Quantitative synaptic alterations in human brain during normal aging and in patients with Alzheimer disease / 中国组织工程研究

ABSTRACT

BACKGROUND: Synaptic density, a key index of structure and function of brain tissues, is related to cognitive function. Synaptic loss occurs during human brain aging and in Alzheimer disease (AD), inducing the changes of synaptic density.OBJECTIVE: To observe quantitative synaptic alterations in human brain and changes of synaptic density in different parts during normal aging so as to compare them with those of AD patients.DESIGN: Sampling survey.SETTING: Senile Neurological Department of General Hospital of Chinese PLA.PARTICIPANTS: Pathological data were selected from General Hospital of Chinese PLA from June 1996 to December 2002. Inclusion criteria had no major nervous system diseases and neuropathological changes. Brain tissues of 28 corpses in normal aging group, 23 males and 5 females aged 23-100 years with an average of (65±22.8) years, were obtained at autopsy.All corpses were divided into three groups according to their age, namely,adult group (23-55 years old, n=9), senile group (64-72 years old, n=7),and ＞75 group (76-100 years old, n=12). Cerebral hippocampal samples of other six corpses diagnosed with AD were selected from clinic. The corpses included 5 men and 1 woman aged 76-94 years with an average of (83±7.7) years.METHODS: Response intensity of synaptophysin immunochemistry remained stable after 4-8 hours of death, so brains were obtained at autopsy after 8-72 hours of death and fixed with 4% formalin for at least 6 weeks.In normal aging group, tissues were taken from left superior frontal gyrus,striatal area of left occipital lobe, left putamen (striatum section, including head of caudate nucleus), and left hippocampus (from lateral geniculate body section to medial occipitotemporal gyrus). In AD cases, tissues were taken from left hippocampus of 4 corpses and right hippocampus of other 2. All sections were stained with hematoxylin eosin (HE), toluidine blue and synaptophysin immunostaining (rabbit anti-human synaptophysin polyclonal antibody from Beijing Zhongshan Biotechnology Co., Ltd.). Morphology and distribution of positive objects in synapse immunologic reaction were observed under the light microscope. Relation between absorbance in each region and age was determined with Pearson's coefficient. Differences among groups were analyzed with nonparametric test, and the differences in hippocampal CA3 area between ＞ 75 group and AD group were analyzed with the same test.MAIN OUTCOME MEASURES:① Absorbency of synaptophysin at various sites of normal aging group and correlation with age; ② absorbance value in CA3 area between AD patients and advanced aged normal subjects (＞75 years) was compared.RESULTS:All the 34 cerebral samples entered the final analysis.①Synaptophysin-positive granules of various size were scattered through neocortex, putamen and hippocampus, neuronal somata, neuroglia, vessels and white matter. Density was particularly strong over layers Ⅱ and Ⅲ in frontal lobe, and layer ⅣV in occipital lobe. ② Synaptophysin density was negatively correlated with age, which was -0.688 in frontal lobe, -0.592 in occipital lobe, -0.458 in putamen and -0.619 in hippocampal CA2 area,respectively (P = 0.000, 0.001, 0.014, and 0.000). ③ Significant difference in synaptic density in CA3 area was found between AD patients (0.031 3±0.003 0)and normal subjects over the age of 75 (0.040 7±0.005 3) (Z=-2.997, P=0.001)in nonparametric test.CONCLUSION:① Synaptic density was found to decrease in frontal lobe, occipital lobe, CA3 area of hippocampus and putamen with age; the changes had significant correlation with age.② Synaptic density of AD patients was lower than that of normal subjects, and their cognitive hypofunction was related to synaptic loss. ③ All tissues were obtained after 8-72 hours of death and fixed over 6 weeks, which to the greatest extent reduced the effects of tissue autolysis and formalin fixation on the results.