Transient Focal Cerebral Ischemia/Reperfusion Induces Early and Chronic Axonal Changes in Rats: Its Importance for the Risk of Alzheimer's Disease

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Abstract
The dementia of Alzheimer's type and brain ischemia are known to increase at comparable rates with age. Recent advances suggest that cerebral ischemia may contribute to the pathogenesis of Alzheimer's disease (AD), however, the neuropathological relationship between these two disorders is largely unclear. It has been demonstrated that axonopathy, mainly manifesting as impairment of axonal transport and swelling of the axon and varicosity, is a prominent feature in AD and may play an important role in the neuropathological mechanisms in AD. In this study, we investigated the early and chronic changes of the axons of neurons in the different brain areas (cortex, hippocampus and striatum) using in vivo tracing technique and grading analysis method in a rat model of transient focal cerebral ischemia/reperfusion (middle cerebral artery occlusion, MCAO). In addition, the relationship between the changes of axons and the expression of β-amyloid 42 (Aβ42) and hyperphosphorylated Tau, which have been considered as the key neuropathological processes of AD, was analyzed by combining tracing technique with immunohistochemistry or western blotting. Subsequently, we found that transient cerebral ischemia/reperfusion produced obvious swelling of the axons and varicosities, from 6 hours after transient cerebral ischemia/reperfusion even up to 4 weeks. We could not observe Aβ plaques or overexpression of Aβ42 in the ischemic brain areas, however, the site-specific hyperphosphorylated Tau could be detected in the ischemic cortex. These results suggest that transient cerebral ischemia/reperfusion induce early and chronic axonal changes, which may be an important mechanism affecting the clinical outcome and possibly contributing to the development of AD after stroke.

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