Impact of Adverse Life Events on Neuroplasticity

长期的压力，如丧偶或睡眠不足，可能导致记忆障碍，增加对阿尔茨海默病的易感性。压力的实验模型表明，在社会心理或环境压力下，空间记忆、情境记忆和物体识别受损。然而，环境压力是否以及如何改变导致正常衰老和AD认知缺陷的细胞和分子改变仍有待确定。我们正在使用小鼠模型来验证慢性社会心理压力和睡眠剥夺会加速正常衰老和AD患者认知障碍的发展这一假设。利用三重转基因AD小鼠模型（3xTgAD小鼠），我们正在确定慢性应激对淀粉样蛋白形成、tau病理、突触功能障碍和学习记忆障碍的影响。我们正在测试衰老和AD损害适应性细胞应激反应途径的假设，导致氧化应激增加，与脑源性神经营养因子（BDNF）和抗氧化酶等神经保护蛋白表达减少相关。在相关研究中，我们发现，在2型糖尿病模型中，暴饮暴食导致神经内分泌应激系统的过度激活，肾上腺糖皮质激素水平升高损害海马突触可塑性和神经发生，这些与压力相关的改变与认知功能缺陷有关。有趣的是，有规律的运动和饮食能量限制可以通过上调神经营养因子BDNF的表达来抵消糖尿病对海马可塑性的不利影响。

Chronic stresses such as loss of a spouse or sleep deprivation, may cause memory impairments and increase susceptibility to AD. Experimental models of stress demonstrate impairments in spatial memory, contextual memory and object recognition in response to psychosocial or environmental stress. Yet, it remains to be determined if and how environmental stress modifies the cellular and molecular alterations that result in cognitive deficits in normal aging and in AD. We are employing mouse models to test the hypothesis that chronic psychosocial stress and sleep deprivation will accelerate the development of cognitive impairment in normal aging and in AD. Using the triple-transgenic AD mouse model (3xTgAD mice) we are determining the effects of chronic stress on amyloidogenes, tau pathology, synaptic dysfunction and learning and memory impairment. We are testing the hypothesis that aging and AD compromise adaptive cellular stress response pathways resulting in increased oxidative stress associated with reduced expression of neuroprotective proteins such as brain-derived neurotrophic factor (BDNF) and antioxidant enzymes. In related studies we have found that, in a model of type 2 diabetes, overeating results in hyperactivation of the neuroendocrine stress system, and that elevated levels of adrenal glucocorticoids impair hippocampal synaptic plasticity and neurogenesis, and that these stress-related alterations are associated with a deficit in cognitive function. Interestingly, regular exercise and dietary energy restriction can counteract the adverse effects of diabetes on hippocampal plasticity by a mechanism involving up-regulation of the expression of the neurotrophic factor BDNF. Chronic stress may be a risk factor for developing Alzheimer's disease (AD), but most studies of the effects of stress in models of AD utilize acute adverse stressors of questionable clinical relevance. We therefore undertook a study to determine how chronic psychosocial stress affects behavioral and pathological outcomes in an animal model of AD, and to elucidate underlying mechanisms. A triple-transgenic mouse model of AD (3xTgAD mice) and nontransgenic control mice were used to test for an affect of chronic mild social stress on blood glucose, plasma glucocorticoids, plasma insulin, anxiety, and hippocampal amyloid, phosphorylated tau (ptau), and brain-derived neurotrophic factor (BDNF) levels. Despite the fact that both control and 3xTgAD mice experienced rises in corticosterone during episodes of mild social stress, at the end of the 6-week stress period 3xTgAD mice displayed increased anxiety, elevated levels of amyloid; oligomers and intraneuronal amyloid;, and decreased brain-derived neurotrophic factor levels, whereas control mice did not. Our findings suggest 3xTgAD mice are more vulnerable than control mice to chronic psychosocial stress, and that such chronic stress exacerbates amyloid; accumulation and impairs neurotrophic signaling. Several mouse models of AD with abundant amyloid and/or aberrantly phosphorylated tau develop memory impairments. However, multiple non-mnemonic cognitive domains such as attention and executive control are also compromised early in AD individuals. Currently, it is unclear whether mutations in the β-amyloid precursor protein (APP) and tau are sufficient to cause similar, AD-like attention deficits in mouse models of the disease. To address this question, we tested 3xTgAD mice (which express APPswe, PS1M146V, and tauP301L mutations) and wild-type control mice on a newly developed touchscreen-based 5-choice serial reaction time test of attention and response