The overall aim of the proposed project is to assess the separate and combined effects of aging and chronic stress on the central nervous system of C57BL/6J mice. This is an expansion of past work and will describe the cumulative effects of stress on spatial, declarative, and contextual learning and memory in aged mice. This project will also contribute to the definition of age-related differences in the immune response to stress. Our hypothesis is that age in combination with stress lead to an up- regulation of cytokine activity in the CNS, resulting in structural damage of the brain and disrupted, learning and memory. Recent findings in this laboratory and others suggests that it is the accumulation of stress that produces the most profound effects on plasma and CNA interleukins and nitric oxide and on brain structure in the aged (Kubra et al., 1998; Shanks et al., 1998; McCann, 1997). The proposed project is to describe the effects of chronic stress on neurotoxic cytokine activity and cognitive impairments. Further questions include: (1) whether the pathology will be defined as cell death or disrupted connectivity due to myelin damage, and (2) to what extent pro-inflammatory molecules and nitric oxide are elevated in the periphery and in brain, and whether these molecules are associated with the observed with the brain pathology. To test our hypothesis, all mice will be behaviorally tested on standard tasks sensitive to learning and memory impairment. Cognitive tests will be administered after the stress regimen, and at the end of testing, the effects of age and stress on brain will be examined. In one study, the brain will be serially sectioned and the distribution of gross age- and stress-related changes, with particular emphasis on white matter changes, will be examined in cortical areas, particularly those interconnected with the hippocampus. Another study will examine biochemical changes. It will first be determined whether elevated levels of pro-inflammatory cytokines in periphery might compromise the integrity of the blood-brain-carrier and induce cytotoxicity in the brain. Parallel immunocytochemical work will be extravasated systemic cytokines in brain. The final study will examine reactive neuroglia including in vitro cytokine elaboration and consequent tissue and myelin damage. Finally, an overall statistical analysis of these measures will be performed using structural equation modeling to test the hypothesized relationships among age, stress, elevated cytokine levels and consequent changes in brain structure and behavior.
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