| BackgroundAlzheimer's disease (AD) is the most common dementia in elderly characterized by an insidious onset and cognitive alterations in the early stage. There were no effective diagnostic biomarkers and pharmacological intervention due to the unclear pathogenesis of AD. Therefore, early diagnosis and prompt intervention are current critical issues. The AD diagnosis criteria began in 1984 and continually revised. The new revised AD diagnosis criteria from 2011 indicate that the AD diagnosis should be established on the combination of episodic memory impairment with abnormal AD biomarkers (A?and tau). And AD has be identified as a continuum spectrum including preclinical AD,mild cognitive impairment due to AD, and dementia due to AD. However, the clinical applications of current AD biomarkers are confronted with various difficulties Therefore, it is a hot spot to update AD biomarkers in the early stage AD and provide key time window for treatment.Magnetic resonance imaging (MRI) has many advantages over other imaging methods, including non-invasive, repeatable, relatively high spatial and temporal resolution and relatively low cost. MRI biomarkers play a crucial role in helping AD early diagnosis, such as regional structure alterations on structural MRI and brain function alterations on BOLD-functional MRI. However, most studies in AD patients began in the middle or late stage of the disease, few was known about the early stage of AD.Transgenic mice of AD provide the ideal model to investigate pathogenesis at the the early stage of the disease. In addition, during the last decade, high-field animal MRI began to emerge as powerful tools to improve the sensitivity of early diagnosis. Further, we can better understand the relationship between behavior impairment, MRI features and pathological alterations using AD transgenic mouse models.Therefore, the main aim of this study was to investigate brain structure and function alterations by 7.0T MRI and their association with emotional and/or cognitive function in the early ages of a transgenic mice model of amyloid pathology (5XFAD mice). 5XFAD mice co-expresses five familialAD (FAD) mutations and additively increase A?42 production. In this work, we sought to investigate:(1) Did brain tissue microstructural integrity impair in the early ages of 5XFAD mice? Did brain tissue microstructural integrity impairment become more severe in 5XFAD mice with age? Did brain tissue microstructural integrity impairment associate with emotional and/or cognitive function impairment in the early ages of 5XFAD mice? (2) Did neuronal activity alterations emerge in the early ages of 5XFAD mice? Did neuronal activity alterations become more severe in 5XFAD mice with age? Did neuronal activity alterations associate with spatial cognitive function impairment in the early ages of 5XFAD mice?Part 1 Evaluation of brain tissue microstructural integrity and its possible relationship with cognitive functions at the early stage of 5XFAD miceObjective: To investigate the brain tissue microstructural integrity and its possible correlations with cognitive function at the early stage of 5XFAD mice.Methods: (1) The behavioral characteristics of 5XFAD mice and wild type mice lines C57BL/6 (at 1-,2-, 3-, and 5- months of age) were test with the sucrose preference test (SPT), the open field test (OFT)and the elevated plus maze (EPM) and Morris water maze test (MWM). (2) Multi-modality (T2WI,T2map) study with 7.0T micro-MRI in these mice were undergone. Both voxel-based analysis (VBA)and region of interest (ROI) approach were used to analyze T2 relaxation time (T2) in various gray matter regions between two mice strains. In addition, ROI was used to further analyse T2 value and the volume in six hippocampal subregions (dorsal and ventral CAl, CA3 and DG). (3) Pearson correlation was conducted to analyze the relationships between T2 value in hippocampal subregions and cognitive behavior in MWM of 5XFAD mice at different ages, respectively.Results: (1) Results of behavioral tests: There were no significant differences between 1-, 2-, 3- and 5-month-old wild-type and 5XFAD mice in the behavioral tests (p > 0.05), including SPT, OFT and EPM. In the MWM test, no statistically significant difference from the controls was observed in the training sessions of 1-month-old 5XFAD mice, but 2- and 3-month-old 5XFAD mice showed significantly prolonged latency of finding the hidden platform on day 3 (p = 0.0024, 0.0300), 5-month-old 5XFAD mice showed significantly prolonged latency on day 3, 4 and 5 (p = 0.0154, 0.0154,0.0011). In the probe trial, all 5XFAD mice showed a significant decrease in the time spent on the target quadrant (p = 0.0365, < 0.001,0,011,0.034). The two genotypes displayed similar swimming speeds at all ages. (2) Results of MRI: No significant difference was found between 1-month-old 5XFAD mice and wild-type mice. Both VBA and ROI approach showed a decreased T2 in the hippocampus in 2-, 3-, and 5-month-old 5XFAD mice (p = 0.0420, 0.0182, < 0.0001). In addition to the hippocampus, VBA also revealed an extended decreased T2 in the cingulate cortex (cg) and amygdala in 5-month-old 5XFAD mice. Furthermore, ROI displayed that T2 in the dorsal CAl, CA3,DG and ventral CAl was decreased of 2- and 3-months old 5XFAD mice (2-month-old: p = 0.0214,0.0030,0.0369,0.0369; 3-month-old: p = 0.0119,0.0031, 0.0119, 0.0119). T2 in the six