Stroke is the third leading cause of human death in the USA and remains the focus of efforts to define the pathophysiologic mechanisms leading to tissue damage. Neuronal damage and cell loss occurs in numerous brain regions after strokes, thus providing a highly-relevant context for study. This project investigates neuroprotection during ischemic stroke through "M-channels" which are critical K+ channels that stabilize resting potentials by counterbalancing the depolarizing effects of excitatory cation currents. Produced by combinations of KCNQ2-5 subunits, voltage-gated M channels play critical roles in control of neuronal excitability, and action potential firing. We have previously shown that most M-type channels to be up- regulated by reactive oxygen species (ROS), molecules commonly produced during and after ischemic cerebrovascular stroke. This study hypothesizes that M current-mediated neuronal silencing has a neuroprotective role by increasing the open-probability of KCNQ channels, thus decreasing neuronal activity and prolonging activation of cellular cascades resulting in cell death. Two in vivo mouse models are used and the first involves a cerebral infarct within the parietal cortex produced by laser-controlled photothrombosis. When the photo-sensitizing dye, Rose Bengal, is irradiated by laser light, free-radical formation occurs causing endothelium damage, leakage of vascular contents into the parenchyma and vascular thrombosis. The second in vivo model is the middle cerebral artery occlusion (MCAo), in which a filament is introduced non-invasively into the MCA via the carotid artery. The MCAo model produces a catastrophic stroke in the ipsilateral hemisphere, with correspondingly pronounced cerebral deficits. The M-current activity will be pharmacologically altered in both mouse models using the M-channel openers, retigabine (RTG) and flupirtine, and the blocker, XE991, with drug application at various time points post-stroke. Additionally, dominant- negative KCNQ3 knock-in mice will be used in both models to confirm a specific M-channel mechanism. Finally, behavioral assays designed to distinguish degrees of injury and neural function will be used to delineate minute changes in function due to channel activation or blockage. Motor and co-ordination deficits will be assayed with the balance beam, ladder dexterity, open-field locomotion and accelerating rotarod tests. Learning deficits will be assayed using the Morris water maze. Thus, this study uses two strong and exciting stroke models, which may provide novel modes of therapeutic intervention for reducing neuronal damage caused during commonly-occurring ischemic attacks, by modulating the activity of M-type K+ channels.
The vital role of M-type K+ channels in limiting ischemic/hypoxic damage during cerebrovascular stroke will be investigated. In vivo studies will provide novel, innovative and ground-breaking pathophysiologic insights into stroke, as well as provide potential new therapeutic approaches to this devastating, common disorder.
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