| Background: Alzheimer's disease(AD) is a neurodegenerative disorder that is characterized by extracellular deposits of amyloid-beta peptide(Ap) and a severe depletion of the cholinergic system. The formation of senile plaques which principal component is Ap, 39- to 43- amino acid peptides derived from the amyloid precursor protein(APP), and cholinergic neuronal loss are two main reasons which cause learning and memory deterioration in AD. The reason and mechanism of reduction and loss of cholinergic neuron is still not clear, and the relationship between deposition of Ap and cholinergic neuronal loss is poorly understood. There are abundant cholinergic neurons in the basal forebrain and nerve growth factor(NGF) is very important in maintaining and regulating the phenotype and function of cholinergic neuron that express the high-affinity neurotrophin receptor, TrkA. TrkA is essential for NGF signal transduction and mediates its biological effects. About 70-90% cholinergic neuron express TrkA. Recent findings indicate an early defect in NGF receptor expression in CBF neurons. Maybe there is correlation between the changes of TrkA and the loss of cholinergic neuron. So it is necessary and important to investigate the influence of Ap to the expression of TrkA of cholinergic basal forebrain neuron. Nicotine/nicotine agonists, which have been thought beneficial for the treatment of AD, Some mechanisms involved remain poorly understood. Whether nicotine can reverse the changes induced by Ap is unknown. So, in this study we undertook the changes of TrkA in cholinergic basal forebrain of rats induced by Ap in vitro and the changes of NGF and its high-affinity receptor TrkA in vivo. We also investigate their changes after the intervention of nicotine and evaluate the role of nicotine.Materials and methods: Our study is divided into two main parts. The first part is finished in vitro as following three steps. Firstly, Primitive rat basal forebrain neurons were cultured and evaluated. Morphologic, cellular vigor and expression of TrkA change were observed by microscop , MTT assay, RT-PCR and immuocytochemistry respectively when these neurons were exposed to differentconcentrations Ap(25-35) after 24 hours to investigate the effects of different concentration Ap(25-35) on survival , growth and expression of specific high-affinity neurotrophin receptor TrkA of the neurons of rat cholinergic basal forebrain neurons. Secondly, primitive cultured rat basal forebrain neurons were exposed to different end concentrations nicotine after 48 hours to investigate the morphologic, celluar vigor and expression of TrkA change by above methods. Then the neurons were cultured with 10M nicotine for different duration(8h 24h 48h respectively), the above indexes investigated. Thirdly, the neurons were exposed to lOuM Ap and lOuM nicotine simultaneously to investigate the changes of above indexs. The second main part included in the following small parts: (1) 80 SD rats were divided into 2 weeks group and 4 weeks group randomly. There are 40 rats in each group which are divided into 5 small groups as control group, mechanical injure group, artificial cerebral spinal fluid(ACSF) injection group, Ap injection group and nicotine intervention group. There are 8 rats in each small group. Using rat stereo-orientation technique and minim push technique, Ap(l-40)(10g/l/each side) were injected in the bilateral basal forebrain of rats of Ap injection group and nicotine intervention group. The nicotine intervention group rats were also administered intraperitoneally nicotine hydrogen tartrate (total dose is 12mg/kg, which were divided into 5 parts averagely and used one time each day for 5 days consecutively). The mechanical injure group were injected nothing, and the ACSF group were injected same volume ACSF. The control don't accept any disposal. Assessment of performance in the Morris water maze was undertook 14 days and 28 days after surgery in the 2 weeks and 4 weeks group respectively to evaluate the ability of learning and memory of rats. (2) U...
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