hippocampal subregions was decreased of 5 months old 5XFAD mice (p = 0.0045, < 0.001,0.0036,0.0007, < 0.0001 ,0.0045). There was no significant difference in the volumes of different hippocampal subregions between the two strains at four different ages. (3) Results of correlation analysis: In the MWM test acquisition trials, there was a significant negative correlation between the escape latency of day 5 and the T2 in the dorsal CAl of 3-month-old mice (r = - 0.6188), and in the dorsal CAl and dorsal DG of 5-month-old mice (r = - 0.5190, - 0.5240). In the probe trial,there was a positive correlation between the time spent in the target quadrant and the T2 in the dorsal CAl of 2-, 3-, and 5-month-old mice (r =0.6144, 0.6645, 0.5629). No such correlation was found between the T2 in the ventral hippocampal subregions and cognitive behavior in the MWM in 5XFAD mice at different ages.Conclusion: The brain tissue microstructural integrity, especially in the hippocampus, impaired early and became more extensive and severe during the progression of disease. Furthermore, the dorsal hippocampus is a crucial component involved in spatial cognition impairment at early ages of 5XFAD mice. T2 value alternation may be a biomarker to help early detection and monitoring the progression of AD.Part 2 Evaluation of brain neuronal activity and its possible relationship with cognitive functions at the early stage of 5XFAD miceObjective: To investigate neuronal activity alterations and its possible correlations with cognitive function at the early stage of 5XFAD mice.Methods: (1) The behavioral characteristics of 5XFAD mice and wild type mice lines C57BL/6 (at 1-,2-, 3-, and 5- months of age) were test with SPT, OFT, EPM and MWM. (2) A baseline scan-T1 weighted imaging (T1WI) study with 7.0T micro-MRI in these mice were undergone prior to MnCl2 injection. A total dose of 55.8 mg/kg MnCl2+4H2O(i.e.,279 ?mol/kg) was injected intraperitoneally(i.p.) in four fractionated doses of 13.95 mg/kg with an inter-injection interval of 24 hours. The mice were imaged (manganese-enhanced magnetic resonance imaging,MEMRI) 24 hours after the last injection to measure the level of Mn2+ uptake in the brain. (3) On the 12th day after the first injection,OFT and MWM were repeated to assess the effect of MnCl2 injection on the animals' behavioral functions. (4) ROI approach were used to analyze the mean signal intensity (SI) of all voxels in various gray matter regions between two mice strains. Normalized ROI SI was calculated before (S0, in baseline scan) and after MnCl2 injection (SI) in the same mouse, and signal change due to Mn2+induced enhancement was calculated as: 100% x (S1-S0)/S0. (5) Pearson correlation was conducted to analyze the relationships between SI and cognitive behavior in MWM at different ages, respectively.Results: (1) Results of behavioral tests: There were no significant differences between 1-, 2-, 3- and 5-month-old wild-type and 5XFAD mice in the behavioral tests (p > 0.05), including SPT, OFT and EPM. In the MWM test, no statistically significant difference was observed in the training sessions between 1-month-old 5XFAD mice and wild mice, but 2- and 3-month-old 5XFAD mice showed significantly prolonged latency on day 3 (p=0.0024, 0.0300), 5-month-old 5XFAD mice showed significantly prolonged latency on day 3, 4 and 5 (p = 0.0154, 0.0154, 0.0011). In the probe trial, all 5XFAD mice showed a significant decrease in the time spent on the target quadrant (p = 0.0365, <0.001, 0.011, 0.034). The two genotypes displayed similar swimming speeds at all ages. (2) Results of MRI: No significant difference was found between 1-month-old 5XFAD mice and wild-type mice.2-month-old 5XFAD mice showed an increased SI in the Hip (p = 0.0167). 3-month-old 5XFAD mice showed an increased SI in the Hip and ERC (p = 0.0167, 0.0684). 5-month-old 5XFAD mice showed an increased SI in the caudate-putamen (CPu), the retrosplenial cortex (RSC), Hip and ERC (p=0.0228, 0.0795, 0.0167, 0.0684). (3) Results of correlation analysis: In the acquisition trials of the MWM test, there was a significant positive correlation between latency to find the platform on day 5 and SI in the Hip (r = 0.8668) of 5-month-old 5XFAD mice. No such correlation was found in Hip of 5XFAD mice 2 or 3 months of age or in other ROls of 5XFAD mice 2, 3 or 5 months of age. In the probe trial, there was a negative correlation between time spent in the target quadrant and SI in the Hip of 3- and 5-month-old 5XFAD mice (r = -0.8269, -0.8364) and in the ERC of 2-, 3- and 5-month-old 5XFAD mice (r = -0.9204, -0.8576, -0.8386). No such correlation was found between SI in the Hip or ERC and cognitive behavior in the MWM of wild-type mice at different ages. (4) Results of Histological analysis: No obvious A? was observed in the wild-type mice and 1-month-old 5XFAD mice. A? was detected in the cortex and hippocampus of 5XFAD mice at 2-, 3-, and 5-months of age.The distribution, size, and intensity of positive staining increased with age.Conclusion: Aberrant increased basal neuronal activity may contribute to the spatial cognitive function impairment at the early stage of 5XFAD mice. Early intervention that targets aberrant neuronal activity may be crucial to prevent cognitive impairment. Basal neuronal activity alternation may be a biomarker to help early detection and monitoring the progression of AD. |
PDF Full Text Request