability of intoxic rats, observing the ultrastructure of hippocampus, detecting metabolism of oxygen free radicals and measuring NOS of hippocampus. Fourthermore, the intervention effects of VitE on lipid peroxidation in rat hippocampus after long-term exposure to CS₂ was also observed. Part one Effects of carbon bisulfide on the learning and memory ability of ratsObjective To study the effect of carbon bisulfide (CS₂) on the learning and memory ability of rats. Methods Rats(n=60) were randomly divided into one control group and three CS₂-poisoned groups (50mg/m³ group, 250mg/m³ group and 1250mg/m³ group). The toxic rat models were made by inhaling various doses CS₂ 4 hours every day, 5 days every week. After 2 months of inhaling intoxication, the learning and memory ability of all groups were examined by Morris water maze and step down test. Results Compared with the controls, Morris water maze showed that the average run away latent period of CS₂-poisoned groups elongated and the swimming time in the platform located quadrant shortened, and both of which were CS₂ concentration dependented. Step down test demonstrated that the error frequency maked by rats during training increased, the latence before rats stepped down the platform after 24h shortened and the total errors in 5min increased, and all of which were CS₂ concentration dependented. Conclusions CS₂ subacute intoxication include low concentration CS₂ subacute intoxication could induce disturbance of learning and memory ability of rats, which was CS₂ concentration dependented.Part Two Effects of carbon bisulfide on metabolism of oxygen- derived free radidicals and the intervention role of VitE in rat hippocampusObjective To explore the effects of CS₂ on ultrastructure of rat hippocampus and metabolism of oxygen-derived free radidicals. To study the effects of VitE on lipid peroxidation induced by CS₂ in rat hippocampus. Methods The toxic rat models were made by inhaling various doses CS₂. After 2 months of inhaling intoxication, the ultrastructure was observed by transmission electron microscope. The content of Maleic Dialdehyde (MDA) and Nitric Oxide (NO) and the activity of Superoxide Dismutase(SOD) in rat hippocampus were detected by Thibabituric Acid test, Nitrate reductase test, xanthine oxidase test and chemistry color match test respectively. Treated with different doses of vitamin E simultaneous, changes of above-mentioned markers were observed. Results The principal influence of CS₂ on rat hippocampus was Chromatin aggregation, nuclear envelope and cell membrane shrinkage or swell, vacuole appearance in mitochondria. There was no obvious change in 50mg/m³group, while the damage in 1250 mg/m³group was the most sever. Compared with the controls, CS₂ treatment significantly increased MDA levels, decreased SOD activity and NO contents. Treated with VitE simultaneous with intoxication, the content of MDA reduced, and when the dose of VitE reached 100mg/kg, the difference between all intoxic groups and the group without intervention is significant; The activity of SOD increased,and when the dose of VitE reached 200mg/kg, the difference between all intoxic groups and the group without intervention is significant; The content of NO increased, and when the dose of VitE reached 200mg/kg, the difference between 50mg/m³ group and the group without intervention is significant. Conclusions The decline of learning and memory ability of CS₂ poisoned rats is related to the impairment of hippocampus induced by oxygen-derived free radidicals and the metabolism disturbance of NO. VitE could interfere neurotoxicity of CS₂.Part Three Effects of carbon bisulfide on the activity and gene expression of nitricoxide synthase in rat hippocampus Objective To explore the effects of CS₂ on the NOS activity and expression of NOS-mRNA of rat hippocampus. Methods The toxic rat models were made by inhaling various doses CS₂. After 2 months of inhaling intoxication, the activity of cNOS and iNOS in hippocampus was detected by NOS Test Kit. The content of nNOS-mRNA and iNOS-mRNA was measured by semi-quantitative reverse transcription polymerase chain reaction(RT-PCR) method. The expression of nNOS and iNOS in rats hippocampus was observed by light microscope after immunohistochemical stain. Results Compared with the controls, the activity of cNOS significantly decreased. The activity of iNOS changed slightly. CS₂ treatment significantly decreased nNOS-mRNA content. The content of iNOS-mRNA in 250mg/kg CS₂ group and 1250mg/kg group increased significantly. Conclusions These results suggested that the activity of cNOS and the expression of nNOS might be related to the effect of CS₂ on learning and memory ability.Part Four Effects of large dose of VitE on the learning and memory ability of CS₂–poisoned ratsObjective To study the influence of large dose of VitE on ultrastructure of hippocampus and the learning and memory ability of CS₂ -poisoned rats. Methods The toxic rat models were made by inhaling various doses CS₂, meanwhile the poisoned rats were treated with 200mg/kg VitE. After 2 months of inhaling intoxication, the learning and memory ability was detected and the ultrastructure was observed by transmission electron microscope. Results Compared with the group without intervention, treated with 200mg/kg VitE simultaneous with intoxication, Morris water maze showed that the average run away latent period of CS₂-poisoned groups shortened and the swimming time in the platform located quadrant elongated. Step down test demonstrated that the error frequency maked by rats during training decreased. The latence before rats stepped down the platform after 24h elongated and the total errors in 5min decreased. The change of ultrastructure of hippocampus in 200mg/kg VitE +250mg/m³ group was obvious, while 200mg/kg VitE +1250 mg/m³ group changed slightly. Conclusions Application of large dose of VitE could partly reduce the damage of rat hippocampus induced by CS₂ and preserve the effect of low concentration CS₂ on the learning and memory ability.