| Background and PurposeAlzheimer's Disease (AD) is the progressive degenerative disease of central nervous system, whose main clinical manifestations is memory impairment, cognitive impairment and personality changes etc. It often occurs in the pre-aged or elderly. The main pathological features of AD are the formation of the senile plaque which is constituted by the deposition ofβ-amyloid peptide in the brain which is derived from the cleavage of the amyloid precursor protein, the amyloid deposition in the cerebral vessels and the decrease of the number of neurons which due to too much neurofibrillary tangles formed in the neurons. The mechanism of the pathogenesy is not very clear so far. Most of the investigators think that it is correlated with the deposition of A(3 closely. There are two kinds Alzheimer's Disease, familial and sporadic, they all correlate with the genetics. So far, we have confirmed 4 genes which are correlated with AD.They are the apolipoprotein E(Apo E),β-amyloid precursor protein (APP), Presenilin 1(PS1) and presenilin 2(PS2) genes respectively. There are direct correlations between APP, PS 1 and the AD. APP is the raw material of Aβ, and the PS1 is the core componet of the y-secretase whose main function is to cut APP and generate the Aβ. Recently, some researcher deem that there is overexpression of the APP and PS1 in the AD via the research of the clinical cases and the experimental animal study, moreover, there is enzymic activity decrease of theγ-secretase by 80% and a magnitude decrease of the amount of Aβin the brain of the PS1 gene knock-out mice. So there is a popular view which consider that AD may be related to the abnormal expression of APP and PS1.At present, cholinesterase inhibitors are widely used in the clinic to alleviate the symptoms of the AD which accompany with the ruduce of the cholinergic neurons in the central nervous system. But this is only the palliative therapy method. Therefore, some researchers propose that the methods which could reduce the production of Aβshould be the main method to prevent or cure the AD, and the proposal is according to the core role of Aβin the process of AD. And the methods include to inhibit A(3 aggregation and toxicity, to speed up the metabolism of Aβ, to inhibit the expression of APP and the regulation of APP enzymatic pathways in order to reduce Aβformation (such as raising the a-secretory activity, and reduced activity of y-secretase) etc. From the research results, reducing the expression of APP and reducing y-secretase activity is the most direct and effective way and also is the hotspot in the current study, but the excessive inhibition of the inhibitors has perplexed researchers, finding an appropriate inhibitors have become the main task.Nicotine is the major alkaloid in tobacco, epidemiologists found that smokers in the incidence of AD was significantly lower than the normal population, and the nicotine is the main functional material to reduce the incidence of AD.Another study has found that nicotine exposure can reduce the Aβdeposition in the brain and cerebral vascular in the APP transgenic mouse, but its detail mechanisms are still unclear. So, this study bases on the mice models of nicotine exposure to investigate whether there is effect of nicotine to reduce the expression of APP and PS1.Materials and Methods1. Animals group and the preparation of mice models of nicotine exposure.60 SPF level male adult Kunming mice, weight 30±5g, supply by the Labrotory Animal Center of China Medical University, divided into Control (Con), Saline (Sal), Experiment 1 (Tes1), Experiment 2 (Tes2) and Experiment 3 (Tes3) 5 groups randomly, They are breeded in the SPF level animal breeding room of Department of Developmental Biology, China Medical University. Experimental groups were injected of nicotine solution 0.1ml (Sigma), total volume dose is 3mg/kg which was diluted with normal saline daily. Control was normally feeding, Saline group were daily injected the same volume of normal saline, T1 administered for 10 days, T2 administered for 20 days and T3 administered 40 days to establish models of nicotine exposure. Six mice of the Experimental groups and saline group were sacrificed in the end of the administration day, cerebrums were removed and after washed with the sterile 0.01M PBS and-70℃cryopreservation; another six were perfused with 4% paraformaldehyde, cerebrum was removed after fixation, dehydration, buried with paraffin thoroughly and consecutive slices.2. Detection the expression changes of the APP and PS1 in the cerebrum of adult Kunming mice.(1) RT-PCR to detect the mRNA expression of APP and PS1.(2) Western blot was used to detect the expression of APP and PS1.(3) Immunohistochemical staining to observe the expression of PS1 in mouse cerebrum distribution.Results1. With the method of RT-PCR, the mRNA of PS1 is decrease (p<0.05) in the T1, T2 and T3 contrast to the control, and there is no difference of the expression of APP mRNA.2. The expression of PS1 is reduction (p<0.05) in the T1, T2 and T3 contrast to the control, and there is no difference of the expression of APP by Western blot.3. In the control, there is a lot of PS1 positive substance distributing in the cortex, IB1, PoDG and the domain between IB1 and PoDG which possibly locate in the nerve fibers, cell layer of the hippocampus and the domain of ArcMP, VTM, LM, PMD and ML in the periphery of the third ventricle; whereas there is PS1 positive cells in the domain of ArcMP, VTM, LM, PMD and ML in the periphery of the third ventricle in the test groups only. Conclusion1. There is no effect of the nicotine exposure to the expression of APP in the Cerebrum of the adult Kunming mice.2. The effect of the exposure of nicotine inhibits the expression of PS1 in the cortex, IB1, PoDG and the domain between IB1 and PoDG and the cell layer of the hippocampus selectively.3. There is no effect of the exposure of nicotine to the expression of PS1 in the domain of ArcMP, VTM, LM, PMD and ML in the periphery of the third ventricle. |
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