control. The 3xTgAD mice attended less accurately to short, spatially unpredictable stimuli when the attentional demand of the task was high, and also showed a general tendency to make more perseverative responses than wild-type mice. The attentional impairment of 3xTgAD mice was comparable to that of AD patients in two aspects: first, although 3xTgAD mice initially responded as accurately as wild-type mice, they subsequently failed to sustain their attention over the duration of the task; second, the ability to sustain attention was enhanced by the cholinesterase inhibitor donepezil (Aricept). These findings demonstrate that familial AD mutations not only affect memory, but also cause significant impairments in attention, a cognitive domain supported by the prefrontal cortex and its afferents. Because attention deficits are likely to affect memory encoding and other cognitive abilities, our findings have important consequences for the assessment of disease mechanisms and therapeutics in animal models of AD. Parkinson's disease (PD) patients often exhibit impaired regulation of heart rate by the autonomic nervous system (ANS) that may precede motor symptoms in many cases. Results of autopsy studies suggest that brainstem pathology, including the accumulation of -synuclein, precedes damage to dopaminergic neurons in the substantia nigra in PD. However, the molecular and cellular mechanisms responsible for the early dysfunction of brainstem autonomic neurons are unknown. Here we report that mice expressing a mutant form of -synuclein that causes familial PD exhibit aberrant autonomic control of the heart characterized by elevated resting heart rate and an impaired cardiovascular stress response, associated with reduced parasympathetic activity and accumulation of -synuclein in the brainstem. These ANS abnormalities occur early in the disease process. Adverse effects of -synuclein on the control of heart rate are exacerbated by a high energy diet and ameliorated by intermittent energy restriction. Our findings establish a mouse model of early dysregulation of brainstem control of the cardiovascular system in PD, and further suggest the potential for energy restriction to attenuate ANS dysfunction, particularly in overweight individuals. Huntington's disease (HD) is associated with profound autonomic dysfunction including dysregulation of cardiovascular control often preceding cognitive or motor symptoms. Brain-derived neurotrophic factor (BDNF) levels are decreased in the brains of HD patients and HD mouse models, and restoring BDNF levels prevents neuronal loss and extends survival in HD mice. We reasoned that heart rate changes in HD may be associated with altered BDNF signaling in cardiovascular control nuclei in the brainstem. Here we show that heart rate is elevated in HD (N171-82Q) mice at presymptomatic and early disease stages, and heart rate responses to restraint stress are attenuated. BDNF levels were significantly reduced in brainstem regions containing cardiovascular nuclei in HD mice and human HD patients. Central administration of BDNF restored the heart rate to control levels. Our findings establish a link between diminished BDNF expression in brainstem cardiovascular nuclei and abnormal heart rates in HD mice, and suggest a novel therapeutic target for correcting cardiovascular dysfunction in HD. In another study we found that ceruloplasmin (Cp; an iron-regulating protein) deficiency results in heightened anxiety-like behavior in the open field and elevated plus maze tests. This anxiety phenotype is associated with elevated levels of plasma corticosterone. Previous studies provided evidence that anxiety disorders and long-standing stress are associated with reductions in levels of serotonin (5HT) and brain-derived neurotrophic factor (BDNF) in the hippocampus. We found that levels of 5HT and norepinephrine (NE), and the expression of BDNF and its receptor trkB, are significantly reduced in the hippocampus of CpKO mice. Thus, Cp deficiency causes an anxiety phenotype by a mechanism that involves decreased levels of iron, 5HT, NE, and BDNF in the hippocampus.