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It is well known that the main brain lesion in Alzheimer's disease (AD) brain is neurofibrillary tangles (NFT) and senile plaques (SP). The amount of NFT is positively correlated with clinical degree of dementia in AD. It is also well studied that the major component of NFT is abnormally hyperphosphorylated microtubule associated protein tau that is caused by an imbalance of protein kinase and protein phosphatase (PP). To reconstitute a specific AD model based on the above hypothesis, we have injected separately calcium calmodulin dependent protein kinase (CaMKKII) activator, bradykinin and PP-2B inhibitor, cyclosporin A into rat hippocampus in the present study. The results showed that the injection of bradykinin caused learning and memory deficient in rats as well as Alzheimer-like tau phosphorylation, including Ser-262/356, Thr-231/235 and Ser-396/404. On the other hand, the injection of cyclosporin A induced the same phosphorylation sites as above except Ser-262/356, however, it did not mimic rat behavior abnormality as bradykinin injection did. The data suggested that activating of CaMKII and the phosphorylation of Ser-262/356 at tau might responsible for the lesion of learning and memory in our model rats. We also incubated PP-2A and PP-1 inhibitor, okadaic acid with human neuroblastoma cell line (SH-SY5Y), and found that (1) inhibition of above PPs induced Alzheimer-like phosphorylation and accumulation of neurofilaments, and Alzheimer-like microtubule disruption, (2) melatonin showed certain protection of the cell from okadaic acid toxicity. The data obtained from this study is significant in AD specific model study.
