Effect Of SVHRP On Rat Models With Alzheimer's Disease Induced By Amyloid Beta Protein Intra-hippocampal Injection

Background: Alzheimer's disease (AD) was the most common form of age-associated dementia. Nowadays, the health and quality of live for the aged were increasingly threatened by AD. The etiology and pathogenesis of AD remained unclear. And the cures for AD were remaining a difficult problem and symptomatic treatment was the main therapy. Due to shortage of ideal animal models which can reflect all the characteristics for AD, the research of foundation and therapeutical drugs of AD was restrictive.Recently, the amyloid cascade hypothesis of AD was proposed and supported by most scholars, suggesting that the formation and accumulation of Aβmay be a primary cause for AD pathogenesis.Objective: In this study, the rat induced by Aβ1-40 intra-hippocampal injection was used as the animal model for AD. And SVHRP was applied through intraperitoneal injection (ip) as intervenor. The aim of our study was to ascertain the availability of experimental AD model rats, to investigate protective and therapeutic effect of SVHRP, and to explore the pathogenesis and therapeutic mechanism of AD by observing the change of ethology, astrocyte, and synapse.Methods: A total of 24 healthy adult Sprague-Dawley (SD) rats, male, weighting 300g±50g were used for this study. The rats screened by the Morris water maze (MWM) were randomly divided into 3 groups:①normal control group (n=9)②Aβinjection group (n=8)③Co-injection of Aβand SVHRP group (n=7). The solvent was used for normal control group. And Aβwas used for the other two groups. The corresponding agent wereinjected into bilateral hippocampus under chloral hydrate (300mg/kg) anaesthesia by a stereotaxic apparatus (coordinate: AP=3.3mm; LR=1.8mm; DV=3.5mm). The rats were administrated with SVHRP or distilled water through intraperitoneal injection (ip) for 10 days. Then the MWM was used to measure the spatial learning and memory ability of rats. And then the rats were perfused through heart by 4% paraformaldehyde (PFA). And the brains were removed, post fixed in 4% PFA for 24 hours, then impregnated with cane sugar for dehydration, and then embedded with OCT for frozen section (consecutive 10μm). The expression of GFAP and synaptophysin (p38) were detected by immunohistochemistry. The results for immunohistochemistry were measured by Nikon microscope picture analysis system. And the data were processed by spss 11.5 software.Results:1. The results of Morris water maze behavior examination were as follows:⑴Place navigation test: The escape latency of the rats with Aβinjection was markedly more than that of normal control group and Co-injection of Aβand SVHRP group. Concerning the tendency change of escape latency for 5 days, normal control group gradually shortened day by day. But the other two groups had not obvious tendency.⑵Spatial probe test: The movement distance percentage and time percentage in the platform quadrant of Aβinjection group were shorter than that of normal control group and Co-injection of Aβand SVHRP group.2. The results of GFAP immunohistochemistry expression: Compared with normal control group and Co-injection of Aβand SVHRP group, the number of GFAP-positive astrocytes around the needle tract was increased significantly in Aβinjection group(p<0.05 or p<0.01). And the form of astrocytes in Aβinjection group was changed obviously characterized by large body, long and thick branching, and strong staining. And there was no significant difference between the normal control group and Co-injection of Aβand SVHRP group.3. The results of p38 immunohistochemistry expression: Compared with normal control group and Co-injection of Aβand SVHRP group, the p38-positive expression in hippocampus was weak andthin in Aβinjection group. And the integrated optical density (IOD) and area of p38-positive expression in Aβinjection group were lower(p<0.05 or p<0.01). And no significant difference was observed between the normal control group and Co-injection of Aβand SVHRP group.Conclusions:1. Aβ1-40 injected into bilateral hippocampus of rats can induce learning and memory impairment, astrocyte activation, and p38-positive expression lower.2. SVHRP can markedly improve learning and memory impairment of rats with Aβinjection, inhibit activation of astrocytes of brain, and promote synaptophysin expression in hippocampus.