| Lead is one of the frequent contamination material in Human living and active environment, Lead is a metal with neurotoxicity,which can cause the environment pollution by long-term savings,and can enter the body through the food, water, soil and air.In recent years, along with the development of urbanization, industrialization, Environmental pollution is aggravating,Lead concentration rising in the environment. even if exposing to low level Lead, it also has toxic effect to the central nervous system of the human body. Lead obtains generally application in Industry and daily living because. Children is the susceptible population in the Lead contamination, and it mainly shows in the decreasing ability of learning and memory as well as behavior dysplasia. Synaptosomal-associated Protein (SNAP-25) mainly disperse in moss-form fiber ending and the molecular film of dentate gyrus in the hippocampus of adult animal. According to the previous research, SNAP-25 is relevant to the development of and dendrites and Axonal, the release of nerve transmitter as well as the Synaptic plasticity after the injury of central nerve, moreover the expression of SNAP-25 increases after hippocampus induces the LTP. Now it has no definite conclusion that the effect of SNAP-25 in the affecting intelligence of Lead. This research is planning to investigate that different level Lead exposing affect the ability of learning and memory of the young mouse as well as the effect of SNAP-25 in the mechanism of lead poisoning.MATERIALS AND METHODS1. SubjectsForty pregnant Kunming mice were randomly divided into four groups and caged individually. Pb acetate was dissolved in distilled at three different concentrations, 0.3g/L, 1.0g/L and 3.0g/L for low, moderate and high concentrations respectively, and supplied to the lead exposure groups. The control group mice were served with distilled water without lead. Lead exposure started from the beginning of gestation and lasted until weaning(PND21). The pups were fed by mother until weaning. 2. Methods2.1 Determination of the lead content in blood and hippocampusThe Pb levels in blood and hippocampus tissue were analyzed by using graphite furnace atomic absorption spectrometry.2.2 Evaluation of learning and memory abilityThe learning and memory ability of the mice offspring were tested by water maze respectively.2.3 Validating on mRNA level by RT-PCRThe SNAP-25 mRNA level of were tested by RT-PCR.2.4 ImmunohistochemistryImmunohistochemistry staining was carried out by SP to dectect expression of cytokines(SNAP-25).2.6 Statistical analysisOne-way ANOVA and Pearson correlation analysis in SPSS 12.0 soft ware was used to analyze the data. The significant level was defined at a=0.05.RESULTS1. The effects of exposure on blood and tissue lead levelsLead exposure affect the Lead concentration in mice blood and hippocampus.The Lead level in blood and brain of mice in Lead exposure groups is obviously super to control group (P<0.01) in all age group, and the difference among Lead exposure groups has statistical significance. The Lead level in blood of mice among Lead exposure groups has change regularity according to day age, that's to say, it is higher at the seventh day, and it descends to some extent at the fourteenth day, however it obviously increases at the twenty-first day. The Lead level in hippocampus of mice among Lead exposure groups also has some change regularity according to day age, but it differs from blood Lead, that is higher at the seventh day, and it is has the highest level the fourteenth day, then it is the lowest at the twenty-first day.2. The test result of water mazeThe errors frequency of mice at the age of 21 days has increasing trend according to the dose increasing of Lead exposure in the other-rat; there is no statistical significance between the low dose group and the control group (P>0.05); there is statistical significance between the middle, high dose group and the control group (P<0.05); and there is statistical significance between the high dose group and the control group (P<0.05) in latency period of escape.3. RT-PCRThe expression of SNAP-25mRNA in the mices'hippocampus on 21 days. The expression of SNAP-25mRNA is higher in hippocampus of the control group, but it has the decreasing trend according to the increase of the dose of Lead exposure in the mother-rat. There is statistical significance between the low, middle, high dose group and the control group (P<0.05).4. The result of Immunohistochemistry methodsThe result of hippocampus of mice at the age of 21 days according to the immunohistochemistry, SNAP-25 protein expression of the the hippocampus CA1 and CA4 area lead exposure groups obviously Lower than those of the control group (P<0.05),but With the increasing doses, Different lead exposure group in different regions of the hippocampus SNAP-25 protein expression is also different.Conclusions1. The Lead exposure in precursor causes the Lead accumulation in mice, and that induces the injury of learning and memory in mice.2. The neurotoxicity caused by Lead maybe the down regulation of expression of SNAP-25 mRNA. That is cause by Lead, and it results in the change of signal transduction channel, what's more, it results in the nervous lesion.
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