Impact of Adverse Life Events on Neuroplasticity

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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.