Adenosine receptor activation in spreading depolarization and ischemic injury

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DESCRIPTION (provided by applicant): The overall research goal of this fellowship proposal is to evaluate the involvement of adenosine receptors in brain injury resulting from ischemic stroke. Repetitive spreading depolarization (SD) events occur spontaneously after ischemic stroke, and contribute to the expansion of injury. SD is a wave of massive cellular depolarization which disturbs ionic homeostasis and depletes energy in the brain. In healthy tissue, SD is followed by an interval of reduced electrical activity and increased blood flow, whereas in injured tissue with minimal electrical activity, SD is followed by decreased blood flow and neuronal cell death. Mechanisms underlying these phenomena are not well understood. Both neuronal and vascular reactions to SD might be explained by adenosine receptor activation. Adenosine, a low-energy metabolite of ATP, accumulates during periods of metabolic imbalance. By activating G-protein coupled receptors on the surface of cells, adenosine can contribute to neuronal silence (via the A1 receptor) and vasodilation (via the A2A receptor). Adenosine A2A receptors are implicated in post-ischemic brain damage in animal models of stroke, but the mechanism is yet unknown and might be related to SD. In this proposal, experiments are designed to determine the role of adenosine receptor activation in recovery from spreading depolarization events in normal tissue and in a stroke model. Aim 1 will evaluate the activation of adenosine A1 and A2A receptors after SD in otherwise normal brain tissue from mice, using in vitro and in vivo methods to parse out neuronal and vascular effects. Aim 2 will use an in vivo mouse model of ischemic stroke to examine mechanisms by which adenosine receptors may persistently reduce neuronal activity and explain the paradoxical drop in blood flow in vulnerable areas. Major methodologies to be utilized include brain slice electrophysiology, in vivo electrophysiology, intrinsic optical signals, laser speckle contrast imaging, and histological assessment of ischemic lesions. These studies will contribute to the fellow's predoctoral training in neurological disease. The results of the proposed experiments will elucidate mechanisms of recovery and injury in the brain after stroke, and may suggest novel treatments to prevent the delayed expansion of ischemic injury.